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How to Configure Cisco Router Interfaces (FastEthernet and Serial Interfaces)-Cisco Certifications

Configuring and checking router interfaces are the main tasks of a network engineer, whether it’s the initial configuration of a router or trouble shooting the network connectivity.

In this tutorial you will learn:

  1. How to configure serial interface of a Cisco router.
  2. How to configure Fast Ethernet interface of a Cisco Router.
  3. And How to Enable an interface of Cisco router.

There is a command which displays all the IP interfaces, which is helpful in troubleshooting and knowing the IP address used on a specific interface.

Show ip interface brief   // this is an enable/privileged mode command.

You have to be at the enable mode/privileged mode for executing this command, this command can also be used to know if an interface is enabled or administratively down.

How to find Cisco router IP addresses:

IP addresses of each functional and configured interface of a router must be different, “show ip interface brief” command will display all the configured interfaces along with their assigned ip addresses. Open your routers command line interface.

UpaaeRouter1> enable                                 // go to enable mode/ privileged mode.

UpaaeRouter1# show ip interface brief  // display all the ip interface of this router

config interface 1

How to configure Ethernet Interface on Cisco Router:

For configuring any interface of a router you should be at global configuration mode.

Assuming you are at user exe mode.

UpaaeRouter1> enable                                                         // entering to enable/privileged mode

UpaaeRouter1# configure terminal                               // entering to global configuration mode

UpaaeRouter1(config)# interface fastethernet 0/0    //  0/0 specifies the port number

UpaaeRouter1(config-if)# ip address 10.1.1.5   255.0.0.0

config interface 2

Confirm if ip address is assigned successfully.

Switch to enable mode, type show ip interface brief” command and press enter, just like the screenshot below.

config interface 3

How to configure serial interface on cisco router:

Before executing the commands for setting the ip address for serial interface you need to be at the line configuration mode of that specific interface.

For configuring IP Address for any interface you must be in global configuration mode and then enter to the line configuration mode of required interface. In this case we are going to set ip address for serial 0/0/0 interface.  Assuming you are at user exe mode.

UpaaeRouter1> enable                                                                  // entering enable/privileged mode

UpaaeRouter1# configure terminal                          // entering global configuration mode

UpaaeRouter1(config)# interface serial 0/0/0        //  0/0/0 specifies the port number

UpaaeRouter1(config-if)# ip address 192.168.1.5   255.255.255.0

config interface 5

Confirming if ip address is assigned successfully.

config interface 6

As you can see that serial interface is properly configured but it is still administratively down, in order to get any interface of cisco router working we need to enable that specific interface.

How to Enable Cisco Router Interface:

By default all of the Cisco router’s interfaces are in down state for security sake, if you want to enable any interface you need to be at the line interface mode, in this example we will enable serial 0/0/0 interface. no shutdown is the command for enabling serial interface.

UpaaeRouter1> enable                                                                  // entering enable/privileged mode

UpaaeRouter1# configure terminal                          // entering global configuration mode

UpaaeRouter1(config)# interface serial 0/0/0        //  0/0/0 specifies the port number

UpaaeRouter1(config-if)# no shutdown            // command for enabling cisco router interface

That’s it, we hope you enjoyed and learned from this tutorial.

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