How Does RIP Determine Route Information?
The routing information is propagated in RIP update packets that are sent
out both periodically and in the event of a network topology change. On
receipt of a RIP update, depending on whether the specified route exists or
does not exist in the route table, the router may modify, delete or add the
route to its route table.
RIP uses hop count, which is the number of routers an IP packet must pass
through, to calculate the best route for a packet. A route with a low hop count
is preferred over a route with a higher hop count. A directly-connected route
has a hop-count of 0. With RIP , the maximum number of hops from source to
destination is 15. Packets with a hop count greater than 15 are dropped
because the destination network is considered unreachable.
What Is Split Horizon?
RIP uses a technique called split horizon to avoid problems caused by
including routes in updates sent to the router from which the route was
originally learned. With simple split horizon, a route is not included in
updates sent on the interface on which it was learned. In split horizon with
poison reverse, a route is included in updates sent on the interface where it
was learned, but the metric is set to infinity.