How to Troubleshoot General Networking Issues

Quick Definition: Network troubleshooting is the systematic process of identifying and fixing issues within computer networks. Common troubleshooting areas include issues like collisions, broadcast storms, and duplicate addresses.

Troubleshooting network problems is a foundational skill for both Network+ exam prep and the real-world job of a network engineer. A network’s uptime often reflects the engineer behind it, and consistent uptime usually comes from following a clear, structured troubleshooting process.

Whether you’re diagnosing issues on an internal LAN or an external connection, proven methods can help you zero in on the problem faster. In this article, we’ll cover key considerations for network troubleshooting, highlight common pitfalls, and walk through five approaches every engineer should keep in mind.

Why is Network Troubleshooting Important? 

One fundamental principle in engineering is that any human-made creation will inevitably fail. Whether it is the International Space Station or a sump pump, something is bound to fail—including your network topology. 

Having a rigorous and structured plan is not for “just in case” but to prepare for the inevitability of network downtime. Establishing a consistent troubleshooting pattern streamlines problem-solving strategy, ultimately saving time and providing a traceable process for auditing purposes. Let’s walk through five troubleshooting topics to incorporate into your attack plan.

7 Common Considerations in Network Troubleshooting

As you gain experience troubleshooting the network, clear patterns emerge in the chaos. The same five or so issues are often the culprit, attributing to degraded connectivity. Let’s talk about them in more detail, starting with device configuration.

Device Configuration

Time and time again, device misconfiguration is the culprit when you have network issues. If network access is blocked, verify the port is open on your firewall software. Often, ports are closed by default for security purposes. Additionally, check the router and switches to verify port forward rules are enabled. It is critical to have a diagram of your network’s topology to verify the data’s chain of custody.

Routing Tables

Routing tables often reside on the router or appliance configured to transmit data over the network. Verify all the routes are correct, none are missing, and none of them conflict with each other. That list is not exhaustive but is often the source of network woes. The routing tables should always be on your network diagnostic chart.

Missing Route

One of the most common reasons a packet never reaches its destination is a missing route. If the destination network doesn’t appear in the routing table, the router simply doesn’t know where to send the traffic. 

This can happen when static routes are forgotten during configuration or dynamic routing protocols fail to properly advertise networks. Always verify route entries for any new subnets or devices added to the network.

Interface Status

Verifying interface status is generally the first step of troubleshooting. Even at home, it is easy to check— is the router's “internet light” red or green? Verify all network interface devices in the chain of custody between the internet and your device. 

This process can be done by physically checking the machines, pinging relevant appliances, or using administrative tools like ipconfig, ifconfig, or netstat.

IP Setting Issues

Even if an interface looks healthy, incorrect IP settings can bring traffic to a halt. Four common culprits include:

• Wrong Default Gateway: Prevents devices from reaching outside networks.

• Incorrect Subnet Mask: Causes devices to misinterpret which hosts are local.

• Static IP Conflicting with DHCP: Leads to duplicate address errors.

• Duplicate Assignment: When two devices share the same IP, both will experience intermittent connectivity.

VLAN Assignment

VLANs are used to logically separate a physical network into smaller, more manageable logical networks. However, they can often be a source of heartburn when troubleshooting connectivity issues. VLANs are often used to enforce network policies and are often misconfigured. Node overlap can also contribute to network problems as well. Node overlap is when one device is incorrectly mapped to more than one VLAN.

Network Performance Baselines

Network performance baselines are well-documented cases of the network operating at optimum efficiency. Monitor any deviation from its typical performance, and consistently gauge whether your troubleshooting actions have brought your transmission speed closer to baseline.

14 Common Areas to Troubleshoot Network Issues

Now that we have discussed broader considerations, let’s discuss common issues where network issues come into play. There are only so many moving parts in a network, and it is important to list each one to ensure that all possible components are verified.

Collisions

Collisions often occur when a network does not have enough bandwidth to support the amount of requests. This occurs on older topologies such as mesh or bus topology and is rarely seen in a modern environment. 

Broadcast Storm

Broadcast traffic consists of data packets that are sent from one device to every device on the network. (Think of how a TV station “broadcasts” shows to all viewers.) Broadcast storms stem from misconfigurations that cause nodes to respond to broadcasts with broadcasts, thus commencing an infinite loop. This broadcast storm can cause significant latency and downtime.

