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MAC addresses falling off forwarding table

steve dowling
Occasional Advisor

MAC addresses falling off forwarding table

While following up some intermittent problems I've found that some IP addresses keep their MAC addresses (through ARP), but lose their physical port association (bridge forwarding table). A section of "sho arp" looks like this: 001558-a43118 dynamic C2 001641-ec87f1 dynamic G4 001a6b-61a349 dynamic G4 0050c2-70b5a2 dynamic H5 0050c2-70b594 dynamic 0050c2-70b593 dynamic 0008c7-996969 dynamic C2 000400-f4b5f8 dynamic G4 001b78-ec0cba dynamic C1

The addresses with no associated ports are unavailable, and these MAC addresses no longer show up in the "sho mac" command.

The problem is; these devices are really alive and should be talking on the network. (Which is why I'm chasing faults)

Device is HP5304 running E.11.21

How do I convince this beastie to keep its forwarding table?
Mohammed Faiz
Honored Contributor

Re: MAC addresses falling off forwarding table

As you say, if the devices are communicating correctly their MAC addresses shouldn't age out but you could try increasing the mac-age timer as a test.

switch(config)# show system
switch(config)# mac-age-time SECONDS
steve dowling
Occasional Advisor

Re: MAC addresses falling off forwarding table

Thanks Mohammed,

MAC-age-time is 300. This is the default, I think. I've increased this to 600.

Let's see if this problem continues...