Fwd: ECN

[Tim Durack via NANOG <nanog () lists nanog org>]

In case it is useful for anyone else, underlying issue looks to be this:

Cisco CSCws27022: ECN bits being included as part of ECMP hash on IPv6 TCP
flows (Workaround: Do not use ECMP)

Appears to be platform specific, affecting Cisco Catalyst C9K UADP ASIC
(C9500-32C)

Another work-around might be to configure "ip cef load-sharing algorithm
original"

Tim:>

On Tue, Mar 25, 2025 at 4:33 PM Tim Durack <tdurack () gmail com> wrote:

> Very helpful, thanks! Will post my own short story once complete...
>
> On Tue, Mar 25, 2025 at 4:24 PM Toke Høiland-Jørgensen <toke () toke dk>
> wrote:
>
> > Tim Durack <tdurack () gmail com> writes:
> >
> > > Toke,
> > >
> > > Resurrecting an old thread, did you ever write this one up?
> >
> > Hi Tim
> >
> > Thank you for the reminder! No, I never did get around to writing
> > anything at the time. However, now that you reminded me, I collected my
> > old notes and posted this:
> >
> >
> > https://blog.tohojo.dk/2025/03/ecn-ecmp-and-anycast-a-cocktail-of-broken-connections.html
> >
> > > I believe I have a customer reporting a similar problem with IPv6 TCP
> > ECN
> > > probably ECMP resulting in RST coming back from anycast services
> > > (Cloudflare).
> > >
> > > Tricky one to debug, looking for similar reports...
> >
> > Hoping the above is helpful :)
> >
> > -Toke
>
>
> --
> Tim:>


-- 
Tim:>


-- 
Tim:>
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