Allnet ALL126AS3, Руководство пользователя

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ALL126AS3
USER’S MANUAL
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The Routing Information Protocol (RIP) is one of the oldest distance-vector routing protocols, which employs the hop count as a
routing metric. RIP prevents routing loops by implementing a limit on the number of hops allowed in a path from the source to a
destination. The maximum number of hops allowed for RIP is 15. This hop limit, however, also limits the size of networks that RIP
can support. A hop count of 16 is considered an infinite distance, in other words the route is considered unreachable.
RIP implements the split horizon, route poisoning and holddown mechanisms to prevent incorrect routing information from being
propagated. These are some of the stability features of RIP. It is also possible to use the Routing Information Protocol with
Metric-Based Topology (RMTI) algorithm to cope with the count-to-infinity problem. With RMTI, it is possible to detect every possible
loop with a very small computation effort.
RIP uses the User Datagram Protocol (UDP) as its transport protocol, and is assigned the reserved port number 520.
RIP version 1 : The original specification of RIP, defined in RFC 1058, was published in 1988 and uses classful routing. The periodic
routing updates do not carry subnet information, lacking support for variable length subnet masks (VLSM). This limitation makes it
impossible to have different-sized subnets inside of the same network class. In other words, all subnets in a network class must have
the same size. There is also no support for router authentication, making RIP vulnerable to various attacks.
RIP version 2 : Due to the deficiencies of the original RIP specification, RIP version 2 (RIPv2) was developed in 1993 and last
standardized in 1998. It included the ability to carry subnet information, thus supporting Classless Inter-Domain Routing (CIDR). To
maintain backward compatibility, the hop count limit of 15 remained. RIPv2 has facilities to fully interoperate with the earlier
specification if all Must Be Zero protocol fields in the RIPv1 messages are properly specified. In addition, a compatibility switch
feature allows fine-grained interoperability adjustments.