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Cisco Network Solutions for the Telco DCN: SONET/SDH OSI Environments
This document is directed to competitive local exchange carriers (CLECs), incumbent local exchange carriers (ILECs), and Post, Telephone and Telegraphs (PTTs), collectively referred to as telcos (short for telephone companies). This document describes Cisco network solutions for transporting data between Synchronous Optical Network (SONET) and Synchronous Digital Hierarchy (SDH) and the Operations Support System (OSS) in a telco data communications network (DCN). The DCN transports network management traffic between network elements and their respective OSS, making them a vital link between the service network and the network operations center (NOC). The solutions presented in this document will help telcos connect their SONET/SDH network elements to a router-based network using the Open System Interconnection (OSI) protocol, which simplifies the DCN and reduces equipment costs.
Version History

Version Number 1

Date April 28, 2004

Notes This document was created as a joint effort between Don Schriner in the Cisco CTO Consulting Engineering Group and Alliene Turner in Cisco IOS Documentation. This document was updated. This document was updated.

2 3

May 6, 2005 January 3, 2008

Contents
The document presents the recommended Cisco architecture for building the OSI network. Several methods for implementing and scaling an OSI network are included with detailed configuration examples. Specific Cisco IOS software features such as Intermediate System-to-Intermediate System (IS-IS) multiareas, VLAN support for International Standards Organization Connectionless Network Service (ISO CLNS), Target Identifier Address Resolution Protocol (TARP), and IS-IS attach bit control are described. These architectures and software features are described in the following main sections:
• •

Prerequisites, page 2 Scaling SONET/SDH in the Telco DCN: Overview, page 2

Americas Headquarters: Cisco Systems, Inc., 170 West Tasman Drive, San Jose, CA 95134-1706 USA

© 2004–2007 Cisco Systems, Inc. All rights reserved.

Cisco Network Solutions for the Telco DCN: SONET/SDH OSI Environments Prerequisites

• • • • • •

The Cisco Three-Tiered DCN Network Architecture, page 12 Access Layer Configuration, page 18 Distribution Layer Configuration, page 87 Core Layer Configuration, page 93 Additional References, page 111 Glossary, page 114

Prerequisites
The features described in this document are supported on the Cisco Telco and Enterprise feature sets. Cisco IOS software is packaged in feature sets that are supported on specific platforms. To get updated information regarding platform support for this feature, access Cisco Feature Navigator at http://www.cisco.com/go/fn. To access Cisco Feature Navigator, you must have an account on Cisco.com. Qualified users can establish an account on Cisco.com by following the directions at http://www.cisco.com/register. If you have an account but have forgotten or lost your account information, send a blank e-mail to cco-locksmith@cisco.com. An automatic check will verify that your e-mail address is registered with Cisco.com. If the check is successful, account details with a new random password will be e-mailed to you.

Scaling SONET/SDH in the Telco DCN: Overview
SONET/SDH has become the transport technology of choice for regional Bell operating companies (RBOCs), inter-exchange carriers (IXCs), Post, Telephone, and Telegraph (PTT) organizations, and other carriers to meet the demand for bandwidth and new services. The growth of SONET/SDH and the increasing demands for both existing time-division multiplexing (TDM) and new packet-based data services necessitate better and more scalable DCNs for network operations and management connectivity between network elements and their respective OSSs. As SONET/SDH rings grow in both size and number, the service provider needs to deploy higher bandwidth and more scalable DCN networks to manage SONET/SDH network elements. RBOCs, Inter-exchange carriers (IXCs), PTTs, and their vendors have worked with standards bodies to define more powerful management networks for SONET/SDH. These standards documents recommend that OSI-based protocols be used by the SONET/SDH network elements’ ring network management. While IP and OSI protocols are being widely adopted and deployed by RBOCs and PTTs within their DCNs, it is not realistic to replace their vast installed infrastructure of overlay networks that support legacy DCN protocols. To streamline operations and stay competitive, telcos must reduce the number of overlay DCNs they currently have deployed to support various legacy protocols. The new DCNs must support both legacy protocols, which will continue to be in use for the foreseeable future, and the new standards-based protocols. The challenge is to provide this support over a common infrastructure and create a seamless network of networks that can manage the network through a single DCN utility. Figure 1 shows a typical DCN network.

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Cisco Network Solutions for the Telco DCN: SONET/SDH OSI Environments Scaling SONET/SDH in the Telco DCN: Overview

Figure 1

Typical DCN Network Elements
Network Elements ADM SONET/SDH ring
TDM

Network Operations Center Operations Support Systems Dialup, leased line IP/OSI Frame Relay, ATM, T1/E1 Mainframe or minicomputer Alarms, control, and test messages Configuration and backup files Billing data collection Software downloads X.25 (XOT)

GNE

Workstation

Dial
MUX

ATM Transmission system

Class 4/5 telephone switch DSL Alarm units
88860

Multiple networks are included in the DCN network cloud. The networks serve to connect a mainframe or minicomputer and workstation configured as an OSS at a NOC to a large array of devices and systems referred to as network elements. Network elements in a DCN include alarm units, telephone switches such as the Lucent 5ESS, SONET/SDH add-drop multiplexers (ADMs) and optical repeaters, voice switches, digital cross-connect systems, Frame Relay or ATM switches, routers, digital subscriber line access multiplexers (DSLAMs), remote access switches, digital loop transmission systems, and so on, that make up the provisioned services infrastructure used to deliver services to customers. The OSS controls and stores the network management data collected about and from the various network elements. DCNs are the networks deployed by a telco or service provider that contain all the cabling, network management (NM) stations, switches, network elements and other necessary equipment for delivering and managing services to the service providers’ customers (see Figure 1). The DCN is an out-of-band network; that is, it does not transit the same bandwidth segment used by services such as voice and its associated in-band signaling. It does, however, share the same transport equipment and interfaces with switching equipment considered to be the infrastructure of the public switched telephone network (PSTN). This document focuses on a design architecture and Cisco IOS software features for scaling the OSI DCNs. In addition to the need for scalability, there are other factors driving change in the traditional DCN that is providing operations support for today’s TDM-based services. These factors are:
• •

The use of IP and OSI-based intranets within the central office to facilitate communication between network elements and management stations (collectively, the OSS) is increasing. “Intelligent” (feature-rich) network elements are requiring more frequent software version updates than their less feature-rich predecessors.

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• • •

Software downloads to intelligent network elements across the management network—some many megabytes in size—are increasing bandwidth requirements. More and more network elements and OSSs are upgrading to support Ethernet interfaces. As competition offers more alternatives, upgraded DCNs are offering the ability to remotely turn up services faster as demanded by their customers.

OSI as a DCN Transport Mechanism
With the advent of SONET/SDH networks, service providers and their equipment vendors foresaw the need for new, more powerful service delivery support networks to manage today’s optical networks. In 1988, the International Telecommunication Union (ITU) adopted the M.30 recommendation, which was revised in 1992 and again in 1996, and today is known as recommendation M.3010, Principles for a Telecommunications Management Network. Recommendation M.3010 defines the architectural requirements for a Telecommunications Management Network (TMN) to support management network operators in planning, provisioning, installing, maintaining, operating, and administering telecommunications networks and services. Within that document, the ITU describes the DCN, which provides the communications backbone between network elements and OSSs in the PSTN. Using the DCN concepts outlined in M.3010, in December 1995 Bellcore developed an industry standard for SONET—GR-253-CORE—that includes generic DCN requirements. GR253-CORE has become the standard for DCNs within the United States. These standards recommend that OSI-based protocols be used by the OSSs for SONET/SDH ring network management. As a result of the GR253 and M.3010 standards, SONET/SDH vendors worldwide use the seven-layer OSI protocol stack for the management of their equipment. One application protocol that rides on Layer 7 of the OSI protocol stack, for example, is Transaction Language 1 (TL1). TL1 provides for the definition of messages and protocols between network elements and management stations, and facilitates the gathering of data from SONET equipment. As SONET/SDH rings grow in both size and number, telcos must deploy higher bandwidth and more scalable DCN networks to manage SONET/SDH network elements. This growth necessitates a migration of DCNs from X.25 networks running from 9.6 kbps to 56 kbps to intranets running at 1.544 Mbps or higher. Both synchronous and asynchronous interfaces are migrating to Ethernet interfaces running at 10 Mbps on network elements and OSSs. OSI protocol stacks used in SONET/SDH network elements for management require that the DCN be able to use OSI to route to and from the network element and its associated OSS, in addition to the higher bandwidth requirements. A typical RBOC, for example, may have already deployed several thousand SONET rings and is rapidly adding new rings by the hundreds or thousands annually. This large number of SONET network elements demands a DCN that can scale.

IP Standards Development for the DCC and the DCN
The ITU-T has developed a new standard outlining architecture requirements for IP-only domains, OSI-only domains, and IP and OSI domains titled Architecture and Specification of the Data Communication Network, document number G.7712/Y.1703. Basically, the standard adds IP to the DCN and the data communications channel (DCC) architectures. The premise of the standard is that SONET/SDH network elements will still act as routers to forward management traffic across the DCC. In OSI environments, IS-IS is the routing protocol of choice. In mixed environments, Integrated IS-IS is the routing protocol of choice. In IP-only environments, the routing protocol can be either Open Shortest

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Cisco Network Solutions for the Telco DCN: SONET/SDH OSI Environments Scaling SONET/SDH in the Telco DCN: Overview

Path First (OSPF) or Integrated IS-IS. The ITU-T document also describes manual tunneling mechanisms for bridging IP-only or for CLNS-only involvements; however, this document focuses on only OSI solutions for SONET/SDH.

DCN Design Considerations for OSI
The current Bellcore and ITU standards recommend the use of the OSI protocol stack for the management of SONET/SDH network elements. Figure 2 shows the packet flow from the OSS to a SONET network element. The packet leaves the OSS and is routed across the DCN by routers to the gateway network element (GNE). The GNE routes the packet from the Ethernet network onto the SONET DCC. The packet is routed around the ring. The SONET network element is acting as an IS-IS router. The SONET DCC is the physical path. The SONET network element and GNE are IS-IS Level 1 routers. The standalone routers in the DCN perform the IS-IS Level 2 function. Notice that the DCC has become part of the DCN. The performance of the DCN is determined by all of the components.
Figure 2 Packet Flow in a DCN Network

L1

Area A CLNS packet flow L1/L2 L1 L1 Area B Intranet IP/OSI OSS L1/L2 L1/L2 L1/L2 L1 L1 L1 L1

Area C
88786

Level 1 and Level 2 router Ethernet hub SONET/SDH NE SONET Data Communications Channel

L1/L2

L1

L1

Fundamental issues to address in designing a DCN today are the routing performance of the IS-IS routers and the bandwidth on the DCC. When designing the DCN network, the service provider must take into account the performance characteristic of all the routers, including the routing engine in the network element. Today, the routing engine in the network elements (NEs) can typically support a routing table of only 50 to 100 entries, so this limitation binds the Level 1 area size to 50 to 100 routers. The section DCC is used for management. The bandwidth of the section DCC is 192 KB. The D1 through D3 bytes of the section overhead DCC are used. A packet should not have to make more than seven hops on the DCC to enter the DCN because of bandwidth limitations and the performance of the router in the network element. As the size of the ring approaches 16 nodes, a second GNE must be added to the ring. The first step for designing a DCN network is to gather information about a particular network environment. The natural geographic groupings of rings should be identified and a breakdown of the average central office size should be computed. This information is required for planning the OSI-based DCN.

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Cisco Network Solutions for the Telco DCN: SONET/SDH OSI Environments Scaling SONET/SDH in the Telco DCN: Overview

Following are the questions that need to be answered before the design process is begun:
• • • • • • • • • • • •

What is the number of SONET nodes in the network today? What is the growth rate (number of nodes added per year) of the SONET/SDH network? What is the size of the Level 1 OSI area that the routing engine can support? In other words, how many Level 1 routers can be in an area? What is the size of the OSI domain that the Level 2 routing engine can support? How many network elements does the service provider want to place in an area to start with? Does the service provider want to leave room for growth within an area? How many central offices does the service provider have in the DCN? Does the service provider want to support a single GNE or dual GNEs? What is the average ring size? How many rings can be aggregated into a single area? How many SONET rings are in a large-sized central office? How many SONET rings are in a medium-sized central office? How many SONET rings are in a small-sized central office?

DCN Design with a Classic OSI Implementation
This document reviews a classic OSI design, and then reviews an improved design using multiareas. For purpose of example, answers to questions from a hypothetical large-sized service provider network are provided. This information is needed to design a network based on the three-tiered architecture.


What is the number of SONET nodes in the network today? There are 25,000 SONET/SDH nodes deployed today.



What is the growth rate (number of nodes added per year) of the SONET/SDH network? There are 4000 SONET/SDH nodes added per year.



What is the size of the Level 1 OSI area that the routing engine can support? In other words, how many Level 1 routers can be in an area? The Level 1 area size is 50 routers.



What is the size of the OSI domain that the Level 2 routing engine can support? The domain size is 500 Level 2 routers.



How many network elements does the service provider want to place in an area to start with? Does the service provider want to leave room for growth within an area? The service provider wants to place 30 network elements in an area and leave address space for 20 additional network elements in an area.



How many central offices does the service provider have in the DCN? There are 1700 central offices in the network.



Does the service provider want to support a single GNE or dual GNEs? Most of the rings have a single GNE. The design will assume a single GNE per ring.



What is the average ring size? Average ring size is ten.

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Cisco Network Solutions for the Telco DCN: SONET/SDH OSI Environments Scaling SONET/SDH in the Telco DCN: Overview



How many rings can be aggregated into a single area? A maximum of three SONET/SDH rings will be placed in an area.



How many SONET rings are in a large-sized central office? The large-sized central office will have 36 SONET rings.



How many SONET rings are in a medium-sized central office? The medium-sized central office will have ten SONET rings.



How many SONET rings are in a small-sized central office? The small-sized central office will have one SONET ring.

To begin the network design, place the central offices in geographic areas. In this network design, there are five geographic areas. Within each geographic area, the service provider can determine the actual number of large-, medium-, and small-sized central offices. This network design example will use the following rules:
• • •

A small-sized central office has 1 ring, a medium-sized central office has up to 10 rings, and a large-sized central office has up to 12 rings. The service provider has estimated the percentage of large-sized central offices to be 10 percent, medium-sized central offices to be 40 percent, and small-sized central offices to be 50 percent. Medium- and large-sized central offices will have redundant routers and redundant WAN links. Small central offices will have a single router and redundant WAN links.

An alternative to estimating the percentage of small-, medium- and large-sized central offices is for the service provider to count the number of central offices. Table 1 lists the central office breakdown by geographic area using the estimated percentages.
Table 1 Central Office Breakdown by Geographic Area

Geographic Location Group 1 Group 2 Group 3 Group 4 Group 5 Totals

Small-Sized Central Offices 150 300 120 360 90 1020

Medium-Sized Central Offices 75 150 60 180 45 510

Large-Sized Central Offices 25 50 20 60 15 170

Total Number of Central Offices 250 500 200 600 150 1700

Next, determine the number of Level 2 routers required in each geographic area. Today in small-sized central offices, the service provider in the classic implementation of this network design would typically not have any SONET rings. The network design allows for one ring per office eventually, for growth. Because of the performance limitations of the SONET/SDH network elements, the design calls for many small areas. Remember that the network element routing engine can support only 50 entries in its routing table. Each area requires a Level 2 router, so the logical place for the Level 2 function to be performed is on a standalone router in each central office. Placing the Level 2 function on the GNE will constrain the size of the routing domain because of performance limitations of the IS-IS routing engine in the GNE. The network design calls for every central office to have at least one OSI area. In this network, large-sized central offices have 36 rings, which equates to 12 Level 2 routers. Also remember that the design criteria questions indicated the

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Cisco Network Solutions for the Telco DCN: SONET/SDH OSI Environments Scaling SONET/SDH in the Telco DCN: Overview

average ring size to be ten network elements, and that three rings should be placed in an area. This design will leave address space in an area to add network elements when the rings grow. The computation for the network design is as follows: 36 rings ÷ 3 rings per area = 12 Level 1 areas The 36 SONET rings in a large-sized central office are split among 12 Level 1 areas. For every Level 1 area, a connection to the backbone is made through a standalone Level 1/Level 2 router, so 12 standalone routers are needed. The medium-sized office has ten SONET/SDH rings per office. The new network design calls for three rings per OSI area. The computation for the network design is as follows: 10 rings ÷ 3 rings per area = 4 Level 1 areas (rounded up) The small-sized central office has at most one SONET ring and requires one router per central office. Given these design parameters, the number of standalone routers that will be required are listed in Table 2.
Table 2 Standalone Router Requirements

Geographic Location Group 1 Group 2 Group 3 Group 4 Group 5 —

Total Number of Offices 250 500 200 600 150 —

Level 2 Small-Sized 150 300 120 360 90 —

Level 2 Medium-Sized 300 600 240 720 180 —

Level 2 Large-Sized 300 600 240 720 180 —

Level 2 Total 750 1500 600 1800 450 5100

Total Number of Domains 2 4 2 4 1 13

To show how the numbers in Table 2 were derived from Table 1, look at Group 1: There are 150 small-sized central offices and one Level 1/Level 2 router per central office. In all, there are 150 Level 2 routers to support small-sized central offices for Group 1, as the following computation indicates: Group 1 small-sized central offices: 150 small-sized central offices x 1 router per central office = 150 Level 2 routers There are 75 medium-sized central offices in Group 1. Each medium-sized central office requires four Level 1/Level 2 routers as previously computed, so the total number of Level 1/ Level 2 routers for medium-sized central offices is as defined in the following equation: Group 1 medium-sized central offices: 75 medium-sized central offices

x 4 routers per central office = 300 Level 2 routers

There are 25 large-sized central offices in Group 1. A large-sized central office requires 12 Level 1/Level 2 routers, as computed in the first equation following Table 1. The following computation indicates the total number of Level 1/Level 2 routers required: Group 1 large-sized central offices: 25 large-sized central offices x 12 routers per central office = 300 Level 2 routers

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Cisco Network Solutions for the Telco DCN: SONET/SDH OSI Environments Scaling SONET/SDH in the Telco DCN: Overview

In Table 2, the number of standalone Level 2 routers is 5,100. The total number of domains for each group was computed as follows: The number of Level 2 routers in a group was divided by the domain size. The domain size was determined by the routing engine performance of the standalone router. In this design, the domain size is 500, and there would be a total of 13 domains for the network. A number of obvious issues come up with this example: It is necessary to purchase a large number of standalone routers to provide the Level 2 functions. All of the routers must be monitored and maintained by a NOC. A method of routing between OSI domains is required, and either an interdomain routing protocol or static routes must be used.

