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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 Version-Specific Message Formats and Features

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RIP Version 1 (RIP-1) Message Format
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RIPng ("RIPv6") Message Format and Features
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RIP Version 2 (RIP-2) Message Format and Features
(Page 3 of 3)

RIP-2 Message Format

The basic message format for RIP-2 is also pretty much the same as it was for RIP-1, with the Version field of course set to 2, to clearly identify the message as being RIP-2. The real differences are in the individual RIP entries, as you can see in Table 121 and Figure 177.


Table 121: RIP Version 2 (RIP-2) Message Format

Field Name

Size (bytes)

Description

Command

1

Command Type: Identifies the type of RIP message being sent. A value of 1 indicates an RIP Request, while 2 means an RIP Response.

Version

1

Version Number: Set to 2 for RIP version 2.

Must Be Zero

2

Reserved: Field reserved; value must be set to all zeroes.

Route Table Entries (RTEs)

20 to 500, in increments of 20

 



Figure 177: RIP Version 2 (RIP-2) Message Format

The RIP Entries of RIP-1 are called Route Table Entries (RTEs) in RIP-2; the message format can contain up to 25. The format of RTE #1 is shown here with each of its subfields (the others are summarized to save space.)

 


As you can see, the unused fields allow the new RIP-2 features to be implemented without changing the basic structure of the RIP entry format. This allows RIP-1 and RIP-2 messages and devices to coexist in the same network. A RIP-2 device can handle both RIP-1 and RIP-2 messages, and will look at the version number to see which version the message is. A RIP-1 device should handle both RIP-2 and RIP-1 messages the same way, simply ignoring the extra RIP-2 fields it doesn't understand.

Note: Note that if authentication is used, one of the RTEs contains authentication information, limiting the message to 24 “real” RTEs.



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RIPng ("RIPv6") Message Format and Features
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