Isolating a mac address

Unanswered Question

I have a rogue DHCP machine and have used Windows "dhcploc" tool - along with Ethereal - to track down both the ip address and mac-address of this rogue device. After obtaining both of these, I went to my switch (Cisco 2950) and ran "show mac-address-table" to find where the mac-address was physically plugged into the switch. The results do not show it to be on any FastEthernet port but rather on my Gigabit port. Even more oddly is, unlike all the other listings which show the ports as either FA0/1 or Gi0/1, this particular one is showing only "Gi0/". How do I find this device when it shows on my fiber port? I've traced everywhere I can think of. Thanks, Lu

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wochanda Thu, 08/09/2007 - 10:14

Grab another PC and have it request an IP address right before you do this. It could be that nobody has requested an IP address in 5 minutes, so the mac-address entries have aged out of your switches.


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