I have problem in understanding the example provided for the Distance Vector Routing Problem.
It's mentioned that "Router D will eventually send out its update and cause Router B to stop routing to Network 5, but routers A and C are still not updated. To them, it appear that Network 5 is still available through Router B with a metric of 3 !
Now Router A sends its regular broadcast of its entire routing table which includes reachability for Network 5. Routers C and B receive the wonderful news that Network 5 can be reached from Router A, so they send out the information that Network 5 is now available !"
Here but routers A and C are still not updated with the failure of Network 5. Hence it sends its regular broadcast saying its reachability to Network 5.
But in the section "Split Horizon", its mentioned that "In our example it would have prevented Router A from sending the updated information it received from Router B back to Router B."
Here it says that Router A received the updated info from Router B. It is contradictory to the earlier explanation " routers A and C are still not updated."
If the scenario is a pointo to point subif, within the same phisycal interface or link, split horizon is still enabled, but each subif, acts as a point to point interface, so split horizon is only disabling the return updates in each subif, and no in the entire phisical interface that contains all daughter subinterfaces.
In the case of multipoint, you can diable split horizon in the multipoint interface, but it depends again in the complexity of the design, that maybe loops can be formed.