When i disbale split horizon any interface, it starts sending the primary network in its updates. Consider the following scenario
R1 is connected to R2 via ethernet link
R1 ethernet ip is 188.8.131.52/8
R2 ethernet ip is 184.108.40.206/8
When i disable split horizon, i can see R1 advertising 220.127.116.11/8 out the same interface !.
Why is this so.
My assumption is, since eigrp doesnt check for subnet mask when forming adjacency, so its quite possible that masks of both neighbors might be different, hence R1 for safe side advertises its original network of the link to R2 for topology sake.
Is my assumption correct ?
I don't see anything unusual in what you have observed. The network 18.104.22.168/8 on R1's ethernet interface is learned by that interface itself. Thus, it is subject to split horizon. If you deactivate the split horizon, it will be advertised along with other routes. The RIP implementation in IOS, as far as I know, behaves in the same way.
There is no subnet mask checking in EIGRP, to my best knowledge - this is contrary to OSPF Hello packets that also carry the netmask of the interface that sourced them.