A postcode for every device
A postcode has two jobs. The first half finds your area. The second half finds your street.
An IPv4 address works the same way. One part names the group a device is in. The other part names the device itself.
The subnet mask tells you where one part stops and the other starts.
Key words
| Word | What it means |
|---|---|
| Network | computers and devices joined together so they can share data |
| Protocol | a set of rules that devices follow to talk to each other |
| Packet | a small piece of data sent over a network |
| IPv4 | the older version of the Internet Protocol, with 32-bit addresses |
| IP address | the number that names a device on a network |
| Octet | one of the four numbers in an IPv4 address, each one byte |
| Subnet | a smaller network inside a larger one |
| Subnet mask | a number that shows which part of an address is the network |
| Network part | the part of an address that names the network |
| Host part | the part of an address that names the device |
| Private address | an address for use inside one organisation, not on the internet |
| Static address | an address typed in by hand that does not change |
| Dynamic address | an address handed out automatically, which may change |
| Router | a device that passes packets between networks |
The cells students fill in are left blank in this preview.
By the end of this lesson
Note
I can read an IPv4 address and subnet mask, say which part is the network, and choose a sensible addressing scheme.
Starter
Have a go
Starter
3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.
What an IPv4 address looks like
An IPv4 address is 32 bits. We write it as four numbers, called octets, with dots between: 192.168.1.20. Each octet is 8 bits, so it runs from 0 to 255.
Part of the address is the network part. The rest is the host part. All devices in one network share the same network part.
The subnet mask picks the network part
| Subnet mask | Slash form | Network part | Host part |
|---|---|---|---|
| 255.0.0.0 | /8 | First octet | Last three octets |
| 255.255.0.0 | /16 | First two octets | Last two octets |
| 255.255.255.0 | /24 | First three octets | Last octet |
The cells students fill in are left blank in this preview.
Worked example: finding the network
| Address | Mask | Network part stays | Host part becomes 0 | Network address |
|---|---|---|---|---|
| 192.168.1.200 | /24 | 192.168.1 | 200 becomes 0 | 192.168.1.0 |
| 10.4.7.9 | /16 | 10.4 | 7.9 becomes 0.0 | 10.4.0.0 |
| 10.0.1.2 | /24 | 10.0.1 | 2 becomes 0 | 10.0.1.0 |
The cells students fill in are left blank in this preview.
Check
Have a go
Check
3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.