Which Icmp Types to Block?

The only essential ICMP traffic you need to allow in and out of your firewall is Type 3 and Type 4. Everything else is either optional or should be blocked.

What is ICMP why should you block it?

Blocking ICMP Traffic for Security

Network administrators often opt to disable ICMP on network devices to evade network mapping applications used by adversaries (e.g., Nmap and Nessus scans). ... Forged ICMP redirects — Network traffic could be fraudulently redirected to an attacker via a forged ICMP redirect message.

Can ICMP be blocked?

Many network administrators feel that ICMP is a security risk, and should therefore always be blocked at the firewall. It is true that ICMP does have some security issues associated with it, and that a lot of ICMP should be blocked. But this is no reason to block all ICMP traffic!