Interfaces on an IOS device

Cisco uses the term interface to refer to physical ports on an IOS device. Interfaces can be configured with different settings, depending on the type of the interface and whether you are configuring an interface on a router or on a switch. For example, the Cisco 7201 Router has four GE physical ports (image source: Cisco):

cisco 7201 router

To display the router interfaces in IOS, use the show ip int brief command from the privileged exec mode:

show ip interface brief

Consider the output for the Fa0/0 interface:

show ip interface fa

Here is a brief description of each column:

  • Interface – displays the type of the interface, in this case Fast Ethernet 0/0. The first zero specifies the physical slot on the router, while the second specifies the port number.
  • IP-Address – displays the interface’s IP address.
  • OK?YES in this column signifies that the IP address is currently valid.
  • Methodmanual means that the interface has been manually configured. DHCP in this column means that the interface has been configured using DHCP.
  • Statusup indicates that the interface is administratively up.
  • Protocolup indicates that the interface is operational.

To configure a specific interface, use the interface TYPE SLOT/PORT command from the global config mode. This puts us in the interface submode, where we can configure various interface options:

interface command

In the example above you can see that we’ve configured the speed of the interface.

By default, all ports on a Cisco switch are up and running as soon as you power-on the device. This means that all you need is to connect your devices and the switch and you are good to go. This isn’t the case with Cisco routers, however. You need to manually enable each interface on a router with the no shutdown interface mode command:

no shutdown command

Geek University 2022