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Ip address release problem

Asked Aug 26, 2006, 05:52 AM — 4 Answers
Have a small network of aprox 850 computers. Mixed novel and Server 2003. Have one computer with error message, duplicate ip address. Tried ipconfig release and renew, that did not work. Unplugged the network connection and did release and renew again, still did not release the ip address. Put in a static ip address, connected to network ok. Took the static address out and let dhcp do its job again, and it came back to the same ip address. IT won't let it go? Any insight would be greatly appreciated.

Dbarlamas

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cajalat's Avatar
cajalat Posts: 470, Reputation: 329
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#2

Aug 26, 2006, 06:04 AM
Chances are someone assigned a machine a static IP that is conflicting with the DHCP scope. The DHCP server keeps assigning the same IP because it thinks it is still a valid lease. The PC doesn't dictate its own IP from the DHCP server. He can only ask for his previous IP *IF* it is still available from the DHCP server. So the fact that you have an IP conflict tells me that someone stole that same DHCP assigned IP.

Here's how you can find that machine:

1. First shut down the PC that's having a problem
2. Go to a new PC on the same IP subnet and issue "arp -a"
3. Look for the MAC address corresponding to that IP address that's in question
4 Go to your network switch and look at the switch database to see which port that MAC address is coming from.
5. You can now trace back to the culprit machine that stole the IP
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tpeters's Avatar
tpeters Posts: 26, Reputation: 5
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#3

Nov 29, 2006, 09:22 AM
If the switches in the network are Cisco, you can do a mac trace. I think the commands are (for CAT/OS switches, like Catalyst) (substitute the mac address you got from the error message for the zeros)(don't type the # sign)
# show cam dynamic 00:00:00:00:00:00

This should get you a port. Show the port using show port (or show interface?)

If the port goes to a pc, that's it, you've found it.
If the port goes to another switch, do this (substitute the port for the zeros

# show cdp neighbor 0/0
Then log into the switch and do the # show cam dynamic... again.

You can do the same thing on am IOS based switch but the commands are slightly different.
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cajalat's Avatar
cajalat Posts: 470, Reputation: 329
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#4

Nov 29, 2006, 06:37 PM
Slight correction to tpeters's post...if it is a Cisco switch running CatOS then leave out the "dynamic" keyword. I.e.

SWITCH-A> (enable) sh cam 00:00:00:00:00:00

If it is a Cisco switch running IOS then the command is:

ROUTER-A#sh mac-address-table address 00:00:00:00:00:00

The rest of the info is ok
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Joey Wiggins's Avatar
Joey Wiggins Posts: 1, Reputation: 1
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#5

Dec 3, 2006, 02:51 PM
I had the same problem with one of my computers. It turns out, it was a bad network adapter.
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