ipv6: update NUD_FAILED neighbors from NA messages

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Transition a FAILED neighbor entry to STALE upon receipt of an NA
message on routers when accept_untracked_na is enabled. This extends the
RFC 9131 accept_untracked_na behavior so that FAILED entries are treated
the same as non-existent entries.

RFC 4861 section 7.3.3 says that an entry should be deleted when address
resolution fails. Linux instead retains the entry in NUD_FAILED, so
treating it as untracked is consistent with the protocol model.

Trying to resolve FAILED neighbors via periodic probing (e.g. using
NTF_EXT_MANAGED) is more work compared to this approach which uses
information in NAs that the kernel may already be receiving. Note that
because this behavior in IPv6 is dependent on the accept_untracked_na
sysctl setting, this approach is more conservative than IPv4 which
transitions FAILED neighbors to STALE by default upon receiving GARPs.

Link: https://lore.kernel.org/r/20260813233344.445265-1-lfqlee314@gmail.com
Signed-off-by: Lawrence Lee <lfqlee314@gmail.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Link: https://patch.msgid.link/6be400e601f4ffa59e47ddb5daa33ecdd85dd88b.1790127207.git.lfqlee314@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

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Lawrence Lee 2026-09-23 01:34:18 +00:00 • committed by Jakub Kicinski

parent 7ab4bbdca9

commit 24717a02ae

2 changed files with 41 additions and 34 deletions

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28

Documentation/networking/ip-sysctl.rst

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47

net/ipv6/ndisc.c

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