For routers to be reachable, the in-band router interfaces must be configured. There are many different types of interfaces available on Cisco routers. In this example, the Cisco 1941 router is equipped with:
Two Gigabit Ethernet interfaces – GigabitEthernet 0/0 (G0/0) and GigabitEthernet 0/1 (G0/1)
A serial WAN interface card (WIC) consisting of two interfaces – Serial 0/0/0 (S0/0/0) and Serial 0/0/1 (S0/0/1)
Notice how they are very similar to configuring a management SVI on a switch.
Although not required, it is good practice to configure a description on each interface to help document the network information. 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 that the interface is connected to and if there are any other routers on that network. If the interface connects to an ISP or service carrier, it is helpful to enter the third party connection and contact information.
Using the no shutdown command activates the interface and is similar to powering on the interface. The interface must also be connected to another device, such as a switch or a router, for the physical layer to be active.