Duplicate Addresses (including MAC and IP)

This can occur in a few different ways. If the IP addresses are static, then the network administrator puts the same IP address twice. Also, if the IP addresses are dynamic, the DHCP server was misconfigured, allowing for duplicate addresses.

Lastly, some DHCP servers allow administrators to reserve specific IP addresses for devices based on their MAC addresses. If the administrator configures conflicting reservations or makes mistakes in the reservation settings, duplicate address conflicts will arise.

Multicast Flooding

Multicast differs from broadcast in that it is sent to multiple recipients but only to recipients with a specific interest in the message being transmitted. Multicast flooding is when ALL machines receive the message, regardless of whether they care about it or not.

Asymmetrical Routing

Asymmetric routing is when a packet is sent to a recipient, but the recipient returns transmission on a different route. This can be a security issue because Access Control Lists (ACLs) are often configured with symmetry in mind. Additionally, asymmetric routing is far more difficult to troubleshoot.

Switching and Routing Loops

These are characterized by the unintentional looping or packet forwarding of data within a network. This can cause extensive network latency and is generally due to misconfigured switches.

Rogue DHCP Server

Rogue DHCP servers are unauthorized servers connected to the network that distribute IP addresses, subnet masks, gateways, and more. These servers are typically introduced to a network maliciously or accidentally. These can cause duplicate addresses and significant latency. 

DHCP Scope Exhaustion

Even with only one DHCP server in play, scope exhaustion can grind connectivity to a halt. This happens when the server has no more addresses available in its pool. New devices won’t receive an IP lease, leaving them unable to join the network. 

Scope exhaustion often results from too many devices connecting at once, leases not expiring correctly, or pools that are simply too small for the environment. Expanding the scope or shortening lease times are common fixes.

Certificate Issues

Certificate issues occur when an HTTPS certificate is not renewed in time. Often, this occurs when the network administrator forgets to renew them. Certificate renewal should always be accomplished by a scheduler like cron.

NTP Issues

Time synchronization is easy to overlook but can break key services. If network devices aren’t syncing with a reliable Network Time Protocol (NTP) source, you may see authentication failures, expired certificates, or logs that don’t align. 

Common causes include blocked NTP traffic, misconfigured time zones, or failed synchronization with upstream time servers. Always confirm system clocks match across critical devices.

Hardware Failure

Hardware failures are when significant components of the network become compromised. For example, if the router short circuits, this will bring traffic to a dead halt. When troubleshooting, check the basics first: are devices powered, indicator lights normal, and fans running? 

Swap in known-good cables or power supplies to rule out simple issues. For enterprise gear, monitor hardware health through SNMP or vendor dashboards to catch early warning signs before they cause outages.

Keeping spare components on hand and scheduling regular hardware refreshes can help minimize downtime when failures inevitably occur.

Firewall Settings

In my experience, this is always the biggest culprit. Often, firewalls are misconfigured to block ports that should otherwise be open. For instance, if a firewall closed port 443, then no internet traffic would enter or leave the network. Modern firewalls generally have the ability to block by service, port, or address.

BYOD Challenges

Modern networks also face challenges from the devices users bring with them. Laptops, tablets, and phones that connect outside the corporate perimeter can bypass normal security controls. These BYOD (Bring Your Own Device) endpoints may introduce malware, act as rogue DHCP sources, or consume more bandwidth than expected. Troubleshooting BYOD problems often requires strong access policies, network segmentation, and device compliance checks.

Licensed Feature Issues

Yet another common issue. When licenses on network devices expire, the network grinds to a halt. That is because proprietary software requires valid licensure to operate. Verify all licenses are up to date and consider either setting reminders or setting licenses up to auto-renew. 

Conclusion

Most network performance problems are usually rooted in one of the mentioned issues. By examining baseline performance expectations, you can pinpoint the most probable cause of the network's troubles.

However, effectively troubleshooting a network takes time and experience. However, life will be much easier if a strategy is already in place to diagnose the issue. For a structured approach, start with some common problems mentioned earlier. First, verify nothing is broken, then verify interface statuses. For example, which nodes can be pinged from where will help you figure out the problem. 

Compiling and thoroughly reviewing these solutions will not only prepare you for the Network+ exam but also establish you as the trusted network expert within your organization.

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