Re: [PATCH net-next v3 1/2] ipv6: update NUD_FAILED neighbors from NA messages

[Ido Schimmel]

On Fri, Sep 18, 2026 at 10:13:23PM +0000, Lawrence Lee wrote:
> 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@xxxxxxxxx
> Assisted-by: LLM Sashiko sparse
> Signed-off-by: Lawrence Lee <lfqlee314@xxxxxxxxx>

Reviewed-by: Ido Schimmel <idosch@xxxxxxxxxx>