1. TCP/IP routing simulation

2. TCP/IP routing
When information is sent over a large network (such as the internet), how does it know which way to go?
The answer lies in the routing table.

3. Routing tables
Each device keeps a table of information about all of the devices that are connected to it.
This table links each device’s IP address (such as ) with its MAC address (such as 1f:e4:87:ad:54:20).
Devices can only send data to devices that they know the MAC address of.

4. Default gateway
So, how does this help us to send data over the internet? If a device can only send data to its nearest connections, how does it get all the way across the world?
The answer is relatively simple – each device has a default gateway – the place where data will be sent if the location of the final destination is unknown.

5. Simulation time!
As a class, we’re now going to simulate how this routing takes place.
You’ll be given a routing table.
At the top of this sheet is your IP address.
Your first task will be to discover who you’re connected to.
Your second task will be to send someone a message.

6. Discovering your connections
Simply find all of the people in the room who have an IP address that’s listed in your routing table.
Write their names in the second column.
Once you’ve finished this, it’ll be time to send a message.

7. Sending a message
In a minute, I’ll put on the board a list of all of the IP addresses in the class.
Choose one that isn’t on your routing table, and write it at the top of your message.
Underneath, write them a friendly message.
Then follow the instructions under your routing table where it says Sending the messages.

8. 15 addresses

9. 24 addresses

10. 32 addresses

11. How this simulation relates to real life
Your names were equivalent to a computer’s MAC address. MAC addresses are required in order for data to be sent over a connection, which is the fundamental basis of networking. Every networked device has one MAC address for each connection it can make (so if you can plug in a cable and use wi-fi, your device will have two MAC addresses)
Extension questions:
What do MAC addresses typically look like?
What about IP addresses?
What would happen if you tried to send data to a non-existent IP address?
How many hops did a message take? How is this number tracked in real life?

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