arp ageing time

Unanswered Question
Jan 13th, 2009

I issue sh arp on my router, and I saw directly connected host and others on the network with thier ageing timer...my questions are.

1.If a host is removed from the network, will it reflect immediately from the 'sh arp',if not,how long.

2.Whats the default ageing timer,and whats it for.

3.Does the ageing timer renew it self?

I have this problem too.
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Richard Burts Tue, 01/13/2009 - 09:20

1) if a host is removed from the network its entry will remain in the ARP table on the router until it times out.

2) in IOS the default ARP ageing timer is 4 hours. it is so that IOS will periodically time out the entries. this removes stale or no longer accurate entries in the table.

3) when the IOS times out an entry in the ARP table and removes the entry it will generate an ARP request for that address and if it receives a response then it puts a new entry into the ARP table. So if the device is still active on the network its entry stays in the ARP table and if the device has been removed from the network the arp entry gets cleaned out.

HTH

Rick

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