[neighbor] Preserve default lo neighbor to prevent the redis operation failure when arp cache overflow #22038
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…n failure The neighbor garbage collector was clearing the default neighbor (0.0.0.0) on the lo interface, causing Redis operations to fail and the SONiC CLI to hang. Syslog entries showed errors like: Mar 14 10:17:38.* INFO kernel: neighbour: arp_cache: neighbor table overflow! and netlink messages confirmed the deletion: [2025-03-14T10:11:14.214473] Deleted 0.0.0.0 dev lo lladdr 00:00:00:00:00:00 NOARP This commit fixes the issue by adding a persistent neighbor entry using: ip neigh replace 0.0.0.0 dev lo lladdr 00:00:00:00:00:00 nud permanent Signed-off-by: gord_chen <gord_chen@edge-core.com>
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Why I did it
Fix the issue #2189.
The neighbor garbage collector was clearing the default neighbor (0.0.0.0) on the loopback interface, causing Redis operations to fail and the SONiC CLI to hang. Syslog entries showed errors like:
Mar 14 10:17:38.* INFO kernel: neighbour: arp_cache: neighbor table overflow!and netlink messages (by
ip -ts monitor) confirmed the deletion:[2025-03-14T10:11:14.214473] Deleted 0.0.0.0 dev lo lladdr 00:00:00:00:00:00 NOARPThis commit fixes the issue by adding a persistent neighbor entry using:
ip neigh replace 0.0.0.0 dev lo lladdr 00:00:00:00:00:00 nud permanentWork item tracking
How I did it
Continuously generating gratuitous ARP to trigger the neighbor table overflow
How to verify it
Which release branch to backport (provide reason below if selected)
Tested branch (Please provide the tested image version)
Description for the changelog
Link to config_db schema for YANG module changes
A picture of a cute animal (not mandatory but encouraged)