EIGRP Split Horizon

EIGRP Split Horizon

Lab Objective:

The objective of this lab exercise is for you to learn and understand the effects of Split Horizon in a typical hub and spoke topology.

Lab Purpose:

Configuring and troubleshooting Split Horizon is a fundamental skill. EIGRP is an advanced Distance Vector protocol, and as such uses Split Horizon to prevent routing loops. Split Horizon mandates that EIGRP will not send updates back out of the interface on which they were received. While this default feature is generally a good thing, it can have a disastrous effect on traditional hub and spoke topologies. As a Cisco engineer, as well as in the Cisco CCNA exam, you will be expected to know how to address Split Horizon issues in EIGRP.

Certification Level:

This lab is suitable for CCNA certification exam preparation

Lab Difficulty:

This lab has a difficulty rating of 8/10

Readiness Assessment:

When you are ready for your certification exam, you should complete this lab in no more than 20 minutes

IMPORTANT NOTE: In order to configure Frame Relay between two routers in your lab, you will need THREE routers! The first two routers will be regular routers, and the third will need to be configured as a Frame Relay switch. This can be any Cisco router that has at least two Serial interfaces. Please refer to Appendix B: Cabling and configuring a Frame Relay Switch For Three Routers for the appropriate configuration to issue on the Frame Relay switch.

Lab Topology:

Please use the following topology to complete this lab exercise:

Task 1:

This lab will only be performed on R1, R2, and R3. Configure the hostnames on routers R1, R2, and R3 as above.

Task 2:

Configure the switch in the topology with the hostname Sw1. Enable F0/1, F0/2, and F0/4 on Sw1 so that when you bring up the router interfaces connected to those switch ports they can come up.

Task 3:

Configure IP addresses on the Fa0/0 interfaces on R1, R2, and R3. Make sure you enable these interfaces and they are up.

Task 4:

Configure Frame Relay on R1, R2, and R3. Use the IP addresses in the topology for their respective Serial interfaces. Use the default Frame Relay encapsulation of Cisco. Configure static Frame Relay maps between R1, R2, and R3, so that each router has a static Frame Relay map to the other two routers on the Frame Relay network.

Task 5:

Enable EIGRP in AS 1760 on R1, R2, and R3 for all the subnets configured on those respective routers. Be sure to prevent EIGRP from automatically summarizing at Classful network boundaries.

Task 6:

If you have configured everything as requested, you will not be able to see the 10.1.1.0/24 route via EIGRP on R3 nor will you be able to see the 172.16.3.0/25 route via EIGRP on R2. However, R1 will have both routes. Verify that this is the case using the appropriate commands.

 Task 7:

Based on your studies, you know that the reason you are not seeing the 10.1.1.0/24 route via EIGRP on R3 and the 172.16.3.0/25 route via EIGRP on R2 is because these routes are both sent to R1 via EIGRP, but since Distance Vector protocols do not send routing information back out of the same interface they received it, R1 will not send the routing information for 10.1.1.0/24 to R3 or the routing information for 172.16.3.0/25 since the routing information was received on the same interface. To prevent this from happening, disable this default feature.

Task 8:

Now verify that you can see the 10.1.1.0/24 route via EIGRP on R3 and the 172.16.3.0/25 route via EIGRP on R2. Ping 10.1.1.1 from R3 and 172.16.3.3 from R2 to verify network connectivity.