IS-IS Multiarea DCN Architecture with SONET/SDH Deployment in All Central Offices
Now let us design the network using the Cisco IOS software IS-IS multiarea feature. Service providers deploying SDH rings today typically are managing all of their rings with OSI, and their network design option assumes that at least one OSI area should be supported in every central office, and that a Level 2 router is placed in every central office. The following are the key assumptions for this network design:


What is the number of SONET nodes in the network today? There are 25,000 SONET/SDH nodes deployed today.



What is the growth rate (number of nodes added per year) of the SONET/SDH network? There are 4000 SONET/SDH nodes added per year.



What is the size of the Level 1 OSI area that the routing engine can support? In other words, how many Level 1 routers can be in an area? The Level 1 area size is 50 routers.



What is the size of the OSI domain that the Level 2 routing engine can support? The domain size is 500 Level 2 routers.



How many network elements does the service provider want to place in an area to start with? Does the service provider want to leave room for growth within an area? The customer wants to place 30 network elements in an area and leave address space for 20 additional network elements in an area.



How many central offices does the service provider have in the DCN? There are 1700 central offices in the network.



Does the service provider want to support a single GNE or dual GNEs? Most of the rings have a single GNE.



What is the average ring size? Average ring size is ten.



How many rings can be aggregated into a single area? Three SONET/SDH rings per area 3 are required.



How many SONET rings are in a large-sized central office? The large-sized central office will have 36 SONET rings.



How many SONET rings are in a medium-sized central office?

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Cisco Network Solutions for the Telco DCN: SONET/SDH OSI Environments Scaling SONET/SDH in the Telco DCN: Overview

The medium-sized central office will have ten SONET rings.


How many SONET rings are in a small-sized central office? The small-sized central office will have one SONET ring.

There are five geographic areas, and within each geographic area the actual number of large-, medium-, and small-sized central offices must be determined. The central office size can be allocated as follows: 10 percent large-sized, 30 percent medium-sized, and 60 percent small-sized. Table 1 will be used again to represent the numbers of central offices per geographic area. The number of rings terminating in a differently sized central office can be as follows: A small-sized central office can have 1, a medium-sized central office can have 10, and a large-sized central office can have 36 rings. Small-sized central offices would have one SONET/SDH ring. Each central office will have at least one OSI area. The next step is to compute the number of Level 2 routers required to implement the design. The design will use Cisco 3621 routers in small-sized central offices, which can support up to twelve Level 1 OSI areas. The assumption is that there will be only one OSI area per small-sized central office, and one Cisco 3621 router will be sufficient per small-sized central office. The Cisco 3631 router has two network modules that can be used for contact closure and serial connectivity. Next, compute the number of small-sized routers for each group. In Group 1, there are 150 small-sized central offices and there is one Level 1/Level 2 router per central office. There are 150 Level 2 routers to support small-sized central offices for Group 1. The computations follow the totals that are listed in Table 3.
Table 3 Level 2 Router Requirements

Geographic Location Group 1 Group 2 Group 3 Group 4 Group 5 —

Total Number of Offices 250 500 200 600 150 1700

Level 2 Small-Sized 150 300 120 360 90 —

Level 2 Medium-Size d 150 300 120 360 90 —

Level 2 Large-Sized 50 100 40 120 30 —

Level 2 Total 350 700 280 840 210 2380

Total Number of Domains 1 2 1 2 1 7

As Table 3 indicates, the number of Level 2 routers has still been substantially reduced over the classic DCN design. Use the following computations to understand how the reductions were made: Group 1 small-sized central office: 150 small-sized central offices x 1 router per central office = 150 Level 2 routers Group 2 small-sized central offices: 300 small-sized central offices x 1 router per central office = 300 Level 2 routers Group 3 small-sized central offices: 120 small-sized central offices x 1 router per central office = 120 Level 2 routers Group 4 small-sized central offices: 360 small-sized central offices x 1 router per central office = 360 Level 2 routers

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Cisco Network Solutions for the Telco DCN: SONET/SDH OSI Environments Scaling SONET/SDH in the Telco DCN: Overview

Group 5 small-sized central offices: 90 small-sized central offices x 1 router per central office = 90 Level 2 routers Next, compute the number of routers required for the medium-sized central offices. The network design uses Cisco 3631-DC-central office or Cisco 3662-DC-central office routers. Both of these routers support 12 Level 1 OSI areas with the IS-IS multiarea software. This design calls for ten OSI rings per central office. The original network design called for four Level 1 areas: 10 rings ÷ 3 rings per area = 4 Level 1 areas (rounded up) One Cisco 3631 or Cisco 3662 router running the IS-IS multiarea software will support a medium-sized central office. The design calls for redundant IS-IS Level 1/Level 2 routers for medium- and large-sized offices. There are 75 medium-sized central offices in Group 1. Each medium-sized central office requires one Level 1/Level 2 router as previously computed, and a second router for backup. The total number of Level 1/ Level 2 routers for medium-sized central offices is as follows (see Table 3): Group 1 medium-sized central offices: 75 medium-sized central offices x 2 routers per central office = 150 Level 2 routers Group 2 medium-sized central offices: 150 medium-sized central offices x 2 routers per central office = 300 Level 2 routers Group 3 medium-sized central offices: 60 medium-sized central offices x 2 routers per central office = 120 Level 2 routers Group 4 medium-sized central offices: 180 medium-sized central offices x 2 routers per central office = 360 Level 2 routers Group 5 medium-sized central offices: 45 medium-sized central offices x 2 routers per central office = 90 Level 2 routers The computation of the large-sized central office numbers for Table 3 is the same process as previously outlined for the medium-sized central offices. (See Table 1 for the number of central offices.) The design uses Cisco 3631-DC-central office or Cisco 3662-DC-central office routers. Both of these routers support 12 Level 1 OSI areas with the IS-IS multiarea software. The design calls for 36 OSI rings per central office, as defined in the original network design computation: 36 rings ÷ 3 rings per area = 12 Level 1 areas One Cisco 3631 or Cisco 3662 router running the IS-IS multiarea software will support a large-sized central office. The design calls for redundant IS-IS Level 1/Level 2 routers for medium- and large-sized offices. A second router will be placed in every large-sized office. There are 25 large-sized central offices in Group 1. The total number of Level 1/ Level 2 routers for large-sized central offices is as follows: Group 1 large-sized central offices: 25 large-sized central offices x 2 routers per central office = 50 Level 2 routers. The following examples show the remainder of the group’s computations: Group 2 large-sized central offices: 50 large-sized central offices x 2 routers per central office = 100 Level 2 routers. Group 3 large-sized central offices: 20 large-sized central offices x 2 routers per central office = 40 Level 2 routers

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Cisco Network Solutions for the Telco DCN: SONET/SDH OSI Environments The Cisco Three-Tiered DCN Network Architecture

Group 4 large-sized central offices: 60 large-sized central offices x 2 routers per central office = 120 Level 2 routers Group 5 large-sized central offices: 15 large-sized central offices x 2 routers per central office = 30 Level 2 routers The total number of Level 2 routers is listed in Table 3. The network is divided into five geographic areas, and each geographic area is a logical grouping of central offices. The logical central office grouping will make up an OSI domain. (In IS-IS, a domain is a logical set of networks, unlike Internet domains that are general groupings of networks based on organization type or geography.) In this design, the performance characteristics of Level 2 routers allow the OSI domain to grow to 500 standalone routers. The domain size assumes that the routers have at least the performance capability of a Cisco 3662 or 3631 router. In Table 3, the number of Level 2 routers in Groups 2 and 4 exceeds 500, so these groups are split into two domains. A domain is made up of standalone access routers and standalone distribution routers; see Figure 3 and the next section.

The Cisco Three-Tiered DCN Network Architecture
Service providers need a basic architecture for the DCN network. The recommended architecture is a three-tiered design. This design is described in the following sections:
• • •

Three-Tiered DCN Network Overview, page 12 OSI Addressing Issues and Suggestions, page 13 OSI Addressing Implementation, page 17

Three-Tiered DCN Network Overview
A three-tiered DCN architecture design will ensure manageable and scalable networks with the ability to easily add network equipment with new features and new services as needed. At the core of the DCN are multiprotocol routers capable of transporting IP, OSI, and X.25. A three-tiered architecture solution as shown in Figure 3 consists of core, distribution, and access elements. A backbone contains routers or WAN switches that form a core or transport utility. Switching centers equipped with distribution routers are located around the backbone to provide symmetric connectivity to central offices. At each central office, access routers provide connectivity into their respective switching and distribution center. Reliability is built into the DCN by designing in redundancy at each tier of the architecture. The access layer defines the DCN interface to the network elements located within the central office. The access routers are configured as Level 1/Level 2. The core and distribution routers are configured as Level 1/Level 2 or Level 2.

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Cisco Network Solutions for the Telco DCN: SONET/SDH OSI Environments The Cisco Three-Tiered DCN Network Architecture

Figure 3

DCN Three-Tiered Architecture

Access central offices

Distribution

Core

The IS-IS routing protocol is run within the OSI domains. Static routes or an interdomain routing protocol can be run between the OSI domains. Cisco recommends running an interdomain routing protocol in the core. Cisco customers have traditionally used ISO-IGRP (the Interior Gateway Routing Protocol developed by Cisco Systems for ISO CLNS) as their interdomain routing protocol. Cisco has developed support for CLNS extensions within multiprotocol Border Gateway Protocol (BGP). The BGP work is based on Internet Engineering Task Force (IETF) RFC 2283. BGP is the mostly widely implemented interdomain routing protocol today. When implementing the three-tier architecture, it is important to look at the bandwidth of the links and location of the NOC. Typically, the NOC or the data centers with the OSS are built as an additional access site in the architecture. The size of the links to the distribution center may be larger because of the amount of traffic. In the DCN environment, the flow of data is between the OSSs and the network elements, which are downstream from the central office. Typically, very little data is sent between network elements and central offices today, but there are applications that will create more traffic between central offices. These applications include remote login and signaling for bandwidth. Remote login allows a technician logged in to a network element to access another network element over the DCN. The remote login feature saves the technician from needing to be physically at a site to perform maintenance and troubleshooting tasks. Bandwidth signaling applications are being defined as part of the following standards:
• • •

ITU-T G.807—Requirements for the Automatic Switched Transport Network (ASTN) ITU-T G.8080—Architecture for the Automatic Switched Optical Network (ASON) Optical Internetworking Forum (OIF) User Network Interface (UNI) 1.0—This standard provides signaling between network elements, and between network elements and clients. It also provides signaling for both in-band and out-of-band or DCN networks, and for bandwidth.

OSI Addressing Issues and Suggestions
In ITU-T Recommendation X.213, Data Networks and Open Systems Communications Open Systems Interconnections Service Definitions, the network layer addressing is described in ANNEX A. The document is also referred to as ISO/IEC 8348:1996(E). Refer to ITU-T Recommendation X.213 for complete details about OSI addressing. This section focuses on basic address information used in the SONET/SDH environments.

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The OSI network address is referred to as a network service access point (NSAP). The NSAP is assigned to the end system (ES) or intermediate system (IS) device. Unlike in IP, which has an address for every network interface, the OSI network device receives only one address, the NSAP address. The NSAP address has two parts, the Initial Domain Part (IDP) and Domain Specific Part (DSP), as shown in Figure 4.
Figure 4 NSAP Addresses

NSAP Address

IDP Initial Domain Part

DSP Domain Specific Part

Initial Domain Part AFI Authority Format Identifier

The IDP of the NSAP is assigned by address authorities. The address authorities allocate the bytes in the DSP. Six address authorities are currently defined, each briefly described as follows:
• • • •

ITU-T E.164—Specifies the initial domain identifier (IDI) as an ISDN number up to 15 digits long. This recommendation also specifies a PSTN up to 12 digits long. ITU-T F.69—Specifies the IDI as an international telex number up to eight digits long. ITU-T X.121—Specifies the IDI as an X.121 address for public X.25 networks, and is up to 14 digits long. International Organization for Standardization/International Electrotechnical Commission (ISO/IEC) Data Country Code (ISO DCC)—Specifies the IDI as a three-digit numeric code as defined by ISO 3166. An ISO member body within a country is assigned a three-digit code. The DSP is allocated by the ISO member body for a country. ISO 6523-ICD—Specifies the IDI as a four-digit International Code Designator (ICD) as defined by ISO 6523. Local—This address is the IDI and, if null, is used for local routing.

• •

The SONET/SDH environments utilize the address authority defined by the ISO DCC. The AFI can have a value of 38 or 39. The value for the IDI is the country code. For the United States, the IDI is 840. The American National Standards Institute (ANSI) is the ISO body in the United States that assigns the 39.840 address space. The DSP addressing is defined in the American National Standard X3.216-1992, Structure and Semantics of the Domain Specific Part of the Network Service Access Point Address. An ANSI-defined DSP is shown in Figure 5. The DSP is 17 binary octets long. The breakdown of the DSP is listed after the figure; the number of octets is shown under each category.

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88788

IDI Initial Domain Identifier

Cisco Network Solutions for the Telco DCN: SONET/SDH OSI Environments The Cisco Three-Tiered DCN Network Architecture

Figure 5

ANSI DSP Structure

IDP AFI 39 1 IDI 840 2 DFI 128 1 org 3 res 2

DSP

rd 2

area 2

system 6

sel 1
88787

Number of Octets
• • • • • • • •

AFI—Authority format identifier value of 39 defines the NSAP type as ISO/IEC. The length is one binary octet. IDI—Initial domain identifier value of 840 defines the country as United States. The length is two binary octets. DFI—Domain Specific Part format identifier specifies the version of the ANSI X3.216. The decimal value is 128. Hexadecimal value is 80. The length is one binary octet. org—The organization is identified by the value that is assigned by ANSI. The length is three binary octets. res—A reserved field set to a value of 0. The length is two binary octets. rd—A routing domain prefix to be used for address summarization. This prefix allows the summarization of the multiple areas with one routing entry. The length is two binary octets. area—This portion of the NSAP identifies the unique Level 1 area. The length is two binary octets. system—This is the unique system identifier of an ES. There can only be one ES within an area with this unique identifier. There is no definition on how to assign the identifier. Implementors often use the MAC address off the first Ethernet port or a portion of the IP address. The length is six binary octets. sel—The NSAP selector is used to specify the network service user. The NSAP selector is used to differentiate multiple applications connections to the same ES. An analogous solution would be TCP/IP port numbers. The network layer is set to a value of 0, so a Cisco router is typically configured to a value of 0. The length is one binary octet.



In the Telcordia Specification GR-253-core, in Section 8 of the document, the NSAP address is described with reference to the DCN and SONET network elements. ISO DCC is the selected address format, and the AFI has a decimal value of 39 that is encoded in binary coded decimal. The AFI is configured into Cisco IOS software in decimal format. The AFI is broken down in Figure 6.
Figure 6 AFI Structure

AFI Octets Decimal Binary Cisco IOS entry 3 0011 3 1 9 1001 9

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The ISO DCC in this example is for the United States, so the IDI decimal value is 840. The IDP portion of the NSAP is encoded in packed binary coded decimal format. The AFI and a portion of the IDI is shown in Figure 7.
Figure 7 AFI and IDI Structure

AFI Octets Decimal Binary Cisco IOS entry 3 0011 3 1 9 1001 9 8 1000 8

IDI 1.5 4 0100 4 0 0000 0

IDI PAD 0.5 None 1111 F

The IDI shown in Figure 7 takes up 1.5 octets. The IDI has two octets set aside. The Telcordia GR-253 specification calls for filling the last four bits of the octet with ones. This process is referred to as the IDI PAD. Because there is no decimal value for the binary number 1111 in Binary Coded Decimal (BCD), the number is represented in hexadecimal as an F. The DSP portion of the NSAP is typically configured in hexadecimal. The DFI portion of the DSP has a decimal value of 128, a binary value of 1000 0000, and a hexadecimal value of 80; see Figure 8.
Figure 8 AFI, IDI , and DFI Structure

AFI Octets Decimal Binary Cisco IOS entry 3 0011 3 9 1001 9 1 8 1000 8

IDI 1.5 4 0100 4 0 0000 0

IDI PAD 0.5 None 1111 F 128 1000 8

DFI 1 0000 0

The next portion of the DSP, which is the organizational identifier, is assigned by ANSI. The organization identifier is made up of three octets that are entered into the Cisco IOS software as six hexadecimal characters. The following example uses an organization identifier of 119999. The NSAP has the following format: 39.840f.80yy.yyyy.rrrr.dddd.aaaa.iiii.iiii.iiiii.ss and can be interpreted as follows:
• • •

y—The organizational identifier as assigned by ANSI or other address authority for your region of the world. r—This portion of the NSAP is reserved and given a value of zero. d—The routing domain portion of the NSAP address. The routing domain is a collection of Level 1 areas. The routing domain allows the collection of Level 1 areas to be summarized among the Level 2 routers. The field can be provided in hexadecimal characters. a—The Level 1 area address as defined by ISO 10589. The field can be provided in hexadecimal characters.



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i—The individual system identifier. The structure of the format of the value is chosen by the customer. Customers typically input the MAC address of the first Ethernet port or a portion of the IP address. s—The NSAP selector. The value for a network entity title (NET) is zero.



