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For CCNA exam achievements, you had greater understand what break up horizon is, how to show it off, and when to show it off. Understanding when to show split horizon off can be important in production networks, as it may cause a hub-and-spoke community to own incomplete routing tables on the spokes.
Split horizon exists for a very good motive – routing loop prevention. The rule of split horizon states that a router can't deliver an ad for any route out a similar interface that it arrived in on. Split horizon is on by default on all interfaces managing RIP, IGRP, and EIGRP.
In this particular CCNA tutorial, R1 will serve, since the hub and R2 and R3 will be the spokes. We’ll to start with configure EIGRP about the 172.16.123.0 /24 community, the community connecting the a few routers.
R1#conf t
R1(config)#router eigrp one hundred
R1(config-router)#no auto-summary
R1(config-router)#network 172.twelve.123.0 0.0.0.255
R2#conf t
R2(config)#router eigrp 100
R2(config-router)#no vehicle-summary
R2(config-router)#community 172.twelve.123.0 0.0.0.255
R3#conf t
R3(config)#router eigrp a hundred
R3(config-router)#no vehicle-summary
R3(config-router)#network 172.twelve.123.0 0.0.0.255
Running present ip eigrp neighbor on R1 demonstrates that adjacencies to R2 and R3 are up.
R1#display ip eigrp neighbor
IP-EIGRP neighbors for procedure 100
H Handle Interface Maintain Uptime SRTT RTO Q Seq Form
(sec) (ms) Cnt Num
one 172.12.123.3 Se0/0 11 00:02:forty five one 5000 0 1
0 172.12.123.two Se0/0 161 00:03:01 1 5000 0 1
Just about every router will now promote its loopback deal with by way of EIGRP.
R1(config-router)#community 1.1.one.0 0.0.0.255
R2(config-router)#network two.two.2.0 0.0.0.255
R3(config-router)#network 3.3.3.0 0.0.0.255
Managing demonstrate ip eigrp route on Each and every router shows that R1 provides a route for both R2s and R3s loopback. R2 and R3 will only see R1s loopback address, instead of Every single Many others. Why?
R1#exhibit ip route eigrp
two.0.0.0/24 is subnetted, 1 subnets
D two.two.two.0 [90/2297856] by means of 172.twelve.123.two, 00:03:19, Serial0/0
3.0.0.0/24 is subnetted, one subnets
D 3.three.three.0 [90/2297856] by using 172.twelve.123.three, 00:03:04, Serial0/0
R2#clearly show ip route eigrp
one.0.0.0/24 is subnetted, 1 subnets
D 1.one.one.0 [ninety/2297856] through 172.12.123.one, 00:03:forty, Serial0/0.123
R3#present ip route eigrp
D 1.one.one.0 [ninety/2297856] through 172.twelve.123.one, 00:05:17, Serial0/0.31
EIGRP uses Break up Horizon by default to forestall routing loops. On this lab, however, it helps prevent full network reachability. R2 and R3 equally form neighbor interactions with R1s Serial physical interface. R2 advertises its loopback deal with to R1s Serial interface, as does R3. Split Horizon isn't going to allow a path to be advertised back again out exactly the same interface it had been obtained on. This prevents R1 from promotion R2s loopback to R3, or R3s loopback to R2.
Break up Horizon should be disabled to permit comprehensive community reachability Within this lab. To do so, run no ip split-horizon eigrp 100 on R1s Serial interface. When Split Horizon is disabled, that will cause the neighbor
associations to are unsuccessful, then reestablish. Run exhibit ip route eigrp a hundred on both R2 and R3. The right path to the remote loopback address will now surface.
R1(config)#int serial0
R1(config-if)#no ip break up-horizon eigrp a hundred
10:02:23: %DUAL-five-NBRCHANGE: IP-EIGRP a hundred: Neighbor 172.twelve.123.two (Serial0/0) down: break up horizon modified
10:02:23: %DUAL-5-NBRCHANGE: IP-EIGRP one hundred: Neighbor 172.12.123.three (Serial0/0) down: split horizon improved
ten:02:27: %Twin-five-NBRCHANGE: IP-EIGRP a hundred: Neighbor 172.12.123.three (Serial0/0) ip: new adjacency
ten:02:fifty four: %Twin-5-NBRCHANGE: IP-EIGRP 100: Neighbor 172.12.123.2 (Serial0/0) ip: new adjacency
D https://socialhattori.com/ 1.one.one.0 [ninety/2297856] through 172.12.123.1, 00:00:06, Serial0/0.123
D three.3.three.0 [90/2809856] by way of 172.12.123.1, 00:00:06, Serial0/0.123
D 1.1.1.0 [ninety/2297856] by way of 172.12.123.one, 00:00:12, Serial0/0.31
D 2.2.two.0 [ninety/2809856] by using 172.12.123.one, 00:00:twelve, Serial0/0.31
Disabling split horizon needs to be performed with treatment, but knowing when and wherever to do so displays that you choose to definitely understand how this technologies operates – and that’s a large action on just how to earning your CCNA!