Re: [PATCH 0/3] net: ioam6: makes IOAM insertion transparent to IPv6 ECMP

[Hangbin Liu]

Hi Jakub,
On Wed, Oct 28, 2026 at 04:58:12PM -0700, Jakub Kicinski wrote:
> On Wed, 28 Oct 2026 16:01:13 +0800 Hangbin Liu wrote:
> > On Wed, Oct 28, 2026 at 01:45:28PM +0800, Hangbin Liu wrote:
> > > This series makes IOAM insertion transparent to IPv6 ECMP, as required
> > > by RFC 9486 (C2): a packet carrying IOAM options must be forwarded
> > > along the same path as the identical packet without them.  
> > 
> > Sorry, forgot to add target repo "net". I will add it in next version.
> 
> CI bot says:
> 
> The new selftest added alongside this series (tools/testing/selftests/net/ioam6_ecmp.sh)
> is failing in our CI on the "Transit input ECMP with/without IOAM" scenario:
> 
>   TEST: Transit input ECMP with/without IOAM (diverged on seed 1: without IOAM via
>         link A, with IOAM via link B)   [FAIL]
>   TEST: Transit input ECMP with/without IOAM (seed 2..12)                [ OK ]
>   TEST: Encapsulating node re-lookup ECMP with/without IOAM (seed 1..12) [ OK ]
> 
> 11 of the 12 "transit input" seeds pass, and the whole "encapsulating node re-lookup"
> scenario passes on all seeds, so this looks like an edge case in the Hop-by-Hop
> nexthdr-recovery logic used for the policy-0 multipath hash, rather than a test
> infra/flake issue. Could you take a look at whether the recovered "virtual" nexthdr
> (or the padding/option-length walk used to compute it) is correct for all IOAM option
> layouts/trace sizes, since one specific packet still ends up hashed to a different ECMP
> sibling than the equivalent packet without IOAM?

Thanks for the report. I run it locally multi times and didn't got this issue.
I will try reproduce it first and check the reason.

Thanks
Hangbin