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How to deny ICMP through the PIX
What is ICMP?
ICMP is one of the simplest protocols in the TCP/IP protocol suite. Most protocols implement a particular type of functionality to either facilitate basic operation of a part of the network stack, or an application. To this end they include many specific algorithms and tasks that define the protocol, which is where most of the complexity lies. ICMP, in contrast, is exactly what its name suggests: a protocol that defines control messages. As such, pretty much all of what ICMP is about is providing a mechanism for any IP device to send control messages to another device.
Inbound Internet Control Message Protocol (ICMP) through the PIX is denied by default. Outbound ICMP is permitted, but the incoming reply is denied by default.
To block ICMP traffic through the PIX, access list (ACL) entries to deny ICMP traffic through the PIX must be created. These are some examples: