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Network

Here's a mini-guide on essential networking commands in Linux:

Essential Networking Commands in Linux

This guide covers several key networking commands in Linux, useful for managing, troubleshooting, and monitoring networks.

ifconfig

The ifconfig command is used to configure, manage, and display network interface information in Linux. While it's considered deprecated in favor of the ip command, it's still widely used.

  • Display network interfaces:

bash ifconfig

  • Bring an interface up or down:

bash ifconfig eth0 up ifconfig eth0 down

  • Assign an IP address to an interface:

bash ifconfig eth0 192.168.1.100 netmask 255.255.255.0

ip

The ip command is the modern replacement for ifconfig, offering more features and flexibility.

  • Display all network interfaces and their IP addresses:

bash ip addr show

  • Bring an interface up or down:

bash ip link set eth0 up ip link set eth0 down

  • Assign an IP address to an interface:

bash ip addr add 192.168.1.100/24 dev eth0

  • Display routing table:

bash ip route show

iptables

The iptables command is used to configure the Linux kernel firewall, allowing you to define rules for packet filtering and NAT (Network Address Translation).

  • View existing rules:

bash sudo iptables -L

  • Allow incoming SSH connections:

bash sudo iptables -A INPUT -p tcp --dport 22 -j ACCEPT

  • Block an IP address:

bash sudo iptables -A INPUT -s 192.168.1.100 -j DROP

  • Save iptables rules (Debian/Ubuntu):

bash sudo iptables-save > /etc/iptables/rules.v4

nc (Netcat)

nc is a versatile networking tool used for creating network connections, scanning ports, and transferring data.

  • Scan for open ports:

bash nc -zv 192.168.1.1 1-1000

  • Create a simple TCP server:

bash nc -l 1234

  • Connect to a TCP server:

bash nc 192.168.1.1 1234

  • Transfer a file:

On the receiving side:

bash nc -l 1234 > received_file

On the sending side:

bash nc 192.168.1.1 1234 < file_to_send

nmap

nmap is a powerful network scanning tool used for discovering hosts and services on a network.

  • Basic scan to detect open ports:

bash nmap 192.168.1.1

  • Scan a range of IP addresses:

bash nmap 192.168.1.1-255

  • Scan using a specific port range:

bash nmap -p 1-1000 192.168.1.1

  • Detect the operating system of a remote host:

bash sudo nmap -O 192.168.1.1

tcpdump

tcpdump is a command-line packet analyzer used for capturing and analyzing network traffic.

  • Capture all packets on a specific interface:

bash sudo tcpdump -i eth0

  • Capture packets from a specific host:

bash sudo tcpdump -i eth0 host 192.168.1.1

  • Capture only TCP packets:

bash sudo tcpdump -i eth0 tcp

  • Save captured packets to a file:

bash sudo tcpdump -i eth0 -w capture.pcap

ping

The ping command is used to test the reachability of a host on an IP network and to measure the round-trip time for messages sent from the source to the destination.

  • Ping a host:

bash ping 192.168.1.1

  • Ping a host with a specific count of packets:

bash ping -c 4 192.168.1.1

traceroute

traceroute displays the route that packets take to reach a network host.

  • Trace the route to a host:

bash traceroute 192.168.1.1

netstat

netstat is a command-line tool that provides information about network connections, routing tables, interface statistics, masquerade connections, and multicast memberships.

  • Display all active connections:

bash netstat -a

  • Display listening ports:

bash netstat -l

  • Display network interface statistics:

bash netstat -i

ss

ss is a utility to investigate sockets. It can display more detailed information than netstat and is considered its replacement.

  • Display all TCP connections:

bash ss -t

  • Display all UDP connections:

bash ss -u

  • Display listening ports:

bash ss -l