IP Addressing & MAC

IPv4 — Internet Protocol Version 4

The most widely used version of IP addresses is IPv4 (Internet Protocol version 4). IPv4 has been the backbone of internet addressing since the 1980s, and the vast majority of internet traffic still uses it today.

How IPv4 Addresses Work

An IPv4 address is a 32-bit number. This means it is made up of 32 binary digits (ones and zeros). However, writing out 32 bits every time would be impractical for humans, so IPv4 addresses are displayed in a more readable format called dotted decimal notation.

In dotted decimal notation, the 32 bits are divided into four groups of 8 bits. Each group of 8 bits is called an octet. Each octet is converted from binary to a decimal number between 0 and 255, and the four octets are separated by dots (full stops).

  Binary:    11000000 . 10101000 . 00000001 . 00000001
  Decimal:      192   .   168    .    1     .    1

  Format:    [octet1] . [octet2] . [octet3] . [octet4]
  Range:      0-255   .  0-255   .  0-255   .  0-255

  Examples:  192.168.1.1    (common home router address)
             10.0.0.5       (private network address)
             8.8.8.8        (Google's public DNS server)
             172.16.0.1     (private network address)
        

The IPv4 Exhaustion Problem

Because IPv4 uses 32 bits, the total number of possible unique addresses is 2³² = approximately 4.3 billion addresses. When IPv4 was designed in the early 1980s, 4.3 billion seemed more than enough — the internet was a small research network with only a few hundred computers. Nobody imagined that billions of smartphones, tablets, laptops, servers, smart devices, and IoT sensors would all need unique addresses.

Today, with over 15 billion internet-connected devices worldwide, we have essentially run out of IPv4 addresses. The last blocks of IPv4 addresses were allocated in 2011. This shortage is known as IPv4 address exhaustion, and it is the primary reason IPv6 was developed.

IPv6 — Internet Protocol Version 6

IPv6 was created specifically to solve the IPv4 address exhaustion problem. It uses a vastly larger address space that can accommodate the growth of the internet for the foreseeable future.

How IPv6 Addresses Work

An IPv6 address is a 128-bit number — four times the length of an IPv4 address. It is written as eight groups of four hexadecimal digits, separated by colons.

  Format:   [group1]:[group2]:[group3]:[group4]:[group5]:[group6]:[group7]:[group8]

  Example:  2001:0db8:85a3:0000:0000:8a2e:0370:7334

  Each group: 4 hexadecimal digits (0000 to ffff)
  Total:      8 groups x 4 hex digits = 32 hex digits = 128 bits

  Simplified: 2001:db8:85a3::8a2e:370:7334
  (Leading zeros in each group can be omitted.
   Consecutive groups of all zeros can be replaced with ::)
        

The Scale of IPv6

With 128 bits, IPv6 provides 2¹²⁸ possible addresses. That is approximately 340 undecillion (340,282,366,920,938,463,463,374,607,431,768,211,456) unique addresses. To put this in perspective, there are enough IPv6 addresses to assign billions of addresses to every grain of sand on Earth. For all practical purposes, IPv6 provides an effectively unlimited supply of addresses.

Why Is IPv6 Adoption Slow?

Despite its advantages, IPv6 adoption has been gradual. Many existing systems and devices only support IPv4, and transitioning an entire network to IPv6 requires significant investment. Technologies like NAT (Network Address Translation) have helped extend the life of IPv4 by allowing many devices to share a single public IPv4 address. However, IPv6 adoption continues to grow steadily, and major companies like Google, Facebook, and Amazon fully support it.

Static vs Dynamic IP Addresses

IP addresses can be assigned to devices in two different ways: statically (permanently) or dynamically (temporarily). The method used depends on the purpose of the device and the needs of the network.

Static IP Addresses

A static IP address is one that is permanently assigned to a device. It never changes, regardless of how many times the device connects or disconnects from the network. Static IPs are manually configured by a network administrator.

Devices that typically use static IP addresses:

• Web servers: A website needs a consistent address so that users (and DNS servers) can always find it
• Email servers: Must be reachable at the same address for reliable mail delivery
• Network printers: So that all computers on the network can always locate the printer
• Routers and gateways: Need a fixed address as the “default gateway” for all devices on the network

Dynamic IP Addresses

A dynamic IP address is one that is automatically assigned to a device each time it connects to the network. The address may change each time the device reconnects. Dynamic IPs are assigned by a DHCP server (Dynamic Host Configuration Protocol).

How DHCP works: When a device connects to a network, it sends a request to the DHCP server. The DHCP server selects an available IP address from its pool of addresses and “leases” it to the device for a set period of time. When the lease expires (or the device disconnects), the address is returned to the pool and can be assigned to a different device.

Devices that typically use dynamic IP addresses:

• Smartphones and tablets: Connect and disconnect frequently from different networks
• Laptops: Move between home, school, and public Wi-Fi networks
• Desktop computers: In most home networks, desktops receive dynamic addresses
• IoT devices: Smart home devices on a home network

Advantages and Disadvantages

Public vs Private IP Addresses

Not all IP addresses are the same. There is an important distinction between public and private IP addresses, and understanding this difference is essential for GCSE Computer Science.

Public IP Addresses

A public IP address is an address that is unique across the entire internet. It is assigned to your network by your ISP (Internet Service Provider) and is used to identify your network on the global internet. No two devices on the internet can have the same public IP address at the same time.

When you visit a website, the web server sees your public IP address as the “return address” for sending the web page data back to you. Your home router typically has one public IP address that represents your entire household on the internet.

Private IP Addresses

A private IP address is an address used within a local area network (LAN) only. Private addresses are not routable on the internet — they cannot be used to communicate directly with devices outside the local network. Multiple different local networks around the world can use the same private address ranges without conflict, because these addresses are never exposed to the public internet.

The following address ranges are reserved for private use:

NAT — Network Address Translation

If private IP addresses cannot be used on the internet, how do devices on a home network access websites and online services? The answer is NAT (Network Address Translation).

NAT is performed by the router. When a device on the local network (e.g., 192.168.1.5) sends data to the internet, the router replaces the private source IP address with its own public IP address before forwarding the data. When the response comes back, the router translates the public address back to the correct private address and delivers the data to the right device. This allows many devices to share a single public IP address.

  Your Phone (192.168.1.5)  ---+
                               |
  Your Laptop (192.168.1.10) --+---> Router ---> Internet ---> Web Server
                               |   (NAT)        (203.0.113.50)
  Smart TV (192.168.1.15)   ---+   Public IP:
                                   86.42.7.201

  Outgoing: Router replaces 192.168.1.5 with 86.42.7.201
  Incoming: Router replaces 86.42.7.201 with 192.168.1.5

  The web server only sees 86.42.7.201 -- it never sees the
  private addresses. All three devices share one public IP.
        

Test Your Knowledge

Try these interactive exercises to check your understanding of IP and MAC addresses. Read each question carefully and think about your answer before clicking.