Given a scenario, use appropriate hardware tools to troubleshoot connectivity issues. This chapter describes the following hardware tools: cable testers, crimpers, punch-down tools, protocol analyzers, multimeters, and others. We cover hardware troubleshooting in our CompTIA Network+ video course.
Cable Testers
Cable testers and certifiers are dedicated hardware devices that can be connected to an end of a cable or to both ends in order to provide diagnostic functions. Generally, a cable tester, shown in Figure 22.1 below, consists of the following:
- A source of electric current
- A volt meter
- A switching matrix used to connect the current source and the volt meter to all of the contact points in a cable
Figure 22.1 – Cable Tester
As their functionality has already been explained in Chapter 18, the problems addressed by cable testing below should serve as a reminder:
- Proper wiring of the cable
- End-to-end signal quality and signal loss
- Crosstalk effects
- Short circuits
- Open circuits
Crimpers
Crimpers are tools used to insert wires into the proper connectors at the end of the cable. These are dedicated tools based on the cable type used, such as the crimper shown in Figure 22.2 below:
- Twisted-pair
- Fiber optics
- Telephone cable
- Coaxial cable
Figure 22.2 – UTP Cable Crimper
Crimping is usually the last step in the cable installment process. You connect the wires to the proper connectors only after the cable has been put in place between the two endpoints. When crimping a UTP cable, the copper connections are pushed into each of the eight wires through the insulation so that the electrical connection can be established. At the same time, the crimper is fixing the connector into the UTP plastic cable jacket to keep it in place.
Figure 22.3 – RJ45 Connector (before and after Crimping)
As can be seen in Figure 22.3 above, before the crimping process, the RJ45 connectors are not pushed inside the plastic connector case and into the actual wire. These pins are very sharp, so once you place the wires inside the connector and use the crimper to push the pins into the wires, these will go right through the insulation of each wire.
Many crimpers have a built-in wire cutter and wire stripper, so they can be considered universal tools in managing cable connectors. Before actually starting to crimp the cables, you should verify a few things:
- Make sure that you use the right type of connectors based on the cable types (check the cable specifications).
- Make sure that you properly align the wire colors with the correct pin positions (be careful when differentiating between straight-through and crossover cables).
- Make sure that you have enough spare cable at each end, as you might have to cut small portions of it if the crimping process is not successful after the first try.
A common mistake in the crimping process is cutting too much of the wire jacket, as shown in Figure 22.4 below. If this happens, you will not be able to secure the connector into the jacket and this can lead to a short life for the cable (i.e., the wires might come out of the pins if you pull on the cable).
Figure 22.4 – Common UTP Crimping Mistake (Jacket too Short)
Butt Set
A butt set (also called a lineman’s handset), shown in Figure 22.5 below, is a tool used to tap into the middle of a connection during a troubleshooting process. It is used mainly for voice signal troubleshooting, which can happen at multiple points in the infrastructure:
- MDF
- IDF
- Wiring closed
A butt set can plug into different connection types because it has a lot of available connectors, such as RJ11, RJ45, or alligator clips. Alligator clips are very useful in situations in which you want to connect to a simple insulated wire because they have sharp edges that reach the copper wire to establish the electrical circuit.
Figure 22.5 – Butt Set
Usually, butt sets are used for analog connections and don’t have digital signal processing capabilities. When using such tools, you must first identify the cable of interest, and after you connect the butt set, you can use it just like a normal phone to test the line. Some of the butt set functionalities include the following:
- Ability to dial into the connection
- Ability to listen to existing signals (voice calls)
- Diagnostic operations
Toner Probe
A toner probe, which is shown in Figure 22.6 below, is a tool that can track where a wire is going. This is useful in large environments to identify both ends of a wire and track cables (usually from a bundle of wires). The toner probe consists of two different pieces:
- A tone generator: a battery-powered device that taps into the connection and sends a signal on the wire
- An inductive probe: allows you to hear the generated tone without even touching the wire
Figure 22.6 – Toner Probe
The first step in using such a device is turning on the toner, selecting the desired tone to be sent, and actually sending that tone over the wire. The tone generator connects to the wire or punch-down block using standard RJ11/RJ45 connectors or alligator clips. The next step is turning on the inductive probe and placing it close to the wire. As you move it closer to the specific wire you are looking for, you can hear it getting louder.
