I've got a 2621XM running 12.3(5a)IP Base. Something just started happening and I can't figure out.
When I start a continous ping to the router the first one suceeds and then the rest fail. Now, where it get's even stranger is that during the failed pings if I tell my computer to "arp -d *" the next ping succeds, but then they go back to failing.
I noticed that the PC's arp table shows the wrong MAC address for the interface that the router is using.
If I create a static arp entry linking the ip address of the router to the correct MAC address, then everything is fine.
It sounds like you have an IP address clash, with two different machines responding to the same address. Have you tried tracking down the MAC address you are seeing in the ARP cache?
The other thing that might be happening is if you have another router on the segment with an incorrectly configured netmask and proxy ARP enabled. Again, look for the MAC address you are seeing in your ARP cache, and track it down by looking in the CAM table of your switches.
Well, I think I found the problem. The incorrect MAC address was 00-50-e8... a MAC Address group that was issued to a company making Wireless Hotspot equipment. So, I think this hardware (somewhere) is trying to pretend that it's every router.
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