ECN

Wed Nov 13 17:00:25 UTC 2019

Not ideal, sure, but if it’s only for the SYN (as you seem to indicate), splitting the flow shouldn’t have material performance degradation? 

> On Nov 13, 2019, at 11:51, Toke Høiland-Jørgensen <toke at toke.dk> wrote:
> 
> 
> 
>> On 13 November 2019 17:20:18 CET, Matt Corallo <netadmin 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.
> 
> Even without anycast, an ECMP shouldn't hash on the ECN bits. Doing so will split the flow over multiple paths; avoiding that is the whole point of doing the flow-based hashing in the first place.
> 
> Anycast "only" turns a potential degradation of TCP performance into a hard failure... :)
> 
> -Toke