Anyone know how long a cisco switch 29xx retains the MAC address in the table after the PC disconnects?
Any reference ?
Thanx in advance
William J. King snipped-for-privacy@hawaii.edu ( e-mail ) Actually 21 degrees 17 minutes 56.2653 seconds North 157 degrees 48 minutes 57.8565 seconds West .,,.-*"*-.,,.-*"*-.,,.-*"*-.,,.-*"*-.,,.-*"*
Switches can't tell that a PC has disconnected, so entries in the ARP table are aged.
"The default is 300" (seconds)
This is true but is not quite the whole story.
When a spanning tree (let's call it) detects a topology change all participating bridges are notified and switch to using the fast aging timer. This timer defaults to
15 seconds.A topology change occurs when a port changes state. An exception is that ports with portfast configured do not cause a topology change notification to be sent and do not themselves do fast aging when they change state.
The scope of a topology change will be one vlan with per vlan spanning tree and may bigger if some sort of single spanning tree is beng used.
802.1d is available free from the IEEE web site. Well it was the last time I looked. I recall that it was not necessarily that easy to find on the site and that it was free because someone was paying the IEEE to publish it in that way.Hi William,
On a Cisco Etherswitch the default MAC address AGING time is 4 hours, but it can be changed on a global switch basis.
An Etherswitch works on the principle that as long as the Ethernet interface on the Switch is UP, then the MAC address that is LEARNT for any connected device on that port is retained for as long as the MAC AGING time.
HOWEVER... If the Interface into the Switch goes DOWN, then the MAC table for ALL devices seen on that port is cleared INSTANTLY. The one catch that many people run into is that if the Etherswitch port connects to say a HUB, and the PC is removed from the HUB, but the Switch link to the HUB remains UP, then the Switch port has NOT gone down so the MAC is still present until it times out. This is the prime reason why it is never a good idea to chain an Etherswitch to a HUB.
Cheers..............pk.
IEEE standards that have -become- standards (not just in progress), and have been standards for at least 6 months, are available free for download.... but not all the approaches tell you that!
802.1D-2004 can be downloaded free fromHave something to add? Share your thoughts — no account required.
Ask the community — no account required
