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9.2.2 RIP
Brief Introduction of RIP
RIP (Routing Information Protocol) is a relatively simple interior gateway protocol (IGP), mainly
used for smaller networks. The complex environments and large networks general do not use RIP.
9.2.2.1 Working Mechanism of RIP
1. Basic Concept of RIP
RIP is a protocol based on Distance-Vector (DV) algorithm. It exchanges routing information
through the UDP package and uses port number 520.
RIP uses Hop Count to measure the distance to the destination address and it is called RoutingCost.
In RIP, the hop count from the router to its directly connected network is 0 and the hop count of
network to be reached through a router is 1 and so on. In order to limit the convergence time, the
specified RoutingCost of RIP is an integer in the range of 0~15 and hop count larger than or equal
to 16 is defined as infinity, which means that the destination network or host is unreachable.
Because of this limitation, the RIP is not suitable for large-scale networks. To improve performance
and prevent routing loops, RIP supports split horizon function. RIP also introduces routing obtained
by other routing protocols.
2. Routing Database of RIP
Each router that runs RIP manages a routing database, which contains routing entries to reach all
reachable destinations. The routing entries contain the following information:
Destination address: IP address of host or network.
Address of next hop: IP address of interface of the router’s adjacent router to be passed by on
the way to reach the destination.
Output interface: The output interface for the router to forward package.
RoutingCost: Cost for the router to reach the destination.
Routing time: The time from the last update of router entry to the present. Each time the router
entry is updated, the routing time will be reset to 0.
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