Yes, you are right. I completely forgot about ICMP Packet Too Big messages since they are effectively not used in practice for application-level stuff. One mino

Yes, you are right. I completely forgot about ICMP Packet Too Big messages since they are effectively not used in practice for application-level stuff. One minor difference between it and the behavior desired by me is that the error packet would be sent directly to an application port (one of the reasons why it would be nice for IP packets to contain source/destination ports), making it possible to conveniently process it. IIUC even assuming PTB messages are reliably delivered, we would need some kind of OS help (and additional APIs) to process them properly.