RIP Fixes
Split Horizon—Rule states that a router will not rebroadcast a learned route back over the interface from which the route was learned.
Hold-Down Timer—Rule states that when a router receives information about a network that is unreachable, the router must ignore all subsequent information about that network for a configurable amount of time.
Poisoned Reverse and triggered updates—Rule states a router is allowed to rebroadcast a learned route over the interface from which it learned it, but the metric is set to 16. A triggered update allows a router to broadcast its table when a network is found to be down.