Toner probes can be used only in copper cable environments (twister-pair or coaxial), as it cannot process light signal in fiber optic cables. You can use advanced cable tester devices instead in fiber environments.
Punch-Down Tool
When building the network infrastructure in large environments using wiring blocks, you need to punch wires down into them. Such punch-down blocks are usually placed inside the MDF or IDF to aggregate the wires coming from different network locations.
The punch-down process may be very tedious, as every wire must be individually punched into the corresponding block. For a UTP cable, you have to punch down each of the eight wires separately. The purpose of this process is not only to electrically connect the wires but also to trim them during the punch in order for everything to be organized. Quality work is very important at Layer 1 because this will prevent many issues from appearing in the network and because Layer 1 issues are hard to troubleshoot.
Figure 22.7 – Punch-Down Tool
Punch-down tools, like the one shown in Figure 22.7 above, are usually very sharp and achieve two purposes:
- Inserting the wire into the proper connector
- Cutting down excess wiring
Some of the punch-down best practices that you should follow during the cable installation process include the following:
- Be very organized because you are dealing with a large number of wires
- Cable management is critical
- Document everything you do, as well as every wire position
- Use labels to identify wires
- Maintain the twists of UTP cables: as you are punching down the wires, you should not untwist too much of each wire pair because that can increase the amount of interference that might be caused by crosstalk
Protocol Analyzers
A protocol analyzer is a powerful tool that gathers packets directly from the network and presents them for analysis. Protocol analyzers are generally used to troubleshoot application problems that require in-depth packet analysis. They can come in two forms:
- Hardware appliances
- Software tools
One of the most common software protocol analyzers is Wireshark, which is an open source application. Although working with such analyzers may be difficult at the beginning, they can provide a lot of information about the specific packet contents on the connection.
Hardware protocol analyzers can come in multiple forms, including stackable appliances that provide functionality similar to software analyzers but on a larger scale, as shown in Figure 22.8 below:
Figure 22.8 – Hardware Protocol Analyzer
To use a protocol analyzer, you first have to capture the traffic and direct it to the analyzer device. This can be achieved in multiple ways:
- Using port mirroring
- Physical tap
- Using a hub
Port mirroring is one of the most useful methods, as it does not require any physical modification to the network. It is a feature offered by many switches that clones traffic that passes through a switch port (source) to another switch port (destination). You can connect the protocol analyzer to the port mirroring destination port and capture all the packets that pass through the source interface.
The objective of this process is capturing as much information as possible and it can be filtered based on the desired criteria at a later time. As a best practice, you should document the packet capturing process with a clear time indication of each operation. The results of the packet capturing process can be saved as capture files, which can be reviewed at a later time.
Loopback Plug
When engaging in some type of lower-level troubleshooting, a loopback plug can be very useful for testing physical ports. Loopback plugs can work with diagnostic tools that are specifically built to work this way or they can be used to trick the application into sending data out just to see its response to data that comes back through the loopback. They are also used when trying to troubleshoot hardware components (e.g., ports) to make sure that the data is going out and coming back in without problems.
Loopback plugs function by sending data out of a connection and then looping it right back in. The amount and type of data received matches exactly the amount and type of data sent. Loopback plugs can be used for any type of connection, for example:
- Ethernet
- Fiber optic
- T1/E1
- Serial connections
On an Ethernet interface, in order to be able to receive the exact same information sent out, you can use a single RJ45 jack with the following connections, as shown in Figure 22.9 below:
- Pin 1 connected to pin 3
- Pin 2 connected to pin 6
- Pin 4 connected to pin 7
- Pin 5 connected to pin 8
Figure 22.9 – RJ45 Loopback Plug (Pin Sequence)
TDR/OTDR
When you need to perform detailed troubleshooting of copper and fiber connections, you can use specialized equipment, such as:
- Time Domain Reflectometer (TDR) for copper connections
- Optical Time Domain Reflectometer (OTDR) for optical fiber connections
Some of the functionalities offered by such devices include:
- Signal quality
- Estimating cable lengths
- Splice locations
- Cable impedance information
- Signal loss
The TDR (see Figure 22.10 below) works by sending an electrical signal (pulse) down the wire (copper) and listening for its reflection. Reflections of the initial signals received are caused by some kind of discontinuity along the cable. The TDR calculates how long it took to receive the reflection and then it calculates the distance to the problem area within a cable.
