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New Member

Router taking on ARP table entry

I'm somewhat new to working with routers since I'm mainly a server guy, so hopefully I can provide enough information to get this resolved or point me in the right direction.

The issue is occuring on our local LAN where my ARP requests are being modified after a period of time by the router for one host.  I'm finding that the host will work fine with the correct MAC IP pairing for a period of time and then about 15-30 minutes later, the arp table is changing so the associated mac/IP address is now the mac address of the router interface.

The FastEthernet 0/1 port has no ip proxy-arp enabled and is set with ip nat inside.

This only started happening after restarting the router, however the running config was saved as the startup config prior to the restart.

I've tried hard-coding the entry with the command arp c82a.1459.0579 ARPA  however that is not working as expected.

The device is an 1841 ISR with the advanced IP Services bundle loaded.  Is there some way that the router is viewing my host (provides DNS, Directory Services) as a intrustion attempt and somehow rejecting the packets?

Thanks for any help.

Cisco Employee

Router taking on ARP table entry

Not sure I am following... can you clarify what you see (in terms of arp entries), on which device you see it and what you would expect to see instead exactly? please also provide info about IP and MAC addresses of the hosts you will mention.


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