Necessary for hosts on different networks to communicate
Default gateway
Router's interface port for all data traffic to be re-directed to if the destination of the IP packet is outside the network
The interface port of a router that is connected to a LAN acts as the default gateway for that LAN
The interface of the router that is connected to a LAN must be in the same network as the hosts in that LAN, else the IP packet from the hosts cannot reach that interface
All the hosts in a LAN must be configured to use the router's interface as the default gateway
When the destination host is in the same network
Default gateway is not needed
When the destination host is outside the network
Default gateway is needed
Router
Has a Console Port for configuration
Has an Auxiliary Port for remote configuration
Has Ethernet ports for connection to LANs
Has Serial ports for connection to WANs
Connecting LANs to WAN
1. LAN connected to Ethernet port of router
2. WAN connected to Serial port of router
Console port is for connection to COM port of computer acting as terminal
Auxiliary port is for connection to modem
Black solid lines represent straight-through Ethernet cable, red line represents a serial connection
