arp timers

[carl_townshend]

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 ?

[Kevin Dorrell]

- 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.

[carl_townshend]

I see, how about the mac address table then ?

[Kevin Dorrell]

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.

[paul.matthews]

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.