ECN

Wed Nov 13 19:35:37 UTC 2019

On Wed, 13 Nov 2019 at 18:27, Matt Corallo <nanog at as397444.net> wrote:

> This sounds like a bug on Cloudflare’s end (cause trying to do anycast TCP is... out of spec to say the least), not a bug in ECN/ECMP.

Not true. Hash result should indicate discreet flow, more importantly
discreet flow should not result into two unique hash numbers. Using
whole TOS byte breaks this promise and thus breaks ECMP.

Platforms allow you to configure which  bytes are part of hash
calculation, whole TOS byte should not be used as discreet flow SHOULD
have unique ECN bits during congestion. Toke has diagnosed the problem
correctly, solution is to remove TOS from ECMP hash calculation.

-- 
  ++ytti