Why network tools diagnose connectivity in Linux CLI - Why It Works

Introduction

Sometimes your computer cannot reach websites or other computers. Network tools help find where the problem is by checking if your device can talk to others on the network.

When a website does not load and you want to check if your internet is working

When you cannot connect to a company server and need to see if the server is reachable

When you want to check if your home router is responding

When you want to see if a specific port on a server is open and accepting connections

When you want to measure how long it takes for data to travel to another computer

Commands

This command sends 4 small messages to Google's DNS server to check if your computer can reach it and how long it takes.

Terminal

ping 8.8.8.8 -c 4

Expected Output

PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data.

64 bytes from 8.8.8.8: icmp_seq=1 ttl=117 time=14.2 ms

64 bytes from 8.8.8.8: icmp_seq=2 ttl=117 time=14.0 ms

64 bytes from 8.8.8.8: icmp_seq=3 ttl=117 time=13.9 ms

64 bytes from 8.8.8.8: icmp_seq=4 ttl=117 time=14.1 ms



--- 8.8.8.8 ping statistics ---

4 packets transmitted, 4 received, 0% packet loss, time 3004ms

rtt min/avg/max/mdev = 13.900/14.050/14.200/0.114 ms

→

-c - Limits the number of ping messages sent

This command shows the path your messages take to reach Google's DNS server, helping find where delays or blocks happen.

Terminal

traceroute 8.8.8.8

Expected Output

traceroute to 8.8.8.8 (8.8.8.8), 30 hops max, 60 byte packets

 1  192.168.1.1 (192.168.1.1)  1.123 ms  1.045 ms  1.012 ms

 2  10.10.0.1 (10.10.0.1)  10.234 ms  10.198 ms  10.167 ms

 3  172.217.0.1 (172.217.0.1)  14.345 ms  14.312 ms  14.280 ms

 4  8.8.8.8 (8.8.8.8)  14.123 ms  14.098 ms  14.067 ms

This command checks if the web server on google.com is accepting connections on port 80 (the standard web port).

Terminal

nc -zv google.com 80

Expected Output

Connection to google.com 80 port [tcp/http] succeeded!

→

-z - Scan without sending data

→

-v - Show verbose output

Key Concept

If you remember nothing else from this pattern, remember: network tools help find where communication stops between your computer and others.

Common Mistakes

Not specifying the number of ping packets and letting it run forever

The ping command will keep running until stopped manually, which can be confusing and waste resources

Use the -c flag to limit the number of ping packets, like ping 8.8.8.8 -c 4

Using traceroute without root permissions on some systems

Traceroute may fail or show incomplete results if not run with proper permissions

Run traceroute with sudo if needed, like sudo traceroute 8.8.8.8

Trying to check a port with nc without the -z flag

Without -z, nc tries to send data, which may cause unexpected behavior or hang

Use nc -zv to just check if the port is open without sending data

Summary

Use ping to check if a device is reachable and measure response time.

Use traceroute to see the path and find where delays or blocks occur.

Use nc with -zv to check if a specific port on a server is open.