User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Firefox/78.0

Steps to reproduce:

With network.http.http3.enabled set to true, I opened the first HTTP3 site I found (https://http3check.net/about) and the very first udp 443 packet wireguard picked up had a length of 1385.

Expected results:

This appears to be in violation of the RFC requirement that datagrams never be sent of size > 1280 unless PMTUd has successfully detected the path supports datagrams > 1280. This is doubly an issue for QUIC/HTTP3 as there is no mechanism for intermediate routers to indicate in-band the maximum packet size as there is with TCP (most big metal routers support TCPMSS clamping, and iptables has a -j TCPMSS target for this reason).

The Bugbug bot thinks this bug should belong to the 'Core::Networking: HTTP' component, and is moving the bug to that component. Please revert this change in case you think the bot is wrong.

See https://github.com/mozilla/neqo/pull/465#issuecomment-801517075 for some additional context.

Per the comments on github linked in comment 2, this appears to be intentional on our part; closing this bug. Please re-open if you think I misinterpreted the situation.