ICMP

Cisco ASA supports stateful inspection of Internet Control Message Protocol (ICMP) packets. To enable inspection of ICMP packets, use the inspect icmp command.

Additionally, Cisco ASA has the ability to translate ICMP error messages. It translates intermediate hops that send ICMP error messages based on the NAT configuration. Cisco ASA does this by overwriting the packet with the translated IP addresses.

Note

NAT for ICMP is disabled by default.

Cisco ASA also has the capability to inspect ICMP error messages. ICMP error messages always contain the full IP header, including options, of the IP packet that failed and the first 8 bytes of the IP data field. Cisco ASA makes sure that this information is present and that it is correct. To enable inspection of ICMP error messages, use the inspect icmp error command. If this command is disabled, Cisco ASA does not translate any ICMP error messages generated by intermediate devices.