1. Network firewall
The first line of defense against unwelcomed users would surely be the firewall. At one point, the use of dual firewalls from different vendors was all the rage, but DMZ is more popular today. There are actually a few different types of firewall implementations. For example, consumer-grade routers typically make use of Network Address Translation (NAT), because the identity of hosts is complicated, NAT is often said to offer firewall capabilities.
2. Virtual Private Network
Employees who need to access company resources from unsecured locations such as public Wi-Fi hotspots are a mainly exposed group. A VPN channels all network traffic through an encrypted channel back to the trusted corporate network. VPN’s can be complex and is costly to support due to the overheads of authentication, processing and bandwidth.
3. IDS and IPS
An intrusion detection system (IDS) is a network-centric strategy that involves monitoring traffic for suspicious activities that may indicate that the corporate network has been compromised. This may require the detection of port scans being created from within the network or excessive attempts to log into a server. The intrusion prevention system (IPS) is usually deployed in-line in order to actively prevent or block intrusions as they are detected. A specific IP address could be automatically blocked.

4. Malware Detection
Malware scanning performed on client devices relies on the processing capabilities of individual devices to check for threats. Given that most malware infestations are a direct result of a user action, the typical anti-malware package has also evolved into complete suites that attempt to offer protection against multiple threat vectors. Malware products specifically optimized for servers are also available, but they are not as popular.
5. Whitelisting
Whitelisting is an anti-malware defense