ICMP Packets.

["Toddb" <toddb () pacifier com>]

To prohibit anyone from 'pinging' our router from the internet, I have disabled certain ICMP packets ( namely echo 
reply ) from exiting our external router interface. They are allowed in, but not out - which effectively disables 
someone from the outside pinging our router, but allows internal machines to ping the outside world. I have a couple of 
questions that someone may be able to answer.
 
1) Is there any reason that echo reply would need to be allowed out in response to an external request? I know this is 
the case for other ICMP messages such as packet-too-big, but I am not sure why echo-reply would ever be needed.
 
2) Is there a list of ICMP message types that are needed as opposed to ones that are just used for troubleshooting ( 
like echo, echo-reply ) that can be blocked without problems.
 
Thanks,
 
Todd
 
toddb () pacifier com