ARP Timer vs CAM Timer

[a1744c]

Does Anyone know why the default aging time for ARP is set to 4hours and CAM aging time is set to 5 mins?

[jarathbu]

Hello,

I suspect that it may have roots back to the integration of companies in the earlier acquisitions (i.e. Calpana, etc.). Both the timers are adjustable and if you're having issues with Unicast Flooding you should adjust them to mitigate excessive flooding.

HTH

Regards,

James

[Richard Burts]

I believe that James has made a good suggestion when he points at the acquisitions Cisco has made.

In addition I believe that one factor is the ARP times comes out of IOS and reflects the outlook of layer 3 routing. In particular since the IOS must actively acquire the content of ARP table (actively sending ARP request to learn the MAC address, timing entries out of the table, and immediately sending another ARP request for the entries timed out) it was more efficient for the router to have a relatively long ARP timer.

The CAM comes out of a layer 2 switching orientation. The switch does not actively acquire content of the CAM (does not send out requests) but listens to incoming traffic to build the CAM. So it made sense to have a short timer on the CAM.

HTH

Rick