Following is an example of the Cisco IOS software commands used to configure the NSAP on a Cisco router: router isis DCN net 39.840f.8011.9999.0000.0001.000b.00e0.f725.3338.00

OSI Addressing Implementation
This section describes how to implement an addressing plan based on the “OSI Addressing Issues and Suggestions” section on page 13. ANSI or the ISO DCC address authority in your geographic area of the world assigns the address space. ANSI can be contacted at http://ansi.org/. Instructions for applying for a unique organizational identifier are included under the registration services portion of the ANSI website. In this example, the unique organizational identifier is 119999. The next portion of the DSP is marked reserved. The reserved portion of the NSAP is two octets. The NSAP up to this point looks like 39.840f.8011.9999.0000, and the format of the DSP is defined, but the service provider determines the assignment of the address space. Because the remainder of the DSP is left up to the service provider, let us look at an example. In the example, the routing domain, the area, the individual system identifier, and NSAP selector will be filled out. The example has the following five OSI routing domains—domain 1111, domain 2222, domain 3333, domain 4444, and domain 5555. The first alternative has five OSI domains or routing domains. Each domain is two octets long. The key to laying out the address space is to allow summarization of domains, as follows: OSI domain 1: 39.840f. 8011.9999.0000.1111 OSI domain 2: 39.840f. 8011.9999.0000.2222 OSI domain 3: 39.840f. 8011.9999.0000.3333 OSI domain 4: 39.840f. 8011.9999.0000.4444 OSI domain 5: 39.840f. 8011.9999.0000.5555 The area addressing can be created by adding the area addresses one at a time within a domain. Therefore, the first area within domain 1111 could be area address 0001, and the NSAP would be as follows: 39.840f.8011.9999.0000.1111.0001 The system identifier uniquely identifies the device within the area. To create this identifier, service providers often use the MAC address of the first Ethernet port on the router, which is displayed by entering the show interface EXEC command on the router (for purpose of example, the MAC address is shown in bold text):
Router# show interface ethernet 0/0 Ethernet0/0 is up, line protocol is down Hardware is AmdP2, address is 00d0.5872.9720 (bia 00d0.5872.9720) Internet address is 172.168.0.22/24 MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec, reliability 231/255, txload 1/255, rxload 1/255 Encapsulation ARPA, loopback not set Keepalive set (10 sec) ARP type: ARPA, ARP Timeout 04:00:00

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Last input never, output 00:00:08, output hang never Last clearing of "show interface" counters never Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0 Queueing strategy: fifo Output queue: 0/40 (size/max) 5 minute input rate 0 bits/sec, 0 packets/sec 5 minute output rate 0 bits/sec, 0 packets/sec 0 packets input, 0 bytes, 0 no buffer Received 0 broadcasts, 0 runts, 0 giants, 0 throttles 0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored 0 input packets with dribble condition detected 12 packets output, 1009 bytes, 0 underruns 12 output errors, 0 collisions, 2 interface resets 0 babbles, 0 late collision, 0 deferred 13 lost carrier, 0 no carrier 0 output buffer failures, 0 output buffers swapped out

The following example shows how to use the MAC address 00d0.5872.9720 to create the area identifier: 39.840f.8011.9999.0000.1111.0001.00d0.5872.9720 It is also acceptable to use the IP address in the station identifier. In the following example, the IP address on the Ethernet interface is 172.168.0.22. Some service providers choose to use the IP address on the loopback interface, but for this example the Ethernet interface is used. The 172 portion of the IP address was left out and the remainder of the IP address was imbedded. 39.840f.8011.9999.0000.1111.0001.0168.0000.0022 The following example is another way to use the IP address to create the area address: 39.840f.8011.9999.0000.0001.1721.6800.0022 A final example would be to take the IP address and encode it in hexadecimal format. This action allows the entire IP address to be placed into the end system identifier, but recognizing the IP address is not as straightforward by doing so. The following list shows the loopback address 172.168.0.22 encoded as hexadecimal numbers:
• • • •

172 = ac 168 = a8 0 = 00 22 = 16

Plugging the hexadecimal numbers into the end system identifier would result in the number 39.840f.8011.9999.0000.1111.0001.0000.aca8.0016. Notice that the first two octets of the system identifier are padded with 0s.

Note

The NSAP selector is set to 00 for an IS-IS device. The following example shows what the NSAP of an IS-IS router would look like: 39.840f.8011.9999.0000.1111.0001.00d0.5872.9720.00.

Access Layer Configuration
This section focuses on the access layer of Cisco’s three-tiered network architecture and contains these sections:
• •

SONET/SDH Scaling Issues for Multiple OSI Areas, page 19 Defining IS-IS Multiareas with ISL Trunking, page 22

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• • • • • • •

Defining IS-IS Multiareas with IEEE 802.1Q Trunking, page 32 Defining Multiple Areas with Manual Area Addressing, page 35 Using Generic Routing Encapsulation Tunnels to Prevent Area Partitions, page 39 IS-IS Attach-Bit Control Feature, page 45 Using IP over CLNS Tunnels to Access Remote Devices, page 50 Mapping NSAPs to Device Names Using TARP, page 55 Maintaining and Troubleshooting the IS-IS Network, page 69

SONET/SDH Scaling Issues for Multiple OSI Areas
All SONET/SDH nodes on a ring are typically Level 1 routers, because of the performance issue described in the “DCN Design Considerations for OSI” section on page 5. SONET/SDH nodes on a ring should be in the same OSI area if the nodes are all Level 1. SONET/SDH devices must be organized into many small-sized OSI areas, as described in earlier sections about IS-IS multiarea DCN architecture. The IS-IS multiarea was added to the Cisco IOS feature set to improve the scaling of an IS-IS network in the SONET/SDH environments. The feature allows the configuration of up to 29 Level 1 IS-IS processes on Cisco routers.

Note

The maximum number IS-IS process that can be configured is 29. However, the configuration of multiprotocol BGP (mBGP) CLNS and ISO-IGRP changes that number. If you configure mBGP CLNS, two IS-IS processes are used and you can configure only one instance of mBGP. On a router with mBGP CLNS configured, the user can only configure 27 IS-IS processes. The configuration for ISO-IGRP takes two IS-IS processes. You can configure multiple ISO-IGRP processes and each ISO-IGRP process configured uses two IS-IS processes. If you configure two ISO-IGRP processes, then four IS-IS processes would be used. You have the ability to configure 25 IS-IS processes, which is 29 IS-IS processes minus the four IS-IS processes used by the two ISO-IGRP instances. If you configure the mBGP CLNS process and one ISO-IGRP processes, you can configure 25 IS-IS processes. You start with 29 IS-IS processes and subtract the two IS-IS processes used by the one ISO-IGRP process and subtract the two IS-IS processes used by the mBGP CLNS process. The number of IS-IS processes supported are specific to a platform, the architecture of the network, and the other tasks being performed on a platform. Specific base guidelines have been released for the Cisco 1800, 2600, and 3600 series platforms, as listed in Table 4.
Table 4 IS-IS Processes Supported on Cisco Router Platforms

Router Platform Cisco 1841 Cisco 2610, Cisco 2611, Cisco 2620, Cisco 2621, and Cisco 2651 Cisco 2691 Cisco 2811 Cisco 2821

IS-IS Processes 3 3 8 8 8

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Table 4

IS-IS Processes Supported on Cisco Router Platforms (continued)

Router Platform Cisco 2851 Cisco 3640 Cisco 3725 Cisco 3631 Cisco 3662 Cisco 3745 Cisco 3825 Cisco 3845

IS-IS Processes 8 8 8 12 12 15 15 20

These numbers assume that the customer is implementing the three-tiered network architecture described in the “The Cisco Three-Tiered DCN Network Architecture” section on page 12. A flat network with many IS-IS adjacencies will not perform as well as the tiered network. For example, a poor design builds a Frame Relay cloud that peers all the sites together. As the number of sites in the Frame Relay network increase, the number of IS-IS adjacencies to maintain and the number of CPU cycles would also increase. The CPU cycles on the router can be affected by other features enabled in the Cisco IOS software. Service providers often perform protocol translation on access routers. The router is translating between a TCP/IP session from the OSS and X.25 to the network element. Each packet is process-switched by the CPU, which affects the amount of CPU cycles available for maintaining IS-IS adjacencies. Cisco routers are used to interconnect each Level 1 area or ring to the Level 2 backbone. A typical routing engine in a SONET network element can support only a routing table of 50 to 100 entries. This limitation bounds the area size to 50 Level 1 SONET routers. The service provider will need to check with their specific SONET/SDH vendors. Basic network designs were reviewed earlier in this document. Also, some SONET/SDH vendors have limitations on the number of ES adjacencies and Level 1 adjacencies that a GNE can support. The number of adjacencies has been as low as 15 on some SONET/SDH nodes. In early deployments, service providers were running into adjacency problems when implementing Ethernet hubs because they were putting multiple GNEs from different OSI areas on the same Ethernet hub, as shown in Figure 9. The GNEs in the different areas were forming ES adjacencies, which caused performance problems for the GNEs.

Note

Gateway network elements are the network elements that are connected to the Ethernet and the optical ring or chain. The gateway network element is a gateway between the DCN and the in-band management channel, which is called the data communication channel (DCC).

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Figure 9

GNEs Forming ES Adjacencies

CLNS packet flow Area VLAN 1 0001 GNE NE Area VLAN 2 0002 GNE NE

Area VLAN 11 0011 GNE NE
95707 95706

Area VLAN 12 0012 GNE NE

Cisco’s solution is shown in Figure 10. Cisco recommends installing an Ethernet switch and separating the GNEs, thereby placing all the GNEs in different OSI areas on a separate VLAN. Figure 10 shows 12 OSI areas that correspond to 12 VLANs.
Figure 10 GNEs Separated by an Ethernet Switch

CLNS packet flow Area VLAN 1 0001 GNE NE Area VLAN 2 0002 GNE NE

Area VLAN 11 0011 GNE NE Area VLAN 12 0012 GNE NE

SONET network elements communicate over a DCC in-band channel in the SONET ring at 192 KB. The in-band channel is used to access SONET nodes on the ring. Typically, there is only one GNE onto smaller rings deployed in a metropolitan setting. The DCC is often used to access the SONET node placed on a customer site or to access an optical amplifier in the fiber. Extending the DCN to these sites would not make sense from an economic or security standpoint. The limited 192 KB bandwidth of the DCC limits the size of the SONET/SDH ring. One method around the DCC bandwidth limitation is to add GNEs to the ring. The GNEs should be separated by four to seven hops. The service provider should consult the GNE vendor.

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Defining IS-IS Multiareas with ISL Trunking
This section describes the configuration for an IS-IS multiarea with VLANs using Inter-Switch Link (ISL) trunking (a Cisco-proprietary protocol that maintains VLAN information as traffic flows between switches and routers). Typically, the multiarea feature is used at the access portion of the network. The OSS is located in the data center, and the CLNS packets are routed across the network to the central office router. Figure 11 shows a typical configuration.
Figure 11 IS-IS Multiarea Network Using ISL

CLNS packet flow VLAN using ISL NE14A Area 0001 NE14B

IP/OSI OSS Central office router

NE15A Area 0002 Area 0003

NE25A

NE25A
95118

NE26A

NE26B

Figure 11 shows three IS-IS Level 1 areas. For purpose of example, the areas are small, with only two or three SONET or SDH network elements per area. A more typical area would have 30 to 50 network elements. This configuration example uses a Cisco 3640 router and a Cisco Catalyst 2924XL switch. The IS-IS multiarea feature supports only one Level 1 or Level 2 IS-IS process per router. The router can be configured for up to 28 independent Level 1 processes and one Level 1/Level 2 process. The number of IS-IS Level 1 processes supported depends upon the router platform. Each Level 1 IS-IS process must have a unique NSAP within an OSI area. The unique portion of the NSAP is the system identifier. The same unique system identifier must be used when creating multiple NSAPS on the Cisco 3640 router. In this example, the system identifier used is MAC address 0010.7bc7.ae40 from Ethernet port 0/0. See the “OSI Addressing Implementation” section on page 17 for more information about selecting system identifiers. The MAC address is listed in the output of the show interface command, as the following example shows (text bolded for purpose of example):
3640A# show interface ethernet0/0 Ethernet0/0 is up, line protocol is up Hardware is AmdP2, address is 0010.7bc7.ae40 (bia 0010.7bc7.ae40) Internet address is 192.168.0.49/24 MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec, reliability 255/255, txload 1/255, rxload 1/255 Encapsulation ARPA, loopback not set Keepalive set (10 sec) ARP type: ARPA, ARP Timeout 04:00:00 Last input 00:00:07, output 00:00:00, output hang never Last clearing of "show interface" counters never Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0 Queueing strategy: fifo Output queue: 0/40 (size/max)

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5 minute input rate 0 bits/sec, 0 packets/sec 5 minute output rate 0 bits/sec, 0 packets/sec 4 packets input, 533 bytes, 0 no buffer Received 3 broadcasts, 0 runts, 0 giants, 0 throttles 0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored 0 input packets with dribble condition detected 11 packets output, 786 bytes, 0 underruns 0 output errors, 0 collisions, 4 interface resets 0 babbles, 0 late collision, 0 deferred 0 lost carrier, 0 no carrier 0 output buffer failures, 0 output buffers swapped out

Using address examples from the “OSI Addressing Implementation” section on page 17, the routing domain number is 1111. The following example configures the access router to handle the following three OSI areas: 39.840f.8011.9999.0000.1111.0001 39.840f.8011.9999.0000.1111.0002 39.840f.8011.9999.0000.1111.0003 The corresponding NSAPs for the Cisco 3640 router are built with a unique system identifier and a network selector value of 00. The network selector for the network layer is 00. The chosen system identifier for this example is the MAC address from Ethernet interface 0/0, so the NSAPs for the Cisco 3640 routers are as follows: net 39.840f.8011.9999.0000.1111.0001.0010.7bc7.ae40.00 net 39.840f.8011.9999.0000.1111.0002.0010.7bc7.ae40.00 net 39.840f.8011.9999.0000.1111.0003.0010.7bc7.ae40.00 An interface can be associated with only one IS-IS processes. In the first solution that Cisco provided to service providers, a separate Ethernet interface was configured for every IS-IS process and LAN. Each LAN was on a separate hub, as shown in Figure 12.
Figure 12 IS-IS Multiarea Network Using Separate Ethernet Interfaces

CLNS packet flow

NE14A E 0/0 E 0/1 Central office router E 0/2 NE15A

Area 0001

NE14B

NE25A

Area 0002 Area 0003

NE25B
95115

NE26A

NE26B

The next solution that Cisco provides makes it possible to consolidate the individual hubs into a Cisco Catalyst switch with VLANs. Each VLAN on the Cisco Catalyst switch had a separate Ethernet connection from the router, as shown in Figure 13.

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Figure 13

IS-IS Multiarea Network Consolidating Hubs on a Switch (VLAN Trunking)

CLNS packet flow Area 0001

E 0/0 E 0/1

NE14A

NE14B

NE15A Central office router Area 0002 Area 0003

E 0/2

NE25A

NE25B
95117 95116

NE26A

NE26B

The number of physical Ethernet interfaces can be reduced by using VLAN trunking. A separate IS-IS process can be assigned to a subinterface. The example in this section focuses on implementing an IS-IS multiarea on an ISL trunk, as shown in Figure 14.
Figure 14 IS-IS Multiarea Network Using VLAN Trunking and ISL Encapsulation

CLNS packet flow

VLAN using ISL

NE14A

Area 0001

NE14B

NE15A 3640A Central office router 2924XL NE25A Area 0002 Area 0003

NE25B

NE26A

NE26B

Configuring an IS-IS Multiarea Network on a VLAN Using ISL Encapsulation
This section uses the network shown in Figure 14 as the basis for the configurations. The examples use a Cisco 3640 router with the Telco Feature Set running Cisco IOS Release 12.2(15)T. Begin by enabling a CLNS routing and enabling TARP (assuming that TARP will be used). TARP is the target identifier (TID) Address Resolution Protocol, which is the name given to a piece of equipment by service providers in the United States. (TARP is an application that automates the mapping of CLNS addresses to TIDs, and will be described in more detail in the “Enabling TARP” section on page 60.) The following example shows how to enable TARP and assign the router a TID using the router’s host name; in this example, the assigned TID is 3640A for a Cisco 3640 router: clns routing tarp run tarp tid 3640A

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Next, create the IS-IS routing processes for the three areas shown in Figure 14. The first IS-IS routing process created can be a Level 1/Level 2, which is a circuit-type Level 1/Level 2. (Note that the circuit-type Level 1/Level 2 configuration will not show up in the system configuration output because “is-type level-1-2” is the default.) The remaining IS-IS processes will be Level 1, which is specified and identified in the Cisco IOS software as “is-type level-1.” After the first Level 1/Level 2 IS-IS process is configured, the remaining processes will automatically be configured by the software as “is-type level-1.” Each IS-IS process has an identifier. In the examples, the IS-IS process identifiers are named after the OSI area. For example, the IS-IS process identifier area0001 is used for area 0001. (Note that the IS-IS process identifier name is arbitrary, but that area names are useful for troubleshooting. The service provider could have named the IS-IS processes after colors, for example.) The system identifier used in the example is the MAC address (0010.7bc7.ae40) from Ethernet port 0/0. The following example shows how to configure the IS-IS routing processes for the three areas: router isis area0001 net 39.840f.8011.9999.0000.1111.0001.0010.7bc7.ae40.00 ! router isis area0002 net 39.840f.8011.9999.0000.1111.0002.0010.7bc7.ae40.00 is-type level-1 ! router isis area0003 net 39.840f.8011.9999.0000.1111.0003.0010.7bc7.ae40.00 is-type level-1

The IS-IS process area0001 is specified in the Cisco IOS software with the is-type level-1-2 command, which is the Cisco IOS software default, but no is-type commands will be displayed in the configuration output. The area0001 process will provide connectivity back to the IS-IS backbone. There can be only one Level 2 IS-IS process, and each additional IS-IS process will be at Level 1. Each IS-IS process must be assigned to a separate interface. Fast Ethernet port 3/0 is configured for ISL trunking with three subinterfaces. The encapsulation on the interface is ISL (specified with the encapsulation isl command).

Designated IS Election Process on a LAN
Generally, service providers configure the Cisco access router to be the designated IS on the Ethernet interface. In IS-IS routing, a broadcast medium such as a LAN is not treated as a fully connected topology. Instead, a logical representation of the LAN is created called a pseudonode, which is generated by a Designated Intermediate System (DIS). The DIS is responsible for creating and updating the pseudonode line-state packet (LSP) and flooding the LSPs over the LAN. On a broadcast medium such as Ethernet, one DIS is selected for Level 1 routers and a separate DIS is selected for Level 2 routers. There is no backup DIS. The election of a DIS can be preempted by a DIS with a higher priority. The routers on the LAN, including the DIS, form an adjacency with the pseudonode. A router elects itself the DIS based on interface priority. The priority range is from 0 (lowest) to 127 (highest). A priority of 64 is the default, and a priority of 127 sets the router to be elected as the DIS. If two routers have the same priority, the router with the highest subnetwork point of attachment (SNPA) wins the election. The SNPA, which is the MAC address on the LAN or the data-link connection identifier (DLCI) on a Frame Relay network, is also used to configure a CLNS route for an interface. For the configuration example in this section, the SONET network elements are configured as Level 1 IS-IS routers. In real network implementations, service providers have found that forcing the Cisco router to be the DIS works best. Service providers are basically offloading the DIS functions onto the CPU of the standalone Cisco routers, as opposed to a SONET/SDH network element. This configuration is done by setting the IS-IS priority to 127 on the interface. A Level 1 IS-IS pseudonode is selected on each VLAN.

