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The TCP/IP Guide

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Table Of Contents  The TCP/IP Guide
 9  TCP/IP Lower-Layer (Interface, Internet and Transport) Protocols (OSI Layers 2, 3 and 4)
      9  TCP/IP Internet Layer (OSI Network Layer) Protocols
           9  TCP/IP Routing Protocols (Gateway Protocols)
                9  TCP/IP Interior Routing Protocols (RIP, OSPF, GGP, HELLO, IGRP, EIGRP)
                     9  TCP/IP Routing Information Protocol (RIP, RIP-2 and RIPng)
                          9  RIP Fundamentals and General Operation

Previous Topic/Section
RIP Route Determination Algorithm and Metric
Previous Page
Pages in Current Topic/Section
1
23
Next Page
RIP Protocol Limitations and Problems
Next Topic/Section

RIP General Operation, Messaging and Timers
(Page 1 of 3)

RIP is a protocol for exchanging routing information, so its operation can best be described in terms of the messages used to exchange this information, and the rules for when messages are sent. The RIP software in each router sends messages and takes other actions both in reaction to certain events and in response to triggers set off by timers. Timers are also used to determine when routing information should be discarded if not updated.

RIP Messages and Basic Message Types

Communication between RIP software elements in routers on an internetwork is accomplished through the use of RIP messages. These messages are sent using the User Datagram Protocol (UDP), with reserved UDP port number 520 for RIP-1 and RIP-2, and 521 for RIPng. Thus, even though RIP is considered part of layer three like other routing protocols, it behaves more like an application in terms of how it sends messages. The exact format of the message is version-dependent, and all three formats (for RIP, RIP-2 and RIPng) are described in detail in their own section. RIP messages can be either sent to a specific device, or can be sent out for multiple devices to receive. If directed to one device they are sent unicast; otherwise, they are either broadcast (in RIP) or multicast (RIP-2 and RIPng).

There are only two basic message types for all three versions of RIP:

  • RIP Request: A message sent by a router to another router asking it to send back all or part of its routing table.

  • RIP Response: A message sent by a router containing all or part of its routing table. Note that despite the name, this message is not sent just in response to an RIP Request message, as we will see. So it's not really that great a name… oh well.

Note: The original RIP also defined a few other message types: Traceon, Traceoff and a special message type reserved for use by Sun Microsystems. These are obsolete and no longer used, and were removed from the RIP-2 and RIPng standards.



Previous Topic/Section
RIP Route Determination Algorithm and Metric
Previous Page
Pages in Current Topic/Section
1
23
Next Page
RIP Protocol Limitations and Problems
Next Topic/Section

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Version 3.0 - Version Date: September 20, 2005

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