H3C Technologies H3C SR8800 - Manual (Page 39)

23
Configuring RIP
RIP overview
RIP is a simple Interior Gateway Protocol (IGP), mainly used in small-sized networks, such as academic
networks and simple LANs. It is not applicable to complex networks.
RIP is widely used in practical networking because it is easy to implement, configure, and maintain.
RIP working mechanism
Introduction
RIP is a distance vector routing protocol, using UDP packets for exchanging information through port
520.
RIP uses a hop count to measure the distance to a destination. The hop count from a router to a directly
connected network is 0. The hop count from a router to a directly connected router is 1. To limit
convergence time, the RIP metric value ranges from 0 to 15. A metric value of 16 (or greater) is
considered infinite, which means the destination network is unreachable. Because of this, RIP is not
suitable for large-sized networks.
RIP prevents routing loops by implementing the split horizon and poison reverse functions.
RIP routing table
A RIP router has a routing table containing routing entries of all reachable destinations, and each routing
entry contains the following elements:
• Destination address—IP address of a host or a network.
• Next hop—IP address of the adjacent router’s interface to reach the destination.
• Egress interface—Packet outgoing interface.
• Metric—Cost from the local router to the destination.
• Route time—Time elapsed since the routing entry was last updated. The time is reset to 0 every time
the routing entry is updated.
• Route tag—Identifies a route, used in a routing policy to flexibly control routes. For more information
about routing policy, see the chapter “Configuring routing policies.”
RIP timers
RIP employs the following timers:
• Update timer—Defines the interval between routing updates.
• Timeout timer—Defines the route aging time. If no update for a route is received within the aging
time, the metric of the route is set to 16 in the routing table.
• Suppress timer—Defines how long a RIP route stays in suppressed state. When the metric of a route
is 16, the route enters the suppressed state. In suppressed state, only routes which come from the
same neighbor and whose metric is less than 16 will be received by the router to replace
unreachable routes.