Model local links and routed networks

Model local links and routed networks — guided practice

Distinguish a switch’s local-link role from a router’s network-to-network role.

Use network-notes.md or paper. All addresses and outputs are fictional. Room A has laptop A at 192.0.2.10/24, printer P at 192.0.2.20/24 and a switch. Router R has A-side 192.0.2.1/24 and B-side 198.51.100.1/24. Room B has server S at 198.51.100.20/24 and its switch. A uses default gateway 192.0.2.1. A supplied DNS record maps catalog.example to 198.51.100.20. For this /24 exercise, matching first three octets means same subnet. No live network access, capture, scanning or device configuration is needed.

1. 1. Draw the local room

   Draw A and P connected through Room A’s switch.

   You should see: Both endpoints belong to 192.0.2.0/24.

   Local communication does not require a route to another subnet.

2. 2. Add the second room

   Draw S through Room B’s switch to R’s B-side.

   You should see: S belongs to 198.51.100.0/24.

   The two room labels correspond to two distinct IP subnets here.

3. 3. Connect the router

   Connect R’s A-side to the first switch and B-side to the second.

   You should see: R has an interface on each subnet.

   A router must have a path into each network it connects.

4. 4. Trace two destinations

   Write A->switch->P and A->switch->R->switch->S.

   You should see: The printer path is local; the server path crosses R.

   Topology determines the next forwarding decision.