Firewall stateful handling of ICMP packets

[Sean Donelan]

You could drop ICMP packets at your firewall if the firewalls properly
implemented stateful inspection of ICMP packets.  The problem is few
firewalls include ICMP responses in their statefull analysis.  So you are
left with two bad choices, permit "all" ICMP packets or deny "all" ICMP
packets.