Addressing

We need a way of identifying computers so data can be directed to the right one, and when that computer responds it knows where the data came from.

Every packet contains a destination and source address.

There’s two ways of identifying a computer on a network:

• IP Addresses
• MAC Addresses

MAC Addresses

When sending data between computers on a LAN we use MAC Addresses. Every Network Interface Card (NIC) has a hard coded unique MAC address.

This address is a 48bit or 64bit binary number, but it is shown in a more human-friendly hexadecimal number.

A device with more than one method of connecting to a network will have multiple unique MAC addresses (one for each connection method).

If there is a situation where two devices had the same MAC address, it would cause a wide range of network errors.

IP Addresses

IP Addresses are needed for communication between different networks. The internet and home networks are based on the IP protocol.

They are either 32bits (IPv4) or 128bits (IPv6) wide. We display IPv4 using denary numbers to make them more user friendly:

IPv4: 51.114.200.99

They can be dynamic or static: 

• Static – A computer gets the same IP address each time it connects to the internet
• Dynamic – A computer gets a different IP address each time it connects to the internet

We mainly use IPv4 addresses, but we have run out of useable addresses.

We have managed by using dynamic addresses and only assigning IP addresses when a device connects to the internet.

Eventually, to continue adding devices to the internet, we will have to (slowly) continue transitioning over to IPv6.

We should never run out of IPv6 addresses: there are enough to give every grain of sand on Earth an address and still have plenty left over!

Every device connected to the internet needs an IP address so that data can be delivered to the right place. There are two versions in use: IPv4 and IPv6. They differ in how many bits they use and in how they are written down.

IPv4

IPv4 addresses are 32-bit numbers. They are written as four decimal numbers separated by dots, and each number is between 0 and 255 because 8 bits can store 256 different values. Four groups of 8 bits give 32 bits in total, so there are 2 to the power of 32 possible IPv4 addresses, which is about 4.3 billion.

For example, 173.42.8.211 is a valid IPv4 address: four decimal numbers, each one 8 bits, joined by dots. As more and more devices came online, IPv4 addresses began to run out, so a larger version was needed.

IPv6

IPv6 addresses are 128-bit numbers. They are written in hexadecimal, using the digits 0 to 9 and the letters a to f, because each hexadecimal digit stands for exactly 4 bits. An IPv6 address has eight groups of four hex digits separated by colons, and each group is 16 bits: 8 groups of 16 bits is 128 bits.

For example, 3f1a:00c8:b45d:7e02:119f:6a3b:00d4:9e50 is an IPv6 address. With 128 bits there are 2 to the power of 128 possible addresses, an enormous number, which means running out of addresses is no longer a problem.

Comparing the two

Every device connected to the Internet needs an IP address so that data can be sent to the right place. An IP address can be static (fixed, so it never changes) or dynamic (it can change).

Static IP addresses stay the same every time the device connects to the Internet, and a network manager sets them up by hand. This is useful for devices that other computers must find reliably, such as a web server that holds a school's website. Because the address never changes, other devices always know where to send their requests.

Dynamic IP addresses are given out automatically and can change. A dynamic IP address may change when a device reconnects to the Internet. For example, each time a smart TV in a cafe reconnects to the Wi-Fi, the network might hand it a different address. Sharing addresses out like this means a network can reuse a smaller pool of them, because not every device is online at the same time.

Comparing the two