CompTIA A+ Core Certification: The Basics of Hardware and Network Troubleshooting - Network Troubleshooting

220-1101: Objective 5.7: Given a scenario, troubleshoot problems with wired and wireless networks.
Most computing devices that an IT professional encounters are connected to a network. The common network issues discussed in the following sections are essential knowledge for an IT professional. Understanding the problems and solutions is important for the 220-1101 exam and to aid in your ongoing work.

No Connectivity
For no connectivity errors, do the following:
- Check the power supply going to the hub, switch, wireless access point, or router. Reset the device.
- Isolate the problem. If only the users connected to a new switch that is connected to an existing switch lose their network connection, check the connection between the existing switch and the new one to make sure they are plugged into similar ports. Most switches have an uplink port that is used to connect an additional switch, and this is the best way to establish a reliable connection.
- If the uplink port appears to be connected properly, check the cable. Uplink ports perform the crossover for the user, enabling you to use an ordinary network cable to add a hub or switch.
Tip: If you use a crossover cable, you must connect the new hub or switch through a regular port, not through the uplink port.

External Interference and Intermittent Wireless Connectivity
Intermittent connectivity can be caused by the following:
- Dead spots (poor signal) on a wireless network: Relocate the wireless router.
- Too many networks using the same channel: Use a wireless network scanning device or app to see local wireless networks and their channels. Reconfigure the network to use a channel with less traffic.
- EMI or RFI interference with the wired network: Alarm systems, elevators, fluorescent lights, and motors can interfere with networks running UTP. Switch to STP cable or relocate cables away from interference.
- A defective network cable, such as a cracked outer jacket or a broken locking tab: Replace the cable.
- Problems with the ISP’s Internet service: If the problem persists after you troubleshoot the local network, contact the ISP.

Slow Network Speeds
Significant drops in network performance and slow transfer speeds can be traced to a variety of causes:
- Damage to cables, connectors, hubs, switches, and routers: Check the cables for damage.
- Connecting high-speed NICs to low-speed switches: When using Gigabit Ethernet switches and routers, confirm that all devices on the network (switches, router, cables, and NICs) meet Gigabit Ethernet standards (CAT 5e, 6, 6a, or 7 cable) and are configured to use Gigabit Ethernet.
- High Internet Demand: Fast local connections but sluggish Internet connections can be caused by too much demand for the Internet connection (perhaps due to multiple downloads or streaming services) or Internet congestion outside the home or office.
- RFI/EMI interference with wireless networks: Check wireless phones and microwave ovens to see if their use interferes with the network. Move the router away from interference sources. Switch to a wireless 802.11ac router and NICs, and use the 5GHz band to avoid most of this type of interference. 802.11ax, which is known as Wi-Fi 6, will broadcast at 2.4GHz or 5GHz and, when authorized by governments, in the 6GHz range. It is in beta testing and will become the standard over the next few years.

Limited Connectivity
A low signal on a wireless network can be caused by the following:
- Interference from other wireless networks: Use a wireless network analyzer to determine the least-used channels for the network, and switch to one of those channels.
- Concrete or masonry walls in the building: If relocating the router is not possible, add another wireless access point (WAP) in places that can broadcast around obstacles.
- Repeaters: In residential construction, consider using powerline repeaters.
- Improper antenna positioning on the router or NICs with adjustable antennas: Follow manufacturer recommendations.
- A router or NICs that do not support MU-MOMO antennas: Multiuser Multiple Input Multiple Output (MU-MIMO) enables a router to make

MIMO connections to multiple users at the same time. MU-MIMO requires routers and client device support, but it can be implemented on client devices that have only a single antenna each. These devices are increasingly common, and prices are falling. With so many wireless devices in homes and businesses competing for wireless bandwidth, a MU-MIMO solution could inexpensively double the speed of downstream traffic on a network.

Latency and Jitter
All networks experience a certain amount of data delay, called latency, which is the time it takes to get a packet of data through the devices between the sender and the receiver. Latency is normal, and networks are designed to accept a certain amount of it on a consistent level. High latency can be caused by router overloads or high demand on a key bottleneck of a network. Network designers know that a certain amount of latency will always exist on a network, but they try to keep it as small as their network devices will allow. Network latency problems can usually be traced to a networking device, such as a router or a switch.

Network jitter is the presence of variations of a network’s latency. Jitter can cause problems for end users on a network. Slow web page loading in browsers and faulty speech in conversations are some of the most noticeable problems.
Jitter is usually caused by too much demand for bandwidth. This can be caused by too many users on a small network, such as in a crowded coffee shop or event space with many devices accessing the network), or by even a few people demanding too much data (say, an uncrowded coffee shop with all patrons trying to stream videos). Either way, the network cannot process all the data. Ways to mitigate jitter can be built into the network in these ways:
- Limiting the number of connections on a Wi-Fi channel
- Limiting the number of users on the Wi-Fi network, to keep the access point from being overworked
- Limiting devices that require large data flows to wired connections (not on the wireless network)
- Blocking gaming and movies, if appropriate
- Putting voice traffic on a different network segment

Poor Voice over Internet Protocol (VoIP) Quality
Voice over Internet Protocol (VoIP) traffic is different from most other network traffic because it must be received in the exact order it was sent to make sense. VoIP is greatly affected by excessive latency and jitter. Poor network quality means that some parts of the conversation arrive out of sequence, causing confusion and frustration, so the quality of the connection must be without jitter. Advanced network configuration allows for VoIP to be prioritized over other traffic.
The best way to ensure that VoIP is stable and high quality is to keep it on a separate local network from regular data. By configuring the router to prioritize VoIP, traffic voice conversations remain reliable and clear.

Port Flapping
Port flapping occurs when the physical port on a device turns on and off intermittently, usually very rapidly. Several network configuration issues cause this and are beyond the scope of the A+ exam. However, sometimes flapping can be a very simple problem, such as a worn or loose cable.
The obvious symptom of flapping is slowed network response as several packets of information get dropped and need to be re-sent. This causes even more congestion, and sometimes the link simply appears to go down because it cannot keep up with traffic. If this is the case, change to a different switch port, if possible. Check the cable, too; sometimes a connection fails because a cable was pulled or twisted and no longer connects properly.