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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

RIP Version 2 (RIP-2) Message Format and Features 1 2 3 Open Shortest Path First (OSPF)

RIPng Message Format

The message format for RIPng is similar to that of RIP-1 and RIP-2, except for the format of the Route Table Entries; it is shown in Table 122 and Figure 178.

Table 122: RIPng Message Format

Field Name	Size (bytes)	Description
Command	1	Command Type: Identifies the type of RIPng message being sent. A value of 1 indicates an RIPng Request, while 2 means an RIPng Response.
Version	1	Version Number: Set to 1 (not 6, since this is the first version of the new protocol RIPng.)
Must Be Zero	2	Reserved: Field reserved; value must be set to all zeroes.
Route Table Entries (RTEs)	Variable

The maximum number of RTEs in RIPng is not restricted to 25 as it is in RIP-1 and RIP-2. It is limited only by the maximum transmission unit (MTU) of the network over which the message is being sent.

When a Next Hop needs to be specified, a special RTE is included as I mentioned before. This RTE is included before all the RTEs to which it applies. It has the same basic structure as shown for regular RTEs in Table 122, with the IPv6 Prefix subfield containing the next hop address, the Route Tag and Prefix Len fields set to 0, and the Metric field set to 255 (0xFF).

RIP Version 2 (RIP-2) Message Format and Features 1 2 3 Open Shortest Path First (OSPF)