Network Troubleshooting

Sometimes the Internet suddenly stops working, a website won't open, or one computer can communicate with another while a different computer cannot.

When something goes wrong in a network, we need a systematic way to find the cause. This process is called Network Troubleshooting.

Network troubleshooting is the process of identifying, diagnosing, and fixing problems that affect network connectivity, performance, or communication.

In simple words:

Network Troubleshooting = Find out why the network isn't working and fix it.

Common Network Problems

Network problems can happen for many different reasons.

Some common problems include:

• No Internet connection

• Slow network speed

• High latency

• Packet loss

• DNS not working

• Incorrect IP configuration

• Wi-Fi connection problems

• A server being unreachable

• Firewall blocking traffic

• Faulty cables or network hardware

The important thing is not to randomly change settings. Instead, troubleshoot the problem step by step.

Basic Network Troubleshooting Process

A simple troubleshooting process is:

Identify the Problem
       ↓
Check Physical Connection
       ↓
Check IP Configuration
       ↓
Test Local Connectivity
       ↓
Test Network Connectivity
       ↓
Test DNS
       ↓
Check Applications
       ↓
Fix and Verify

This approach helps narrow down the problem instead of guessing.

Step 1: Check the Physical Connection

Before checking complicated network settings, start with the basics.

For wired networks, check:

• Is the Ethernet cable connected?

• Are link/activity lights working?

• Is the switch powered on?

• Is the network interface enabled?

For Wi-Fi, check:

• Is Wi-Fi enabled?

• Are you connected to the correct network?

• Is the signal strong enough?

• Is Airplane Mode disabled?

Sometimes the solution really is as simple as reconnecting a cable.

Step 2: Check IP Configuration

Every device communicating over an IP network needs appropriate network configuration.

A typical device may have:

IP Address
Subnet Mask / Prefix
Default Gateway
DNS Server

For example:

IP Address:      192.168.1.20
Subnet:          192.168.1.0/24
Gateway:         192.168.1.1
DNS Server:      192.168.1.1

If the device has an incorrect IP address, subnet configuration, or gateway, communication may fail.

Useful Command: ipconfig / ifconfig / ip

Different operating systems provide different commands for checking network configuration.

Windows

ipconfig

Linux

ip addr

macOS

Commands such as:

ifconfig

can be used to inspect network interfaces.

These commands help you see whether your device has received an IP address and other network information.

Step 3: Test the Local Network

Once you've checked your configuration, test whether your device can reach its default gateway.

For example:

Computer
   ↓
Default Gateway
   ↓
Local Network

You can commonly use ping for this.

ping 192.168.1.1

If the gateway responds, your device can likely communicate with that local network endpoint.

If it doesn't, the problem may be related to:

• Wi-Fi

• Ethernet

• IP configuration

• VLAN configuration

• Local firewall rules

• Router or access-point issues

Step 4: Test Internet Connectivity

If the local gateway is reachable, test whether you can reach a remote IP address.

For example:

Computer
   ↓
Gateway
   ↓
Internet
   ↓
Remote Host

You can use:

ping 8.8.8.8

If the remote IP is reachable but websites still don't open, DNS could be the problem.

Keep in mind that some hosts intentionally block or deprioritize ICMP, so a failed ping does not always mean that the host or Internet connection is completely unavailable.

Step 5: Check DNS

Suppose this works:

ping 8.8.8.8

but this doesn't:

ping example.com

One possible cause is DNS resolution failure.

You can test DNS using tools such as:

nslookup example.com

or:

dig example.com

If DNS is not working, your device may be unable to translate:

example.com
      ↓
IP Address

even though the network itself is working.

Step 6: Check Routing

Sometimes the device has a valid IP address but doesn't have a correct path to the destination.

You can inspect the routing table using commands such as:

Windows

route print

Linux

ip route

macOS

netstat -rn

Look for:

• Default route

• Incorrect routes

• Missing routes

• Unexpected gateways

Routing problems can prevent packets from reaching the correct network.

