A parcel with no map
A courier van arrives at a depot with a parcel for the next town. The worker checks a list on the wall. It says which road to take for each town.
A router (a device that sends data on its way) does the same job. It checks a list for every packet (a small piece of data) it gets.
By the end of this lesson
Note
I can read a routing table and say where a packet will go next.
Key words
| Word | What it means | Example |
|---|---|---|
| Network | computers joined so they can share data | |
| Router | a device that passes packets between networks | |
| Packet | a small piece of data sent over a network | |
| IP address | the number that names a device on a network | 10.0.1.2 |
| Routing table | the list a router uses to choose where a packet goes | |
| Network ID | the part of an address that names the network | 10.0.3.0 |
| Subnet mask | numbers that show how much of an address is the network ID | 255.255.255.0 |
| Next hop | the next router on the way to the network | |
| Interface | the port or connection a packet leaves from | eth0 |
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.
A routing table is a list of roads
A router keeps a routing table. Each line is called a route.
A route says: to reach this network, send the packet this way. The router finds the line that matches the packet's destination. Then it sends the packet on.
What each column means
| Column | What it holds | Example |
|---|---|---|
| Network ID | The network the route is for | `10.0.3.0` |
| Subnet mask | How much of an address is the network ID | `255.255.255.0` |
| Next hop | The router to send the packet to next | `10.0.12.2` |
| Interface | The port the packet leaves from | `to-r2` |
The cells students fill in are left blank in this preview.
The mask shows the network part
An address has two parts. One part names the network. The other names the device.
The subnet mask shows where the split is. With mask 255.255.255.0, the first three numbers are the network. So 10.0.3.2 is device 2 on network 10.0.3.0.
You may also see the short form /24. It means the same as 255.255.255.0.
Check
Have a go
Check
3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.