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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 Version-Specific Features

Even though RIPng is a new protocol, a specific effort was made to make RIPng like its predecessors. Its basic operation is almost entirely the same, and it uses the same overall algorithm and operation, as described in the general section on RIP operation. RIPng also does not introduce any specific new features compared to RIP-2, except those needed to implement RIP on IPv6.

RIPng maintains most of the enhancements introduced in RIP-2; some are implemented as they were in RIP-2, while others appear in a modified form. Here's specifically how the five extensions in RIP-2 are implemented in RIPng:

• Classless Addressing Support and Subnet Mask Specification: In IPv6 all addresses are classless, and specified using an address and a prefix length, instead of a subnet mask. Thus, a field for the prefix length is provided for each entry instead of a subnet mask field.
  
  
• Next Hop Specification: This feature is maintained in RIPng, but implemented differently. Due to the large size of IPv6 addresses, including a Next Hop field in the format of RIPng RTEs would almost double the size of every entry. Since Next Hop is an optional feature, this would be wasteful. Instead, when a Next Hop is needed, it is specified in a separate routing entry.
  
  
• Authentication: RIPng does not include its own authentication mechanism. It is assumed that if authentication and/or encryption are needed, they will be provided using the standard IPSec features defined for IPv6 at the IP layer. This is more efficient than having individual protocols like RIPng perform authentication.
  
  
• Route Tag: This field is implemented the same way as it is in RIP-2.
  
  
• Use of Multicasting: RIPng uses multicasts for transmissions, using reserved IPv6 multicast address FF02::9.

There are two basic RIPng message types, RIP Request and RIP Response, which are exchanged using the User Datagram Protocol (UDP) as with RIP-1 and RIP-2. Since RIPng is a new protocol, it cannot use the same UDP reserved port number 520 used for RIP-1/RIP-2. Instead, RIPng uses well-known port number 521. The semantics for the use of this port is the same as those used for port 520 in RIP-1 and RIP-2. For convenience, here are the rules again:

• RIP Request messages are sent to UDP destination port 521. They may have a source port of 521 or may use an ephemeral port number.
  
  
• RIP Response messages sent in reply to an RIP Request are sent with a source port of 521, and a destination port equal to whatever source port the RIP Request used.
  
  
• Unsolicited RIP Response messages (sent on a routine basis and not in response to a request) are sent with both the source and destination ports set to 521.

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