Introduction To Rip - 3Com 8807 Configuration Manual

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Introduction to RIP

RIP Operation
Mechanism
RIP C
ONFIGURATION
Routing Information Protocol (RIP) is a relatively simple interior gateway protocol
(IGP), which is mainly applied to small scale networks.
It is easy to implement RIP. You can configure and maintain RIP more easily than
OSPF and IS-IS, so RIP still has a wide application in actual networking.
RIP basic concepts
RIP is a kind of Distance-Vector (D-V) algorithm-based protocol and exchanges
routing information via UDP packets.
It employs Hop Count to measure the distance to the destination host, which is
called Routing Cost. In RIP, the hop count from a router to its directly connected
network is 0, and that to a network which can be reached through another router
is 1, and so on. To restrict the time to converge, RIP prescribes that the cost value
is an integer ranging from 0 to 15. The hop count equal to or exceeding 16 is
defined as infinite, that is, the destination network or the host is unreachable.
To improve the performance and avoid route loop, RIP supports Split Horizon and
allows importing the routes discovered by other routing protocols.
RIP route database
Each router running RIP manages a route database, which contains routing entries
to all the reachable destinations in the network. These routing entries contain the
following information:
Destination address: IP address of a host or a network.
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Next hop address: The interface address of the next router that an IP packet will
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pass through for reaching the destination.
Output interface: The interface through which the IP packet should be
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forwarded.
Cost: The cost for the router to reach the destination, which should be an
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integer in the range of 0 to 16.
Timer: Duration from the last time that the routing entry is modified till now.
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The timer is reset to 0 whenever a routing entry is modified.
RIP timer
In RFC1058, RIP is controlled by the following timers: Period update, Timeout and
Garbage-Collection.
Period Update is triggered periodically to send all RIP routes to all neighbors.
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