Should firewall block ICMP Packets?

I honestly don't even know the purpose for ICMP packets other than to query if a port is open or an IP address exists, which honestly only sounds useful to hackers!

Currently I do block ALL ICMP packets (incoming and outgoing). I have noticed no real problems while they're blocked, but perhaps there's something I don't notice?

I want to know if anyone suggests blocking ICMP packets, and also if there is any harm in letting them pass. Also if anyone could explain the purpose of ICMP packets and how they may be used, I would greatly appreciate it. Thanks!

Hello MrDoomMaster,

How are you blocking ICMP packets and how are your computers connected? If you have a NAT router, that is a good layer of protection. It acts like a firewall and will protect your entire LAN from incoming traffic. Blocking ICMP incoming requests will block ping which can be useful when troubleshooting a network.

If you are running Windows XP Firewall, the ICMP incoming packets will automatically be accepted when file and printer sharing is enabled. The ping and tracert tools both use ICMP. For more information, see the following MS KB Article.

Description of the Ping and Tracert Tools
http://support.microsoft.com/default...b;en-us;217014