One big room or four small ones?
An office has one big open room. The guests, the staff and the finance team all sit together and can see each other's papers.
Now put up walls. Each group has its own room, and a door that you can lock. A network (computers and devices joined together) split into parts works the same way.
By the end of this lesson
Note
I can split one address range into subnets that are the right size for each group.
Key words
| Word | What it means | Example |
|---|---|---|
| Network | computers and devices joined together so they can share data | |
| Router | a device that passes messages from one network to another | |
| Subnet | a smaller network cut out of a bigger address range | |
| Prefix | the number after a slash that says how much of the address names the network | /26 |
| Usable address | an address a device can have, not counting the first and last | |
| Segmentation | splitting a network into parts so one part cannot freely reach another | |
| Scalability | room for the network to grow without a rebuild |
The cells students fill in are left blank in this preview.
Starter
Have a go
Starter
3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.
This is practice
Important
The real design task gives you a brief and its own needs. The firm here is invented. Learn the method, then apply it to the numbers in your real brief.
Worked example: how big is each size?
| Prefix | Addresses | Usable addresses | Fits about |
|---|---|---|---|
| /24 | 256 | 254 | A large floor |
| /25 | 128 | 126 | A big team |
| /26 | 64 | 62 | A department |
| /27 | 32 | 30 | A small team |
| /28 | 16 | 14 | A server room |
| /29 | 8 | 6 | A few devices |
| /30 | 4 | 2 | One link between two routers |
The cells students fill in are left blank in this preview.
Each step down halves the room
Add 1 to the prefix and the network has half as many addresses. /24 has 256. /25 has 128. /26 has 64.
Two addresses in every network are not for devices. The first names the network. The last is the broadcast address, used to talk to everyone. So take 2 away: /26 has 64 minus 2, which is 62.
Check
Have a go
Check
3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.