| IPv6 Operations | T. Anderson |
| Internet-Draft | Redpill Linpro |
| Updates: 6145 (if approved) | December 13, 2014 |
| Intended status: Standards Track | |
| Expires: June 16, 2015 |
Explicit Address Mappings for Stateless IP/ICMP Translation
draft-anderson-v6ops-siit-eam-02
This document extends the Stateless IP/ICMP Translation Algorithm (SIIT) with an Explicit Address Mapping (EAM) algorithm, and formally updates RFC 6145. The EAM algorithm facilitates stateless IP/ICMP translation between arbitrary (non-IPv4-translatable) IPv6 endpoints and IPv4.
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The Stateless IP/ICMP Translation Algorithm (SIIT) [RFC6145] specifies that when translating IPv4 addresses to IPv6 and vice versa, all addresses must be translated using the algorithm specified in [RFC6052]. This document specifies an alternative to the [RFC6052] algorithm, where IP addresses are translated according to a table of Explicit Address Mappings configured on the stateless translator. This removes the previous constraint that IPv6 nodes that communicate with IPv4 nodes through SIIT must be configured with IPv4-translatable IPv6 addresses.
The Explicit Address Mapping Table does not replace [RFC6052]. For most use cases, it is expected that both algorithms are used in concert. The Explicit Address Mapping algorithm is used only when a mapping matching the address to be translated exists. If no matching mapping exists, the [RFC6052] algorithm will be used instead. Thus, when translating an individual IP packet, an SIIT implementation might translate one of the two IP address fields according to an EAM, while the other IP address field is translated according to [RFC6052].
This document makes use of the following terms:
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 [RFC2119].
Section 3.2.1 of [RFC6144] notes that "stateless translation mechanisms typically put constraints on what IPv6 addresses can be assigned to IPv6 nodes that want to communicate with IPv4 destinations using an algorithmic mapping". In practice, this means that the IPv6 nodes must be configured with IPv4-translatable IPv6 addresses. For the reasons discussed below, some environments may find that the use of IPv4-translatable IPv6 addresses is not desired or even possible.
An operator could overcome the above two problems by building an IPv6 network using regular (non-IPv4-translatable) IPv6 addresses, and assign IPv4-translatable IPv6 addresses as secondary addresses on the nodes that want to communicate with IPv4 nodes through SIIT only. However, doing so may result in a new set of undesired properties:
In short, the use of IPv4-translatable IPv6 addresses in parallel with regular IPv6 addresses is in many ways analogous to the use of Dual Stack [RFC4213]. While no actual IPv4 packets are used, the IPv4-translatable IPv6 addresses creates a secondary "stack" in the infrastructure that must be treated and operated separately from the primary one. This increases the complexity of the overall infrastructure, in turn increasing operational overhead, and reducing reliability. An operator who for such reasons finds the use Dual Stack unappealing, might feel the same way about using SIIT with IPv4-translatable IPv6 addresses.
This normative section defines the EAM algorithm. SIIT implementations are REQUIRED to support the specifications herein.
An SIIT implementation MUST include an Explicit Address Mapping Table (EAMT). By default, the EAMT SHOULD be empty. The operator MUST be able to populate the EAMT using the implementation's normal configuration interfaces. The implementation MAY additionally support other ways of populating the EAMT.
The EAMT consists of the following columns:
SIIT implementations MAY include other columns in order to support proprietary extensions to the EAM algorithm.
Throughout this document, figures representing the EAMT contain an Index column using the pound sign as the header. This column is not a required part of this specification; it is included only as a convenience to the reader.
An EAM consists of an IPv4 Prefix and an IPv6 Prefix. The prefix length MAY be omitted, in which case the implementation MUST assume it to be 32 for IPv4 and 128 for IPv6. Figure 1 illustrates an EAMT containing examples of valid EAMs.
