[PATCH 0/3] Avoid TCP resets when using ECMP for load-balancing between multiple servers.

[Sriram Yagnaraman <sriram.yagnaraman@est.tech>]

All packets in the same flow (L3/L4 depending on multipath hash policy)
should be directed to the same target, but after [0]/[1] we see stray
packets directed towards other targets. This, for instance, causes RST
to be sent on TCP connections.

The first two patches solve the problem by ignoring route hints for
destinations that are part of multipath group, by using new SKB flags
for IPv4 and IPv6. The third patch is a selftest that tests the
scenario.

Thanks to Ido, for reviewing and suggesting a way forward in [2].

[0]: commit 02b24941619f ("ipv4: use dst hint for ipv4 list receive")
[1]: commit 197dbf24e360 
        ("ipv6: introduce and uses route look hints for list input.")
[2]: https://lore.kernel.org/netdev/20230815201048.1796-1-sriram.yagnaraman@est.tech/

Sriram Yagnaraman (3):
  ipv4: ignore dst hint for multipath routes
  ipv6: ignore dst hint for multipath routes
  selftests: forwarding: Add test for load-balancing between multiple
    servers

 include/linux/ipv6.h                          |   1 +
 include/net/ip.h                              |   1 +
 net/ipv4/ip_input.c                           |   3 +-
 net/ipv4/route.c                              |   1 +
 net/ipv6/ip6_input.c                          |   3 +-
 net/ipv6/route.c                              |   2 +
 .../testing/selftests/net/forwarding/Makefile |   1 +
 .../net/forwarding/router_multipath_vip.sh    | 403 ++++++++++++++++++
 8 files changed, 413 insertions(+), 2 deletions(-)
 create mode 100755 tools/testing/selftests/net/forwarding/router_multipath_vip.sh

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2.34.1