[Backport v3.7-branch] net: ipv6: Fix a few compliance issues with RFC 4861 #85799
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When Router Advertisement with Source Link-Layer Address option is received, host should register a new neighbor marked as STALE (RFC 4861, ch. 6.3.4). This behavior was broken however, because we always added a new neighbor in INCOMPLETE state before processing SLLA option. In result, the entry was not updated to the STALE state, and a redundant Neighbor Solicitation was sent. Fix this by moving the code responsible for adding neighbor in INCOMPLETE state after options processing, and only as a fallback behavior if the SLLA option was not present. Signed-off-by: Robert Lubos <robert.lubos@nordicsemi.no> (cherry picked from commit fce5392)
According to RFC 4861, ch. 7.3.3: "Upon entering the PROBE state, a node sends a unicast Neighbor Solicitation message to the neighbor using the cached link-layer address." Zephyr's implementation was not compliant with behavior, as instead of sending a unicast probe for reachability confirmation, it was sending a multicast packet instead. This commit fixes it. Signed-off-by: Robert Lubos <robert.lubos@nordicsemi.no> (cherry picked from commit 8cd213e)
According to RFC 4861, ch. 7.2.5: "If the Override flag is set, or the supplied link-layer address is the same as that in the cache, or no Target Link-Layer Address option was supplied, the received advertisement MUST update the Neighbor Cache entry as follows ... If the Solicited flag is set, the state of the entry MUST be set to REACHABLE" This indicates that Target Link-Layer Address option does not need to be present in the received solicited Neighbor Advertisement to confirm reachability. Therefore remove `tllao_offset` variable check from the if condition responsible for updating cache entry. No further changes in the logic are required because if TLLA option is missing, `lladdr_changed` will be set to false, so no LL address will be updated. Signed-off-by: Robert Lubos <robert.lubos@nordicsemi.no> (cherry picked from commit 02c153c)
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Backport 02c153c~3..02c153c from #85673.
Fixes #85674