In this case I think the robustness principle is actually counter productive, here me out: MTU discovery is "robust". Most nodes already forward any packet the

In this case I think the robustness principle is actually counter productive, here me out: MTU discovery is "robust". Most nodes already forward any packet they can handle. The problem is that _some_ nodes filter out ICMP packets (hence breaking MTU discovery) but the link still "kind-of-works" (tm). Nodes that break MTU discovery should be considered 100% broken, but instead of fixing them we "accommodate" them by statically (manually) lowering our outgoing MTU, hence proliferating the problem. Robustness works against us. If half-broken firewalls were considered fully-broken, they would be replaced instead of accommodated. Aside: the `Fragmentation Needed` packet should have been part of the IP header, not a separate protocol.