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2. Networking Commands.md

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Networking Commands

Networking is a critical aspect of Linux system administration, and knowing how to use networking commands effectively can help you manage, troubleshoot, and optimize your network connections. This page covers the most commonly used networking commands in Linux, providing practical examples and explanations.

Checking Network Interfaces: ip and ifconfig

ip Command

The ip command is a modern replacement for the older ifconfig command and provides more comprehensive network management capabilities.

  • Display Network Interfaces:

    ip addr show

    This command shows all network interfaces and their IP addresses.

  • Bring an Interface Up/Down:

    sudo ip link set dev eth0 up
sudo ip link set dev eth0 down

    These commands bring the eth0 interface up or down.

  • Assign an IP Address to an Interface:

    sudo ip addr add 192.168.1.100/24 dev eth0

    This assigns the IP address 192.168.1.100 with a subnet mask of 24 to the eth0 interface.

ifconfig Command

Although ifconfig is deprecated, it is still used on many systems.

  • Display Network Interfaces:

    ifconfig

    This command lists all network interfaces along with their IP addresses.

  • Bring an Interface Up/Down:

    sudo ifconfig eth0 up
sudo ifconfig eth0 down

    These commands bring the eth0 interface up or down.

  • Assign an IP Address to an Interface:

    sudo ifconfig eth0 192.168.1.100 netmask 255.255.255.0

    This assigns the IP address 192.168.1.100 with a subnet mask of 255.255.255.0 to the eth0 interface.

Checking Network Configuration: nmcli and nmtui

nmcli Command

nmcli is a command-line tool for managing NetworkManager and can be used to control network connections.

  • Show All Connections:

    nmcli con show

    This lists all network connections and their statuses.

  • Connect to a Network:

    nmcli con up id "connection_name"

    This brings up the specified network connection.

  • Disconnect from a Network:

    nmcli con down id "connection_name"

    This disconnects the specified network connection.

nmtui Command

nmtui provides a text-based user interface for managing NetworkManager connections.

  • Launch nmtui:

    sudo nmtui

    This launches the nmtui interface, where you can easily manage network connections.

Monitoring Network Traffic: netstat, ss, and tcpdump

netstat Command

netstat is a classic command used to monitor network connections, routing tables, interface statistics, masquerade connections, and multicast memberships.

  • Display All Connections:

    netstat -a

    This command lists all active connections, including TCP and UDP.

  • Display Listening Ports:

    netstat -tuln

    This shows all listening ports with numeric IP addresses and port numbers.

ss Command

ss is a modern alternative to netstat, offering faster performance and more detailed information.

  • Display All Connections:

    ss -a

    This command lists all active connections.

  • Display Listening Ports:

    ss -tuln

    This shows all listening ports with numeric IP addresses and port numbers.

tcpdump Command

tcpdump is a powerful command-line packet analyzer used for network troubleshooting and security analysis.

  • Capture Packets on an Interface:

    sudo tcpdump -i eth0

    This command captures packets on the eth0 interface.

  • Save Captured Packets to a File:

    sudo tcpdump -i eth0 -w capture.pcap

    This saves the captured packets to a file named capture.pcap.

Testing Network Connectivity: ping, traceroute, and mtr

ping Command

ping is used to test the reachability of a host on a network and measure the round-trip time for messages sent from the originating host.

  • Ping a Host:

    ping google.com

    This sends ICMP echo requests to google.com and reports the results.

traceroute Command

traceroute is used to track the path that packets take from your system to a destination.

  • Trace the Route to a Host:

    traceroute google.com

    This shows the path taken by packets to reach google.com.

mtr Command

mtr combines the functionality of ping and traceroute in a single network diagnostic tool.

  • Run mtr on a Host:

    mtr google.com

    This command provides a real-time view of the network path to google.com.

Network Configuration Files

Understanding the key network configuration files in Linux is essential for manual network setup and troubleshooting.

/etc/network/interfaces

This file is used to configure network interfaces on Debian-based systems.

Example configuration:

auto eth0
iface eth0 inet static
    address 192.168.1.100
    netmask 255.255.255.0
    gateway 192.168.1.1

/etc/sysconfig/network-scripts/

This directory contains configuration files for network interfaces on Red Hat-based systems.

Example configuration for eth0:

DEVICE=eth0
BOOTPROTO=static
ONBOOT=yes
IPADDR=192.168.1.100
NETMASK=255.255.255.0
GATEWAY=192.168.1.1

Conclusion

Mastering networking commands in Linux is essential for configuring, managing, and troubleshooting network connections. Whether you are a system administrator or a casual user, understanding these commands will help you maintain a robust and secure network environment.

Next: SSH: Secure Shell

Previous: Networking Basics