Figure 22.10 – TDR
The OTDR functions in the same way as the TDR does, except on optical fibers instead of copper cables. It sends a light beam down the fiber and then it listens for the optical reflection in order to calculate the distance to the trouble area.
| Note: When an electrical or optical signal reaches a cable area that presents discontinuities, part of the signal reflects back to the source and the rest continues down the wire. |
TDR and OTDR devices are expensive tools and they require special training, but they offer a lot of functionalities in terms of Layer 1 analysis.
Multimeters
A multimeter is an electrical meter that has multiple functions. Also called a volt-ohm meter (VOM), it can measure the following parameters:
- Voltage
- Current
- Resistance
There are different types of multimeters with different accuracy ranges. They can be either analog or digital and can come in either handheld form (see Figure 22.11 below) or as a bulky appliance. Multimeters generally do not require any kind of training and are relatively easy to use.
Figure 22.11 – Multimeter
A common use of a multimeter is to check the voltage coming out of a power source to confirm that the power source can be used with the type of equipment you need. Such devices can measure both AC (alternating current), which is the voltage in a wall outlet, and DC (direct current), which is the voltage in a network device power supply on the motherboard.
Multimeters can also check cable continuity by generating a small electrical signal on one pin and capturing it on the other. This can identify a pair of wires that are part of the same cable. Other functionalities of these devices include checking battery power and fuse status.
Environmental Monitors
When working with critical equipment and data centers, you should install an environmental monitoring system (see Figure 22.12 below) that measures different parameters in the room, such as:
- Temperature
- Humidity
- Water level
- Power voltages
These devices function by controlling different types of sensors and they usually provide network connectivity to ensure real-time monitoring. Verifying parameters like the temperature and humidity in the room can help identify possible cooling system failures that might lead to the devices overheating and stop functioning. Power supply monitoring is another useful feature, as outages and voltage drops can happen even in the most advanced environments.
Figure 22.12 – Environmental Monitoring System (Image © ravica.com)
Environmental monitors might have sensors on the floor that alert whenever liquid is present, which can mean that flooding is in progress. Network devices and servers also have such sensors (e.g., temperature, humidity, fan speed, etc.) built in and these can be integrated into the environmental monitoring system to provide a full view of the data center.
Summary
Cable testers and certifiers are dedicated hardware devices that can be connected to an end of a cable, or to both ends, to provide diagnostic functions.
Crimpers are tools used to insert the wires into the proper connectors at the end of the cable.
A butt set (also called a lineman’s handset) is a tool used to tap into the middle of a connection during a troubleshooting process.
A toner probe is a tool that can track where a wire is going. This is useful in large environments when you need to identify both ends of a wire and track cables (usually from a bundle of wires). The toner probe is usually made up of two different pieces:
- A tone generator: a battery-powered device that taps into the connection and sends a signal on the wire
- An inductive probe: allows you to hear the generated tone without even touching the wire
When building the network infrastructure in large environments using wiring blocks, you need to punch wires down into them using a punch-down tool. Punch-down blocks are usually placed inside the MDF or IDF to aggregate the wires coming from different network locations.
Protocol analyzers are powerful tools that gather packets directly from the network and present them for analysis. Protocol analyzers are generally used to troubleshoot application problems that require in-depth packet analysis.
A loopback plug can work with diagnostic tools that are specifically built to work this way or they can be used to trick the application into sending data out to see its response to data that comes back through the loopback. A loopback plug is also used when trying to troubleshoot hardware components (e.g., ports) to make sure that the data is going out and coming back in without problems.
When you need to perform detailed troubleshooting of copper and fiber connections, you can use specialized equipment, such as the following:
- TDR (Time Domain Reflectometer) for copper connections
- OTDR (Optical Time Domain Reflectometer) for optical fiber connections
Multimeters are an electrical meter that has multiple functions. Also called a VOM (volt-ohm meter), multimeters can measure parameters like voltage, current, or resistance.
When working with critical equipment and data centers, you should install an environmental monitoring system that measures different parameters in the room, such as temperature, humidity, water level, and power voltage.
Hardware troubleshooting guide from DNS Stuff.
