Firewalls are a key security technology in the modern network infrastructure. This section details their evolution and the technologies that have resulted.
The firewall should
• Be resistant to attacks.
• Be the only transit point.
• Enforce the access control policy of the organization.
These work at Layers 3 and 4, examining packets one at a time and are implemented on a Cisco router using access control lists (ACL).
Advantages of these firewalls include the following:
• Based on simple
• Low impact on network performance
• Easy to implement
• Supported on most routers
• Initial security at a low network layer