Routing protocol optimizations:
Distance vector protocols suffer from "count to infinity" problems.  Several protocol features exist to prevent or reduce the possibility of its occurrence.  We describe each in turn.

• Triggered updates: Triggered updates are an attempt to speed up convergence. To get triggered updates, we simply add a rule that whenever a node changes the metric for a route, it is required to send update messages almost immediately, even if it is not yet time for one of the regular update message. (The timing details will differ from protocol to protocol. Some distance vector protocols, including RIP, specify a small time delay, in order to avoid having triggered updates generate excessive network traffic.)

• Split-horizon with poision reverse: It is never useful to claim reachability for a destination network to the neighbor(s) from which the route was learned. "Split horizon" is a scheme for avoiding problems caused by including routes in updates sent to the node from which they were learned. The "simple split horizon" scheme omits routes learned from one neighbor in updates sent to that neighbor. "Split horizon with poisoned reverse" includes such routes in updates, but sets their metrics to infinity.

• Route poisoning: Advertise cost as infinity when cost from next hop has been increasing and continue to stay with current next hop for "a while".
  

• Path hold-down: Do not switch route for n update periods after cost goes up. This reduces the likelihood of switching to a route that is invalid due to the count to infinity problem.