Example EAMT
+---+----------------+----------------------+
| # | IPv4 Prefix | IPv6 Prefix |
+---+----------------+----------------------+
| 1 | 192.0.2.1 | 2001:db8:aaaa:: |
| 2 | 192.0.2.2/32 | 2001:db8:bbbb::b/128 |
| 3 | 192.0.2.16/28 | 2001:db8:cccc::/124 |
| 4 | 192.0.2.128/26 | 2001:db8:dddd::/64 |
| 5 | 192.0.2.192/31 | 64:ff9b::/127 |
+---+----------------+----------------------+
Figure 1
An EAM's IPv4 Prefix value MUST have an identical or smaller number of suffix bits than its corresponding IPv6 Prefix value.
Overlapping EAMs SHOULD be considered an error, and attempts to insert them into the EAMT SHOULD be blocked. The behaviour of an SIIT implementation when overlapping EAMs are present in the EAMT is left undefined.
When translating a packet between IPv4 and IPv6, an SIIT implementation MUST individually translate each IP address it encounters in the packet's IP headers (including any IP headers contained within ICMP errors) according to Section 3.3.
This section describes step-by-step how an SIIT implementation translates addresses between IPv4 and IPv6. Only the outcome of the algorithm described should be considered normative, that is, an SIIT implementation MAY implement the exact procedure differently than what is described here, but the outcome of the algorithm MUST be the same.
For concrete examples of IP addresses translations, refer to Appendix B.
When one or both of the address fields in an IP/ICMP packet are translated according to EAM, the translation can not be relied upon to be checksum neutral, even if the well-known prefix 64:ff9b::/96 is used. This consideration is discussed in more detail in Section 4.1 of [RFC6052].
The EAM algorithm does not introduce any new security issues beyond those that are already discussed in Section 7 of [RFC6145].
This draft makes no request of the IANA. The RFC Editor may remove this section prior to publication.
This document was conceived due to comments made by Dave Thaler in the v6ops session at IETF 91 as well as e-mail discussions between Fred Baker and the author.
Valuable reviews, suggestions, and other feedback was given by Cameron Byrne, Brian E Carpenter, Alberto Leiva, and Andrew Yourtchenko.
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. |
| [RFC6052] | Bao, C., Huitema, C., Bagnulo, M., Boucadair, M. and X. Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052, October 2010. |
| [RFC6145] | Li, X., Bao, C. and F. Baker, "IP/ICMP Translation Algorithm", RFC 6145, April 2011. |
| [I-D.anderson-v6ops-siit-dc] | tore, t., "SIIT-DC: Stateless IP/ICMP Translation for IPv6 Data Centre Environments", Internet-Draft draft-anderson-v6ops-siit-dc-01, October 2014. |
| [RFC4213] | Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms for IPv6 Hosts and Routers", RFC 4213, October 2005. |
| [RFC4862] | Thomson, S., Narten, T. and T. Jinmei, "IPv6 Stateless Address Autoconfiguration", RFC 4862, September 2007. |
| [RFC6144] | Baker, F., Li, X., Bao, C. and K. Yin, "Framework for IPv4/IPv6 Translation", RFC 6144, April 2011. |
| [RFC6219] | Li, X., Bao, C., Chen, M., Zhang, H. and J. Wu, "The China Education and Research Network (CERNET) IVI Translation Design and Deployment for the IPv4/IPv6 Coexistence and Transition", RFC 6219, May 2011. |
| [RFC6877] | Mawatari, M., Kawashima, M. and C. Byrne, "464XLAT: Combination of Stateful and Stateless Translation", RFC 6877, April 2013. |
| [RFC7335] | Byrne, C., "IPv4 Service Continuity Prefix", RFC 7335, August 2014. |
The following subsections lists some use cases that at the time of writing leverage SIIT with the EAM algorithm.
When the CLAT component in the 464XLAT [RFC6877] architecture does not have a dedicated IPv6 prefix assigned, it may instead use "one interface IPv6 address that is claimed by the CLAT". This IPv6 address might not be IPv4-translatable. If this is the case, the CLAT essentially implements the EAM algorithm using an EAMT as follows (assuming the CLAT's IPv4 address is picked from the IPv4 Service Continuity Prefix [RFC7335]):
Example EAMT for an 464XLAT CLAT
+---+--------------+-------------------------------+
| # | IPv4 Prefix | IPv6 Prefix |
+---+--------------+-------------------------------+
| 1 | 192.0.0.1/32 | CLAT_claimed_IPv6_address/128 |
+---+--------------+-------------------------------+
Figure 2
In this particular use case, the EAM algorithm is used to translate IPv6 destination addresses to IPv4, and conversely, IPv4 source addresses to IPv6. Other addresses are translated using [RFC6052]. Note that this is the exact opposite of the SIIT-DC use case [usecase_siit_dc].
