Interface IP Address Configuration

Knowing how to assigning IP Addresses to Cisco hardware is a deal breaker when it comes to the CCNA and any networking job dream you have. This lab will discuss how to assign IP addresses to specific interfaces on Cisco Routers and/or Switches.

Real World Application

As a Cisco Network Engineer, you will be required to know how to configure an IP Address on different types of interfaces. After all, what good is a Cisco router if it cannot route?

Assigning an IP address to an interface is the foundational requirement for all Cisco devices as Cisco devices are networking devices.

You can however assign multiple IPv4 addresses to a single interface but there is one catch. When dealing with dynamic routing protocols, advertisements are sourced from the primary address. Secondary addresses are commonly used during IP address migrations such as moving from a Class C to a Class A address scheme.

>Lab Prerequisites

  • If you’re using GNS3 than load the Stub Area Networking GNS3 topology than Router 1.
  • Establish a console session with Router 1.

Lab Objectives

  • Configure the Primary IP Address of 10.234.51.254/24 on interface FastEthernet0/0
  • Configure a Secondary IP Address of 172.27.48.254/24 on Interface FastEthernet0/0
  • Activate the FastEthernet0/0 Interface.
  • Verify your configuration changes via the running-configuration.

Lab Instruction

Configuring an IP address on a Cisco router and/or switch is a very common task and you’re required know how to do it without referencing any documentation as a CCNA.

To get started, navigate your way into Global configuration mode as shown below;

Router con0 is now available



Press RETURN to get started.



Router>enable
Password: 
Router#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Router(config)#

Step 1. – Configure the IP address 10.234.51.254 on interface FastEthernet0/0. In order to to this configuration you’ll need to place yourself into FastEthernet0/0 interface configuration mode as shown below;

To view the available interfaces for configuration execute the interface ? from global configuration mode.

Router(config)#interface FastEthernet 0/0
Router(config-if)#

Once in interface configuration mode you use the command syntax ip address n.n.n.h s.s.s.m; to complete the first lab objective we’ll need to execute the ip address 10.234.51.254 255.255.255.0 from the FastEthernet0/0 interface configuration mode as shown below;

Router(config-if)#ip address 10.234.51.254 255.255.255.0
Router(config-if)#

Step 2. – Configure a Secondary IP Address of 172.27.48.254/24 on Interface FastEthernet0/0

As noted in the beginning of the lab, secondary IP addresses are commonly used during network re-ip migrations. Using secondary IP Addresses in production as a architectural design is not recommended by Cisco. To complete the second objective of this lab you’ll need to issue the ip adddress command again with the correct address and just add the word secondary to the end of the command syntax.

Router(config-if)#ip address 172.27.48.254 255.255.255.0 secondary
Router(config-if)#

Step 3. – Activate the FastEthernet0/0 Interface. By default, all interfaces on a Cisco router are placed in “Administratively Down”. To bring an interface up, issue the no shutdown command.

Router(config-if)#no shutdown
Router(config-if)#
%LINK-3-UPDOWN: Interface FastEthernet0/0, changed state to up
%LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/0, changed state to up
Router(config-if)#

Step 4. – Verify your configuration changes via the running-configuration.

To verify your configuration changes, exit the interface configuration mode to privileged mode by pressing CTRL + Z and executing the command show run interface FastEthernet 0/0

Router(config-if)#^Z
%SYS-5-CONFIG_I: Configured from console by console
Router#show run interface FastEthernet 0/0
Building configuration...

Current configuration : 148 bytes
!
interface FastEthernet0/0
 ip address 172.27.48.254 255.255.255.0 secondary
 ip address 10.234.51.254 255.255.255.0
 duplex auto
 speed auto
end

Router#
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