One of the most frustrating things I have had to deal with in networking was trying to figure out what cable went where in a building. It is a super common problem. I have been asked many times how to find the other end of an Ethernet cable.
Depending on the network there are several ways to find the other end of an Ethernet cable. If you are lucky they will be labeled with some information that can give you a clue as to where to start looking. If you are not so lucky there are still a hand full of tools and techniques that you can use to track down the other end of a cable including your network router, multi-meters, and specialized tools called toners.
Look for clues that might tell you where the cable goes
When you set out to trace an Ethernet cable the very first thing that you want to do is to look for labels and other clues that might help you find where the cable goes in the building. You may think that you would have seen any labeling if it existed but many installers do not like to leave the labels out in the open.
If there are no obvious labels on the face plates for your network locations the very first thing that I would recommend doing is unscrewing the faceplates from the wall and taking a look at the cables themselves. Very commonly installers will have wrapped the end of your cable with a label or maybe have even written directly on the cable itself with a sharpie.
It may feel like a bit of Hail Mary to go digging around looking for labels or notes from the person who originally installed your network but if you get lucky and find what you are looking for it can save you a lot of time so it is always worth taking the time to look.
Even if you do not find a clear cut set of labels that tell you where each cable goes there may be other clues that you can gather from looking at the cables themselves.
- Are there different styles or colors of cables?
- Are some of the cables older or newer then the rest?
- Is there any print on the cable that will tell you the brand or model?
- Do you see any length markings printed on the cable that you can use to match up the end with its pair on the other side?
- Can you see any of the pathway of the cable?
- What direction does it go in?
It may take a bit of time and some detective work but it is relatively common to be able to figure out what cable goes where just by looking for clues and putting together the pieces.
How to use your router to figure out where a cable goes
Another great way to find what cable goes where in your house is to use your network equipment to map out what port is plugged into what device. Most network equipment has an easy way to be able to tell what is plugged in where. For example, here is a screen shot of a typical consumer grade wireless router.
You can see that I have a desktop computer plugged into port number one. If I had a mystery cable in this network I might be able to easily find the other end of it simply by plugging it into port number two and then walking around and plugging my laptop into all of the ports around my house. As long as the mystery cable is finished with a termination on the end eventually it will come on line and show up in this interface.
One of the best things about this method is that it can be used to locate several cables at one time. If you have multiple cables and you do not know where any of them go you can plug them all into different ports on the router at the same time. Once all of the mystery cables are plugged in you can go around the house and plug a laptop or other piece of network equipment into each of the ports around the house. With a little luck it will show up on one of the mystery cables. You can then label the cable and move on to the next port to hopefully find where the rest of the mystery cables connect to.
The other great thing about this method is that most people have some sort of network equipment that has this feature so many people can use it to find the other end of their mystery cable without having to buy any special tools.
The main drawback of this method is that it will not work for everyone. If your cables do not have the ends installed on them you obviously cannot plug anything in to test them. Additionally if the cable you are looking for is finished on both sides but it has a problem either with one of the terminations or with the cable in the middle your network equipment may not be able to see the device that you plug in even if you plug it into the correct place.
In the next two sections I will go over how to find the other end of a network cable even if it is not finished or if you think that there might be a problem with it.
What tool works best for finding the other end of an Ethernet cable?
By far the fastest way to find the other end of an Ethernet cable is by using a tool called a toner. It can quickly help you find the other end of your cable whether there is a termination on the other end or not. It can even work on all but the most damaged of cables so it is a great option even if there are problems with your cabling.
This is the Fluke Networks Pro 3000 Toner. It has been my toner of choice for over ten years. There are lots of options out there, many of which are quite a bit cheaper, but every time I end up using one of the budget models I find that they are not as consistent as the Fluke. Additionally, if you are trying to tone a cable that has a network device plugged into the other end many of the cheaper toners will not work at all. If you only have a few cables to tone out one of the cheaper models might be okay but if you are trying to tone a lot of cables, very long cables, or cables that already have network equipment attached a higher end piece of equipment just might be worth the extra cost.
How to use a cable toner
The way that the tool works is pretty simple. The first thing that you need to do is connect the tone generator to your mystery cable. If your cable already has a jack on it all you need to do is plug in the generator and switch it on. If the cable is not terminated or if you think that the jack might have a problem with it you can use the metal clamps to attach directly to the wire. Just be sure that if you are using the leads not to let them touch. If the leads touch they will ground out and the toner will not work at all.
Many tone generators have a set of sharp metal pins that you can use to push right through the plastic coating on the wires. It is fine to use these but if you are having a hard time hearing the tone on the other end of a cable one of the things that you can do to make a tone a bit louder is to strip away the plastic jacket and get a better connection.
Another thing that you can do to make a toner work a bit better is by sending the tone down more than one wire in a cable at a time. In the pictured example I have stripped back the insulation on the orange, white/orange, green, and white/green wires. After the insulation was stripped away I attached both of the orange wires to one lead and both of the green wires to the other. This is the configuration that I find works best if I am in a very electrically noisy environment or if I am using a cheaper toner that is not as loud or clear as I would like.
Once the tone generator is connected up all you need to do is use the probe to find the other end of the wire. Before you walk away from the generator I would recommend that you take a quick second to push the button on the probe and make sure that there is tone in the cable a foot or two above where you connected the tone generator. Not only will this test all of the connections and make sure that everything is working the way it should but it will give you a chance to hear what the tone should sound like if you have never used a toner before.
Now that you know what tone you are listening for and the connections have all been tested you can go looking for the other end of the cable. Here are a few tips that might help you find the cable you are looking for as quickly and easily as possible.
- The tone will be the loudest close to the tone generator and at the termination.
- If a computer or other piece of network equipment is plugged into the other end of the cable the tone will be much quieter and may even disappear completely if you are using a budget tool.
- If there is electrical noise in your house that sounds close to the tone your tool is making most tools have an option to change the tone that it is generating.
- Most probes have a volume setting that can help you if the tone is really quite but will not help you if you are in an environment that is very electrically noisy because it will turn up the volume on all of the signals the probe picks up, not just the tone from the generator.
- If you are having a hard time finding the other end of your cable sometimes you can find the cable in the middle of its run and this can give you some clues as to what is going on with it.
- There are some situations where the tone can leak from one cable to the next. If this happens you may be able to hear tone on more than one cable. The tone will be the loudest on the cable you are looking for.
How to find the other end of an Ethernet cable without any special tools
If your cable does not have jacks terminated onto its ends and you do not have the budget for a toner you can still find the other end of the cable using a multimeter with a continuity test option. This technique is much slower than using a toner but it can also much cheaper. You may even already own a multimeter that will work well.
The first step to identifying the other end of a network cable with a multimeter is to connect two of the wires inside of the cable that you are looking for . In this example I stripped back and twisted together the orange pairs of wire.
Now that the orange pairs are shorted together the next step is to head to the other end of a cable you would like to test, turn the multi-meter to its continuity or resistance test settings, and touch the leads of the multimeter to the orange pairs of wire. If you have guessed correctly the continuity setting will make a beeping sound while the resistance setting will display some numbers. If the cable you are testing is not the same cable that you shorted the orange pairs together on nothing will happen and you will need to keep testing cables until you find the end that matches your mystery cable.
Conclusion
At the end of the day finding the other end of an Ethernet cable really just comes down to using tools and techniques to gather clues about a cable and putting them together to track down where it goes. I have ran into cables that were time consuming and frustrating to identify but I have never had one that didn’t turn up in the end with some determination and the techniques I wrote about above.