Network hardware

Computer Science · Hardware. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.

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The idea

To join a network, a device needs a network interface card (NIC). Every NIC is given a MAC address when it is made.

A MAC address identifies the device itself. It is set by the manufacturer and normally does not change. An IP address identifies where the device is on a network. It is given by the network, so it can change when the device joins a different network.

A router joins networks together, for example a home network to the internet. It reads the destination IP address in each packet and sends the packet on towards the correct network. It can also give IP addresses to the devices on its own network.

Rules to remember

MAC address: 48 bits, written as 6 pairs of hex digits, e.g. 00:1A:2B:3C:4D:5E
First 3 pairs of a MAC address = manufacturer code; last 3 pairs = serial number of the device
IPv4: 32 bits, 4 denary numbers from 0 to 255 separated by dots, e.g. 192.168.0.12
IPv6: 128 bits, 8 groups of hex digits separated by colons. Introduced because IPv4 was running out of addresses
Static IP address: stays the same; used for servers so they can always be found
Dynamic IP address: can change each time the device connects; given out automatically

Common mistake

Students mix up the two addresses. MAC is from the manufacturer and stays with the device; IP is from the network and can change.

Worked example

A student uses the same laptop on the home network and then on the school network. Which address stays the same and which changes?

The MAC address belongs to the laptop's NIC and was set when it was made, so it stays the same.
The IP address is given by the network the laptop joins.
The school network is a different network, so it gives the laptop a different IP address.

Answer: The MAC address stays the same; the IP address changes.

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