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The Cisco router labeled “3640A” in Figure 14 is the DIS for each VLAN, and Fast Ethernet interface 3/0.1 is configured first. In the following example, the interface is configured with ISL encapsulation and VLAN 1 is assigned to the interface. IS-IS process area0001 is assigned to the interface using the clns router isis area0001 command. The assignment of the IS-IS processes to the interfaces is shown in the following example. The IS-IS priority for selecting the DIS is modified to 127, from the default 64, to force the Cisco 3640 router to be the DIS. TARP is enabled on the interface. An IP subnet is assigned to VLAN 1 so that the network administrator can assign an IP address to the Cisco Catalyst 2924XL switch for management of the switch. The following example shows how to configure the Cisco router labeled “3640A” as the DIS for each VLAN. The IS-IS priority is set to 127 on the interface. interface FastEthernet3/0 no ip address duplex auto speed auto no cdp enable ! interface FastEthernet3/0.1 description IS-IS area 0001 encapsulation isl 1 ip address 192.168.2.61 255.255.255.192 no ip redirects no cdp enable clns router isis area0001 isis priority 127 tarp enable

Fast Ethernet interface 3/0.2 is configured next. In the following example, the interface is configured with ISL encapsulation, and VLAN 2 is assigned to the interface. IS-IS process area0002 is assigned to the interface by the clns router isis area0002 command. The assignment of the IS-IS processes to the interfaces is shown in the following example. The IS-IS priority for selecting the DIS is modified to 127 from the default 64, to force the Cisco 3640 router to be the DIS. TARP is enabled on the interface. interface FastEthernet3/0.2 description IS-IS area 0002 encapsulation isl 2 no cdp enable clns router isis area0002 isis priority 127 tarp enable

Fast Ethernet interface 3/0.3 is the third subinterface to be configured. As with the first two subinterfaces, this interface is configured with ISL encapsulation, and VLAN 3 is assigned to the interface. IS-IS process area0003 is assigned to the interface by the clns router isis area0003 command. The assignment of the IS-IS processes to the interfaces is shown in the following example. The IS-IS priority for selecting the DIS is modified to 127 from the default 64, to force the Cisco 3640 router to be the DIS. TARP is enabled on the interface. interface FastEthernet3/0.3 description IS-IS area 0003 encapsulation isl 3 no cdp enable clns router isis area0003 isis priority 127 tarp enable !

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Verifying an IS-IS Multiarea Network Using VLAN Trunking and ISL Encapsulation
The next step is to verify that CLNS is operating on the router. Use the show clns EXEC command to verify that CLNS is running. The following example shows typical output of the show clns command:
3640A# show clns Global CLNS Information: 3 Interfaces Enabled for CLNS NET: 39.840f.8011.9999.0000.1111.0001.0010.7bc7.ae40.00 NET: 39.840f.8011.9999.0000.1111.0002.0010.7bc7.ae40.00 NET: 39.840f.8011.9999.0000.1111.0003.0010.7bc7.ae40.00 Configuration Timer: 60, Default Holding Timer: 300, Packet Lifetime 64 ERPDU's requested on locally generated packets Intermediate system operation enabled (CLNS forwarding allowed) IS-IS level-1-2 Router: area0001 Routing for Area: 39.840f.8011.9999.0000.1111.0001 IS-IS level-1 Router: area0002 Routing for Area: 39.840f.8011.9999.0000.1111.0002 IS-IS level-1 Router: area0003 Routing for Area: 39.840f.8011.9999.0000.1111.0003

The sample output shows that the router has CLNS enabled on three interfaces. The three OSI NSAPs are listed. Notice that the system identifier—0010.7bc7.ae40—is the same for all three NSAPs. The three IS-IS processes are listed with their respective process identifiers—area0001, area0002, and area0003. The routing area assigned to each process is also listed. The three interfaces running CLNS can be further examined using the show clns interface EXEC command. Sample command output for all three interfaces follows, starting with Fast Ethernet interface 3/0.1:
3640A# show clns interface fastethernet 3/0.1 FastEthernet3/0.1 is up, line protocol is up Checksums enabled, MTU 1497, Encapsulation SAP ERPDUs enabled, min. interval 10 msec. RDPDUs enabled, min. interval 100 msec., Addr Mask enabled, last sent 00:47:38 Congestion Experienced bit set at 4 packets CLNS fast switching enabled CLNS SSE switching disabled DEC compatibility mode OFF for this interface Next ESH/ISH in 23 seconds Routing Protocol: IS-IS (area0001) Circuit Type: level-1-2 Interface number 0x0, local circuit ID 0x1 Level-1 Metric: 10, Priority: 127, Circuit ID: 3640A.01 Level-1 IPv6 Metric: 10 Number of active level-1 adjacencies: 2 Level-2 Metric: 10, Priority: 127, Circuit ID: 3640A.01 Level-2 IPv6 Metric: 10 Number of active level-2 adjacencies: 0 Next IS-IS LAN Level-1 Hello in 1 seconds Next IS-IS LAN Level-2 Hello in 2 seconds

In this sample output for Fast Ethernet interface 3/0.1, the interface is up and the line protocol is up. Notice that CLNS fast switching is enabled by default. The routing protocol is IS-IS and the associated IS-IS process identifier is area0001. The Circuit Type report indicates whether this circuit is Level 1, Level 2, or Level-1-2. In this case, the circuit type is Level-1-2. The IS-IS priority is 127 on the interface for the Cisco router labeled “3640A.” The Cisco 3640 router is the DIS and identified as the DIS in the Circuit ID field. In other words, the circuit identifier lists the designated router’s host name or system identifier if the routers do not know the host name. In this case, the designated router’s host name is

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3640A. Remember that the Cisco 3640 router interface is set to IS-IS priority of 127, which is the highest value. There are two active Level 1 adjacencies. The adjacency numbers correspond to those shown in Figure 14. The Cisco router labeled “3640A” should have a Level 1 adjacency with the SONET/SDH nodes labeled “NE14A” and “NE15A.” The Level 2 routing metric is 10 and the IS-IS Level 2 priority is 127. The Circuit ID field lists 3640A as the designated router. There are no Level 2 IS-IS adjacencies on Fast Ethernet interface 3/.01. (Normally, the Level 2 adjacency would come from the WAN connection back to the distribution router, or to a Level 2 adjacency with a second Level-1-2 router in the central office configured for a different OSI area on the Level-1-2 IS-IS process.) The following example shows sample output for Fast Ethernet interface 3/0.2:
3640A# show clns interface fastethernet 3/0.2 FastEthernet3/0.2 is up, line protocol is up Checksums enabled, MTU 1497, Encapsulation SAP ERPDUs enabled, min. interval 10 msec. RDPDUs enabled, min. interval 100 msec., Addr Mask enabled Congestion Experienced bit set at 4 packets CLNS fast switching enabled CLNS SSE switching disabled DEC compatibility mode OFF for this interface Next ESH/ISH in 40 seconds Routing Protocol: IS-IS (area0002) Circuit Type: level-1-2 Interface number 0x0, local circuit ID 0x1 Level-1 Metric: 10, Priority: 127, Circuit ID: 3640A.01 Level-1 IPv6 Metric: 10 Number of active level-1 adjacencies: 1 Next IS-IS LAN Level-1 Hello in 2 seconds

This sample output indicates the second VLAN is configured on Fast Ethernet interface 3/0.2. The interface is up and the line protocol is up. CLNS fast switching is enabled by default. The routing protocol is IS-IS and the associated IS-IS process identifier is area0002. The circuit type is Level-1-2 . Fast Ethernet interface 3/0.2 is a Level 1/Level 2 link. The IS-IS priority is 127 on the interface for the Cisco router labeled “3640A,” so 3640A is the DIS and is identified as the DIS in the Circuit ID report. There is one active Level 1 adjacency with SONET/SDH node NE25A. The following example shows sample output for Fast Ethernet interface 3/0.3:
3640A# show clns interface fastethernet 3/0.3 FastEthernet3/0.3 is up, line protocol is up Checksums enabled, MTU 1497, Encapsulation SAP ERPDUs enabled, min. interval 10 msec. RDPDUs enabled, min. interval 100 msec., Addr Mask enabled Congestion Experienced bit set at 4 packets CLNS fast switching enabled CLNS SSE switching disabled DEC compatibility mode OFF for this interface Next ESH/ISH in 17 seconds Routing Protocol: IS-IS (area0003) Circuit Type: level-1-2 Interface number 0x0, local circuit ID 0x1 Level-1 Metric: 10, Priority: 127, Circuit ID: 3640A.01 Level-1 IPv6 Metric: 10 Number of active level-1 adjacencies: 1 Next IS-IS LAN Level-1 Hello in 1 seconds

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The third VLAN is configured on Fast Ethernet interface 3/0.3. The interface is up and the line protocol is up. CLNS fast switching is enabled by default. The routing protocol is IS-IS, and the associated IS-IS process is area0003. The circuit type is Level-1-2. The IS-IS priority is 127 on the interface for the Cisco router labeled “3640A,” so 3640A is the DIS and is identified as the DIS as part of the Circuit ID report. There is one active Level 1 adjacency with SONET/SDH node NE26A. The next step is to examine the IS-IS adjacencies. Use the show clns is-neighbor detail EXEC command to see the adjacency to the SONET/SDH node NE14A:
3640A# show clns is-neighbor detail Area area0001: System Id Interface State Type Priority Circuit Id NE15A Fa3/0.1 Up L1 55 3640A.01 Area Address(es): 39.840f.8011.9999.0000.1111.0001 Uptime: 00:04:16 NE14A Fa3/0.1 Up L1 64 3640A.01 Area Address(es): 39.840f.8011.9999.0000.1111.0001 Uptime: 00:04:16 Area area0002: System Id Interface State Type Priority Circuit Id NE25A Fa3/0.2 Up L1 64 3640A.01 Area Address(es): 39.840f.8011.9999.0000.1111.0002 Uptime: 00:04:17 Area area0003: System Id Interface State Type Priority Circuit Id NE26B Fa3/0.3 Up L1 64 3640A.01 Area Address(es): 39.840f.8011.9999.0000.1111.0003 Uptime: 00:04:16

Format Phase V

Phase V

Format Phase V

Format Phase V

In this sample output, the three IS-IS processes running on the Cisco router are listed by process identifier. The IS-IS process identifiers are area0001, area0002, and area0003. Examining the IS-IS process identifier area0001 in more detail indicates the following:


IS-IS process identifier area0001 lists two system identifiers—NE14A and NE15A—on Fast Ethernet interface 3/0.1. The IS-IS adjacency state is up for both SONET network elements. The adjacency type is a Level 1. The priority advertised by device NE14A is 64 and the priority advertised by device NE15A is 55. The Circuit ID field uniquely identifies the interface on the IS-IS router with a one-octet number. On an Ethernet or multiaccess network, the circuit and system identifier of the DIS are concatenated to create the pseudonode (.3640A.01). The system identifier has been replaced with the host name by Cisco IOS software, so the pseudonode of IS-IS process area0001 is 3640A.01. The Circuit ID field in the output actually shows the pseudonode identifier. The neighbor considers the Cisco router labeled “3640A” to be the DIS. Router 3640A was selected as the DIS because its priority was set to 127, which is higher than the value of 64 advertised by device NE14A, or the value of 55 advertised by device NE15A. The adjacency type is Phase V OSI, as opposed to a Phase IV DECNet adjacency. SONET/SDH will always be Phase V. The area address is 39.840f.8011.9999.0000.1111.0001. The uptime is how long the adjacency has been up, which is a little over 4 minutes. Adjacency uptime is useful debugging information.





• • •

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Configuring a Cisco Catalyst 2924XL VLAN Using ISL Encapsulation
This section reviews configuration for the Cisco Catalyst switch seen in Figure 14 on page 24. The example configures three VLANs, one VLAN for each OSI area. VLAN 1 is the default. For management of the switch interface, VLAN 1 is defined and assigned an IP address, as shown in the following example: interface VLAN1 ip address 192.168.12.50 255.255.255.0 no ip route-cache

In the following example, Fast Ethernet ports 0/1 through 0/4 and 0/13 through 0/22 are assigned to VLAN 1: interface ! interface ! interface ! interface ! interface ! interface ! interface ! interface ! interface ! interface ! interface ! interface ! interface ! interface ! FastEthernet0/1 FastEthernet0/2 FastEthernet0/3 FastEthernet0/4 FastEthernet0/13 FastEthernet0/14 FastEthernet0/15 FastEthernet0/16 FastEthernet0/17 FastEthernet0/18 FastEthernet0/19 FastEthernet0/20 FastEthernet0/21 FastEthernet0/22

The switch ports are configured as both access and for VLAN 1. VLAN 1 is the default and does not display in the Cisco IOS software configuration file. The OSI area 39.840f.8011.9999.0000.1111.0001 is assigned to IS-IS routers or network elements connected to VLAN 1. Device NE14A in Figure 14 on page 24 is connected to switch port 0/2. Device NE15A is connected to switch port 0/3. In the following example, Fast Ethernet ports 0/5 through 0/8 are assigned to VLAN 2: interface FastEthernet0/5 switchport access vlan 2 ! interface FastEthernet0/6 switchport access vlan 2 ! interface FastEthernet0/7 switchport access vlan 2 ! interface FastEthernet0/8 switchport access vlan 2

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The switch ports are configured as both access and for VLAN 2. The OSI area 39.840f.8011.9999.0000.1111.0002 is assigned to IS-IS routers or network elements connected to VLAN 2. Device NE25A in Figure 14 on page 24 is connected to switch port 0/5. In the following example, Fast Ethernet ports 0/9 through 0/12 are assigned to VLAN 3:
! interface FastEthernet0/9 switchport access vlan 3 ! interface FastEthernet0/10 switchport access vlan 3 ! interface FastEthernet0/11 switchport access vlan 3 ! interface FastEthernet0/12 switchport access vlan 3 !

The switch ports are configured as both access and for VLAN 3. The OSI area 39.840f.8011.9999.0000.1111.0003 is assigned to IS-IS routers or network elements connected to VLAN 3. Device NE26A in Figure 14 is connected to switch port 0/10. In the following example, switch ports 0/23 and 0/24 are configured as trunks with ISL encapsulation. The Cisco IOS software default trunk encapsulation type is ISL. interface FastEthernet0/23 switchport mode trunk ! interface FastEthernet0/24 switchport mode trunk

Verifying the Cisco Catalyst 2924XL VLAN Configuration Using ISL Encapsulation
To verify port assignment to the VLANs, use the show vlan brief EXEC command:
Router-2924XL# show vlan brief VLAN Name Status Ports ---- -------------------------------- --------- ------------------------------1 default active Fa0/1, Fa0/2, Fa0/3, Fa0/4, Fa0/13, Fa0/14, Fa0/15, Fa0/16, Fa0/17, Fa0/18, Fa0/19, Fa0/20, Fa0/21, Fa0/22 2 VLAN0002 active Fa0/5, Fa0/6, Fa0/7, Fa0/8 3 VLAN0003 active Fa0/9, Fa0/10, Fa0/11, Fa0/12 1002 fddi-default active 1003 token-ring-default active 1004 fddinet-default active 1005 trnet-default active

Status of a specific port such as the device NE14A connection can be verified using the show interface EXEC command:
Router-2924XL# show interface fastethernet 0/3 FastEthernet0/3 is up, line protocol is up Hardware is Fast Ethernet, address is 00d0.796c.acc3 (bia 00d0.796c.acc3) MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec, rely 255/255, load 1/255 Encapsulation ARPA, loopback not set, keepalive not set Full-duplex, 100Mb/s, 100BaseTX/FX

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ARP type: ARPA, ARP Timeout 04:00:00 Last input never, output 00:00:00, output hang never Last clearing of "show interface" counters never Queueing strategy: fifo Output queue 0/40, 0 drops; input queue 0/75, 0 drops 5 minute input rate 2000 bits/sec, 0 packets/sec 5 minute output rate 7000 bits/sec, 2 packets/sec 2186 packets input, 1256415 bytes, 0 no buffer Received 1535 broadcasts, 0 runts, 0 giants, 0 throttles 105 input errors, 105 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort 0 watchdog, 1528 multicast 0 input packets with dribble condition detected 12421 packets output, 5859914 bytes, 0 underruns 0 output errors, 0 collisions, 1 interface resets 0 babbles, 0 late collision, 0 deferred 0 lost carrier, 0 no carrier 0 output buffer failures, 0 output buffers swapped out

Defining IS-IS Multiareas with IEEE 802.1Q Trunking
This section describes the requirements for implementing an IS-IS multiarea using IEEE 802.1Q encapsulation, instead of the ISL encapsulation used in the “Defining IS-IS Multiareas with ISL Trunking” section. In this configuration, which is shown in Figure 15, the network is basically the same as that used in the ISL example—the OSS is located in the data center and the CLNS packets are routed across the network to the central office router. The difference is that IEEE 802.1Q encapsulation will be used for the VLAN trunks.
Figure 15 IS-IS Multiarea Network with an IEEE 802.1Q Trunk

CLNS packet flow VLAN using 802.1Q NE14A Area 0001

NE14B

IP/OSI OSS Central office router

NE15A Area 0002 Area 0003

NE25A

NE25B
95629

NE26A

NE26B

Figure 16 shows three IS-IS Level 1 areas. For the purpose of example, the areas are small, with only two or three SONET/SDH network elements per area. A typical area would have 30 to 50 network elements. This configuration is done using a Cisco 3640 router and Cisco Catalyst 2924XL switch.

