Oh man, I could rant about this forever. PMTUD is very broken on the internet. This leads to things like MSS clamping based on the route your packet will take.

Oh man, I could rant about this forever. PMTUD is very broken on the internet. This leads to things like MSS clamping based on the route your packet will take. If you run an ISP, or really a network of any sort, and block ICMP indiscriminately, your network is broken. Please stop.