The big idea: An IP address identifies a device on a network, so traffic can be sent to it.
Routers read the destination address and decide where to forward each packet — without addresses there is no routing at all.
Three questions, three pairs: How long is the address? IPv4 or IPv6. Can the internet reach it? Public or private. Does it change? Static or dynamic.
The three are independent: an address can be private, dynamic and IPv4 all at once.
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IPv4
- 32 bits, written as four numbers: 192.168.1.14
- About 4 billion possible addresses
- Ran out — there are more connected devices than addresses
- Still overwhelmingly what local networks use
IPv6
- 128 bits, written as groups of hex digits
- So many addresses the supply is effectively unlimited
- Designed to remove the need for workarounds
- Adoption has been slow, so both are in use together
Why 4 billion was not enough: Four billion sounds vast until every phone, laptop, television, doorbell and car wants one.
Running out is the reason the next two ideas exist.
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Public addresses
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Private addresses
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NAT — one public address for everyone
4
Static and dynamic
NAT also hides the inside: Because private addresses are not routable, nothing on the internet can address an internal machine directly — it can only reply to a conversation that machine started.
That is a real security benefit, though a firewall is still needed.
How this is tested — you must connect the address type to what the device needs to do. It comes up two ways:
Paper 1 Section A
- Describe or distinguish the address types, 2-4 marks
- Explain the purpose of NAT
- Say which type a stated device needs
Paper 1 Section B — case study
- Explain the addressing in the case study's network
- Justify static or dynamic for their devices
The classic trap: Treating private and dynamic as the same thing. They answer different questions: private means not reachable from the internet; dynamic means it may change. An address can be one, both, or neither.
IB-style questionExplain[4 marks]
A company has thirty computers and one web server, but only one public IP address. Explain how it can put all of them on the internet.
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