Ip conflict finding foreign mac

Unanswered Question
Nov 6th, 2008

My server group is saying they are getting an ip conflict error on the windows 2003 server. i see no problem and my managment sofwtare only sees one mac to that ip address. Is there a debug command to see if there is an ip conflict. Two mac's to one ip address. This server farm are staticly addressed so if there is a conflict the staff configured it. I would expect an error on my 6509 msfc as well. In addition does anyone know of any kind of acl that would only allow a specified mac address to a specified pc. Thanks in advance.

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chris.king@csu-... Thu, 11/06/2008 - 08:43

As regarding the access list, you can use mac access-lists on most cisco switches or port security that will auto learn the macs and then not allow any more macs to access the network. Just check out the switch command reference and search for 'MAC access list' and 'switchport port security'.



MUHAMMAD SHAHEEN Thu, 11/06/2008 - 09:00


ask the server Group to check the event viewer it will give the mac address of the device which has conflicting IP address. Then you can trace that mac-address on the switch.

Hope This Helps....


nate-miller Thu, 11/06/2008 - 09:19

The switch will only complain about duplicate IPs when the duplicate is for an address that is supposed to ride on the switch. (The VLAN interface, for example.)

Otherwise, there's no easy way to lock this down- you can start investigating Dynamic Arp Inspection (DAI) coupled with Port Security and DHCP snooping.

This is a VERY involved process, and you ahve to be careful implementing this- in an environment where quite a few addresses are statically assigned, you're in for a lot of detective work and overhead! If you don't know what you're doing, there could be a lot of issues!

The quickest thing to do is get the MAC address of the duplicate IP address and track down that port on your network.


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