Netgear XCM8806 Chassis User Manual - Page 663

NETGEAR 8800 User Manual Overview of RIP RIP is an IGP first used in computer routing in the Advanced Research Projects Agency Network (ARPAnet) as early as 1969. It is primarily intended for use in homogeneous networks of moderate size. To determine the best path to a distant network, a router using RIP always selects the path that has the least number of hops. Each router that data must traverse is considered to be one hop. Routing Table The routing table in a router using RIP contains an entry for every known destination network. Each routing table entry contains the following information: • IP address of the destination network • Metric (hop count) to the destination network • IP address of the next router • Timer that tracks the amount of time since the entry was last updated The router exchanges an update message with each neighbor every 30 seconds (default value), or when there is a change to the overall routed topology (also called triggered updates). If a router does not receive an update message from its neighbor within the route timeout period (180 seconds by default), the router assumes the connection between it and its neighbor is no longer available. Split Horizon Split horizon is a scheme for avoiding problems caused by including routes in updates sent to the router from which the route was learned. Split horizon omits routes learned from a neighbor in updates sent to that neighbor. Poison Reverse Like split horizon, poison reverse is a scheme for eliminating the possibility of loops in the routed topology. In this case, a router advertises a route over the same interface that supplied the route, but the route uses a hop count of 16, which defines that router as unreachable. Triggered Updates Triggered updates occur whenever a router changes the metric for a route. The router is required to send an update message immediately, even if it is not yet time for a regular update message to be sent. This generally results in faster convergence, but may also result in more RIP-related traffic. Chapter 22. RIP | 663