1. IPv4

Every device connected to a network has a unique address, known as an IP (Internet Protocol) address. For this course, we will focus on IPv4 addresses, which are the most common type you will encounter. Understanding them is a core part of learning networking on Linux.

An IPv4 address is a 32-bit number typically represented in a human-readable format, like this:

204.23.124.23

This address contains two distinct parts: the network portion, which identifies the specific network the device is on, and the host portion, which identifies the specific device on that network.

The Structure of an IP Address

An IPv4 address is divided into four sections separated by periods. Each section is called an octet. In computer science, an octet is a group of 8 bits, and since 8 bits equal 1 byte, an IPv4 address is 4 bytes long. This structure is fundamental, and mastering it is one of the best resources to learn linux command line for beginners in networking.

Finding Your IP Address on Linux

For any beginner linux user, one of the first tasks is to find the system's IP address. You can do this using command-line tools.

The traditional command for this is ifconfig. While it is still found on many systems, it is considered a legacy tool.

pete@icebox:~$ ifconfig -a
eth0      Link encap:Ethernet  HWaddr 1d:3a:32:24:4d:ce
          inet addr:192.168.1.129  Bcast:192.168.1.255  Mask:255.255.255.0
          inet6 addr: fd60::21c:29ff:fe63:5cdc/64 Scope:Link

In the output above, the IPv4 address is 192.168.1.129.

The Modern Approach with ip addr

The best way to learn linux networking today involves using the modern ip command. The ip addr command has replaced ifconfig and is the standard on most current Linux distributions.

pete@icebox:~$ ip addr show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 1d:3a:32:24:4d:ce brd ff:ff:ff:ff:ff:ff
    inet 192.168.1.129/24 brd 192.168.1.255 scope global dynamic eth0
       valid_lft 85646sec preferred_lft 85646sec

Here, you can find the same IPv4 address, 192.168.1.129, listed next to inet for the eth0 interface.