What happens with ARP Table on request timeout

So say I have two servers - master and slave - and a Virtual IP. During normal operation only one server responds to ARP requests. When master goes down slave starts responding to ARP requests. Basically simplified keepalived.

The problem I see with this approach is that on large LAN networks devices can have various ARP caches. The situation:


Let’s say Server0 is our master. So on PC0 we have the following ARP Table: x.x.x.40 --> BBB.
Then Server0 dies and Server1 starts responding to ARP requests. The problem is that since PC0 is on the same LAN it will still try reaching IP .40 by MAC BBB and the requests will timeout as Server0 is down. Will PC0 send another ARP request for .40 even though it still has BBB cached?

Unforutnetely Cisco’s Packet Tracer can’t handle mid-simulation changes :disappointed:

Topic title?

Guess you can suggest better topic name so we can reach Google

The answer is: depends on the configuration of caching and how busy the arp table is.

You may wish to feed the new Mac to the switch on changeover by sending an arp response even when not asked for it

So is it safe to say that modern equipment is expected to resend ARP request on timeout?

As for the feeding:
In belive feeding just the switch won’t do a thing. It would only update MAC Table (ie. which port corresponds to which MAC, but in this case there won’t be any changes). The ARP response would have to get to PC0 as that’s where ARP Table resides. So the question is, can ARP responses be broadcasted?

Yes, you can broadcast ARP response.
No, there’s nothing expected about ARP re-try.

If I am a switch or a router and I have a valid cache of ARP addresses or IP bindings with ARP addresses I don’t care whether the host responds or not so long as my cache has not expired, that’s the very definition of cache - to not flood the other end all the time asking ‘who-has’. The fact that the host does not respond to TCP or UDP OR $ANY_PROTOCOL is not normally relevant event from the perspective of router/switch arp cache.