I am going to show you how
RIP loop protection works. Let’s take the topology from the previous
post to demonstrate the features.

There are 2 methods of loop protection: Split Horizon and Poison Reverse.
Split Horizon
It prohibits a router to advertise a route back to neighbors, through the interface that receives the routes. Split Horizon is enabled by default on Huawei routers:
[R1]display rip 1 interface Serial 0/0/0 verbose
Serial0/0/0(192.168.20.1)
State : UP MTU : 500
Metricin : 0
Metricout : 1
Input : Enabled Output : Enabled
Protocol : RIPv2 Multicast
Send version : RIPv2 Multicast Packets
Receive version : RIPv2 Multicast and Broadcast Packets
Poison-reverse : Disabled
Authentication type : None
Replay Protection : Disabled
Split Horizon is disabled by
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