4 ms·
Unfortunately you can't really rely on PMTU discovery these days. Not only is it regularly filtered, it slows every connection down since you add a RTT for the
by r1ch 3y ago
Unfortunately you can't really rely on PMTU discovery these days. Not only is it regularly filtered, it slows every connection down since you add a RTT for the ICMP packets for every TCP host you talk to. In this case I would say the VPN client would be at fault for not adjusting the TCP MSS.
- devman0 3y agoRelying on MSS to not break layer 3 is going to be interesting when QUIC is more prevalent. PMTUD should be better supported.
- r1ch 3y agoQUIC unfortunately defaults to 1370 bytes to avoid having to deal with PMTUD :(. Endpoints are free to negotiate higher and the protocol does provide a way to generate arbitrary sized ping frames, but it's likely most implementations will just stick with the default.