R1#debug ip rip
RIP protocol debugging is on
RIP: sending v1 update to 255.255.255.255 via Ethernet0 (18.104.22.168) RIP: build update entries network 22.214.171.124 metric 1
This problem occurs because the next hop of 126.96.36.199/24 is 188.8.131.52. With split horizon, RIP will suppress this update from going out the same interface that 184.108.40.206/24 is learned. Notice that the route 220.127.116.11/24 was advertised by R1 because the next-hop address of that route was 10.10.10.4, which is a different interface on R1.
The solution lies in turning off split horizon on the Ethernet 0 interface of R1.
A similar situation would arise if 18.104.22.168/24 was defined as a secondary interface address on R1, which will not advertise this secondary interface address in its RIP update unless split horizon is turned off.
Example 3-95 shows the new configuration on Router R1 to solve this problem. Example 3-95 Disabling Split-Horizon on R1's Ethernet 0 Interface
interface Ethernet0 ip address 22.214.171.124 255.255.255.0 no ip split-horizon
Example 3-96 shows that after making the configuration changes, R2 is receiving 126.96.36.199/24 in the RIP updates.
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