ARP Timeout

[pe1chl]

@ZeroByte

Interestingly, the Cisco sends gratuitous ARP requests whenever I change the MAC address. (to make sure there’s no IP duplication I suppose…)
Just this is enough to trigger the Mikrotik to update its ARP cache to the new MAC. (the Mikrotik doesn’t even send its own ARP request out in this case)

I don’t know if Cisco maybe has fixed a longstanding problem in recent versions… but in Cisco the issue always was:

• the default ARP timeout was very very long (I think 6 hours)
• the router would not learn remote MAC addresses from incoming ARP requests, only from replies to its own outgoing requests.

Net result: when you replace a device connected to a network with a Cisco router, and assign the new device (with new MAC) the IP address of the old device, it would just sit there like a dead duck until Cisco liked to timeout their ARP entry and re-issue the ARP request. Which in default config could take hours.