whichSwitch and How I Use It

A good friend of mine Joe Wollard, an excellent programmer and technician, and I worked on an application together called whichSwitch.  It is an application that is simple in concept, but after years of waiting around for someone else to make it, Joe and I decided to just make it ourselves.

What is whichSwitch

whichSwitch Application Logo


Basically, whichSwitch is a user friendly application that will detect and display CDP and LLDP packets.  CDP and LLDP are protocols that are used by most enterprise network devices so that administrators can see what equipment is directly plugged into each other and on what ports, what VLAN’s, etc.  Since I started working in the networking field I have leveraged CDP and LLDP countless times.

So, if you want to know what port, and on what switch, a given computer connects whichSwitch will tell you.  You can see more detail on whichSwitch and its features on the whichSwitch documentation page if your interested or you can head over to the download page and get a copy.  If you are still a little confused by the jargon or don’t really see why this ability would be useful, check out the following examples to give you an idea of how I use whichSwitch.

How I use whichSwitch

Printer Problems

Oddly, CDP and LLDP seem to be really useful when troubleshooting printer problems.  I think because people often configure ports in a special way for printers.  Be it the port speed or duplex, or maybe the VLAN is special for printers in your setup, and so on.  This goes for any specialty device that can connect to a network, printers are just the most common example.

Inevitably, someone rearranges their office and plugs the printer back into the wrong port in the room.  All that is mentioned to you, of course, is that “the printer is broken”.  In this case, you can use whichSwitch to check CDP and LLDP packets on the port the printer is connected to and quickly figure out that the printer is connected to a port that isn’t configured the way the printer needs it to be.  This is especially helpful if the ports in question aren’t labeled or are behind a filing cabinet or cubical wall and you can’t directly access them.

Non-network People Use it Too

A tech may be out working on a computer already.  Rather then passing a ticket to me to log into the network equipment and follow up, the technician can figure out what port/VLAN, etc. the computer is connected to and call in with answers to all the questions they know I’m going to ask.  So I can help them out right then.  Win-Win.  They get to solve a problem right then, the client can get back to what they wanted to do, and I can get back to project work that will make the network even more awesome then it already is.

Document an Existing Network

One use for whichSwitch that is really nice is the semi-automated way you can use it to audit data ports.  At a University that I worked at for some time we would send student workers out every summer to check that the data ports in the dorm rooms were not damaged and document where the port label on the wall connected into the network.

At the time we didn’t have whichSwitch, but I can see how useful it would be in this scenario.  Basically, you can take a laptop running whichSwitch into a room, start a session, then plug the cable into each port in that room, one at a time, until a CDP packet is found on each port.  Once you have the room done, stop the session, rename it to the room number, then repeat for the next room.

Keep My Blood Pressure Down

Seriously!  In the past, I would use Fluke Link-Runners for identifying ports.  These are network cable testing and identification devices.  Really nice devices actually, and they did the job well.  That wasn’t the problem.  The problem was two fold.

  1. I inevitably wouldn’t have a Link-Runner on me when I needed it.
  2. Whenever I did have it with me the batteries would somehow be dead.

Now, being a respectable geek, I’m rarely ever without my laptop or its power adapter!  So having an application that could do this critical task for me was a clear move in the right direction.  So… problem solved and my blood pressure remains low.


Go grab a copy of whichSwitch.  Hows that for a conclusion?

Seriously though, go grab a copy and let me know what you think.  Does it work on your network?  What could we do to the application to help improve your life and simplify your workflow?  Or better yet, what other applications have you been looking for that you just can’t find?

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