Clear a single arp cache

Unanswered Question
Oct 20th, 2008

I need to clear the arp cache for 2 interfaces on a Switch. The Cat 6509 is running

c6sup22-psv-mz.121-19.E1a.bin.

How can I do this?

And if I have to do it for all, what effect will it have on devices that are also connected to the switch?

Thanks

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satish_zanjurne Mon, 10/20/2008 - 02:09

Hi,

1.Use "clear arp interface" commamnd.

2.Utilization of arp process (ARP Input) will go up for some time.

HTH...rate if helpful..

Richard Burts Mon, 10/20/2008 - 09:44

Using the interface parameter on the clear arp command is the optimum solution for this but it is available in recent releases and not in older releases. I am not sure whether it is supported in this particular release or not.

If the interface parameter is not supported in this version of code, an alternative would be to shut/no shut the layer 3 interface. This effectively clears the ARP cache for only that interface. But it is a potentially disruptive thing to do (impacting routing logic as well as ARP). I would be inclined to just clear the entire ARP table if the interface parameter is not available.

The impact of clearing the ARP entries is that the switch must rebuild the entries in the ARP table. There will be some increase in traffic on the interface as the ARP requests and sent and replies are received, and some (probably small) increase in CPU utilization to process the ARP responses. I would expect that for most switches and for most interfaces the impact of clearing ARP would be pretty small.

HTH

Rick

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