250 Chapter 11 • Intrusion Prevention and Protection
If the Guard decides that the zone is really being attacked, it determines which traffic may be spoofed and drops all spoofed sources. It does this by a number of techniques, the most effective being TCP cookies or TCP SYN-cookies. With HTTP, it even spoofs an HTTP redirect to verify the authen-ticity of the sender. Obviously, if the source address is spoofed, this is a sure way to confirm it.The redirect will never happen!
For all other traffic,TCP, UDP, and IP, it drops anomalous sources (pri-marily based on rate) or imposes rate limits on them.
It can operate in a number of modes—notably both Layer 3 and Layer 2. However, at Layer 3 or 4, if you can live with your device having an IP
# IPLists are just lists of IP addresses for specific processing
Ethernet1 is defined as the outside interface and Ethernet0 the inside. Packets are simply forwarded across the bridge.The configuration file also shows that the default actions were (the configuration is long gone): 1. Tell the console.
The other great feature is the “mangle” feature, which allows you to alter packets more extensively:
message=attempt to retrieve /etc/passwd
■ Sending reset commands or killing processes
■ Dropping individual packets
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