Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. If you'd prefer to explore, try our test area to get started. And see here for current known issues.

New Member

arp timers

Hi all, can anyone tell me how often switches flush there arp table, and I was told that when a new pc is plugged in there is a total topology change ?


Re: arp timers

- Switches only have an ARP table for hosts or routers that are addressing the management features of the switch.

- If the port is set to portfast, there is no topology change.

- The ARP table entries are flushed after 4 hours by default

- The forward table entries are flushed after 5 minutes of inactivity.

New Member

Re: arp timers

I see, how about the mac address table then ?

Re: arp timers

The MAC forwarding table entries are cleared after 5 minutes of inactivity from the particular address, or immediately if the corresponding port goes of line. If there is a Topology Change Notification going round the network, then the aging time on all entries is reduced to 15 seconds, if I remember correctly.

Re: arp timers

You do remember correctly, though not all switches in a spanning tree will see the TCN, so only those that see it will change the timer to 15 secs.