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RIPng ("RIPv6") Message Format and Features
(Page 2 of 3)
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
- 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
- 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.
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Version 3.0 - Version Date: September 20, 2005
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