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Figure 16

IS-IS Multiarea Network Using VLAN Trunking and IEEE 802.1Q Encapsulation

CLNS packet flow

VLAN using 802.1Q

NE14A

Area 0001

NE14B

NE15A Central office router 2924XL NE25A Area 0002 Area 0003

NE25B
95119

NE26A

NE26B

Configuring an IEEE 802.1Q Trunk Router
The following configuration shows the IEEE 802.1Q encapsulation changes on the Cisco router interfaces. The configuration is the same as that seen in the “Configuring an IS-IS Multiarea Network on a VLAN Using ISL Encapsulation” section except for the encapsulation scheme. The encapsulation dot1q command is used on the three subinterfaces, which enables IEEE 802.1Q encapsulation. interface FastEthernet3/0.1 description IS-IS area 0001 encapsulation dot1Q 1 native ip address 192.168.12.24 255.255.255.0 no ip redirects no cdp enable clns router isis area0001 isis priority 127 tarp enable ! interface FastEthernet3/0.2 description IS-IS area 0002 encapsulation dot1Q 2 no ip redirects no cdp enable clns router isis area0002 isis priority 127 tarp enable ! interface FastEthernet3/0.3 description IS-IS area 0003 encapsulation dot1Q 3 no ip redirects no cdp enable clns router isis area0003 isis priority 127 tarp enable

Configuring a Cisco Catalyst 2924XL VLAN with IEEE 802.1Q Encapsulation
This section describes the changes required for the Cisco Catalyst switch configuration using the ISL implementation shown in Figure 14 on page 24, to using the IEEE 802.1Q implementation shown in Figure 15 on page 32. The configuration is the same as that in the “Configuring a Cisco Catalyst 2924XL VLAN Using ISL Encapsulation” section except for the VLAN encapsulation scheme. The VLAN

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trunking encapsulation changes from ISL to IEEE 802.1Q encapsulation. Fast Ethernet port 0/23 is set up as the switch trunk port in both examples. In the following example, the switchport trunk encapsulation dot1q command is used on the switch port trunk, which enables IEEE 802.1Q encapsulation: interface FastEthernet0/23 switchport trunk encapsulation dot1q switchport mode trunk ! interface FastEthernet0/24 switchport trunk encapsulation dot1q switchport mode trunk

Verifying a Cisco Catalyst 2924XL VLAN with IEEE 802.1Q Encapsulation
To verify port assignments of the VLANs, use the show vlan brief EXEC command:
Router# show vlan brief VLAN Name Status Ports ---- -------------------------------- --------- ------------------------------1 default active Fa0/1, Fa0/2, Fa0/3, Fa0/4, Fa0/13, Fa0/14, Fa0/15, Fa0/16, Fa0/17, Fa0/18, Fa0/19, Fa0/20, Fa0/21, Fa0/22 2 VLAN0002 active Fa0/5, Fa0/6, Fa0/7, Fa0/8 3 VLAN0003 active Fa0/9, Fa0/10, Fa0/11, Fa0/12 1002 fddi-default active 1003 token-ring-default active 1004 fddinet-default active 1005 trnet-default active

Status of a specific port, such as the device NE14A connection, can be verified using the show interface EXEC command:
Router# show interface fastethernet 0/10 FastEthernet0/10 is up, line protocol is up Hardware is Fast Ethernet, address is 00d0.796c.accb (bia 00d0.796c.accb) MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec, rely 255/255, load 1/255 Encapsulation ARPA, loopback not set, keepalive not set Half-duplex, 10Mb/s, 100BaseTX/FX ARP type: ARPA, ARP Timeout 04:00:00 Last input never, output 00:00:00, output hang never Last clearing of "show interface" counters never Queueing strategy: fifo Output queue 0/40, 0 drops; input queue 0/75, 0 drops 5 minute input rate 0 bits/sec, 0 packets/sec 5 minute output rate 0 bits/sec, 1 packets/sec 1 packets input, 64 bytes, 0 no buffer Received 0 broadcasts, 0 runts, 0 giants, 0 throttles 0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort 0 watchdog, 0 multicast 0 input packets with dribble condition detected 72 packets output, 4039 bytes, 0 underruns 0 output errors, 0 collisions, 1 interface resets 0 babbles, 0 late collision, 0 deferred 0 lost carrier, 0 no carrier 0 output buffer failures, 0 output buffers swapped out

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Defining Multiple Areas with Manual Area Addressing
The designers of the ISO IS-IS protocol realized that there would be situations when the network would need to be readdressed. A provision was made in ISO 10589 to allow multiple area addresses to be associated with one area. ISO 10589 defines a management parameter for manual area addresses. A manual area address parameter is set in each IS-IS router that contains a list of all of the area addresses. The list of area addresses is distributed in the Level 1 LSP. The area comprises the union of all of the area addresses advertised, and the Level 2 router creates a composite list. All of the IS-IS routers, according to ISO 10589, must support at least three area addresses within an area. Two IS-IS routers must have at least one area address in common for an adjacency to be formed. Originally, the Cisco IOS software supported only three area addresses within an area. Cisco changed this limit to support a minimum of three and a maximum of 254 addresses. The change was made to accommodate the SONET/SDH environment.

Caution

The number of manual area addresses that are configured should match between two IS-IS routers. Cisco routers will not form an adjacency if the number of areas do not match. Therefore, changing the number of manual area addresses in a live network can cause a loss of connectivity. Service providers have used manual area addressing as a tool to expand their networks without readdressing the network. Manual area addressing was used before the IS-IS multiarea feature was available. Incumbent local exchange carriers (ILECs) and PTTs typically deploy large numbers of small-sized SONET/SDH rings or chains. The rings and chains grow over time. Service providers did not want to readdress the network as it grew in size, so they would split the rings into groups and assign an area address. As SONET/SDH nodes were added to the rings or chains in the group, the overall area grew in size. The number of Level 1 IS-IS routers also grew. Eventually, the area size needed to be split. When a new standalone router was added to the area, one of the groups was migrated to the new router, and the NET was removed from the old group. This technique is used less frequently since the introduction of the IS-IS multiarea feature. The configuration to add the manual area addressing is based on the network shown in Figure 17. NETs will be added to IS-IS process area 0001.
Figure 17 Sample Network for Configuring Manual Area Addresses

CLNS packet flow Fast Ethernet 3/0.1 VLAN using 802.1Q NE14A

Area 0001

NE14B

NE15A Central office Router 3640A Area 0002 Area 0003

NE26A

NE26B

Cisco Network Solutions for the Telco DCN: SONET/SDH OSI Environments

95630

Fast Ethernet 3/0.2 Fast Ethernet 3/0.3

NE25A

NE25B

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Cisco Network Solutions for the Telco DCN: SONET/SDH OSI Environments Access Layer Configuration

The following example shows the configuration before manual area addresses are added: router isis area0001 net 39.840f.8011.9999.0000.1111.0001.0010.7bc7.ae40.00

Configuring Manual Area Addressing
This section shows how to configure manual area addresses using the max-area-addresses router configuration command. The default value for this command is three addresses (which will not appear in router configurations). The following example shows how to change the maximum number of manual area addresses to four, and configure four corresponding NETs:
3640A(config)# router isis area0001 3640A(config-router)# max-area-addresses 4 3640A(config-router)# net 39.840f.8011.9999.0000.1111.0004.0010.7bc7.ae40.00 3640A(config-router)# net 39.840f.8011.9999.0000.1111.0005.0010.7bc7.ae40.00 3640A(config-router)# net 39.840f.8011.9999.0000.1111.0006.0010.7bc7.ae40.00 3640A(config-router)# net 39.840f.8011.9999.0000.1111.0007.0010.7bc7.ae40.00 %The maximum allowed addresses already configured

The IS-IS router configured for manual area addressing with multiple areas will have multiple NETs associated with one IS-IS process. There will still be one IS-IS process and one IS-IS area.

Note

Do not confuse this configuration with the IS-IS multiarea configuration, which has multiple IS-IS processes and areas. The following example displays the new IS-IS portion of the configuration. Under IS-IS process area0001, there are now four NET statements; one area will advertise the multiple NETs. router isis area0001 max-area-addresses 4 net 39.840f.8011.9999.0000.1111.0001.0010.7bc7.ae40.00 net 39.840f.8011.9999.0000.1111.0004.0010.7bc7.ae40.00 net 39.840f.8011.9999.0000.1111.0005.0010.7bc7.ae40.00 net 39.840f.8011.9999.0000.1111.0006.0010.7bc7.ae40.00 ! router isis area0002 net 39.840f.8011.9999.0000.1111.0002.0010.7bc7.ae40.00 is-type level-1 ! router isis area0003 net 39.840f.8011.9999.0000.1111.0003.0010.7bc7.ae40.00 is-type level-1

Use the show clns EXEC command to display all the NETs that are configured:
3640A# show clns Global CLNS Information: 3 Interfaces Enabled for CLNS NET: 39.840f.8011.9999.0000.1111.0001.0010.7bc7.ae40.00 NET: 39.840f.8011.9999.0000.1111.0004.0010.7bc7.ae40.00 NET: 39.840f.8011.9999.0000.1111.0005.0010.7bc7.ae40.00 NET: 39.840f.8011.9999.0000.1111.0006.0010.7bc7.ae40.00 NET: 39.840f.8011.9999.0000.1111.0002.0010.7bc7.ae40.00 NET: 39.840f.8011.9999.0000.1111.0003.0010.7bc7.ae40.00 Configuration Timer: 60, Default Holding Timer: 300, Packet Lifetime 64 ERPDU's requested on locally generated packets

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Intermediate system operation enabled (CLNS forwarding allowed) IS-IS level-1-2 Router: area0001 Routing for Area: 39.840f.8011.9999.0000.1111.0001 IS-IS level-1 Router: area0002 Routing for Area: 39.840f.8011.9999.0000.1111.0002 IS-IS level-1 Router: area0003 Routing for Area: 39.840f.8011.9999.0000.1111.0003

The show clns protocol EXEC command provides useful information about the manual area addresses configured. The following example displays the system identifier and the IS type as Level-1-2. There are four manual area addresses and four areas are listed. This example displays one area, but all area addresses would be advertised. An adjacent host still needs to be configured for the same number of manual area addresses and matching NETs to form balanced adjacencies.
3640A# show clns protocol IS-IS Router: area0001 System Id: 0010.7BC7.AE40.00 IS-Type: level-1-2 Maximum nr of area adresses in this area is 4 Manual area address(es): 39.840f.8011.9999.0000.1111.0001 39.840f.8011.9999.0000.1111.0004 39.840f.8011.9999.0000.1111.0005 39.840f.8011.9999.0000.1111.0006 Routing for area address(es): 39.840f.8011.9999.0000.1111.0001 39.840f.8011.9999.0000.1111.0004 39.840f.8011.9999.0000.1111.0005 39.840f.8011.9999.0000.1111.0006 Interfaces supported by IS-IS: FastEthernet3/0.1 - OSI Redistribute: static (on by default) Distance for L2 CLNS routes: 110 RRR level: none Generate narrow metrics: level-1-2 Accept narrow metrics: level-1-2 Generate wide metrics: none Accept wide metrics: none IS-IS Router: area0002 System Id: 0010.7BC7.AE40.00 IS-Type: level-1 Manual area address(es): 39.840f.8011.9999.0000.1111.0002 Routing for area address(es): 39.840f.8011.9999.0000.1111.0002 Interfaces supported by IS-IS: FastEthernet3/0.2 - OSI Redistribute: static (on by default) Distance for L2 CLNS routes: 110 RRR level: none Generate narrow metrics: level-1-2 Accept narrow metrics: level-1-2 Generate wide metrics: none Accept wide metrics: none IS-IS Router: area0003 System Id: 0010.7BC7.AE40.00 IS-Type: level-1 Manual area address(es): 39.840f.8011.9999.0000.1111.0003 Routing for area address(es): 39.840f.8011.9999.0000.1111.0003

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Cisco Network Solutions for the Telco DCN: SONET/SDH OSI Environments Access Layer Configuration

Interfaces supported by IS-IS: FastEthernet3/0.3 - OSI Redistribute: static (on by default) Distance for L2 CLNS routes: 110 RRR level: none Generate narrow metrics: level-1-2 Accept narrow metrics: level-1-2 Generate wide metrics: none Accept wide metrics: none

Verifying Adjacencies in a Network with Manual Area Addresses
Use the show clns neighbors EXEC command to verify that adjacencies are being formed. The following example indicates that an adjacency is up for IS-IS process area0001. The adjacency type is IS but the protocol is End System-Intermediate System (ES-IS) (see bold text), so an IS-IS adjacency is not being formed for IS-IS process area0001:
3640A# show clns neighbors Area area0001: System Id Interface NE15A Fa3/0.1 NE14A Fa3/0.1 Area area0002: System Id Interface NE25A Fa3/0.2 Area area0003: System Id Interface NE26A Fa3/0.3

SNPA 0010.7bd8.c7d0 00e0.b064.4325

State Up Up

Holdtime 263 293

Type Protocol IS ES-IS IS ES-IS

SNPA 00e0.b064.434e

State Up

Holdtime 22

Type Protocol L1 IS-IS

SNPA 00d0.5872.9720

State Up

Holdtime 28

Type Protocol L1 IS-IS

Troubleshooting Adjacencies in a Network with Manual Area Addresses
Use the debug isis adj-packets command to debug IS-IS adjacency packets. In the following example, an IS-IS Hello (IIH) message comes in on Fast Ethernet interface 3/0.1 and causes a maximum area address mismatch error report to be displayed. (In the following output, text is in bold for purpose of example.) The network element with MAC address 00e0.b064.4325, which is device NE14A, is sending an IIH. The IIH has a different number of maximum area addresses than router 3640A. The number of maximum area addresses needs to be changed to match router 3640A. The change also needs to be made to device NE15A.
3640A# debug isis adj-packets IS-IS Adjacency related packets debugging is on 3640A# 00:45:07: ISIS-Adj (area0001): Rec L1 IIH from 00e0.b064.4325 (FastEthernet3/0.1), cir type L1, cir id 00E0.B064.4324.02, length 147 00:45:07: ISIS-Adj (area0001): Max-area-addresses mismatch, in L1 IIH from FastEthernet3/0.1

In the network configuration, the maximum number of manual area addresses has been changed to four on devices NE14A, NE14B, and NE15A. The show clns neighbors command now indicates that the adjacency is up and the protocol being used is IS-IS:
3640A# show clns neighbors Area area0001: System Id Interface

SNPA

State

Holdtime

Type Protocol

Cisco Network Solutions for the Telco DCN: SONET/SDH OSI Environments

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Cisco Network Solutions for the Telco DCN: SONET/SDH OSI Environments Access Layer Configuration

NE15A NE14A

Fa3/0.1 Fa3/0.1

0010.7bd8.c7d0 00e0.b064.4325

Up Up

27 24

L1 L1

IS-IS IS-IS

Area area0002: System Id Interface NE25A Fa3/0.2 Area area0003: System Id Interface NE26A Fa3/0.3

SNPA 00e0.b064.434e

State Up

Holdtime 22

Type Protocol L1 IS-IS

SNPA 00d0.5872.9720

State Up

Holdtime 23

Type Protocol L1 IS-IS

Using Generic Routing Encapsulation Tunnels to Prevent Area Partitions
A GNE provides a gateway between the DCN LAN and the SONET DCC. The DCC is the embedded operations channel. There are two DCCs in the SONET/SDH frame: the section DCC and the line DCC. The section DCC is embedded in the section overhead and is made up of three bytes that create a 192-kbps data path. The section DCC has been standardized in TMN for management of the downstream SONET network elements. The line DCC is made up of nine bytes that create a 576-kbps data channel. The standards have carved out the bandwidth in the line DCC, but the TMN standards do not define use of the line DCC. Therefore, vendors have implemented proprietary uses for the line DCC. Figure 18 shows the flow of CLNS packets across the network. For a CLNS packet to move from the OSS to device NE3, the packet must be routed across the DCN to the LAN in central office Router A or Router B. For purpose of example, assume that the packet arrives at the LAN in central office Router A. Device GNE 1 routes the packet from the LAN to the DCC and forward the packet across the section DCC to device NE2. Device NE2 forwards the packet across the section DCC to device NE3. The action of routing packets between the DCN and the section DCC is the definition of a GNE.
Figure 18 Typical GNE Configuration

CLNS packet flow GNE 1 NE 2 NE 3 NE 7 NE 4 Central office Router B GNE 6 NE 5
95655

IP/OSI OSS

Central office Router A

The service provider will typically implement one GNE per SONET/SDH ring on small-sized rings. The definition of small is typically six network elements or fewer. ILECs and PTTs typically have many small-sized rings or chains to extend services out from the central office to businesses. The service provider will build large collector rings to aggregate bandwidth from the small-sized rings. The larger rings typically have multiple GNEs to add redundancy to ring access, as shown in Figure 18. This section describes generic routing encapsulation (GRE) tunnels and the IS-IS default Originate features, both of which can be used to improve redundancy.

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Cisco Network Solutions for the Telco DCN: SONET/SDH OSI Environments Access Layer Configuration

CLNS over GRE Tunnels
Traditionally the SONET/SDH technology is deployed in ring topologies for redundancy. In the event of a fiber cut (see Figure 19), the ring will wrap and the traffic will be either path switched or line switched onto the protected portion of the fiber. The DCC will be preserved as well. There are times when it may be necessary to deploy fiber-optic cable in a long chain without the geographic diversity shown in Figure 19.
Figure 19 GRE Tunnel over CLNS with Cut Fiber Link

CLNS packet flow Central office Router A

GNE 1 Fiber cut X OSI area 0001

NE2 X NE3

IP OSI OSS

GRE tunnel

NE4 Central office Router B
117174

GNE 6

NE5

If the fiber gets cut, the OSI area will become partitioned and the OSS will not be able to communicate with some of the network elements. One solution to the partitioned Level 1 area is to build a GRE tunnel between the Cisco routers for CLNS. The GRE tunnel will pass the IS-IS traffic between the partitioned parts of the network, as shown in Figure 19.

Configuring a GRE Tunnel
This section describes a sample GRE configuration. The sample network is shown in Figure 20 and depicts the following scenario: Router 3640A is in central office A and router 2600D is in central office D. The two central offices have a SONET/SDH chain running between them. The SONET/SDH network elements are all Level 1 routers. Network elements NE14A and NE25A are both GNEs to the SONET/SDH chain, which is in area 00001. The routers 3640A and 2600D are both Level 1/Level 2 access routers. A fiber cut between the network elements would partition area 0001.

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Cisco Network Solutions for the Telco DCN: SONET/SDH OSI Environments Access Layer Configuration

Figure 20

Typical Network Before GRE Tunnel Configuration

Level 2 adjacency

3640A Central office A

2924XL

NE14A Area 0001

NE14B

NE15A
103354

Level 2 adjacency 2600D Central office D 2924XL

NE25A

NE25B

Network element (NE) = SONET or SDH node

The configuration builds a GRE tunnel between router 3640A and router 2600D. The GRE tunnel and the IP addresses that are used in the tunnel are shown in Figure 21.
Figure 21 GRE Tunnel Configuration

192.168.5.252 3640A Central office A
Level 2 adjacency 2924XL GRE tunnel NE14A Area 0001 NE14B

NE15A

Level 2 adjacency 2600D 2924XL Central office D 192.168.14.252

The following configuration example for the GRE tunnel shows that the router labeled 2600D in Figure 21 is configured for IS-IS routing in area 0001: router isis area0001 net 39.840f.8011.9999.0000.1111.0001.00e0.1ee3.c720.00

Router 2600D is connected to the SONET/SDH device NE25A over Ethernet interface 0/0: interface Ethernet0/0 ip address 192.168.5.189 255.255.255.192 half-duplex clns router isis area0001

A loopback interface has been created for the GRE tunnel to terminate on router 2600D: interface Loopback0 ip address 192.168.5.252 255.255.255.192

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103355

NE25A

NE25B

Cisco Network Solutions for the Telco DCN: SONET/SDH OSI Environments Access Layer Configuration

The source of the GRE tunnel on router 2600D is the loopback address 192.168.5.252. The tunnel destination is the loopback IP address 192.168.14.252 on the router labeled 3640A in Figure 21. The routing metric assigned to the GRE tunnel is 30. Some service providers prefer to use the tunnel only in the event of an outage. IS-IS routing for CLNS has been turned up on the tunnel. The IS-IS metric can range from 1 to 63, with 63 being the worst route. The GRE keepalive feature is implemented in the example. The keepalive feature will take down the GRE tunnel interface if the far end of the tunnel becomes unavailable. See the following example: interface Tunnel1 no ip address keepalive 3 3 clns router isis area0001 isis metric 30 tunnel source 192.168.5.252 tunnel destination 192.168.14.252 tarp enable

The following example shows how to configure router 3640A for IS-IS routing in area 0001: router isis area0001 net 39.840f.8011.9999.0000.1111.0001.0010.7bc7.ae40.00

In the following example, router 3640A is connected to SONET/SDH device NE14A over Fast Ethernet interface 3/0.1: interface FastEthernet3/0.1 description ISIS area 0001 encapsulation dot1Q 1 native ip address 192.168.12.24 255.255.255.0 no ip redirects no cdp enable clns router isis area0001 isis priority 127 tarp enable

The following example creates a loopback interface for the GRE tunnel to terminate on router 3640A: interface Loopback0 ip address 192.168.14.252 255.255.255.192

The source of the GRE tunnel on router 3640A is the loopback 0 IP address 192.168.14.252. The tunnel destination is loopback IP address 192.168.5.252 on router 2600D. The routing metric assigned to the GRE tunnel is 30. The GRE keepalive feature is implemented. See the following example: interface Tunnel1 no ip address keepalive 3 3 clns router isis area0001 isis metric 30 tunnel source 192.168.5.252 tunnel destination 192.168.14.252 tarp enable

Note

The source and destination IP addresses must match on each end of the tunnel. If the IP addresses do not match, the tunnel line protocol will not come up. If you choose to use a source or destination interface when configuring the tunnel, the IP address of the interface of the tunnel will be used. The status of the tunnel can be examined with the show interface command. In the following example, tunnel 1 is up and line protocol is up. The keepalive option is set to send keepalives every 3 seconds, and set to retry three times before marking the interface line protocol down.

