legacy MTU of 1500 bytes [LWN.net]

legacy MTU of 1500 bytes

Posted Nov 3, 2022 17:39 UTC (Thu) by Cyberax (✭ supporter ✭, #52523)
In reply to: legacy MTU of 1500 bytes by farnz
Parent article: Moving past TCP in the data center, part 1

> Switches are the big pain here - they've created a world in which, because the switch can only forward or drop frames

The MTU should have been reified to the IP level. Not doing this was one of the most unforgivable errors in the IPv6 development.

In the ideal world all the IP packets would have two fields: forward minimum packet size and the reverse minimum packet size. A switch/router during packet forwarding sets the forward minimum size to their max size, if it's less than the current value. Reverse size is simply propagated back.

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legacy MTU of 1500 bytes

Posted Nov 3, 2022 17:45 UTC (Thu) by guus (subscriber, #41608) [Link]

> The MTU should have been reified to the IP level. Not doing this was one of the most unforgivable errors in the IPv6 development.

Actually the same should be done for congestion control; it makes no sense that multiple TCP connections to the same host each implement their own congestion control loop when all packets go via exactly the same path. This is in effect what QUIC is doing: combine multiple reliable, in-order streams with a single congestion control loop. But of course that only is effective if you really use a single QUIC connection.