One distinguishing feature between switches and routers is the type of interfaces supported by each. For example, Layer 2 switches support LANs and, therefore, have multiple FastEthernet or Gigabit Ethernet ports.
Routers support LANs and WANs and can interconnect different types of networks; therefore, they support many types of interfaces. For example, G2 ISRs have one or two integrated Gigabit Ethernet interfaces and High-Speed WAN Interface Card (HWIC) slots to accommodate other types of network interfaces, including serial, DSL, and cable interfaces.
To be available, an interface must be:
- If using IPv4, configured with an address and a subnet mask - Use the ip address ip-address subnet-mask interface configuration command.
- Activated - By default, LAN and WAN interfaces are not activated (shutdown). To enable an interface, it must be activated using the no shutdown command. (This is similar to powering on the interface.) The interface must also be connected to another device (a hub, a switch, or another router) for the physical layer to be active.
Optionally, the interface could also be configured with a short description. It is good practice to configure a description on each interface. The description text is limited to 240 characters. On production networks, a description can be helpful in troubleshooting by providing information about the type of network to which the interface is connected. If the interface connects to an ISP or service carrier, it is helpful to enter the third party connection and contact information.
Depending on the type of interface, additional parameters may be required. For example, in the lab environment, the serial interface connecting to the serial cable end labeled DCE must be configured with the clock rate command.
Note: Accidentally using the clock rate command on a DTE interface generates a %Error: This command applies only to DCE interface message.
Figures 1 through 3 provide examples of configuring the router interfaces of R1.
Use the Syntax Checker in Figure 4 to configure router R2.