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Cisco Network Solutions for the Telco DCN: SONET/SDH OSI Environments Access Layer Configuration

3640A# show interface tunnel 1 Tunnel1 is up, line protocol is up Hardware is Tunnel MTU 1514 bytes, BW 9 Kbit, DLY 500000 usec, reliability 255/255, txload 28/255, rxload 28/255 Encapsulation TUNNEL, loopback not set Keepalive set (3 sec), retries 3 Tunnel source 192.168.14.252, destination 192.168.5.252 Tunnel protocol/transport GRE/IP, key disabled, sequencing disabled Tunnel TTL 255 Checksumming of packets disabled, fast tunneling enabled Last input 00:00:07, output 00:00:00, output hang never Last clearing of "show interface" counters never Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 29 Queueing strategy: fifo Output queue: 0/0 (size/max) 5 minute input rate 1000 bits/sec, 0 packets/sec 5 minute output rate 1000 bits/sec, 0 packets/sec 1767 packets input, 705632 bytes, 0 no buffer Received 0 broadcasts, 0 runts, 0 giants, 0 throttles 0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort 1945 packets output, 712879 bytes, 0 underruns 0 output errors, 0 collisions, 0 interface resets 0 output buffer failures, 0 output buffers swapped out

Use the debug tunnel command to debug the tunnel. The following example shows the debug tunnel command output:
3640A# debug tunnel Tunnel Interface debugging is on 3640A# 01:11:24: 01:11:24: 01:11:24: 01:11:24: 01:11:25: len=1537) 01:11:27: 01:11:27: 01:11:30: 01:11:30: 01:11:31: 01:11:31: Tunnel1: Tunnel1: Tunnel1: Tunnel1: Tunnel1: Tunnel1: Tunnel1: Tunnel1: Tunnel1: Tunnel1: Tunnel1: GRE/IP to decaps 192.168.5.252->192.168.14.252 (len=1537 ttl=253) GRE decapsulated CLNS packet GRE/IP encapsulated 192.168.14.252->192.168.5.252 (linktype=7, len=48) GRE/IP to decaps 192.168.5.252->192.168.14.252 (len=24 ttl=252) GRE/IP encapsulated 192.168.14.252->192.168.5.252 (linktype=25, GRE/IP encapsulated 192.168.14.252->192.168.5.252 (linktype=7, len=48) GRE/IP to decaps 192.168.5.252->192.168.14.252 (len=24 ttl=252) GRE/IP encapsulated 192.168.14.252->192.168.5.252 (linktype=7, len=48) GRE/IP to decaps 192.168.5.252->192.168.14.252 (len=24 ttl=252) GRE/IP to decaps 192.168.5.252->192.168.14.252 (len=1537 ttl=253) GRE decapsulated CLNS packet

Use the debug tunnel keepalive command to debug the tunnel keepalive. In the following example, notice that the keepalive packets are being sent every 3 seconds:
3640A# debug tunnel keepalive Tunnel keepalive debugging is on 3640A# 01:12:27: counter=1 01:12:27: resetting 01:12:30: counter=1 01:12:30: resetting Tunnel1: sending keepalive, 192.168.5.252->192.168.14.252 (len=24 ttl=255), Tunnel1: keepalive received, 192.168.5.252->192.168.14.252 (len=24 ttl=252), counter Tunnel1: sending keepalive, 192.168.5.252->192.168.14.252 (len=24 ttl=255), Tunnel1: keepalive received, 192.168.5.252->192.168.14.252 (len=24 ttl=252), counter

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Cisco Network Solutions for the Telco DCN: SONET/SDH OSI Environments Access Layer Configuration

01:12:33: counter=1 01:12:33: resetting 01:12:36: counter=1 01:12:36: resetting 01:12:39: counter=1 01:12:39: resetting 01:12:42: counter=1 01:12:42: resetting 01:12:45: counter=1 01:12:45: resetting

Tunnel1: sending keepalive, 192.168.5.252->192.168.14.252 (len=24 ttl=255), Tunnel1: keepalive received, 192.168.5.252->192.168.14.252 (len=24 ttl=252), counter Tunnel1: sending keepalive, 192.168.5.252->192.168.14.252 (len=24 ttl=255), Tunnel1: keepalive received, 192.168.5.252->192.168.14.252 (len=24 ttl=252), counter Tunnel1: sending keepalive, 192.168.5.252->192.168.14.252 (len=24 ttl=255), Tunnel1: keepalive received, 192.168.5.252->192.168.14.252 (len=24 ttl=252), counter Tunnel1: sending keepalive, 192.168.5.252->192.168.14.252 (len=24 ttl=255), Tunnel1: keepalive received, 192.168.5.252->192.168.14.252 (len=24 ttl=252), counter Tunnel1: sending keepalive, 192.168.5.252->192.168.14.252 (len=24 ttl=255), Tunnel1: keepalive received, 192.168.5.252->192.168.14.252 (len=24 ttl=252), counter

The next step is to look at the IS-IS topology after breaking the link between SONET/SDH nodes. The following example shows the IS-IS topology with the GRE tunnel up and the SONET/SDH chain in place:
3640A# show isis topology Area area0001: IS-IS IP paths to level-1 routers System Id Metric Next-Hop 3640A -NE15A 30 NE14A NE25B 40 NE14A NE14B 20 NE14A 2600D 30 2600D NE14A 10 NE14A NE25A 40 2600D IS-IS IP paths to level-2 routers System Id Metric Next-Hop 3640A -2600D 30 2600D

Interface Fa3/0.1 Fa3/0.1 Fa3/0.1 Tu1 Fa3/0.1 Tu1

SNPA 00e0.b064.4325 00e0.b064.4325 00e0.b064.4325 *Tunnel* 00e0.b064.4325 *Tunnel*

Interface Tu1

SNPA *Tunnel*

All of the network elements can be reached within the area from router 3640A, even though the IS-IS metric was raised to 30 on the tunnel. The tunnel is still the preferred path to router 2600D and network element device NE25A. The traffic could be forced out of the tunnel and onto the SONET/SDH DCC by raising the IS-IS metric. The next part of this example breaks the connection between devices NE14B and NE15A, as shown in Figure 22. The example after the figure displays the new IS-IS topology after the connection break. All of the network elements and routers are still listed, and the connection to devices NE15A and NE25B has moved to the tunnel.

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Cisco Network Solutions for the Telco DCN: SONET/SDH OSI Environments Access Layer Configuration

Figure 22

GRE Tunnel with Broken Connection

192.168.5.252 3640A Central office A Level 2 adjacency 2924XL GRE tunnel NE14A Area 0001 NE14B

NE15A

Level 2 adjacency 2600D 2924XL Central office D 192.168.14.252
3640A# show isis topology Area area0001: IS-IS IP paths to level-1 routers System Id Metric Next-Hop 3640A -NE15A 60 2600D NE25B 50 2600D NE14B 20 NE14A 2600D 30 2600D NE14A 10 NE14A NE25A 40 2600D

Interface Tu1 Tu1 Fa3/0.1 Tu1 Fa3/0.1 Tu1

SNPA *Tunnel* *Tunnel* 00e0.b064.4325 *Tunnel* 00e0.b064.4325 *Tunnel*

Without the tunnel connection, routers 3640A and 2600D would not be able to see the entire IS-IS area 0001. Devices may not be able to communicate, depending upon where the devices sit in the network. The loss of connectivity can be demonstrated by shutting down the tunnel interface. The following example displays the new IS-IS topology and indicates that packets reaching router 3640A from the network cloud could be forwarded only to devices NE14A and NE14B.
3640A# show isis topology Area area0001: IS-IS IP paths to level-1 routers System Id Metric Next-Hop 3640A -NE15A ** NE25B ** NE14B 20 NE14A 2600D ** NE14A 10 NE14A NE25A **

Interface

SNPA

Fa3/0.1 Fa3/0.1

00e0.b064.4325 00e0.b064.4325

IS-IS Attach-Bit Control Feature
Routing traffic between Level 1 areas is done by Level 2 routers. Level 1 routers forward the packets to their nearest Level 1/Level 2 router. Typically located at the access layer of the network, the Level 1/Level 2 routers are standalone Cisco routers, and Level 1 routers are SONET/SDH network elements.

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103356

NE25A

NE25B

Cisco Network Solutions for the Telco DCN: SONET/SDH OSI Environments Access Layer Configuration

The Level 1/Level 2 Cisco router identifies itself by setting the attach-bit in the link-state packets (LSPs). Often service providers have more than one Level 1/Level 2 router per area for redundancy. On large rings, there may be multiple GNEs with access to separate Level 1/Level 2 routers. A Level 1/Level 2 router can lose connectivity to the area with the OSS or the network backbone. If a Level 1/Level 2 Cisco router is configured for IS-IS multiarea, the Level 1/Level 2 router will set the attach bit. If there are multiple Level 1/ Level 2 routers in the same central office networked to share the WAN link, these two routers would form a Level 2 adjacency. The Level 2 attach bit would be set. In either case, the central office Level 1/Level 2 routers will not have access to the OSS systems in the NOC if the WAN link is down. Packets forwarded to the Level 1/Level 2 router destined for the NOC will be discarded. The service provider wants the packets to be sent out the alternate GNE to an alternate central office. There is a solution to this problem. For purpose of example, we will use a router named “3640A” (see Figure 23) to show the configurations and verifications. Router 3640A will continue to set the attach-bit when it has another Level 2 adjacency or the Cisco IOS IS-IS Multiarea feature is configured. In other words, router 3640A will set the attach-bit if it can reach multiple areas. The Level 1 routers nearest router 3640A will continue to forward traffic to router 3640A. Traffic sent to router 3640A is most likely destined for the area containing the OSS. The traffic, which is usually alarms destined for the NOC and alarm packets, will be dropped. Cisco developed the IS-IS Attach-Bit Control feature to provide the network administrator with more control in setting the attach-bit. The feature is modeled after the IP default-information originate route-map router subcommand. The new command, set-attach-bit, is an IS-IS CLNS router subcommand and its syntax is as follows: router isis set-attach-bit {always | never | route-map mapname} The route-map keyword can be used to specify multiple CLNS routes or prefixes. If one of the routes or prefixes is matched in the Level 2 CLNS routing table, the Level 1/Level 2 router sets the attach bit in the LSP. The following example contains five SONET/SDH network elements in a chain between central office A and central office D. NE14A and router 3640A are located in central office A. NE14A is a GNE between the SONET/SDH DCC and the Ethernet. Device NE14A forwards traffic destined for another area to the nearest Level 2 router, which is router 3640A. Located in central office D is the Level 1/Level 2 router labeled 2600D and GNE NE25A. The other three SONET/SDH network elements are located is separate central offices. All of these devices are configured for area 0001. Router 3640A is configured for IS-IS multiarea and is located in area 0003. Figure 23 shows the network and the connections to the backbone, which is area 9999.

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Cisco Network Solutions for the Telco DCN: SONET/SDH OSI Environments Access Layer Configuration

Figure 23

Network with IS-IS Attach-Bit Control Configured

Area 0003 VLAN3 Level 2 adjacency NE26A NE26B

Backbone area 9999

3640A Central office A 2600D Central office D

2924XL

VLAN1 NE14A Area 0001

NE14B

NE15A
103518

Level 2 adjacency

2924XL

NE25A

NE25B

Verifying IS-IS Attach-Bit Control
To verify that the IS-IS Attach-Bit Control feature is configured, first display a baseline configuration without the IS-IS Attach-Bit Control feature configured. The network administrator can look at the attach-bit settings using the show isis database EXEC command. The following example shows output for router 3640A. In the IS-IS process called area000, router 3640A’s attach-bit is set to 1 in the Level-1 link state database. The attach-bit field is labeled “ATT.” The router is configured to run two IS-IS processes, area0001 and area0003.
3640A# show isis database Area area0001: IS-IS Level-1 Link State Database: LSPID LSP Seq Num LSP Checksum 3640A.00-00 * 0x00000009 0x7AB5 3640A.03-00 * 0x00000007 0x6705 NE15A.00-00 0x00000009 0x88E2 NE25B.00-00 0x0000000A 0x1DB6 NE25B.02-00 0x00000007 0x2941 NE14B.00-00 0x00000008 0xF840 NE14B.02-00 0x00000007 0x622C 2600D.00-00 0x0000000A 0xC715 NE14A.00-00 0x00000008 0x7C68 NE14A.01-00 0x00000007 0x8232 NE25A.00-00 0x00000007 0x8E92 NE25A.01-00 0x00000007 0x95E2 NE25A.02-00 0x00000007 0x69E3 IS-IS Level-2 Link State Database: LSPID LSP Seq Num LSP Checksum BackBoneR1.00-00 0x0000000D 0x6BEF 3640A.00-00 * 0x0000000A 0x8457 3640A.02-00 * 0x00000007 0xC0AC 2600D.00-00 0x00000009 0xDE1C 2600D.02-00 0x00000007 0xFA61 Area area0003: IS-IS Level-1 Link State Database: LSPID LSP Seq Num 3631A.00-00 0x00000008 NE26B.00-00 0x00000009 NE26B.02-00 0x00000007 3640A.00-00 * 0x00000008

LSP Holdtime 758 649 520 660 871 744 794 758 578 735 563 745 578 LSP Holdtime 599 758 886 765 847

ATT/P/OL 1/0/0 0/0/0 0/0/0 0/0/0 0/0/0 0/0/0 0/0/0 1/0/0 0/0/0 0/0/0 0/0/0 0/0/0 0/0/0 ATT/P/OL 0/0/0 0/0/0 0/0/0 0/0/0 0/0/0

LSP Checksum 0x33D5 0xAFE0 0x87A3 0x52DE

LSP Holdtime 827 652 554 564

ATT/P/OL 0/0/0 0/0/0 0/0/0 1/0/0

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3640A.01-00 NE26A.00-00 NE26A.02-00

* 0x00000007 0x00000009 0x00000008

0x5325 0xA756 0x8904

532 668 1128

0/0/0 0/0/0 0/0/0

Next, use the ping clns and show clns route EXEC commands to verify connectivity. Following is the output of ping to an IS-IS router in the area backbone:
3640A# ping clns 39.840f.8011.9999.0000.1111.9999.000d.bc2e.6d80.00 Type escape sequence to abort. Sending 5, 100-byte CLNS Echos with timeout 2 seconds !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 1/2/4 ms

The following example shows the CLNS routing table with a route to backbone area 9999 (text in bold is for purpose of example only and indicates the backbone route):
3640A# show clns route Codes: C - connected, S - static, d - DecnetIV I - ISO-IGRP, i - IS-IS, e - ES-IS B - BGP, b - eBGP-neighbor C C C C i 39.840f.8011.9999.0000.1111.0003 [2/0], Local IS-IS Area 39.840f.8011.9999.0000.1111.0001 [2/0], Local IS-IS Area 39.840f.8011.9999.0000.1111.0003.0010.7bc7.ae40.00 [1/0], Local IS-IS NET 39.840f.8011.9999.0000.1111.0001.0010.7bc7.ae40.00 [1/0], Local IS-IS NET 39.840f.8011.9999.0000.1111.9999 [110/10] via BackBoneR1, Ethernet0/1

Disconnect the connection to the backbone from router 3640A as shown in Figure 24, and display the IS-IS database again using the show isis database EXEC command.
Figure 24 Broken Network Link with IS-IS Attach-Bit Control Configured

3640A Central Level 2 adjacency Office A

Area 0003 VLAN3 NE26A NE26B

VLAN1 Backbone area 9999 2924XL

NE14A Area 0001

NE14B

NE15A

Level 2 adjacency 2600D Central Office D

2924XL

Router 3640A still has the attach-bit set because the router is configured for the IS-IS Multiarea feature, so router 3640A can reach multiple areas. (You can determine the attach-bit setting by looking at the ATT field in the show isis database command output. The attach-bit is set when the value is 1.)
3640A# show isis database

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103519

NE25A

NE25B

Cisco Network Solutions for the Telco DCN: SONET/SDH OSI Environments Access Layer Configuration

Area area0001: IS-IS Level-1 Link State Database: LSPID LSP Seq Num LSP Checksum 3640A.00-00 * 0x00000004 0x84B0 3640A.03-00 * 0x00000002 0x71FF NE15A.00-00 0x00000004 0x92DD NE25B.00-00 0x00000004 0x29B0 NE25B.02-00 0x00000003 0x313D NE14B.00-00 0x00000003 0x033B NE14B.02-00 0x00000002 0x6C27 NE14A.00-00 0x00000005 0x8265 NE14A.01-00 0x00000003 0x8A2E NE25A.00-00 0x00000003 0x46FD NE25A.02-00 0x00000002 0x73DE IS-IS Level-2 Link State Database: LSPID LSP Seq Num LSP Checksum 3640A.00-00 * 0x00000001 0x4A75 Area area0003: IS-IS Level-1 Link State Database: LSPID LSP Seq Num 3631A.00-00 0x00000003 NE26B.00-00 0x00000004 NE26B.02-00 0x00000003 3640A.00-00 * 0x00000005 3640A.01-00 * 0x00000004 NE26A.00-00 0x00000005 NE26A.02-00 0x00000003

