3Com Switch 4800G 24-Port Configuration Manual page 259

Operation of RIP
1 After RIP is enabled, the router sends Request messages to neighboring routers.
2 After receiving such information, the router updates its local routing table, and
3 By default, a RIP router sends its routing table to neighbors every 30 seconds.
4 RIP ages out routes by adopting an aging mechanism to keep only valid routes.
RIP Version
n
RIP Message Format
The following procedure describes how RIP works.
Neighboring routers return Response messages including information about their
routing tables.
sends triggered update messages to its neighbors. All routers on the network do
the same to keep the latest routing information.
RIP has two versions, RIPv1 and RIPv2.
RIPv1, a classful routing protocol, supports message advertisement via broadcast
only. RIPv1 protocol messages do not carry mask information, which means it can
only recognize routing information of natural networks such as Class A, B, C. That
is why RIPv1 does not support discontiguous subnets.
RIPv2 is a classless routing protocol. Compared with RIPv1, RIPv2 has the following
advantages.
Supporting route tags. Route tags are used in routing policies to flexibly control
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routes.
Supporting masks, route summarization and Classless Inter-Domain Routing
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(CIDR).
Supporting designated next hops to select the best next hops on broadcast
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networks.
Supporting multicast routing update to reduce resource consumption.
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Supporting plain text authentication and MD5 authentication to enhance
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security.
RIPv2 has two types of message transmission: broadcast and multicast. Multicast is
the default type using 224.0.0.9 as the multicast address. The interface working in
the RIPv2 broadcast mode can also receive RIPv1 messages.
RIPv1 message format
A RIPv1 message consists of a header and up to 25 route entries.
Figure 69 shows the format of RIPv1 message.
RIP Overview 259