A good toolbag contains many different hardware tools. In this video, you’ll learn about tone generators, cable testers, taps, port mirror, wi-fi analyzers, and more.
As a network administrator, you’ll be working with a lot of cables. There may be hundreds of cables in large bunches coming out of the ceiling and going into an IDF or MDF where you’re punching it down or putting it in patch panels. And very often, you’ll need to find one cable that’s located in this large bunch of cables that’s in your data center. One of the ways you can easily find this cable is through the use of a tone generator. A tone generator puts an analog tone on the wire, and you can listen into that tone using an inductive probe.
This means that you only need to get the probe close to the cable to be able to identify where that tone might be. This makes the process of finding a single cable in a large bunch of cables very, very easy. You would connect the tone generator on one end of the wire. This can be connected through a modular jack, there’s coax connections, or you might even punch it down into a punchdown block. There could also be alligator clips so you can manually connect it to a piece of copper.
You would then use the probe to locate where that might be in that large grouping of cables, and eventually, when you come across the tone, you know you’ve found the right cable. Let’s use a tone generator and an inductive probe to find where the end of a cable might be. I’ve connected one cable to a tone generator, and you can see the flashing light that’s on the tone generator tells me that there is a analog signal that’s being sent over this wire.
So I have this group of cables and at the end of one of these cables is the tone generator. I will use this inductive probe that is listening in to try to find that particular signal on this wire. To be able to test it, all you have to do is touch the outside of the cable. We can start to hear some of that signal coming through, but it’s not very strong for that particular cable. Let’s try a different cable and see if we have a different response. That one has about the same signal level. We’ll try this third wire. And we finally come across the wire that is connected to the other end where the tone generator happens to be.
So by simply using that tone generator and moving back and forth across these wires, we’re very easily able to identify where the end of that cable might be. Another useful tool to have around is a cable tester. This is a relatively simple tester that checks continuity from one end of the cable to the other. If you want to know if pin 1 is connected to pin 1 and pin 2 is connected to pin 2, the cable tester will tell you very, very quickly. This also means that you can identify pins that are not connected.
So if you have a short in the cable, it will identify that. Or if there are crossed wires, you will see that pin 1 connects to pin 3 or pin 2 connects to pin 6. You’ll notice that in the cable tester as well. These are usually very simple continuity tests. They don’t show you any information about how much signal can be supported over that link or what category of cable this happens to match. But it can provide you with verification that you’ve performed the punchdown properly or that you have the right connectors on both ends of the cable. The tone generator and the inductive probe I used earlier also double as a cable tester.
So I plugged in one end of the cable to what is the tone generator, and I put it into the mode of being used as a cable tester. On the inductive probe, there is an RJ45 connector at the bottom of the inductive probe. I’m going to plug that in and it’s going to act as a cable tester. And as long as it lights up from pins 1 through pin 8 in that order, it’s telling me that each one of those is wired correctly. And I have continuity for all eight of those connections.
If you’d like to capture data from the network itself, you may need to use some type of external tap. This allows you to intercept network traffic and send a copy of that traffic to a protocol analysis tool or packet capture device. For a physical tap you would physically break the connection and put the tap in the middle of this connection. So this might require some downtime to initially install the tap. This could be a passive tap, which means that it’s not powered. You often see passive taps used for optical fiber, or it might be an active tap that requires additional power to be able to regenerate that signal through the tap.
If you don’t have a physical tap, you may be able to perform a similar function inside of the switch itself. Many switches support a port mirroring or a SPAN connection– SPAN stands for Switched Port Analyzer, where you can tell the switch to take any data from any of those interfaces and send a copy of that data to a different interface on the switch where, of course, you’ve plugged in a protocol analyzer. One of the challenges with a port mirror or SPAN connection is that there’s a limited amount of bandwidth available. You may be tapping a connection that could send a total of 2 gigabits per second.
That would be 1 gigabit in each connection. But obviously the port you’re connecting to the analyzer only has 1 gigabit down into the analyzer. So for very large bandwidth uses, you may not want to use a port mirror, you may instead want to use a physical tap. Here’s an example of a coax tap, but it works very similarly whether you’re using fiber or twisted pair copper. You would be connecting two devices, one on each side of the network. You can see there are a transmit and a receive pair on each side, and those will go into the in and out connection.
So you would complete a circuit on one connection and complete the circuit on the other connection. There’s a copy of this information that is being sent to monitor ports on the tap, and that is where you would plug in your analysis tools or your protocol analyzer. If you have a wireless network, you may want to gather details about what’s going over the air with a wireless survey tool. Wireless survey tools can tell you information about the coverage of the signal that’s being received on the network.
You may be able to identify potential interference, especially if it’s coming from another access point. This might be a tool that’s built into your operating system or a wireless access point, or it might be a third party tool like this one that you can install into your operating system and be able to gather these wireless statistics. If you need detailed wireless information, it may require specialized hardware, and you can use a Wi-Fi analyzer to provide that level of detail. This would be able to see all of the 802.11 information that’s going through the air and, in many cases, show you other information that’s sharing those same frequencies.
This can provide you with channel strengths. You can see what channels are in use, see what access points might be in the area, and identify any potential sources of interference. And if you have a more advanced version of a Wi-Fi analyzer, it may include a spectrum analyzer where you can see an entire range of frequencies and see every signal that’s being broadcast on any of those frequencies, whether it’s associated with an 802.11 wireless network or some other source. If you’re concerned that there’s interference coming from a third party piece of equipment or from a microwave oven, you can verify that using a spectrum analyzer.
Here are the results of information that was gathered with the Wi-Fi analyzer. You can see in this case that we have a little bit of noise at the bottom of this signal and then a little bit of wireless signal on top of that. You can see that the signal-to-noise ratio in this particular example is very narrow. It’s very close to each other. This is very different than another view of the network, where we can see there is a much stronger signal. There’s much more signal than there is noise at the bottom.
Our Wi-Fi analyzer is able to provide us with a lot of detail about just how well our wireless network is operating. If you work a lot with fiber optics, you might be concerned about having breaks in the fiber optics, especially if there’s a lot of bends in a particular fiber optic, or maybe you’re unsure if a particular fiber is in good condition. One of the ways that you can check this is with a visual fault locator. You can think of this as a flashlight that has been specifically designed for optical fiber.
The light that you shine down the fiber with this visual fault locator can be used to identify any breaks in the fiber because you’ll see the light leaking out from around that particular break. You may need to turn the lights off in the room to see this a little bit better, but it will be very obvious once you turn on your visual fault locator. This is a relatively low tech device, but it is very effective at finding problems with this fiber. So you may be able to locate those faults before you ever install that particular fiber patch into your network.