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LABS
Finding the Port Location on a Switch when You Know the MAC Address

Abstract

Often we need to put certain devices on specific VLANs.
To do this, we need to know which port the device is connected to on the switch. However, in very mature and active wiring closets, it’s quite a challenge tracing cable from the patch panel to the switch port.

We have found that by using the MAC tools on our switch (knowing the MAC address of the device), we were able to determine the port the device was attached to without having to physically trace the cable.

This blog post is directed at:

  • Operations Staff
  • Environments with more than one VLAN
  • 3Com Baseline Switch 29xx

The Problem

We had to move an HP Color LaserJet CP5225dn printer to a separate VLAN. The cabling in the wiring closet was so tangled we couldn’t easily trace the cable from the patch panel to the switch.

Procedure

We needed to determine the MAC addresses of the printers.

  1. Browse to the printer’s web interface.
  2. Locate the networking configuration area in the interface (Note different printers may have different menu options)
    (In this case, we navigated to Networking → Network Summary → Network Hardware Configuration → Hardware Address)
  3. Locate the MAC address(Hardware address). For example, the color printer’s MAC address is 9c:8e:99:86:5e:12.
  4. Log into the 3com switch’s web interface, e.g. http://sw-3com-01.nyc.pivotallabs.com.
  5. Navigate to Network → MAC
  6. In the Search Item drop-down, select MAC, and in the Keywords field, enter the MAC address of the printer (or device). The MAC address must be formatted four octets per division, e.g. 9c8e-9986-5e12 (It’s often easier to search with the last four digits, e.g. 5e12 )
  7. You should only see one entry. Look at the port field; it should resemble something like this:
    GigabitEthernet1/0/44. You should only be concerned with the digits after the last ” / “. In this case, 44.
  8. As a safeguard against accidentally switching the VLAN of a trunk, do a lookup of the port to ensure the device in question, is the only one attached to that port. In the Search Item drop-down, select Port, and in the Keywords field, enter the port number, e.g. 44.

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