Linux Network Troubleshooting: Using ping, traceroute, nslookup, netstat, and telnet

If a company website is inaccessible, the issue may stem from network problems; similarly, remote connection tools or MySQL may fail due to network issues. This guide shows how to troubleshoot Linux server network problems.

ping tests connectivity between hosts using an IP address or domain name. It works on both Linux and Windows. Example usage and output:

# ping -c 4 8.210.247.5

PING 8.210.247.5 (8.210.247.5) 56(84) bytes of data.

64 bytes from 8.210.247.5: icmp_seq=1 ttl=64 time=1.54 ms

64 bytes from 8.210.247.5: icmp_seq=2 ttl=64 time=1.48 ms

64 bytes from 8.210.247.5: icmp_seq=3 ttl=64 time=1.46 ms

64 bytes from 8.210.247.5: icmp_seq=4 ttl=64 time=1.48 ms

--- 8.210.247.5 ping statistics ---

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

rtt min/avg/max/mdev = 1.460/1.494/1.548/0.042 ms

A shell script can scan a LAN to list reachable IPs:

#!/bin/bash

net='192.168.2.'

seqs=`seq 1 254`

for seq in $seqs

do

ip=$net$seq

/usr/bin/ping -c 1 -W 1 $ip >/dev/null 2>&1

if [ "$?" == "0" ]; then

echo "$ip is UP"

fi

done

traceroute shows each network hop between the local host and a destination, useful for diagnosing slow website access:

# traceroute -n google.com

traceroute to google.com (172.217.163.238), 30 hops max, 60 byte packets

1 * * *

2 11.109.220.61 1.444 ms 1.577 ms 11.109.216.189 1.500 ms

3 11.109.220.190 5.512 ms * 11.109.220.174 5.382 ms

4 11.131.180.222 1.660 ms 11.131.180.218 1.519 ms 11.131.180.250 1.365 ms

nslookup resolves a domain name to its IP address:

nslookup 5iqm.com

Server: 100.100.2.136

Address: 100.100.2.136#53

Non-authoritative answer:

Name: 5iqm.com

Address: 121.196.12.64

netstat displays listening ports and active connections, helping verify whether required services (e.g., port 80 for HTTP) are open:

# netstat -tlunp

Active Internet connections (only servers)

Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name

tcp        0      0 0.0.0.0:80              0.0.0.0:*               LISTEN      30721/nginx: master

tcp        0      0 0.0.0.0:21              0.0.0.0:*               LISTEN      1275/pure-ftpd (SER

tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN      1167/sshd

tcp        0      0 0.0.0.0:888             0.0.0.0:*               LISTEN      30721/nginx: master

tcp        0      0 0.0.0.0:8888            0.0.0.0:*               LISTEN      2068/python

telnet tests whether a specific port on a remote host is reachable:

# telnet 8.210.110.139 22

Trying 8.210.110.139...

Connected to 8.210.110.139.

Escape character is '^]'.

SSH-2.0-OpenSSH_7.4

# telnet 8.210.110.139 3306

Trying 8.210.110.139...  (if it keeps trying, the port is closed)

By following these steps—pinging the server IP, pinging the domain, checking DNS resolution, verifying that required ports are open with netstat or telnet—you can systematically identify and resolve most Linux network connectivity issues.