LSP Holdtime 1181 1180 612 491 1165 417 537 1179 1170 1056 409 LSP Holdtime 1173

ATT/P/OL 1/0/0 0/0/0 0/0/0 0/0/0 0/0/0 0/0/0 0/0/0 0/0/0 0/0/0 0/0/0 0/0/0 ATT/P/OL 0/0/0

LSP Checksum 0x3DD0 0xB9DB 0x8F9F 0x58DB 0x5922 0xAF52 0x93FE

LSP Holdtime 503 576 538 1177 1177 1178 1166

ATT/P/OL 0/0/0 0/0/0 0/0/0 1/0/0 0/0/0 0/0/0 0/0/0

The CLNS routing table displayed by the show clns route EXEC command shows that no connection to the backbone is available. There are only routes for areas 39.840f.8011.9999.0000.1111.0003 and 39.840f.8011.9999.1111.0001. The backbone route 39.840f.8011.9999.0000.1111.9999 has dropped out of the routing table. Packets destined to the backbone are dropped by router 3640A.
3640A# show clns route Codes: C - connected, S - static, d - DecnetIV I - ISO-IGRP, i - IS-IS, e - ES-IS B - BGP, b - eBGP-neighbor C C C C 39.840f.8011.9999.0000.1111.0003 [2/0], Local IS-IS Area 39.840f.8011.9999.0000.1111.0001 [2/0], Local IS-IS Area 39.840f.8011.9999.0000.1111.0003.0010.7bc7.ae40.00 [1/0], Local IS-IS NET 39.840f.8011.9999.0000.1111.0001.0010.7bc7.ae40.00 [1/0], Local IS-IS NET

The following example configures the set-attach-bit command. The route-map command sets conditions for setting the attach-bit. The route-map name or map tag assigned for the example is BackBone_Connection. The match clns command names the clns filter command that contains the NSAP address to match in the route table. In this example, the focus is on connectivity to the backbone. clns filter-set BackBone_Area permit 39.840f.8011.9999.0000.1111.9999 ! router isis area0001 net 39.840f.8011.9999.0000.1111.0001.0010.7bc7.ae40.00 set-attached-bit route-map BackBone_Connection ! route-map BackBone_Connection permit 10 match clns address BackBone_Area

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The following example reexamines the IS-IS database and the CLNS routing table after the set-attach-bit command is configured. The Level 1 database for the IS-IS area process area0001 shows that router 3640A is no longer setting the attach bit. The ATT field is set to zero for the LSP from router 3640A. Router 2600D is setting the attach-bit and providing access to the backbone. The ATT field is set to 1 for the LSP from router 2600D.
3640A# show isis database Area area0001: IS-IS Level-1 Link State Database: LSPID LSP Seq Num LSP Checksum 3640A.00-00 * 0x00000011 0x62CD 3640A.03-00 * 0x0000000E 0x590C NE15A.00-00 0x00000011 0x78EA NE25B.00-00 0x0000000F 0x13BB NE25B.02-00 0x0000000E 0x1B48 NE14B.00-00 0x0000000F 0xEA47 NE14B.02-00 0x0000000E 0x5433 2600D.00-00 0x00000011 0xB91C NE14A.00-00 0x0000000F 0x6E6F NE14A.01-00 0x0000000F 0x723A NE25A.00-00 0x0000000E 0x8099 NE25A.01-00 0x0000000F 0x85EA NE25A.02-00 0x0000000F 0x59EB IS-IS Level-2 Link State Database: LSPID LSP Seq Num LSP Checksum BackBoneR1.00-00 0x00000010 0x65F2 3640A.00-00 * 0x00000010 0x2C84 3640A.02-00 * 0x0000000E 0xB2B3 2600D.00-00 0x0000000F 0xD222 2600D.02-00 0x0000000F 0xEA69 Area area0003: IS-IS Level-1 Link State Database: LSPID LSP Seq Num 3631A.00-00 0x0000000F NE26B.00-00 0x00000010 NE26B.02-00 0x0000000F 3640A.00-00 * 0x0000000F 3640A.01-00 * 0x0000000E NE26A.00-00 0x00000011 NE26A.02-00 0x0000000F 3640A#

LSP Holdtime 1143 557 910 766 671 700 512 1013 647 1106 879 917 1140 LSP Holdtime 426 1131 541 454 818

ATT/P/OL 0/0/0 0/0/0 0/0/0 0/0/0 0/0/0 0/0/0 0/0/0 1/0/0 0/0/0 0/0/0 0/0/0 0/0/0 0/0/0 ATT/P/OL 0/0/0 0/0/0 0/0/0 0/0/0 0/0/0

LSP Checksum 0x25DC 0xA1E7 0x77AB 0x44E5 0x452C 0x975E 0x7B0B

LSP Holdtime 491 523 975 562 510 1151 1144

ATT/P/OL 0/0/0 0/0/0 0/0/0 1/0/0 0/0/0 0/0/0 0/0/0

Additional information on the IS-IS Attach-Bit Control feature can be found on CCO. Refer also to the Cisco IOS Product Marketing Application Note, Using the IS-IS Attach-Bit Control Feature.

Using IP over CLNS Tunnels to Access Remote Devices
The SONET/SDH DCC is an extension of the telco DCN. Service providers do not want to build the DCN out to every SONET/SDH location. Figure 25 shows a typical telco network where each of the network elements are located at different physical locations. The DCC is used to communicate to remote SONET/SDH add/drop multiplexers (ADMs) on the ring.

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Figure 25

Typical Telco Network with Network Elements at Different Locations

CLNS packet flow NE14A NE14B

IP OSI NE15A OSS Central office router

Area 0001 NE26B

NE25A NE26A
103351

NE25A

Service providers need to reach asynchronous and IP devices in the same location as the SONET/SDH nodes. Typically, the service providers are trying to access a contact closure device, as shown in Figure 26. Service providers can use the DCC by tunneling IP over CLNS. The router located in the central office in front of the GNE is usually the one used to create the tunnel. The router in the remote location usually terminates the CLNS tunnel and the TCP/IP session. The data is sent out the asynchronous connection to the contact closure device.
Figure 26 Telco Network Data Flow to a Contact Closure Device
TCP/IP over CLNS TCP/IP DCC IP OSS NE GNE NE DCC GNE
103352

Asynchronous

Contact Closure

Cisco has developed a contact closure device, which is a network module called the NM-AIC-64 that can be installed in the Cisco 2600, 3600, and 3700 series routers. The tunneling examples in this section use a Contact Closure device (the NM-AIC-64) embedded in router 3631A shown in Figure 27.

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Cisco Network Solutions for the Telco DCN: SONET/SDH OSI Environments Access Layer Configuration

Figure 27

Telco Network with Cisco Contact Closure Device

CLNS packet flow

NE14A VLAN using ISL NE15A

Area NE14B 0001

3640A Central office router

2924XL

NE25A

Area NE25B 0002 IP over CLNS tunnel Area 0003 NE26B
103353

NE26A

3631A

Configuring a Tunnel Using IP over CLNS
In Figure 27, the IP over CLNS tunnel is created from the Cisco 3640A router to the Cisco 3631A router. The following example shows the CLNS tunnel configuration for the two routers:
Cisco 3640A Router Configuration interface CTunnel1 description connection remote site with 3631A ip address 192.168.10.1 255.255.255.252 ctunnel destination 39.840f.8011.9999.0000.1111.0003.0001.6444.3410.cc ! router isis area0003 net 39.840f.8011.9999.0000.1111.0003.0010.7bc7.ae40.00 is-type level-1

Cisco 3631A Router Configuration clns routing ! interface CTunnel1 ip address 192.168.10.2 255.255.255.252 ctunnel destination 39.840f.8011.9999.0000.1111.0003.0010.7bc7.ae40.cc ! router isis area0003 net 39.840f.8011.9999.0000.1111.0003.0001.6444.3410.00 is-type level-1

Verifying the IP over CLNS Tunnel Configuration
The tunnel is actually configured as an interface and the status of the tunnel can be checked with the show interfaces ctunnel1 command, as follows:
3640A# show interfaces ctunnel1 CTunnel1 is up, line protocol is up Hardware is CTunnel Description: connection remote site with 3631A Internet address is 192.168.10.1/30 MTU 1514 bytes, BW 9 Kbit, DLY 500000 usec,

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reliability 255/255, txload 56/255, rxload 28/255 Encapsulation TUNNEL, loopback not set Keepalive set (10 sec) Tunnel destination 39.840f.8011.9999.0000.1111.0003.0001.6444.3410.cc Last input 00:00:00, output 00:00:00, output hang never Last clearing of "show interface" counters never Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0 Queueing strategy: fifo Output queue: 0/0 (size/max) 5 minute input rate 1000 bits/sec, 3 packets/sec 5 minute output rate 2000 bits/sec, 2 packets/sec 217 packets input, 13104 bytes, 0 no buffer Received 0 broadcasts, 0 runts, 0 giants, 0 throttles 0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort 177 packets output, 33658 bytes, 0 underruns 0 output errors, 0 collisions, 0 interface resets 0 output buffer failures, 0 output buffers swapped out

The report shows that the CLNS tunnel is physically up. The “line protocol is up” report indicates that the router has a route to the CLNS tunnel destination. The hardware report indicates the interface type is CTunnel. The tunnel destination is 39.840f.8011.9999.0000.1111.0003.0001.6444.3410.cc, which is the NET for the Cisco 3631A router. Additional information about the show interfaces ctunnel command can be found in the Cisco IOS Software Release 12.1T IP over a CLNS Tunnel feature module at the following URL: http://www.cisco.com/en/US/partner/products/sw/iosswrel/ps1834/products_feature_guide09186a0080 080382.html

Note

Cisco released the IP over CLNS Tunnel feature before an industry standard existed. An RFC has been created to tunnel IPv4 and IPv6 over CLNS. Cisco supports the feature beginning in Cisco IOS Release 12.3(7)T. The default tunnel mode is the original Cisco solution. An option on the tunnel interface allows the tunnel to be set to GRE. The Cisco IOS Release 12.3(7)T document describing the CLNS Support for GRE Tunneling of IPv4 and IPv6 Packets in CLNS Networks feature module at the following URL: http://www.cisco.com/en/US/partner/products/sw/iosswrel/ps5207/products_feature_guide09186a0080 1ffb3d.html

Configuring a Contact Closure Device
The tunnel in the previous configuration example was created to access the Contact Closure device (the NM-AIC-64) in the Cisco 3631 router. The NM-AIC-64 is installed in the second network module slot and communicates across the PCI bus in the router. The NM-AIC-64 requires an IP address to access it, and must be assigned an IP address and a static route that points to the IP address of the NM-AIC-64. The static route should be redistributed into the IP routing protocol. The following example shows the basic configuration for the NM-AIC-64: alarm-interface 2 ip address 192.168.10.5 ! ip route 192.168.10.5 255.255.255.255 Serial2/0 ! router ospf 795 log-adjacency-changes redistribute static subnets network 192.168.0.0 0.0.255.255 area 0

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Verifying the Contact Closure Device Configuration
The following example shows the report from issuing the show ip route command on the Cisco 3631A router. The static route to reach NM-AIC-64 is highlighted in bold text for purpose of example. Notice that the NM-AIC-64 looks like a serial device connected to the router.
3631A# show ip route Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2 i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area * - candidate default, U - per-user static route, o - ODR P - periodic downloaded static route Gateway of last resort is not set O C S O O O O 192.168.12.0/24 [110/11112] via 192.168.10.1, 00:10:51, CTunnel1 192.168.10.0/24 is variably subnetted, 2 subnets, 2 masks 192.168.10.0/30 is directly connected, CTunnel1 192.168.10.5/32 is directly connected, Serial2/0 192.168.0.0/24 [110/11121] via 192.168.10.1, 00:10:51, CTunnel1 192.168.2.0/26 is subnetted, 2 subnets 192.168.2.64 [110/11112] via 192.168.10.1, 00:10:51, CTunnel1 192.168.2.128 [110/11112] via 192.168.10.1, 00:10:51, CTunnel1 192.168.3.0/26 is subnetted, 1 subnets 192.168.3.128 [110/11122] via 192.168.10.1, 00:10:52, CTunnel1

The following example shows the report from issuing the show ip route command on the Cisco 3640A router. The static route to reach the NM-AIC-64 is highlighted in bold text for purpose of example, and looks like an external route learned over OSPF.
3640A# show ip route Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2 i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area * - candidate default, U - per-user static route, o - ODR P - periodic downloaded static route Gateway of last resort is 192.168.0.1 to network 0.0.0.0 C 192.168.12.0/24 is directly connected, FastEthernet3/0.1 192.168.10.0/24 is variably subnetted, 2 subnets, 2 masks C 192.168.10.0/30 is directly connected, CTunnel1 O E2 192.168.10.5/32 [110/20] via 192.168.10.2, 00:09:48, CTunnel1 C 192.168.0.0/24 is directly connected, Ethernet0/0 12.0.0.0/32 is subnetted, 1 subnets R 12.222.16.0 [120/1] via 192.168.0.1, 00:00:16, Ethernet0/0 192.168.2.0/26 is subnetted, 2 subnets C 192.168.2.64 is directly connected, FastEthernet3/0.2 C 192.168.2.128 is directly connected, FastEthernet3/0.3 192.168.3.0/26 is subnetted, 1 subnets O 192.168.3.128 [110/11] via 192.168.2.190, 00:09:48, FastEthernet3/0.3 R* 0.0.0.0/0 [120/1] via 192.168.0.1, 00:00:16, Ethernet0/0

For more information about configuring the NM-AIC-64, refer to the document NM-AIC-64, Contact Closure Network Module.

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Mapping NSAPs to Device Names Using TARP
This section describes a method of mapping NSAPs to device names. In North America, ILECs and long distance carriers use a TID—a network-wide unique target identifier—to name a piece of equipment. The TID is a string of up to 20 case-sensitive characters. Service providers needed a dynamic method to map TIDs to NSAPs or network entity titles (NETs)—the terms NSAP and NET are often used interchangeably within the telco industry—and TARP serves that purpose. TARP runs over the Connectionless Network Protocol (CLNP), as defined in ISO 8473, and all Cisco routers that support CLNS routing support TARP. TARP is documented in GR-253-Core section 8. Additional documentation about TARP can be found on the ATIS website at www.atis.org. TARP was developed as part of the SONET Interoperability Forum (SIF). TARP was developed to map the name for a network element (NE) to an NSAP. The OSS administrator typically knows the network element TID when building a profile for the device, but often does not know the NSAP. TARP was designed to dynamically map the TID to the NSAP. TARP was implemented on the router to facilitate the mapping across a network. Typically, the service provider has an OSS in the data center that needs to communicate with a network element in the central office, as shown in Figure 28.
Figure 28 Typical TARP Configuration and Packet Flow

TARP packet flow VLAN using ISL NE14A Area 0001 NE14B

IP/OSI OSS Central office router

NE15A Area 0002 Area 0003

NE25A

NE25A
95114

NE26A

NE26B

A router can be configured to participate in TARP. The router is actually assigned a TID. The NET of a router is associated with the TID.

Note

The network layer for a device cannot have an address in OSI; instead, the device must have an NET. The NET at the network layer is actually an NSAP with a selector value of 00. IS-IS routers are assigned NETs. The TARP cache maps the NET of the IS-IS router to the TID. The following example shows how to configure the IS-IS router to assign the NET (notice that the NET is the NSAP with a network selector value of 00): router isis area0001 net 39.840f.8011.9999.0000.1111.0001.0010.7bc7.ae40.00

In OSI, File Transfer, Access, and Management (FTAM) and other applications have a specific network selector (also called N-selector) value that identifies the application. The network selector value for the TARP application are the hexadecimal digits AF. The network selector is analogous to a TCP port number.

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Cisco Network Solutions for the Telco DCN: SONET/SDH OSI Environments Access Layer Configuration

TARP uses five types of protocol data units (PDUs):


Type 1 PDU is a request for the NSAP with a specific TID value within a Level 1 routing area. The type 1 PDU is propagated to all of the IS-IS Level 1 adjacencies and ES-IS adjacencies. A separate type 1 PDU is sent to every adjacency. A type 1 packet can be issued from a Cisco router using the tarp resolve tid or tarp resolve tid 1 EXEC command. Type 2 PDU is a request for the NSAP with a specific TID value within a Level 2 routing area. A type 2 request PDU is propagated by an individual type 2 PDU being sent to all of the IS-IS and ES-IS adjacencies in the IS-IS router. A type 2 packet can be issued from a Cisco router using the tarp resolve tid 2 EXEC command. The tarp resolve tid EXEC command issues a type 2 packet after the type 1 fails. Type 3 PDU is a response to a TARP request. The TARP request could be a type 1, type 2, or type 5 PDU. The type 3 packet is a unicast PDU, and a single PDU is sent directly back to the originator. Type 4 PDU is a notification of an NSAP address change or a TID change. The type 4 PDU is propagated through the entire network. The type 4 PDU is sent to all of the adjacencies of the network element. Type 5 PDU is a request for a TID that matches a specific NSAP. The type 5 PDU is sent directly to a specific NSAP. A type 5 PDU can be issued from a Cisco router using the tarp query EXEC command.



• •



In a traditional IS-IS implementation, a single IS-IS process is configured. The TARP application uses the NET in the single process for creating the NSAP. If the router is configured with an IS-IS multiarea, TARP will behave as follows:
• •

The router uses the NET of the Level 2 area if a Level 2 process is configured, so that the NSAP for the TID will be the NET of the Level 2 process with a selector value of AF. If no Level 2 process is configured and multiple Level 1 processes are configured, the first active Level 1 process NET will be used.

Note

Multiple Level 1 processes are sorted by the process name alphanumerically, and capital letters are sorted ahead of lowercase letters. If a Level 1 process is added or removed, the NSAP associated with the TID can change at the next reload of the router.



Type 1 PDUs received are processed as normal. The TARP data cache is checked for an entry. If no entry is present, the type 1 PDU is propagated to all Level 1 IS-IS and ES-IS adjacencies in the same Level 1 area. Type 2 PDUs received are processed as normal. The TARP data cache is checked for an entry. If no entry is present, the type 2 PDU is propagated to all IS-IS and ES-IS adjacencies. If the PDU originated in a different Level 1 IS-IS area, the TID and NET of the source will be cached in the TARP data cache. Type 4 PDUs are forwarded to all ES-IS and IS-IS adjacencies. Type 3 and type 5 PDUs are sent to a specific NSAP and are therefore routed. The type 3 PDU is a response to a type 1 or type 2 PDU originated at a specific address.



• •

The Cisco router labeled “3640A” in Figure 29 is configured with multiple IS-IS processes.

