Role of routers in a WAN
Connecting router LAN interfaces
This page will teach you how to connect LAN interfaces.
A router is usually connected to a LAN through an Ethernet or Fast Ethernet interface. The router is a host that communicates with the LAN through a hub or a switch. A straight-through cable is used to make this connection. A 10BASE-TX or 100BASE-TX router interface requires Category 5, or better, unshielded twisted-pair (UTP) cable, regardless of the router type.
In some cases the Ethernet connection of the router is connected directly to the computer or to another router. For this type of connection, a crossover cable is required.
The correct interface must be used. If the wrong interface is connected, it can damage the router or other networking devices. Many different types of connections use the same style of connector. For example Ethernet, ISDN BRI, console, AUX, integrated CSU/DSU, and Token Ring interfaces use the same eight-pin connector, which is RJ-45, RJ-48, or RJ-49.
Cisco uses a color code scheme to help distinguish the connections that are used on a router.
The next page will discuss WAN interface connections.
More Cisco material can be found here