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New Member

tracking down ports for VLAN setup


first time to the forum.

I have 3 24-port managed switches.  I can telnet (I know not preferred off SSH) into all 3. 

We've been told I have to put some people on a separate VLAN.

I'm trying to track down which machine goes to which port so that I can put them on the correct VLAN.

My first thought was just to print the mac address table, but because there are 3 switches in series the port number displayed for the matching MAC isn't actually the port connected to.

It's strange, if I plug in direct it might say I am on port 23 and correctly so.

But if I plug in back at my workstation where I don't know the port number and it says port 14 and I use the cable tester on ever switch port 14, none come back positive and there is nothing else between my station and the switch.  It's not displaying the right port.

Is there a way to track who is on what port without using a cable tester and physically unplugging ALL the cables until I find which 1 repeated for every end point?

Maybe I'm going about this wrong.

any help would be greatly appreciated, small company and this is not my strong area of expertise.

Everyone's tags (3)

Re: tracking down ports for VLAN setup

The easiest way is to know where your uplinks are. Let's assume you're on switch 3 on port 1 and it connects to port 3 on switch 1. Switch 2 connects to port 2 on switch 1. Now let's say you ping host If you look in your arp table, you'll see the address that you pinged (as long as you're in the same subnet). You get the Mac address from the arp entry and then look at it in your Mac table. It says that to get to that Mac address, you go out port 1 which leads to switch 1. You do the same thing on switch 1 and notice to get to that Mac address you would go out port 2, which is toward switch 2. On switch 2, you notice that the Mac address is on port 14. So you should know where your uplinks are and you'll be able to find your hosts. The way to find the uplinks if you don't already know is to do the same thing. Get on switch 1 and ping your other switches from there. It will resolve the same way like finding the host as explained above.



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HTH, John *** Please rate all useful posts ***
New Member

tracking down ports for VLAN setup

Of course,

ping the switch

show arp

show mac address-table

telnet to the next switch and just follow it on out.

Thanks, I can't believe I didn't think of this. Probably because I have never had to.


tracking down ports for VLAN setup

You can use sh mac address-table address this give you to which port that device is connected to.If its a uplink interface you can login to that switch and use the same command.

3560X# sh mac address-table address 0120.3482.5467

          Mac Address Table


Vlan    Mac Address       Type        Ports

----    -----------       --------    -----

   2   0120.3482.5467  DYNAMIC     Gi0/6