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Cisco Network Solutions for the Telco DCN: SONET/SDH OSI Environments Access Layer Configuration

Figure 29

IS-IS Multiarea Network Using VLAN Trunking and ISL Encapsulation

CLNS packet flow

VLAN using ISL

NE14A

Area 0001

NE14B

NE15A 3640A Central office router 2924XL NE25A Area 0002 Area 0003

NE25B
95116

NE26A

NE26B

Use the show tarp tid-cache EXEC command to examine the TARP TID cache. The following is sample output from this command:
3640A# show tarp tid-cache TID ('*' : static; & : local) & 3640A 3640A# NSAP 39.840f.8011.9999.0000.1111.0001.0010.7bc7.ae40.00

The following example lists the configuration for the Cisco 3640 router. The first IS-IS process listed is area0001. The NET associated with the process area0001 is 39.840f.8011.9999.0000.1111.0001.0010.7bc7.ae40.00, which matches the NET listed in the TARP TID cache for the Cisco router labeled “3640A.” (Remember the rule that the NET of the Level 2 IS-IS process would be associated with the TID.)
3640A# show configuration Using 2849 out of 129016 bytes ! version 12.2 service timestamps debug uptime service timestamps log uptime no service password-encryption ! hostname 3640A ! boot system slot1: boot system flash boot system rom boot system slot0: logging queue-limit 100 ! ip subnet-zero clns routing mpls ldp logging neighbor-changes no ftp-server write-enable ! ! ! ! interface Ethernet0/0 ip address 192.168.0.49 255.255.255.0

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half-duplex no cdp enable ! interface Ethernet0/1 no ip address shutdown half-duplex no cdp enable ! interface Ethernet0/2 no ip address shutdown half-duplex no cdp enable ! interface Ethernet0/3 ip address 10.19.250.33 255.255.255.248 shutdown half-duplex no cdp enable ! interface Serial1/0 no ip address clockrate 9600 no cdp enable ! interface Serial1/1 no ip address shutdown no cdp enable ! interface Serial1/2 no ip address clockrate 9600 no cdp enable ! interface Serial1/3 no ip address clockrate 9600 no cdp enable ! interface FastEthernet3/0 no ip address duplex auto speed auto no cdp enable ! interface FastEthernet3/0.1 description ISIS area 0001 encapsulation dot1Q 1 native ip address 192.168.12.24 255.255.255.0 no ip redirects no cdp enable clns router isis area0001 isis priority 127 tarp enable ! interface FastEthernet3/0.2 description ISIS area 0002 encapsulation dot1Q 2 ip address 192.168.2.125 255.255.255.192 no ip redirects no cdp enable clns router isis area0002

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isis priority 127 tarp enable ! interface FastEthernet3/0.3 description ISIS area 0003 encapsulation dot1Q 3 ip address 192.168.2.189 255.255.255.192 no ip redirects no cdp enable clns router isis area0003 isis priority 127 tarp enable ! router ospf 795 no log-adjacency-changes network 192.168.0.0 0.0.255.255 area 0 ! router isis area0001 net 39.840f.8011.9999.0000.1111.0001.0010.7bc7.ae40.00 ! router isis area0002 net 39.840f.8011.9999.0000.1111.0002.0010.7bc7.ae40.00 is-type level-1 ! router isis area0003 net 39.840f.8011.9999.0000.1111.0003.0010.7bc7.ae40.00 is-type level-1 ! router rip network 192.168.0.0 ! no ip http server no ip classless ip route 0.0.0.0 0.0.0.0 172.31.232.17 ! ! no cdp run clns host NE14A 39.840f.8011.9999.0000.1111.0001.00e0.b064.4324.00 clns host NE14B 39.840f.8011.9999.0000.1111.0001.0050.7363.7b40.00 clns host NE25A 39.840f.8011.9999.0000.1111.0002.00e0.b064.434e.00 clns host NE25B 39.840f.8011.9999.0000.1111.0002.0030.94e2.6ce0.00 clns host NE26A 39.840f.8011.9999.0000.1111.0003.00d0.5872.9720.00 clns host NE26B 39.840f.8011.9999.0000.1111.0003.0010.7b17.f880.00 clns host NE15A 39.840f.8011.9999.0000.1111.0001.0010.7bd8.c7d0.00 clns host 3640A 39.840f.8011.9999.0000.1111.0001.0010.7bc7.ae40.00 ! tftp-server slot1: tarp run tarp tid 3640A ! line con 0 password cisco line aux 0 line vty 0 4 exec-timeout 0 0 password cisco login line vty 5 99 login ! end

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Enabling TARP
The following example shows the tarp run and tarp tid global configuration commands used to enable TARP on a central office router: tarp run tarp tid 3640A

TARP must be enabled on an interface in order for TARP packets to be forwarded. TARP is enabled on the Cisco router labeled “3640A,” shown in Figure 30 on page 62. The configuration for Fast Ethernet interface 3/0.1 is listed in the following example; the tarp enable interface configuration command is the last command listed. interface FastEthernet3/0.1 description ISIS area 0001 encapsulation dot1Q 1 native ip address 192.168.12.24 255.255.255.0 no ip redirects no cdp enable clns router isis area0001 isis priority 127 tarp enable

Use the show tarp EXEC command to display the global TARP configuration information on a router:
3640A# show tarp Global TARP information: TID of this station is "3640A" Timer T1 (timer for response to TARP Type 1 PDU) is 15 seconds Timer T2 (timer for response to TARP Type 2 PDU) is 25 seconds Timer T3 (timer for response to ARP request) is 40 seconds Timer T4 (timer that starts when T2 expires) is 15 seconds Loop Detection Buffer entry timeout : 300 seconds Loop Detection Buffer zero sequence timer is 300 seconds TID cache entry timeout : 3600 seconds This station will propagate TARP PDUs This station will originate TARP PDUs TIDNET cache is enabled Sequence number that next packet originated by this station will have : 1 Update remote cache (URC) bit is 0 Packet lifetime : 100 hops Protocol type used in outgoing packets : "FE" N-Selector used in TARP PDU's : "AF"

Use the following information to interpret the report:
• •

TID of this station is 3640A. (Remember that the TID is case-sensitive.) Timers T1, T2, T3, and T4 are set at the default values defined in GR-253-Core Section 8:
– Timer T1 is the time that the router waits for a response to a TARP type 1 PDU. Timer T1 can

be altered with the tarp t1-response-timer seconds global configuration command. The range of seconds is from 0 to 3600 with a default of 15.
– Timer T2 is the time that the router waits for a response to a TARP type 2 PDU. Timer T2 can

be altered with the tarp t2-response-timer seconds global configuration command. The range of seconds is from 0 to 3600 with a default of 25.
– Timer T3 is the time that the router waits for a response to an address resolution request, which

is a TARP type 5 PDU. Timer T3 can be altered with the tarp arp-request-timer seconds global configuration command. The range of seconds is from 0 to 3600 with a default of 40.

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– Timer T4 starts when timer T2 expires. The timer is used for error recovery, and can be altered

with the tarp post-t2-response-timer seconds global configuration command. The range of seconds is from 0 to 3600 with a default of 15.


The Loop Detection Buffer helps prevent TARP type 1, type 2, and type 4 packets from looping throughout the network. The entry timeout value determines the amount of time that mapping data will be stored in the loop detection database. The Loop Detection Buffer zero sequence timer starts when a TARP packet with a value of 0 (zero) is received. Additional TARP packets with a sequence value of 0 that are received before the timer expires are discarded. The timer value displayed in the example is set to 5 minutes (300 seconds). TID cache entry timeout indicates the amount of time the TID-to-NSAP maps will be cached in the router, which in this example is 3600 seconds (1 hour). The TID cache timer is configurable with the tarp cache-timer seconds global configuration command. The caching of the TID can be turned on or off with the tarp allow-caching global configuration command. TID caching is on by default. “This station will propagate TARP PDUs” indicates that the router can forward TARP PDUs. “This station will originate TARP PDUs” indicates that the router can originate TARP PDUs. “TIDNET cache is enabled” indicates that the TID-to-NSAP maps will be cached by the router. The cache timer is set to 3600 seconds (1 hour). The cache value can range from 30 to 86400 seconds (24 hours). “Sequence number that the next TARP packet originated by this router will have” indicates a value of 1; the value can range from 0 to 65535. The sequence number prevents broadcast storms and is the next outgoing TARP packet. The sequence number can be changed with the tarp sequence-number number global configuration command. An update remote cache (URC) bit value of 0 (zero) indicates that remote routers should store the TARP type 3 packet in their cache. A value of 1 would tell the remote hosts not to store the packet in the remote router’s cache. The URC value can be changed using the tarp urc {0 | 1} global configuration command. Packet lifetime is the number of hops that the packet can live. Each IS-IS router the packet traverses is counted as one hop. The default hop number is 100, and the range is from 0 to 65535. Protocol type “FE” is used to identify the CLNP, as specified in GR-253-CORE section 8. This parameter can be configured using Cisco IOS software. The protocol type can be specified in outgoing TARP PDUs with the tarp protocol hex-digit global configuration command. N-selector is the network selector value used in TARP PDUs. In this example, the network selector value are the hexadecimal digits AF, which designates the TARP application as specified in GR-253-CORE section 8. This parameter can be configured using Cisco IOS software. The N-selector value generated with the TARP PDU can be changed with the tarp selector hex-digit global configuration command.





• • •





• •



Using TARP with Remote Login Applications
One reason TARP was developed was to assist remote login applications. Central office technicians may not know the NSAP of the device that they want to log in to remotely, but they can determine the name of the equipment or the TID. Network monitoring applications such as Telcordia’s Network Management Application (NMA) or Provision applications such as Fujitsu’s Flexr can also take advantage of TARP as a dynamic method to map TIDs to NSAPs or NETs. The system administrator would have to type in only the TID for the device that was to be monitored or provisioned, which is much easier than typing the NSAP. The OSS application would then issue a TARP type 1 or type 2 packet to learn the NET.

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To issue a TARP type 1 or type 2 request on a Cisco router, use the tarp resolve tid EXEC command. Use Figure 30 as an example network for interpreting the reports displayed.
Figure 30 Sample Network for Interpreting TARP Reports

CLNS packet flow

VLAN using 802.1Q

NE14A

Area 0001

NE14B

NE15A Central office Router 3640A Area 0002 Area 0003

NE25A

NE25B
95623

NE26A

NE26B

Issue a TARP type 1 request for the NET for device NE15A using the tarp resolve tid EXEC command:
3640A# tarp resolve tid NE15A Type escape sequence to abort. Sending TARP type 1 PDU, timeout 15 seconds ... NET corresponding to TID NE15A is 39.840f.8011.9999.0000.1111.0001.0010.7bd8.c7d0.00

The request returns a message indicating that a TARP type 1 PDU was sent out. The software will wait for 15 seconds for a reply (the default time value for the T1 timer). If no response is received after 15 seconds, a type 2 PDU would be sent out to all of the IS-IS and ES-IS nodes that support TARP. In this example, the network element with the TID value of NE15A did respond with a TARP type 3 PDU, and the software picked up and displayed the NET on the screen. The NET is 39.840f.8011.9999.0000.1111.0001.0010.7bd8.c7d0.00. The TID-to-NET map will be stored in the router’s TARP data cache. To display the contents of the TARP data cache, use the show tarp tid-cache EXEC command. The TID for router 3640A and device NE15A is listed in the TARP data cache.
3640A# show tarp tid-cache TID ('*' : static; & : local) & 3640A NE15A NSAP 39.840f.8011.9999.0000.1111.0001.0010.7bc7.ae40.00 39.840f.8011.9999.0000.1111.0001.0010.7bd8.c7d0.00

To clear the TARP cache, use the clear tarp tid-cache command:
3640A# clear tarp tid-table

Check the TARP TID cache after clearing it to verify that only the Cisco router labeled “3640A” is listed:
3640A# show tarp tid-cache TID ('*' : static; & : local) & 3640A NSAP 39.840f.8011.9999.0000.1111.0001.0010.7bc7.ae40.00

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Cisco Network Solutions for the Telco DCN: SONET/SDH OSI Environments Access Layer Configuration

It is possible to watch the propagation of the TARP PDUs, for example, to watch router 3640A generate a TARP type 1 PDU for every adjacency. Use the show clns neighbors EXEC command to show all of the adjacencies:
3640A# show clns neighbors Area area0001: System Id Interface NE15A Fa3/0.1 NE14A Fa3/0.1 Area area0002: System Id Interface NE25A Fa3/0.2 Area area0003: System Id Interface NE26A Fa3/0.3

SNPA 0010.7bd8.c7d0 00e0.b064.4325

State Up Up

Holdtime 27 21

Type Protocol L1 IS-IS L1 IS-IS

SNPA 00e0.b064.434e

State Up

Holdtime 22

Type Protocol L1 IS-IS

SNPA 00d0.5872.9720

State Up

Holdtime 21

Type Protocol L1 IS-IS

Four adjacencies are listed and all are of type Level 1. Figure 30 has been redrawn in Figure 31 with an arrow depicting each of the TARP type 1 PDUs being sent out. One important point to note is that TARP is not a broadcast protocol. A type 1 packet is generated and sent out to each of the IS-IS adjacencies. Sending separate PDUs to each adjacency will generate more network traffic than a single broadcast packet.
Figure 31 Transmission of TARP Type 1 PDUs

TARP type 1 PDUs

NE14A

Area 0001

NE14B

NE15A Central office Router 3640A Area 0002 Area 0003

NE25A

NE25B
95624

NE26A

NE26B

TARP debug commands can also help track the packets that are being sent. Before the debug command is issued, a list of the system identifiers will help analyze the command output:
3640A NE14A NE14B NE25A NE25B NE26A NE26B NE15A system system system system system system system system id is id id is id id id 0010.7bc7.ae40 00e0.b064.4324 0050.7363.7b40 00e0.b064.434e 0030.94e2.6ce0 00d0.5872.9720 0010.7b17.f880 0010.7bd8.c7d0

To verify the TARP type 1 PDUs that are being sent out, issue the debug tarp packet command. In addition, issue the debug tarp events command to track additional TARP PDU activity.
3640A# debug tarp packets TARP packet info debugging is on 3640A# debug tarp events TARP events debugging is on

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Cisco Network Solutions for the Telco DCN: SONET/SDH OSI Environments Access Layer Configuration

Next issue the tarp resolve tid EXEC command for device NE15A. In the following example, the router will wait 15 seconds for a response before issuing a TARP type 2 PDU. Device NE15A responds within 15 seconds with its NET, which is the NSAP address and selector value of 00.
3640A# tarp resolve tid NE15A Type escape sequence to abort. Sending TARP type 1 PDU, timeout 15 seconds ... NET corresponding to TID NE15A is 39.840f.8011.9999.0000.1111.0001.0010.7bd8.c7d0.00

The debug tarp packets command output shows a TARP type 1 PDU being sent to each of the four IS-IS adjacencies over the Fast Ethernet interface connection; four type 1 PDU packet will be sent out. The first type 1 packet is sent to device NE15A (0010.7bd8.c7d0) from the Cisco router labeled “3640A” (0010.7bc7.ae40):
3640A# 00:16:50: TARP-PA: Propagated TARP packet, type 1, out on FastEthernet3/0.1 00:16:50: Lft = 100, Seq = 7, Prot type = 0xFE, URC = TRUE 00:16:50: Dtid len = 5, Stid len = 5, Prot addr len = 20 00:16:50: Destination NSAP : 39.840f.8011.9999.0000.1111.0001.0010.7bd8.c7d0.00 00:16:50: Originator's NSAP : 39.840f.8011.9999.0000.1111.0001.0010.7bc7.ae40.00 00:16:50: Target TID : NE15A 00:16:50: Originator's TID : 3640A

The debug tarp packets output continues by showing the second type 1 packet being sent to device NE14A (00e0.b064.4324) from the Cisco router labeled “3640A” (0010.7bc7.ae40):
00:16:50: TARP-PA: Propagated TARP packet, type 1, out on FastEthernet3/0.1 00:16:50: Lft = 100, Seq = 7, Prot type = 0xFE, URC = TRUE 00:16:50: Dtid len = 5, Stid len = 5, Prot addr len = 20 00:16:50: Destination NSAP : 39.840f.8011.9999.0000.1111.0001.00e0.b064.4324.00 00:16:50: Originator's NSAP : 39.840f.8011.9999.0000.1111.0001.0010.7bc7.ae40.00 00:16:50: Target TID : NE15A 00:16:50: Originator's TID : 3640A

The debug tarp packets output continues by showing the third type 1 packet being sent to device NE25A (00e0.b064.434e) from the Cisco router labeled “3640A” (0010.7bc7.ae40):
00:16:50: TARP-PA: Propagated TARP packet, type 1, out on FastEthernet3/0.2 00:16:50: Lft = 100, Seq = 7, Prot type = 0xFE, URC = TRUE 00:16:50: Dtid len = 5, Stid len = 5, Prot addr len = 20 00:16:50: Destination NSAP : 39.840f.8011.9999.0000.1111.0002.00e0.b064.434e.00 00:16:50: Originator's NSAP : 39.840f.8011.9999.0000.1111.0001.0010.7bc7.ae40.00 00:16:50: Target TID : NE15A 00:16:50: Originator's TID : 3640A

The debug tarp packets output shows a fourth type 1 packet being sent to device NE26A (00d0.5872.9720) from the Cisco router labeled “3640A” (0010.7bc7.ae40):
00:16:50: TARP-PA: Propagated TARP packet, type 1, out on FastEthernet3/0.3 00:16:50: Lft = 100, Seq = 7, Prot type = 0xFE, URC = TRUE 00:16:50: Dtid len = 5, Stid len = 5, Prot addr len = 20 00:16:50: Destination NSAP : 39.840f.8011.9999.0000.1111.0003.00d0.5872.9720.00 00:16:50: Originator's NSAP : 39.840f.8011.9999.0000.1111.0001.0010.7bc7.ae40.00 00:16:50: Target TID : NE15A 00:16:50: Originator's TID : 3640A

Next, the debug tarp packets output shows a type 3 packet being received on Fast Ethernet interface 3/0.1 by router 3640A (0010.7bc7.ae40) from device NE15A (0010.7bd8.c7d0):
00:16:50: TARP-PA: Received TARP type 3 PDU on interface FastEthernet3/0.1 00:16:50: Lft = 100, Seq = 3, Prot type = 0xFE, URC = TRUE

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Cisco Network Solutions for the Telco DCN: SONET/SDH OSI Environments Access Layer Configuration

00:16:50: Ttid len = 0, Stid len = 5, Prot addr len = 20 00:16:50: Packet sent/propagated by 39.840f.8011.9999.0000.1111.0001.0010.7bd8.c7d0.af 00:16:50: Originator's NSAP : 39.840f.8011.9999.0000.1111.0001.0010.7bd8.c7d0.00 00:16:50: Originator's TID : NE15A

Finally, the debug tarp events output shows a TARP cache entry being created. A value is set for the loop detection buffer (LDB). The loop detection buffer is a method of deterring packets from propagating TARP packets that the IS-IS router has already seen.
00:16:50: 00:16:50: discarded 00:16:50: 00:16:50: discarded 00:16:50: TARP-PA: Created new TARP-EV: Packet from - sequence number (7)

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