To join a network a computer needs the right hardware and two kinds of address. The MAC address is fixed into the network card when it is made; the IP address is given by the network. A router uses them to get data to the right place.
A computer needs a network interface card (NIC) to access a network. Each NIC is given a unique MAC address at the point of manufacture: 48 bits, usually written as 12 hexadecimal digits, made of the manufacturer code and the serial code. An IP address is allocated by the network to identify a device on it; it can be static (stays the same) or dynamic (can change each time the device connects), and is either IPv4 (32 bits) or IPv6 (128 bits). A router sends data to a specific destination on a network, can assign IP addresses, and can connect a local network to the internet.
Fig. 1: a laptop's NIC connects to a router; its MAC address is made of a manufacturer code and a serial code
Section 01
The NIC and the MAC address.
In the lab, look at a device's MAC address and IP address, and see what changes when it joins a different network. The MAC address stays the same; the IP address does not.
NIC: a network interface card is the hardware that lets a device connect to a network, wired or wireless. Without one, the computer cannot access a network.
MAC address: media access control address, a unique identifier given to the NIC at the point of manufacture. Its purpose is to identify the device on a network.
Structure: 48 bits, written as 12 hex digits in 6 pairs, e.g. 00-1A-2B-3C-4D-5E. The first half is the manufacturer code; the second half is the serial code of that device.
Why hex: 12 hex digits are shorter and easier for people to read and write than 48 bits of binary.
Examiner trap
The MAC address belongs to the NIC and is set when it is made. It is not given by the network or the router: that is the IP address.
Section 02
IP addresses.
An IP (internet protocol) address identifies a device on a network so that data can be sent to it. Unlike a MAC address, it is allocated by the network the device joins.
IPv4
IPv6
Size
32 bits
128 bits
Written as
4 denary numbers (each 0 to 255) separated by full stops
8 groups of 4 hex digits separated by colons
Example
192.168.1.15
2001:0db8:85a3:0000:0000:8a2e:0370:7334
Number of addresses
232, about 4.3 billion: not enough for every device
2128: far more than will ever be needed
Static IP address: stays the same every time the device connects. Used for servers, such as a web server, that must always be found at the same address.
Dynamic IP address: allocated by the network each time the device connects, so it can change. Used for most home devices; addresses can be reused when devices leave.
Worked example Valid or not?
Is 192.168.300.4 a valid IPv4 address?
IPv4 has 4 numbers, each stored in 8 bits.
8 bits can only hold 0 to 255.
300 is greater than 255.
Answer: Not valid
Your turn
Why was IPv6 introduced?
IPv4 has only 232 (about 4.3 billion) addresses, which is not enough for all the devices now connected; IPv6's 128 bits give vastly more addresses.
Stage 1 · Learn
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What hardware does a computer need to access a network?
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In the lab, what happens to a device's MAC address when it joins a different network?
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Which two parts make up a MAC address?
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How many bits are in an IPv6 address?
Section 03
The router.
A home router sits between the devices in the house and the internet. Its jobs are the three in the syllabus.
Sends data to a specific destination: it reads the destination IP address of each packet and forwards it towards the correct device or network.
Assigns IP addresses: it can give each device that joins the local network a (dynamic) IP address.
Connects a local network to the internet: it links the LAN in a home or school to the wider internet.
MAC address
IP address
Given by
The manufacturer, at the point of manufacture
The network (for example the router)
Can it change?
No, it is fixed to the NIC
Yes if dynamic; no if static
Written as
12 hex digits (48 bits)
IPv4: 4 denary numbers; IPv6: 8 hex groups
Examiner trap
A router does more than "connect to the internet". For full marks, give its specific roles: forwarding data to a destination using IP addresses and assigning IP addresses.
Stage 2 · Exam
Exam-style questions
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Which is a valid IPv4 address?
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What is a dynamic IP address?
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Which is a role of a router?
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Why are MAC addresses usually written in hexadecimal?
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