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How do I find out which machine it is from the mac address?

Posted on 2009-05-13
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Last Modified: 2012-05-06
I have found that somewhere in the network, lives the same IP address as a windows 2003 server.

On the server side, it says there is an IP conflict with the mac address.

Question is how to pinpoint which device is causing the issue?
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Question by:binele
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goss34 earned 250 total points
ID: 24375496
Hi binele,

If you have the MAC address you can trace it through your network switches providing you have access.

Basically you need to find which port the mac address is coming in on then follow the cable to see which patch port that connects to then go to the corresponding floor ports and you should find the connected PC.

If you need help with the commands etc on the switches post back and il write them out.

Cheers
Dan
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by:goss34
ID: 24375511
Meant to say if you dont have the MAC address you can check on your DHCP server to see which MAC address has that IP then follow it through the switches.
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by:Bryan Butler
ID: 24375529
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by:inbox788
ID: 24375592
How big is your network? For a small network, just look at each device. There are several ways, here's one: Start -> Run -> type "cmd" -> type "ipconfig /all"  (type "exit" to quit)

 Bigger networks may require some snooping or sniffing. If you have multiple segments and routers, see if you can't localize where the duplicate is located. Check the router status to see where things are coming from. If you're not finding it on traditional pc's, don't overlook other potential sources like printers, copiers, portable units, etc.



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by:ngravatt
ngravatt earned 250 total points
ID: 24375942
on cisco switch do the following if you are looking for IP address 10.20.1.113

sw#show arp | include 10.20.1.113
Internet  10.20.1.113            10   0003.ba21.91f7  ARPA   Vlan20

sw#show mac-address-table address 0003.ba21.91f7
Legend: * - primary entry
        age - seconds since last seen
        n/a - not available

  vlan   mac address     type    learn     age              ports
------+----------------+--------+-----+----------+--------------------------
Supervisor switch 1 Module 5
*   20  0003.ba21.91f7   dynamic  Yes         20   Gi1/9/6
Supervisor switch 2 Module 5
*   20  0003.ba21.91f7   dynamic  Yes         95   Gi1/9/6

this indicates a device with the IP address of 10.20.1.113 is connected to port GI1/9/6


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by:goss34
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Cheers ngravatt, saves me typing it out.

binele,

The above will work used it multiple times to track down rogue computers etc.

Cheers
Dan
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by:binele
ID: 31581005
Thanks guys! Helped alot.
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