Routers and gateways

## Gateway — the "exit door" When a computer wants to send to an address on another network, it hands its packet to the **default gateway**. The gateway is the address of the router's interface that faces that network. ``` 192.168.1.0/24 192.168.2.0/24 PC1 192.168.1.10 ─┐ ┌─ PC3 192.168.2.10 SW1 ── R1 ── SW2 PC2 192.168.1.11 ─┘ .1 .1 └─ PC4 192.168.2.11 ``` - One interface of R1 is `192.168.1.1/24`, the other is `192.168.2.1/24`. - Gateway for PC1 and PC2: `192.168.1.1` - Gateway for PC3 and PC4: `192.168.2.1` ## Common mistakes | Symptom | Cause | |---|---| | Ping to classmates works, but no internet | Gateway wrong / not set | | "IP conflict" | Two devices have the same IP | | Port light doesn't turn on | Cable or plug badly crimped | | On the same switch but ping fails | Given an address from a different network | > 🎮 **Network lab → Tasks 7, 8** > > 🧮 Problems: **Networks → Level 9**