IPv6 Address Type - Multicast
Overview:
As part of your assigned readings and material covered in class lecture, you have learned about IPv6 address types, including unicast and multicast addresses. For this assignment, you will expand your knowledge of the use of multicast addresses compared to the use of broadcast addresses in IPv4.

Required Resources:
 Textbook and lecture notes
 Internet access Research Resources:
• IPv6 multicast address – overview o http://www.tcpipguide.com/free/t_IPv6MulticastandAnycastAddressing.htm
• IPv6 subnet scanning RFC o http://www.ietf.org/rfc/rfc5157.txt

Deliverables
 Perform additional research to understand the use of multicast addresses in IPv6 protocol compared to IPv4 broadcast addresses with emphasis on: o Neighbor discovery o All nodes address o All routers address
 Describe the process of neighbor discovery including the use the all nodes address for achieving the same result as the IPv4 ARP protocol.
 Include the IPv6 multicast address for all routers and all hosts.
 Perform research to determine: o Are you able to perform subnet “scanning” by simple sending an ICMP echo packet to the “all hosts” multicast address? Similar to the concept of sending an ICMP echo packet to the broadcast address on an IPv4 subnet. o Provide an estimate of how long it would take to scan, through a tool similar to NMAP, an entire /64 IPv6 subnet to find every possible host, not using the multicast “all host” address. Use an Internet search engine to aid in this response.
Provide citations for the Internet resources you used. A big feature of IPv6 is the implementation of stateless autoconfiguration. With stateless autoconfiguration, a host dynamically learns the /64 prefix used on the subnet, and then calculates the rest of the address by using an EUI-64 interface id based on the network interface card MAC address. This process is accomplished by using the IPv6 Neighbor Discovery Protocol (NDP) to figure out the prefix used on the particular LAN. A part of NDP supersedes IPv4’s ARP protocol. Where ARP allowed devices on the same subnet to learn the MAC addresses of both devices, NDP accomplishes the same thing with NDP.
Router Solicitations (RS) and Router Advertisements (RA) are used by NDP to gather this information. A host sends out a router solicitation, asking any routers to respond with both the prefix of the subnet and the IPv6 address of default routers on the subnet. Because of the use of multicast addressing, RS messages only need to be received by the routers—other hosts on the network don’t need to bother with them. Multicasting eliminates the need for a broadcast address, which was utilized in IPv4. RS messages have a destination IPv6 address of FF02::2, which is only used by IPv6 routers. The resulting RA that is sent by the IPv6 router uses the multicast address of FF02::1, which is used by all IPv6 hosts on link. So, not only will the original host learn the prefix and IPv6 address of the router, all other hosts will too. In a DHCPv6 environment, the server may supply details of all possible IPv6 router addresses or just let NDP RS/RA take over for that role, accomplishing the same task. In the default process, routers periodically send out RAs automatically. When a host connects, they may wait for the next RA or send an RS out to all listening routers for an immediate RA. The format for multicast addresses are broken down as such: the first eight bits of the address are always “1111 1111” or “FF” in hexadecimal. The next four bits are called Flags, of which the first three are currently unused and set to zero. The fourth bit is called the “transient” flag. If left as zero, it means the address is marked as a permanently-assigned, “well-known” multicast address. If the bit is set to 1, it means it is a transient address, or not permanently assigned. The next four bits are used to define the scope, of which there are 16 different values (0 to 15). It governs the visibility of the link, from global to the internet to restricted to smaller networks like an organization, site, or link. The next 112 bits define the particular group within each scope level. Yes it is possible to discover all hosts on an IPv6 network by pinging the “all hosts” address which all IPv6-capable hosts should subscribe. Though, the limitations of this method include that if the network uses more than one interface, only a portion of the network may respond. If the network’s hosts’ security settings are such that they may not respond to ping requests, this renders this method ineffective as none would respond. As for how long it would take a program such as NMAP to scan the entirety of an IPv6 subnet, a conservative estimate of one ping per second would last about 584 billion years. Even if it was a thousand times faster, it would still take 584 million years. The length of time to scan the entirety of an IPv6 subnet is so large it is generally considered unfeasible to undergo.
Sources
Textbook, Chapter 23 http://www.tcpipguide.com/free/t_IPv6MulticastandAnycastAddressing.htm http://www.ietf.org/rfc/rfc5157.txt
http://ipv6exchange.net/questions/14/how-can-i-find-all-the-ipv6-hosts-on-a-network