Cisco CCNA Exam Tutorial Split Horizon And Hub-And-Spoke Networks
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Cisco CCNA Exam Guide: Mastering Split Horizon and Hub-And-Spoke Networks
Overview
Understanding split horizon is crucial for both CCNA exams and real-world networking. It's not just about knowing its definition; you must be able to apply and disable it effectively. This guide, provided by Chris Bryant, CCIE
12933, will help you grasp these essential skills.
What is Split Horizon?
Split horizon is a technique used to prevent routing loops by restricting a router from sending an advertisement for a route back out the same interface it was received. This feature is enabled by default for RIP, IGRP, and EIGRP.
Scenario Setup
In this tutorial, we’ll simulate a hub-and-spoke network with R1 as the hub and R2 and R3 as the spokes. We'll configure EIGRP on the 172.16.123.0/24 network connecting these routers.
Configuration Steps
Configuring R1
```plaintext
R1
conf t
R1(config)router eigrp 100
R1(config-router)no auto-summary
R1(config-router)network 172.12.123.0 0.0.0.255
```Configuring R2
```plaintext
R2
conf t
R2(config)router eigrp 100
R2(config-router)no auto-summary
R2(config-router)network 172.12.123.0 0.0.0.255
```Configuring R3
```plaintext
R3
conf t
R3(config)router eigrp 100
R3(config-router)no auto-summary
R3(config-router)network 172.12.123.0 0.0.0.255
```Checking Adjacencies
On R1, use:
```plaintext
R1
show ip eigrp neighbor
```This shows the connections to R2 and R3 are established.
Advertising Loopback Addresses
Each router will now advertise its loopback address via EIGRP.
For R1:
```plaintext
R1(config-router)
network 1.1.1.0 0.0.0.255
```For R2:
```plaintext
R2(config-router)
network 2.2.2.0 0.0.0.255
```For R3:
```plaintext
R3(config-router)
network 3.3.3.0 0.0.0.255
```Show Route Details
When you run the `show ip route eigrp` command, R1 displays routes for both R2 and R3’s loopbacks, but R2 and R3 can only see R1’s loopback and not each other’s due to split horizon.
Disabling Split Horizon
To achieve full network reachability, split horizon needs to be disabled.
On R1:
```plaintext
R1
conf t
R1(config)int serial0
R1(config-if)no ip split-horizon eigrp 100
```Disabling split horizon will temporarily disrupt and then re-establish neighbor relationships. Verify by running `show ip route eigrp` on R2 and R3, where you will now see routes to each other's loopbacks.
Conclusion
Disabling split horizon requires careful consideration, but understanding when and how to do it demonstrates a deep comprehension of network technologies?"a significant step towards obtaining your CCNA certification!
You can find the original non-AI version of this article here: Cisco CCNA Exam Tutorial Split Horizon And Hub-And-Spoke Networks.
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