Local-use IPv4/IPv6 Translation PrefixRedpill LinproVitaminveien 1A0485 OsloNorway+47 959 31 212tore@redpill-linpro.comhttp://www.redpill-linpro.com
General
IPv6 Operations
This document reserves the IPv6 prefix 64:ff9b:1::/48 for local use with
IPv4/IPv6 translation mechanisms. It updates RFC6890 in order to reflect
this reservation.
This document reserves 64:ff9b:1::/48 for local use with IPv4/IPv6
translation mechanisms. This facilitates the co-existence of multiple
IPv4/IPv6 translation mechanisms in the same network without requiring
the use of a Network-Specific Prefix assigned from the operator's
allocated global unicast address space.
This document makes use of the following terms:
A globally unique
prefix assigned by a network operator for use with and IPv4/IPv6
translation mechanism, cf. The prefix 64:ff9b::/96,
which is reserved for use with the IPv4/IPv6
address translation algorithm.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in .
Since the WKP 64:ff9b::/96 was reserved by ,
several new IPv4/IPv6 translation mechanisms have been defined by the
IETF. These target various different use cases. An operator might
therefore wish to make use of several of them simultaneously.
The smallest possible prefix supported by the
algorithm is a /96. Because the WKP is a /96, an operator preferring to
use a WKP over an NSP can only do so for only one of his IPv4/IPv6
translation mechanisms. All others must necessarily use an NSP.
The WKP is reserved specifically for use with the algorithm specified in
. More recent IETF documents describe IPv4/IPv6
translation mechanisms that use different algorithms. An operator
deploying such mechanisms can not make use of the WKP in a legitimate
fashion.
Section 3.1 of imposes certain restrictions on
the use of the WKP. These restrictions might conflict with the
operator's desired use of an IPv4/IPv6 translation mechanism.
In summary, there is a need for a prefix that facilitates the
co-existence of multiple IPv4/IPv6 translation mechanisms (that do not
necessarily use the algorithm).
The primary reason for choosing 64:ff9b:1::/48 is that it is adjacent to
the WKP 64:ff9b::/96. As these two prefixes are
intended for very similar uses, it is prudent to allow them to be
referred to using a single aggregate (64:ff9b::/47).
The prefix length of 48 bits was chosen in order to attain the goal of
facilitating multiple simultaneous deployments of IPv4/IPv6 translation
in a single network. The shortest IPv4/IPv6 translation prefixes
reported to the V6OPS working group as being used in production was 64
bits. 64:ff9b:1::/48 will accommodate up to 65536 such prefixes.
While the algorithm specifies IPv4/IPv6
translation prefixes as short as /32, facilitating for multiple
instances of these was considered as too wasteful by the V6OPS working
group.
64:ff9b:1::/48 is intended as a technology-agnostic and generic
reservation. A network operator may freely use it in combination with
any kind of IPv4/IPv6 translation mechanism deployed within his network.
By default, IPv6 nodes and applications must not treat IPv6 addresses
within 64:ff9b:1::/48 different from other globally scoped IPv6
addresses. In particular, they must not make any assumptions regarding
the syntax or properties of those addresses (e.g., the existence and
location of embedded IPv4 addresses), or the type of associated
translation mechanism (e.g., whether it is stateful or stateless).
64:ff9b:1::/48 or any other more-specific prefix may not be advertised
in inter-domain routing, except by explicit agreement between all
involved parties. Such prefixes MUST NOT be advertised to the
default-free zone.
When 64:ff9b:1::/48 or a more-specific prefix is used with the algorithm, it is considered to be a
Network-Specific Prefix.
Use of 64:ff9b:1::/48 does not in itself guarantee checksum neutrality,
as many of the IPv4/IPv6 translation algorithms it can be used with are
fundamentally incompatible with checksum-neutral address translations.
The Stateless IP/ICMP Translation algorithm is
one well-known algorithm that can operate in a checksum-neutral manner,
when using the algorithm for all of its address
translations. However, in order to attain checksum neutrality is
imperative that the translation prefix is chosen carefully.
Specifically, in order for a 96-bit prefix to
be checksum neutral, all the six 16-bit words in the prefix must add up
to a multiple of 0xffff.
The following non-exhaustive list contains examples of translation
prefixes that are checksum neutral when used with the and algorithms:
64:ff9b:1:fffe::/9664:ff9b:1:fffd:1::/9664:ff9b:1:fffc:2::/9664:ff9b:1:abcd:0:5431::/96
Section 4.1 of contains further discussion
about IPv4/IPv6 translation and checksum neutrality.
The IANA is requested to add the following entry to the IPv6
Special-Purpose Address Registry:
The IANA is furthermore requested to add the following footnote to the
0000::/8 entry of the Internet Protocol Version 6 Address Space
registry:
64:ff9b:1::/48 reserved for Local-use IPv4/IPv6 Translation [TBD]
The reservation of 64:ff9b:1::/48 is not known to cause any new security
considerations beyond those documented in Section 5 of .
The author would like to thank Fred Baker, David Farmer, Holger
Metschulat and Pier Carlo Chiodi for contributing to the creation of
this document.