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From: blancher at cartel-securite.fr (Cedric Blancher)
Subject: ICMP (was: daily internet traffic report)

Le dim 17/10/2004 ? 22:21, James Edwards a ?crit :
> So, blocking ***all*** ICMP ***types*** is bad but you can block some
> ***types*** without getting into trouble. Till you understand that all
> the types do in relation to networking I would leave the alone.

Nowadays, using a decent stateful firewall allows one to get rid of ICMP
filtering by associating ICMP errors to existing connections. As an
example, when filtering using Netfilter, ICMP errors triggered by known
IP connections are recognized as such (i.e. RELATED state) and thus can
be filtered in a different way unsollicited ones (i.e. INVALID state)
are.

This kind of feature allows one not to block valid ICMP stuff and keep
away from direct ICMP solicitations you can filter the way you want.

My 0.02?...


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