IP Address – What It Looks Like, Its Structure, and What Each Part Means

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An IP address (Internet Protocol address) is the “home address” of a device on a network. It allows data packets to be routed from sender to receiver. Today, there are two versions: IPv4 and IPv6. Below is a clear explanation of both formats.

1) IPv4 – Dotted-Decimal Notation (e.g., 192.168.1.42)

Format: Four numbers separated by dots.
Range of each number (octet): 0–255.
Total bits: 32 bits (4 × 8 bits) → about 4.29 billion possible addresses.

Structure

  • Octets (four numbers): each represents 8 bits. Example:

    • 192.168.1.42

      • 192 = first octet

      • 168 = second

      • 1 = third

      • 42 = fourth

Meaning of the numbers

An IPv4 address is usually divided into a network part and a host part. How many bits are used for the network and how many for the host is defined by the subnet mask.

  • Subnet mask looks like:

    • Decimal: e.g., 255.255.255.0

    • Or CIDR notation: e.g., /24 (means first 24 bits are the network part).

Example:

  • Address: 192.168.1.42

  • Mask: /24 ≡ 255.255.255.0

  • Network: 192.168.1.0/24

  • Host part: .42 identifies the specific device in the network

  • Broadcast: 192.168.1.255 (message sent to all devices in the network)

In short: the earlier octets usually describe the network, the last octet(s) identify the device.

Common IPv4 ranges

  • Private addresses (for local networks):

    • 10.0.0.0/8

    • 172.16.0.0/12 (172.16.0.0–172.31.255.255)

    • 192.168.0.0/16

  • Loopback: 127.0.0.1

  • APIPA (when DHCP fails): 169.254.0.0/16

  • Multicast: 224.0.0.0–239.255.255.255

  • Default route: 0.0.0.0

2) IPv6 – Eight Hexadecimal Groups (e.g., 2001:db8:85a3:0:0:8a2e:370:7334)

Format: 8 groups of hexadecimal numbers (0–9 and a–f) separated by colons.
Total bits: 128 bits → enormous address space.

Shortening rules

  • Leading zeros can be omitted: 03af → 3af.

  • One sequence of consecutive :0: can be replaced by :: (only once).

    • Example: 2001:0db8:0000:0000:0000:8a2e:0370:7334
      → 2001:db8::8a2e:370:7334

Structure

  • IPv6 address = prefix (network part) + interface ID (host part).

  • Prefix length is written in CIDR notation: e.g., 2001:db8:abcd::/64

    • /64 means: first 64 bits = network, last 64 bits = device ID.

Common IPv6 ranges

  • Link-local: fe80::/10 (valid only on local link)

  • Unique local (private): fc00::/7 (commonly fdxx::/8)

  • Loopback: ::1

3) Are IPs “human-readable”?

  • IPv4 is somewhat readable (four numbers), but the numbers don’t have geographic or semantic meaning. They are only identifiers for routing. This is why we use DNS (www.example.com → 93.184.216.34) to map names to numbers.

  • IPv6 is even harder to remember due to length and hex format, but follows the same principle.

4) Who assigns IP addresses?

  • Public IP address (the one your router uses on the internet) is usually assigned by your ISP via DHCP, or statically if contracted.

  • Private/local IP addresses inside your home/office are assigned by your router (also using DHCP) to devices like phones, laptops, or TVs.

5) Examples

IPv4 example

  • Address: 10.0.5.23

  • Mask: /16 ≡ 255.255.0.0

  • Network: 10.0.0.0/16

  • Host part: .5.23 identifies the device

  • Broadcast: 10.0.255.255

IPv6 example

  • Address: fd12:3456:789a:1::b3

  • Prefix: /64 → fd12:3456:789a:1::/64

  • Interface ID: ::b3 identifies the device

  • Note: fd… indicates a unique-local (private) address.

6) Key notes for practice

  • Default gateway = your router’s IP (e.g., 192.168.1.1).

  • DNS servers map names to IPs (e.g., 8.8.8.8, 1.1.1.1).

  • NAT allows multiple devices in your LAN to share one public IPv4 address.

  • CIDR is the standard notation today, instead of old A/B/C classes.

Summary

  • IPv4: a.b.c.d (0–255), 32 bits, divided into network + host by subnet mask (/n).

  • IPv6: x:x:x:x:x:x:x:x, 128 bits, divided into prefix /n + interface ID.

  • Numbers are for routing, not human meaning. We rely on DNS for names.

  • Public IPs are assigned by ISPs, private IPs by your router.



Picture: IPv4 Address Format (Source: https://www.geeksforgeeks.org/computer-science-fundamentals/what-is-an-ip-address/)

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