Master Linux Network Troubleshooting: Essential Commands and Step‑by‑Step Guide

ifconfig – Network Interface Configuration and Inspection

The ifconfig command displays interface status, configures IP addresses and netmask, and enables or disables interfaces.

Show all interfaces: ifconfig -a Assign an IP address and netmask to an interface (e.g., eth0):

ifconfig eth0 192.168.1.110 netmask 255.255.255.0

Enable or disable a specific interface:

ifup eth0   # enable
ifdown eth0 # disable

Changes made with ifconfig are not persistent across reboots; edit the appropriate network configuration files for permanent settings.

ping – Test Network Connectivity

ping

sends ICMP echo requests to verify that a host is reachable and measures round‑trip latency.

Ping the local loopback address: ping 127.0.0.1 Ping a remote host with a limited packet count (e.g., 5 packets):

ping -c 5 www.example.com

traceroute – Trace Packet Path

traceroute

shows each hop a packet takes to reach its destination, which helps locate routing problems.

traceroute 8.8.8.8

netstat and ss – View Network Connections

Both commands list active sockets and listening ports. ss is generally faster.

Show all listening TCP and UDP ports:

netstat -tuln

ss -tuln

Display the routing table:

netstat -r

dig and nslookup – DNS Queries

Use dig or nslookup to inspect DNS records.

dig www.google.com
nslookup google.com

route – Manipulate Routing Table

The route command displays or modifies the system’s routing information.

Show current routes: route Add a default gateway (replace with your gateway address):

route add default gw 192.168.1.1

ethtool – Ethernet Interface Settings

ethtool

queries or changes Ethernet driver parameters, useful for hardware‑level diagnostics.

ethtool eth0

arp – Manage ARP Cache

arp

displays or modifies the ARP table, helping resolve MAC address conflicts.

arp -e

Practical Troubleshooting Workflow

When a website is unreachable, follow these steps to isolate the problem:

Check interface status: ifconfig Verify local loopback connectivity: ping 127.0.0.1 Test reachability of the default gateway (replace with your gateway address): ping <code>gateway_IP</code> Query DNS records for the target host:

dig www.example.com

nslookup www.example.com

Inspect the routing table to ensure a valid route exists: netstat -r Combining these commands enables rapid identification of connectivity, DNS, or routing issues, allowing efficient resolution.