from CCCN Route book 300-101 page 628
“Of the two commands for outbound filtering, the post-filter command is somewhat obvious,
but there is no command to specifically display a pre-filter view of the BGP Update sent to a neighbor. However, BGP advertises the best route for each prefix in the BGP table, within certain restrictions. Those restrictions state that BGP will not advertise iBGP-learned routes to an iBGP peer, and a router will not advertise the best route back to the same neighbor that advertised that route.”
in eigrp when R1 advertise 1.1.1.1/32 to R2, R2 is not allowed to advertise the exact same network out of the exact same ingress interface because of split-horizon.so, bgp is using split-horizon mechanism in order to prevent the router from advertising the exact same network back again to R1.so far so good.
in ospf, idk,maybe R2 advertise 1.1.1.1/32 to R1 back again . the mechanism used here is all routers has entire visibility for the topology and choose the best route.
but in bgp ,ibgp or ebgp, what is the mechsm that is used by R2 in order to stop R2 from advertising 1.1.1.1/32 back again to R1?