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Lab 9 EIGRP Configuration and Operation This CCNA Video Mentor lab shows how to configure EIGRP in an internetwork having one Class B network that uses variable-length subnet masks (VLSM). The objectives of this lab are as follows: ■

Configure the EIGRP network command

■

Confirm on which interfaces a router has enabled EIGRP

■

Interpret the show ip route command output when VLSM are used

Scenario This lab contains two main steps, as follows: Step 1.

Configure EIGRP in a network that uses only subnets of the Class B network 172.22.0.0

Step 2.

Discover the impact when a router does not enable EIGRP on an interface

Initial Configurations Examples 9-1 through 9-3 show the pertinent initial configurations of routers R1, R2, and R3 in the lab video. Note that this lab begins with these three routers having the correct IP addresses configured, but only router R2 has been configured for EIGRP. As usual, the parts of the configurations not relevant to this lab have been omitted. Example 9-1

Initial Configuration for R1

hostname R1 ! interface FastEthernet 0/0 ip address 172.22.11.1 255.255.255.128 ! interface serial 0/1/0 ip address 172.22.112.101 255.255.255.252 clock rate 1536000 ! interface serial 0/1/1 ip address 172.22.113.209 255.255.255.252 clock rate 1536000

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Example 9-2

Initial Configuration for R2

hostname R2 ! interface FastEthernet 0/0 ip address 172.22.12.202 255.255.255.192 ! interface serial 0/1/0 ip address 172.22.112.102 255.255.255.252 ! interface serial 0/1/1 ip address 172.22.123.97 255.255.255.252 ! router eigrp 1 network 172.22.0.0

Example 9-3

Initial Configuration for R3

hostname R3 ! interface FastEthernet 0/0 ip address 172.22.13.103 255.255.255.224 ! interface serial 0/1/0 ip address 172.22.123.98 255.255.255.252 clock rate 1536000 ! interface serial 0/1/1 ip address 172.22.113.210 255.255.255.252

Ending Configurations This lab does not change any of the initial configurations in routers R1, R2, or R3. However, it does add to the configurations of R1 and R3, as shown in Examples 9-4 and 9-5. Example 9-4

Configuration Added to R1 During the Lab

router eigrp 1 network 172.22.0.0

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Example 9-5

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Configuration Added to R3 During the Lab

router eigrp 1 network 172.22.113.0 0.0.0.255 network 172.22.123.0 0.0.0.255 network 172.22.13.0 0.0.0.255

Video Presentation Reference This video includes several figures that contain the same images used in the lab video. Because the video is organized into two separate steps, the reference materials have been organized into two separate sections. Each section simply lists these figures and tables for reference.

Step 1 Reference Figure 9-1

Three Routers, Six Subnets of Class B Network 172.22.0.0     

    



    

    

    



    

    

    

         

    



    

Table 9-1 lists the subnets shown in Figure 9-1. Table 9-1

Four Key Internet Layer Protocols

Location

Subnet Number

Range of IP Addresses

Subnet Broadcast Address

R1 LAN

172.22.11.0/25

172.22.11.1–172.22.11.126

172.22.11.127

R2 LAN

172.22.12.192/26

172.22.12.193–172.22.12.254

172.22.12.255

R3 LAN

172.22.13.96/27

172.22.13.97–172.22.13.126

172.22.13.127

R1-R2 Serial

172.22.112.100/30

172.22.112.101–172.22.112.102

172.22.112.103

R1-R3 Serial

172.22.113.208/30

172.22.113.209–172.22.113.210

172.22.113.211

R2-R3 Serial

172.22.123.96/30

172.22.123.97–172.22.123.98

172.22.123.99

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Figure 9-2

Subnet Reference for Step 1

   







         







 



        



  

Figure 9-3



  

The Original Format of the EIGRP network Command

network

The network command

network-number

Class A, B, or C network number Tells router to “do EIGRP” on all interfaces in that network “Doing EIGRP” on an interface means: 1. Send EIGRP messages 2. Listen for EIGRP messages 3. Advertise about the subnet connected to the interface

Figure 9-4

The Newer Format of the EIGRP network Command

network

address

wildcard-mask

The network command

Any dotted decimal number, typically an IP address or subnet number

Limits which parts of the network number must match an interface

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Figure 9-5

The Impact of the EIGRP network Command – R1, Step 1 172.22.11.1 Fa0/0

EIGRP

S0/1/0 172.22.112.101

1

S0/1/1 172.22.113.201

router eigrp 1 network 172.22.11.0 0.0.0.255 network 172.22.112.0 0.0.0.255

EIGRP

Step 2 Reference Figure 9-6

Problem of Not Advertising Subnet 172.22.13.96/27





   



   





 

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