By the end of this chapter, you will be able to:
These skills will help you ensure networks run smoothly and keep communication reliable in any workplace.
Compiled by: Peter Langat
Network testing is the planned checking of a network, or of a part of it, to prove that it works as designed. It is carried out after installation, after any change and whenever a fault is suspected. Tests compare what the network actually does with what the design and the user requirements say it should do: whether every outlet has a working link, whether devices can reach each other and the internet, whether speed is adequate and whether the security settings hold. A network handed over without testing is a network whose faults will be found by its users instead.
Testing protects both the technician and the client. It gives evidence that the work was done correctly, it catches faults while they are cheap to fix, and it provides a baseline against which later problems can be measured.
A network that has been tested before use fails less often in daily work. Testing exposes loose connectors, faulty cables, wrong settings and failing equipment that would otherwise cause intermittent outages. A print shop that depends on a connection to send artwork to customers, for example, loses orders every time the link drops, so tests that confirm stable connectivity protect its income.
Testing confirms that bandwidth, latency and throughput meet the levels written in the design. If the design promised that a point-of-sale system would process a sale in a few seconds even when all tills are in use, a performance test during a busy period shows whether that promise is met.
Faults found at installation are simple and quick to correct, while the same fault found months later may be mixed up with other problems. Tests uncover configuration errors, damaged cables and security weaknesses before the network carries live work.
Testing checks that firewall rules, access controls and wireless encryption actually do what they are meant to. A guest network, for example, must be tested to confirm that a guest device cannot reach the accounts computer.
Before a network is extended, testing shows how much spare capacity the existing network has and whether new equipment works with it. A lodge adding a second wing, for instance, measures the existing Wi-Fi coverage and link speeds first so that the extension fills the gaps and does not create new interference.
Testing uses two kinds of tools. Hardware instruments, such as meters and cable testers, check the electrical and physical parts of the network. Software tools and commands, such as ping, traceroute and Wireshark, check addressing, paths and traffic. The right choice depends on where the fault is likely to be: a dead outlet calls for a cable tester, while slow internet calls for ping and traceroute. The hand tools used to build the cabling, such as crimpers and punch-down tools, are covered under Network Tools and materials assembly in the chapter on installing a computer network.
| Tool | What it checks | Typical use |
|---|---|---|
| Clamp meter | Current flowing in a power cable | Checking the load on the circuit that feeds a rack |
| Voltmeter | Voltage at a power point or battery | Checking mains and UPS output before connecting equipment |
| Cable tester | Continuity, wiring and length of a cable | Proving that a new cable run is wired correctly |
| Signal tester | Strength and quality of wireless or optical signal | Surveying Wi-Fi coverage or measuring fibre loss |
| Ping | Whether a host replies and how fast | Checking that a device is reachable |
| Traceroute | The path packets take and where they stop | Finding which hop breaks a connection |
| Wireshark | The packets actually on the network | Examining what a device sends and receives |
A clamp meter measures the current flowing in a conductor without breaking the circuit. The jaws are opened and clamped around one conductor, and the meter reads the magnetic field the current produces. In network work it checks the power circuits that supply the equipment room, not the data cables.
Worked example. A rack of switches, a router and a server draws 1,440 W from a 240 V supply, which is the nominal mains voltage in Kenya. The current is 1,440 ÷ 240 = 6 A, so a clamp meter should read about 6 A, and the circuit breaker must be rated comfortably above that. A reading much higher than expected points to a fault or to equipment that was not counted.
A voltmeter measures the voltage between two points, and most technicians use a digital multimeter set to its voltage range. The probes are placed across the supply, never in series with it.
A cable tester checks a twisted-pair cable for faults. A basic tester has a main unit and a remote unit that plug into the two ends and light up pins in order; an advanced certification tester measures the cable against the limits of a standard.
Every new cable run should be tested and the result recorded against the label of the outlet.
A signal tester measures the strength and quality of a signal. For wireless networks it is a Wi-Fi analyser, which may be a handheld instrument or an app on a laptop or phone. For fibre cable it is an optical power meter.
Ping is a command that tests whether another host can be reached. It sends a small ICMP echo request to the target and waits for an echo reply, reporting the time each reply takes. During testing it is used as a quick check of one link at a time.
C:\> ping 192.168.1.1
Pinging 192.168.1.1 with 32 bytes of data:
Reply from 192.168.1.1: bytes=32 time=2ms TTL=64
Reply from 192.168.1.1: bytes=32 time=1ms TTL=64
Reply from 192.168.1.1: bytes=32 time=2ms TTL=64
Reply from 192.168.1.1: bytes=32 time=2ms TTL=64
Ping statistics for 192.168.1.1:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss)
A systematic test pings in a fixed order so the fault can be placed:
The command reports "Request timed out" when no reply arrives and "Destination host unreachable" when a router reports that it has no route. Windows sends four requests by default, while Linux and macOS continue until stopped. A device that does not reply may not be down at all: many firewalls block echo requests on purpose.
Traceroute shows the path that packets take to a destination and the delay at each router along the way. It sends packets whose time-to-live (TTL) value starts at 1 and increases by one each time. Every router that receives a packet with a TTL of 1 discards it and sends back a message, which reveals the router's address and the time taken. On Windows the command is tracert, and on Linux and macOS it is traceroute.
C:\> tracert -d 203.0.113.10
Tracing route to 203.0.113.10 over a maximum of 30 hops
1 <1 ms <1 ms <1 ms 192.168.1.1
2 8 ms 7 ms 9 ms 10.20.0.1
3 12 ms 11 ms 13 ms 198.51.100.5
4 * * * Request timed out.
5 25 ms 24 ms 26 ms 203.0.113.10
Trace complete.
Wireshark is a free, open-source protocol analyser. It captures the packets passing through a network interface and displays them in detail, layer by layer, so the technician can see exactly what a device sends and receives. It runs on Windows, Linux and macOS, and on Windows it uses a capture driver installed with it.
Capturing traffic on a network is allowed only with the owner's permission. Traffic can contain personal information, so captures are handled under the Data Protection Act, 2019, and unauthorised interception is an offence under the Computer Misuse and Cybercrimes Act, 2018, as amended. The different use of Wireshark for continuous monitoring is covered under Computer network Monitoring in the maintenance chapter.
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Create a free accountThis chapter provided a comprehensive overview of testing computer networks, starting with an introduction that highlighted the critical role of network testing in ensuring reliable and efficient network performance. The importance of network testing was emphasized, showing how it helps detect faults, verify configurations, and maintain optimal operation. The discussion then moved to network components testing, explaining various types of network testing such as functional, performance, and security tests. Procedures and standards governing network testing were outlined to guide systematic and consistent evaluation. Attention was given to the preparation of network testing reports, underlining their significance in documenting findings and supporting decision-making processes. The chapter detailed the essential components of a network test report, including test objectives, methodologies, results, and recommendations. Finally, methods for effectively presenting network test reports were explored to ensure clear communication of technical information to stakeholders.
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