Step 7: Use Traceroute

Sometimes you know that a destination is unreachable, but you don't know where the path is failing.

Tools such as traceroute can help show the path packets take through intermediate routers.

Windows

tracert example.com

Linux/macOS

traceroute example.com

A simplified result might look like:

Your PC
  ↓
Router 1
  ↓
Router 2
  ↓
Router 3
  ↓
Destination

This can help identify where connectivity problems may be occurring.

However, some routers intentionally don't respond to traceroute probes, so missing responses do not necessarily indicate a failure.

Step 8: Check Ports and Services

Sometimes the network is working, but a particular service is unavailable.

For example:

Server
 ├── Port 22  → SSH
 ├── Port 80  → HTTP
 └── Port 443 → HTTPS

If a website isn't working, you can investigate whether the expected service is reachable.

Tools such as curl, nc, or platform-specific connection-testing tools can help test services.

For example:

curl https://example.com

This can help distinguish between a general network problem and an application/service problem.

Step 9: Check Firewall Rules

A firewall can sometimes block legitimate traffic.

For example:

Client
  ↓
Firewall
  X
Server

If other network connectivity works but one specific service does not, check whether a firewall rule is blocking:

• Source address

• Destination address

• Port

• Protocol

• Application traffic

Always verify the intended security policy before changing firewall rules.

Step 10: Check the Application

Sometimes the network is perfectly fine and the problem is actually with the application or server.

For example:

Internet ✓
DNS ✓
Routing ✓
Port ✓
        ↓
Application ✗

The application may be:

• Crashed

• Misconfigured

• Overloaded

• Unable to connect to its database

• Returning an error

This is why troubleshooting should move from the lower layers toward the application instead of assuming every problem is a network problem.

Useful Network Troubleshooting Commands

Here are some commonly used tools:

The exact commands available depend on the operating system.

Troubleshooting Using Layers

One of the best ways to troubleshoot networks is to think in layers.

For example:

Application
    ↓
Transport
    ↓
Network
    ↓
Data Link
    ↓
Physical

You can move from the bottom upward.

Physical

Check:

• Cables

• Power

• Wi-Fi signal

• Network interface

Data Link

Check:

• Ethernet/Wi-Fi connection

• VLAN configuration

• MAC-level connectivity

Network

Check:

• IP address

• Subnet

• Gateway

• Routing

Transport

Check:

• TCP/UDP

• Ports

• Firewall rules

Application

Check:

• DNS

• HTTP/HTTPS

• Server configuration

• Application errors

This layered approach makes troubleshooting much more organized.

Example: Website Is Not Opening

Suppose your browser cannot open a website.

Don't immediately assume the website is down.

Try:

1. Check Wi-Fi/Ethernet
          ↓
2. Check IP address
          ↓
3. Ping gateway
          ↓
4. Test Internet connectivity
          ↓
5. Test DNS
          ↓
6. Check HTTPS connectivity
          ↓
7. Check browser/application

This gradually narrows down the possible cause.

For example:

Gateway works ✓
Internet IP works ✓
DNS fails ✗

Now you have a strong clue that the problem is related to DNS, rather than your Wi-Fi connection.

Conclusion

Network troubleshooting is a systematic process of finding and fixing network problems.

The most important rule is:

Don't guess—test.

Start with the simplest possibilities and gradually move toward more complex ones.

Remember the basic troubleshooting flow:

Physical Connection → IP Configuration → Gateway → Internet → DNS → Routing → Ports → Application

And some useful tools are:

• ping → Test reachability

• traceroute/tracert → Examine the network path

• nslookup/dig → Test DNS

• ipconfig/ip/ifconfig → Check network configuration

• curl → Test application-level connectivity

Once you develop the habit of troubleshooting step by step and layer by layer, even complicated network problems become much easier to understand and diagnose.