CCNA 640-802 Lab - Connect, configure, and verify operation status of a device interface

Exam: 640-802

Exam Objective: Connect, configure, and verify operation status of a device interface

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Contents

• Introduction
• Technology Background
• Lab Scenario
• Lab Objectives
• Lab Solution

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Introduction

Two types of interfaces are supported on Cisco Routers: Physical and Virtual interfaces. The types of physical interfaces on a device depend on its interface processors or port adapters. The virtual interfaces that Cisco routers support include subinterfaces and IP tunnels.
Some of the interface types supported by Cisco routers are:

• Asynchronous serial
• ATM
• Dialer
• Ethernet
• Fast Ethernet
• FDDI
• High-Speed Serial Interface (HSSI)
• ISDN BRI
• ISDN PRI
• Loopback
• Null
• Synchronous serial
• Token Ring
• Tunnel

Technology Background

Interface configuration is one of the most important parts of configuring a router because without correct configuration the router will not communicate with the network and would not be able to perform any of its function. You can configure Network Layer Address, Layer 2 Protocol, bandwidth and other various things on the interface.
Different routers number their interfaces differently. Some older routers such as the 2500 series number their interfaces as <type><number>. For example: ethernet0 or serial1. New modular routers number their interface as <type> <slot>/<port>. For example: Serial 0/0 or Fastethernet 1/0. This is because they have slots where modules containing interfaces can be added.
To know what interfaces exist on a router; you can use the "show interface" or "show ip interface brief" command. This is what you would see:
Router#show ip interface brief
Interface                  IP-Address      OK? Method Status                Protocol
FastEthernet0/0            unassigned      YES manual administratively down down    
FastEthernet0/1            unassigned      YES manual administratively down down    
This tells us that this Router has to FastEthernet interfaces in slot0.
To enter the interface configuration mode use the "interface <type> <slot>/<number>" global configuration command. In the Router mentioned above we have to use the "interface Fastethernet0/0" or "interface fa0/0" command.
By default all interfaces are in "administratively down" status. This means that the interface has been shutdown by configuration. You can bring up the interface using the "no shutdown" interface command.
At this stage the interface is ready for Layer 2 and Layer 3 configuration. Some interfaces like the Serial interface support multiple Layer 2 protocols. On Cisco Routers Serial interfaces support HDLC (default), PPP and Frame Replay protocols at Layer 2. Layer 2 protocol can be changed using the "encapsulation <protocol>" command at the interface level.
Most interfaces support multiple Layer 3 protocols such as IPv4, IPv6, IPX, AppleTalk etc depending on the Layer 2 protocol. IP is the most used Layer 3 protocol and that is what Cisco requires you to know for CCNA.
IP address can be configured on an interface using the "ip address <address> <subnet mask>" command. An interface can have two IP addresses belonging to different subnets. The second IP address can be used using the "ip address <address> <subnet mask> secondary" command. Without the secondary keyword, the command will override previously configured address. If you want to the interface to get an IP address using DHCP then the "ip address dhcp" command can be used.
Special care must be taken with Serial Interfaces because by default these interfaces are configured for Data Terminal Equipment (DTE). This means that they receive clocking from a DCE connected via a CSU/DSU. In the lab when you connect two Routers back-to-back using a Serial cable, you will need to configure one of the interfaces to provide clocking as a DCE. This can be done using the "clock rate <speed in bits>" command.
On all interfaces you can add a description so that you remember where the link connects to in future. This can be done using the "description <text>" command.
Another important interface command is the bandwidth command. It has nothing to do with how data is transferred but the configured bandwidth is used by routing protocols such as EIGRP to calculate the best path to a destination. The significance of it can be realized by understanding that by default the bandwidth of a Serial Interface is 1.544MBps. If you have a 128Kbps connection terminating on the Serial link then the Routing protocol is miscalculating the metrics of the path by using 1.544Mpbs instead of 128Kbps. In such situations correcting the bandwidth is essential. Bandwidth is specified in Kilobits.

Lab Scenario

We need help in initial configuration of routers in our network. Your task is to configure the following in the network shown in Figure 1:

• Configure the Interface with IP information shown. Fa0/0 of RouterA must belong to both the networks
• RouterA's s0/0 interface should be configured such that any Cisco Router can connect to it back-to-back using a serial interface. No additional configuration apart from IP address should be required on any device connecting to RouterA's s0/0 interface in such manner.
• EIGRP should always take the bandwidth of RouterA's s0/0 interface as 512KBps

Figure 1

Lab Objectives

• Configure IP Addresses on the shown interfaces. RouterA's fa0/0 interface will have a secondary address also
• Clock rate needs to be configured on Serial1/0 interface of RouterA
• Bandwidth needs to be configured on Serial1/0 interface of RouterA

Lab Solution

IP address configuration on all the Routers will be done using the following commands:
RouterA(config)#interface s1/0
RouterA(config-if)#ip address 192.168.3.1 255.255.255.0
RouterA(config-if)#no shut
RouterA(config)#interface fa0/0
RouterA(config-if)#ip address 192.168.1.1 255.255.255.0
RouterA(config-if)#ip address 192.168.2.1 255.255.255.0 secondary
RouterA(config-if)#no shut
RouterB(config)#interface fa0/0
RouterB(config-if)#ip address 192.168.1.2 255.255.255.0
RouterB(config-if)#no shut
RouterB(config)#interface fa0/0
RouterB(config-if)#ip address 192.168.2.2 255.255.255.0
RouterB(config-if)#no shut
We need to configure the clock rate on RotuerA's s0/0 interface since it would be connecting back-to-back with other Cisco Routers which will be in DTE mode:
RouterA(config)#interface s1/0
RouterA(config-if)#clock rate 512000

Finally we need to configure the bandwidth on RouterA's s0/0 interface so that EIGRP uses 512Kbps to calculate the route metrics:
RouterA(config)#interface s1/0
RouterA(config-if)#bandwidth 512

We can verify the configuration using the "show ip interface brief" command:
RouterA#show ip interface brief
Interface                  IP-Address      OK? Method Status Protocol
FastEthernet0/0    192.168.1.1      YES manual up        up
Serial1/0               192.168.3.1      YES manual up        up
RouterB#show ip interface brief
Interface                  IP-Address      OK? Method Status Protocol
FastEthernet0/0    192.168.1.2      YES manual up        up
RouterC#show ip interface brief
Interface                  IP-Address      OK? Method Status Protocol
FastEthernet0/0    192.168.2.2      YES manual up        up
References:

Cisco IOS Interface Configuration�Guide - Configuring LAN Interfaces
http://www.cisco.com/en/US/docs/ios/12_2/interface/configuration/guide/icflanin.html#wp1012559