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Webcast-Catalyst9k
New Member

4500 ARP Issue

I have a network consisting of 2 4500's and 16 or so 3750's. The network has 12 or so VLAN's and a few hundred devices. The 4500's do all inter VLAN routing. I had a computer that had become intermittent on the network when contacted from a different subnet (would answer 30-50% of pings) but was fine on the local subnet. I checked the ARP cache on the 4500 and the IP/MAC info was correct. I chased down the MAC in the CAM and that was correct also. As soon as I deleted the ARP entry, the problem cleared up.

We believe this problem has happened several times over the past few weeks on different computers.

Can anyone explain why a seemingly correct ARP entry would cause this intermittent problem?

Thanks in advance

5 REPLIES

Re: 4500 ARP Issue

Could be ARP Spoofing issue !!!

In that case Dynamic ARP inspection would be useful..

http://www.cisco.com/en/US/docs/switches/lan/catalyst3750/software/release/12.2_25_see/configuration/guide/swdynarp.html

HTH...rate if helpful..

Re: 4500 ARP Issue

I have experienced similar issues before. most cases it down to bad patch cable or the NIC driver needs updating.

Franco

New Member

Re: 4500 ARP Issue

I don't believe it is ARP spoofing. I would expect to see the incorrect MAC address if that were correct. The ARP table shows the correct IP -> MAC mapping, yet clearing that mapping seems to correct (temporarily as I am now told) the problem

New Member

Re: 4500 ARP Issue

Did you ever resolve this issue? I am seeing similar behavior. Switch is a 4507R with a single SUPIV.

It's driving me nuts!

New Member

Re: 4500 ARP Issue

No. We haven't resolved the issue but it seems to have calmed down lately, so it is unfortunately no longer on the front burner. Please update this string if you find anything out and I will do the same, but unless it acts up again I don't foresee me getting back to it in the next couple of weeks.

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