At this point, your routers have their basic configurations. The next step is to configure their interfaces. This is because routers are not reachable by end devices until the interfaces are configured. There are many different types of interfaces available on Cisco routers. For example, the Cisco ISR 4321 router is equipped with two Gigabit Ethernet interfaces:

  • GigabitEthernet 0/0/0 (G0/0/0)
  • GigabitEthernet 0/0/1 (G0/0/1)

The task to configure a router interface is very similar to a management SVI on a switch. Specifically, it includes issuing the following commands:

  Router(config)# interface type-and-number  
  Router(config-if)# description description-text  
  Router(config-if)# ip address  ipv4-address subnet-mask  
  Router(config-if)# ipv6 address  ipv6-address/prefix-length  
  Router(config-if)# no shutdown

Note: When a router interface is enabled, information messages should be displayed confirming the enabled link.

Although the description command is not required to enable an interface, it is good practice to use it. It can be helpful in troubleshooting on production networks by providing information about the type of network connected. For example, if the interface connects to an ISP or service carrier, the description command would be helpful to enter the third-party connection and contact information.

Note: The description-text is limited to 240 characters.

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.

Note: On inter-router connections where there is no Ethernet switch, both interconnecting interfaces must be configured and enabled.