I commonly see advice to block all ICMP traffic which is even crazier. I think perhaps the general suspicion of ICMP might be related to things like this http:

I commonly see advice to block all ICMP traffic which is even crazier. I think perhaps the general suspicion of ICMP might be related to things like this http://en.wikipedia.org/wiki/Ping_of_death http://en.wikipedia.org/wiki/Ping_of_death which are now mostly irrelevant. Some sort of naive attempt to stop attackers mapping your network too perhaps? It's not exactly a high tech (or effective) means of intrusion detection though.