IVI [RFC6219] describes a stateless translation model that embeds IPv4 addresses in a 40-bit translation prefix where bits 33-40 are required to be 1. The embedded IPv4 address is located in bits 41-72 of the IPv6 address. Bits 73-128 are required to be 0.
The location of the eight least significant IPv4 address bits makes the IVI address mapping differ from [RFC6052].
Example EAMT for IVI
+---+-------------+--------------------+
| # | IPv4 Prefix | IPv6 Prefix |
+---+-------------+--------------------+
| 1 | 0.0.0.0/0 | 2001:db8:ff00::/40 |
+---+-------------+--------------------+
Figure 3
In this particular use case, all addresses are translated according to the EAM algorithm. In other words, [RFC6052] mapping is not used at all.
SIIT-DC [I-D.anderson-v6ops-siit-dc] describes the use of SIIT to facilitate connectivity from the IPv4 Internet to services hosted in an IPv6-only data centre. In order to avoid the constraints relating to the use of IPv4-translatable IPv6 addresses discussed in Section 2 the stateless IPv4/IPv6 translators are provisioned with an EAMT containing one entry per IPv6-only service that are to be made available from the IPv4 Internet, for example (assuming 2001:db8:aaaa::1 and 2001:db8:bbbb::1 are assigned to load balancers or servers that provides the IPv6-only services in question):
Example EAMT for SIIT-DC
+---+--------------+----------------------+
| # | IPv4 Prefix | IPv6 Prefix |
+---+--------------+----------------------+
| 1 | 192.0.2.1/32 | 2001:db8:aaaa::1/128 |
| 2 | 192.0.2.2/32 | 2001:db8:bbbb::1/128 |
+---+--------------+----------------------+
Figure 4
In this particular use case, the EAM algorithm is used to translate IPv4 destination addresses to IPv6, and conversely, IPv6 source addresses to IPv4. Other addresses are translated using [RFC6052]. Note that this is the exact opposite of the 464XLAT use case [usecase_464xlat].
Figure 5 demonstrates how a set of example IP addresses are translated given the example EAMT in Figure 1. Implementors may use the examples given to develop test cases to validate correct operation. Note that the address translations are bidirectional, so a single row in the table describes two address translations: IPv4 to IPv6, and IPv6 to IPv4.
It is also assumed that the [RFC6052] translation prefix is configured to be 64:ff9b::/96.
Example IP Address Translations
+--------------+----------------------+-----------------------+
| IPv4 Address | IPv6 Address | Comment |
+--------------+----------------------+-----------------------+
| 192.0.2.1 | 2001:db8:aaaa:: | According to EAM #1 |
| 192.0.2.2 | 2001:db8:bbbb::b | According to EAM #2 |
| 192.0.2.16 | 2001:db8:cccc:: | According to EAM #3 |
| 192.0.2.24 | 2001:db8:cccc::8 | According to EAM #3 |
| 192.0.2.31 | 2001:db8:cccc::f | According to EAM #3 |
| 192.0.2.128 | 2001:db8:dddd:: | According to EAM #4 |
| 192.0.2.152 | 2001:db8:dddd:0:18:: | According to EAM #4 |
| 192.0.2.183 | 2001:db8:dddd:0:37:: | According to EAM #4 |
| 192.0.2.191 | 2001:db8:dddd:0:3f:: | According to EAM #4 |
| 192.0.2.193 | 64:ff9b::1 | According to EAM #5 |
| 192.0.2.200 | 64:ff9b::c000:2c8 | According to RFC 6052 |
+--------------+----------------------+-----------------------+
Figure 5