**Note The Serial Link between R3-R1 is down. R2 cannot reach Loopback 0 of R4 Network (10.1.4.0/24)
Split-horizon route advertisement is a method of preventing routing loops in distance-vector routing protocols by prohibiting a router from advertising a route back onto the interface from which it was learned.
# Issue Split Horizon
R2#show ip route eigrp
10.0.0.0/24 is subnetted, 6 subnets
D 10.1.3.0 [90/409600] via 10.1.23.3, 00:03:26, FastEthernet0/0
D 10.1.5.0 [90/2297856] via 10.1.245.5, 00:07:56, Serial0/0
D 10.1.50.0 [90/2195456] via 10.1.245.5, 00:07:56, Serial0/0
# Desable The Split-Horizon
R5#conf terminal
R5(config)#in serial 0/0
R5(config-if)#no ip split-horizon eigrp 1
*Mar 1 07:03:57.838: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 10.1.245.2 (Serial0/0) is resync: split horizon changed
*Mar 1 07:03:57.842: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 10.1.245.4 (Serial0/0) is resync: split horizon changed
R2#
*Mar 1 07:03:53.442: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 10.1.245.5 (Serial0/0) is resync: peer graceful-restart
R2#show ip route eigrp
10.0.0.0/24 is subnetted, 11 subnets
D 10.1.3.0 [90/409600] via 10.1.23.3, 00:00:09, FastEthernet0/0
D 10.1.1.0 [90/2835456] via 10.1.245.5, 00:00:09, Serial0/0
D 10.1.6.0 [90/2835456] via 10.1.245.5, 00:00:09, Serial0/0
D 10.1.5.0 [90/2297856] via 10.1.245.5, 00:08:43, Serial0/0
D 10.1.4.0 [90/2809856] via 10.1.245.5, 00:00:09, Serial0/0
D 10.1.60.0 [90/2733056] via 10.1.245.5, 00:00:09, Serial0/0
D 10.1.50.0 [90/2195456] via 10.1.245.5, 00:08:43, Serial0/0
D 10.1.146.0 [90/2707456] via 10.1.245.5, 00:00:09, Serial0/0
