[EvanAnderson]

Every time I've had to fight with path MTU discovery not working I've cursed the people who block all ICMP, though. If ICMP echo / echo-reply is the problem just block that. At the very least, allow destination unreachable / fragmentation needed thru (type 3, code 4).

[yardstick]

I am sure someone will find a way to exfiltrate data using any ICMP type. How good are firewalls at validating the packets are legit?

[pixl97]

Most of the people blocking ICMP have no clue that ICMP codes/types even exist.