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

[Hangbin Liu]

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.

Patch 1 fixes the transit side: hash policy 0 hashed the raw IPv6
nexthdr, which becomes NEXTHDR_HOP once an IOAM Hop-by-Hop header is
inserted. The policy-0 key (and the ICMPv6-error flow selection) now
uses the nexthdr the packet would have had if the Hop-by-Hop header
carried only IOAM options and padding.

Patch 2 fixes the injecting node: the ioam6 output re-lookup on a
destination-cache miss hashed the transformed packet's NEXTHDR_HOP
instead of the original nexthdr (inline) or IPPROTO_IPV6 (encap), and
rebuilt the flow keys from the outer header only.

Patch 3 adds selftests/net/ioam6_ecmp.sh, covering both places: a
transit forwarder with a multipath route, and an encapsulating node
compared against a plain ip6ip6 baseline.

The issue was found while reviewing RFC9486. It can be reproduced and
verified by the newly added ioam6_ecmp.sh test.

Tested with:
ecmp_rehash.sh
fib_nexthops.sh
ioam6_ecmp.sh
tcp_ecmp_failover.sh
forwarding/gre_inner_v4_multipath.sh
forwarding/gre_inner_v6_multipath.sh
forwarding/gre_multipath_nh_res.sh
forwarding/gre_multipath_nh.sh
forwarding/gre_multipath.sh
forwarding/ip6gre_inner_v4_multipath.sh
forwarding/ip6gre_inner_v6_multipath.sh
forwarding/router_mpath_nh_res.sh
forwarding/router_mpath_nh.sh
forwarding/router_multipath.sh

Signed-off-by: Hangbin Liu <liuhangbin@xxxxxxxxxx>
---
Hangbin Liu (3):
      ipv6: route: consider IOAM options in ECMP hash policy 0
      ipv6: ioam6: use transformed packet nexthdr for ECMP re-lookup
      selftests: net: add ioam6 ECMP test (RFC 9486 C2)

 include/uapi/linux/in6.h                  |   1 +
 net/ipv6/ioam6_iptunnel.c                 |   4 +-
 net/ipv6/route.c                          |  67 +++++-
 tools/testing/selftests/net/Makefile      |   1 +
 tools/testing/selftests/net/ioam6_ecmp.sh | 349 ++++++++++++++++++++++++++++++
 5 files changed, 419 insertions(+), 3 deletions(-)
---
base-commit: 5d7f3375cd574fc83f0cd30839b21455c0e79ae2
change-id: 20261020-ipv6_ioam_ecmp-ae4ef0a4bdae

Best regards,
--  
Hangbin Liu <liuhangbin@xxxxxxxxxx>