Number Name

4 source quench 8 echo request (ping) 12 parameter problem Table 5: ICMP Message Types to Allow Inbound at the Perimeter Router/Firewall Message Types Number Name 0 echo reply 3 destination unreachable 4 source quench 11 time exceeded 12 parameter problem

This section describes methods using filters to defend the router, the firewall and the protected network from information gathering and attacks. Note that one needs to be careful with combining the below recommendations together in any filter in order to prevent contradictions or other problems.
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