chassis-packet: Update arp_update script for FAILED and STALE check (#16311)
1. Fixing an issue with FAILED entry resolution retry.
Neighbor entries in arp table may sometimes enter a FAILED state when the far end is down and reports the state as follows:
2603:10e2:400:3::1 dev PortChannel19 router FAILED
While the arp_update script handles the entries for FAILED in the following format, the above was not handled due to the token location (extra router keyword at index 4):
2603:10e2:400:3::1 dev PortChannel19 FAILED
The former format may appear if an arp resolution is tried on a link that is known but the far end goes down, e.g., pinging a STALE entry while the far end is down.
2. Refreshing STALE entries to make sure the far end is reachable.
STALE entries for some backend ports may appear in chassis-packet when no traffic is received for a while on the port. When the far end goes down, it is expected for BFD to stop sending packets on the session for which the far end is not reachable. But as the entry is known as stale, on the Cisco chassis, BFD keeps sending packets. Refreshing the stale entry will keep active links as reachable in the neighbor table while the entries for the far end down will enter a failed state. FAILED state entries will be retired and entered reachable when far end comes back up.
2b302e83c0