IPv6 operations D. Lamparter
Internet-Draft NetDEF, Inc.
Obsoletes: 6791 (if approved) J. Linkova
Updates: 7915 (if approved) Google
Intended status: Standards Track 21 March 2025
Expires: 22 September 2025
Using Dummy IPv4 Address and Node Identification Extensions for IP/ICMP
translators (XLATs)
draft-equinox-v6ops-icmpext-xlat-v6only-source-02
Abstract
This document suggests that when a source IPv6 address of an ICMPv6
message can not be translated to an IPv4 address, the protocol
translators use the dummy IPv4 address (192.0.0.8) to translate the
IPv6 source address, and utilize the ICMP extension for Node
Identification (draft-ietf-intarea-extended-icmp-nodeid) to carry the
original IPv6 source address of ICMPv6 messages.
About This Document
This note is to be removed before publishing as an RFC.
Source, version control history, and issue tracker for this draft can
be found at https://github.com/eqvinox/icmpext-clat-source.
(Note the draft was renamed (clat → xlat) prior to submission but
changing the repository name on github breaks too many things to be
worth the effort.)
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 22 September 2025.
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Copyright Notice
Copyright (c) 2025 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Translation Behavior . . . . . . . . . . . . . . . . . . . . 4
4.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 4
4.2. Adding Node Identification Extension Object . . . . . . . 5
4.2.1. Order of Operations and Translating ICMPv6 Packet Too
Big . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Previous Work . . . . . . . . . . . . . . . . . . . . . . . . 6
6. Updates to RFC7915 . . . . . . . . . . . . . . . . . . . . . 6
7. Applicability Considerations . . . . . . . . . . . . . . . . 7
8. Security Considerations . . . . . . . . . . . . . . . . . . . 8
9. Privacy Considerations . . . . . . . . . . . . . . . . . . . 8
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
11. Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . 8
11.1. Adding Node Identification Extension Object: Suggested
Algorithm . . . . . . . . . . . . . . . . . . . . . . . 8
11.1.1. Adding New ICMP Extension Structure . . . . . . . . 8
11.1.2. Adding Node Identification Extension Object to
Existing ICMP Extension Structure . . . . . . . . . . 8
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
12.1. Normative References . . . . . . . . . . . . . . . . . . 9
12.2. Informative References . . . . . . . . . . . . . . . . . 10
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
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1. Introduction
To allow communication between IPv6-only and IPv4-only devices, IPv4/
IPv6 translators translate IPv6 and IPv4 packet headers according to
the IP/ICMP Translation Algorithm defined in [RFC7915]. For example,
464XLAT ([RFC6877]) defines an architecture for providing IPv4
connectivity across an IPv6-only network. The solution contains two
key elements: provider-side translator (PLAT) and customer-side
translator (CLAT). CLAT implementations translate private IPv4
addresses to global IPv6 addresses, and vice versa, as defined in
[RFC7915].
To map IPv4 addresses to IPv6 ones the translators use the
translation prefix (either a well-known or a network-specific one,
see [RFC6052]). The resulting IPv6 addresses can be statelessly
translated back to IPv4. However it's not the case for an arbitrary
global IPv6 addresses. Those addresses can only be translated to
IPv4 by a stateful translators and only if the corresponding
translation rule exists.
One of scenarios when it might be required but not currently possible
is translating ICMPv6 error messages send by intermediate nodes to
the CLAT address in the 464XLAT environment. The most typical
example is a diagnostic tool like traceroute sending packets to an
IPv4 destination from an IPv6-only host. Received ICMPv6 Time
Exceeded are translated to ICMP Time Exceeded. If those packets were
originated from an IPv4 address and translated to ICMPv6 by the PLAT
(NAT64) device, then the source address of such packet can be mapped
back to IPv4 by removing the translation prefix. However ICMPv6
error messages sent by devices located between the IPv6-only host and
the NAT64 device have "native" IPv6 source addresses, which can not
be mapped back to IPv4. Those packets are usually dropped and tools
like traceroute can not represent IPv6 intermediate hops in any
meaningful way. Such behaviour complicates troubleshooting. It's
also confusing for users and increases operational costs, as users
report packet loss in the network based on traceroute output.
Some CLAT implementations are known to workaround this issue by
representing IPv6 addresses in IPv4 traceroute by using a reserved
IPv4 address space and using the hop limit as the last octet, so an
IPv6 device 5 hops away is shown as 225.0.0.5 etc.
It should be noted that the similar issue occurs in IPv6 Data Center
Environments when an ICMPv6 error message needs to be sent to an
IPv4-only client. As per Section 4.8 of [RFC7755], ICMPv6 error
packets are usually dropped by the translator.
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[I-D.ietf-intarea-extended-icmp-nodeid] defines the Node
Identification Object which can carry an IP Address Sub-Object,
containing an IP address. This document proposes that when an ICMPv6
error message is translated to an ICMP one, and the IPv6 source
address can not be mapped or translated to an IPv4 one, the
translator uses the dummy IPv4 address as an IPv4 source one and
appends the Node Identification Object with the IP Address Sub-
Object, containing the original IPv6 address of an ICMPv6 error
message.
2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Terminology
Translator: a device performing translation between IPv6 and IPv4
packet headers according to the IP/ICMP Translation Algorithm defined
in [RFC7915]. Translators can be stateless ([RFC7915]) or stateful
([RFC6146]).
Translatable IPv6 address: an IPv6 address which matches the NAT64
prefix known to the translator, or for which the translator has a
stateful entry, mapping that IPv6 address to an IPv4 one.
Untranslatable IPv6 address: an IPv6 address which does not match the
NAT64 prefix(es) configured on the translator, and for which the
translator does not have a stateful entry, mapping this IPv6 address
to an IPv4 one.
4. Translation Behavior
4.1. Overview
Whenever a translator translates an ICMPv6 Destination Unreachable,
ICMPv6 Time Exceeded or ICMPv6 Packet Too Big ([RFC4443]) to the
corresponding ICMPv4 ([RFC0792]) message, and the IPv6 source address
in the outermost IPv6 header is an untranslatable one, the translator
SHOULD use the dummy IPv4 address (192.0.0.8) as IPv4 source address
for the translated packet.
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To preserve the original IPv6 source address of the packet, the
translator SHOULD append a Node Identification Object
([I-D.ietf-intarea-extended-icmp-nodeid]) with an IP Address Sub-
Object containing the IPv6 source address of the ICMPv6 packet.
The translator MUST NOT use 192.0.0.8/32 to translate the source IPv6
address and MUST NOT add the extension if the packet IPv6 source
address is translatable.
4.2. Adding Node Identification Extension Object
A Node Identification Extension Object SHOULD be added when
translating:
* ICMPv6 Destination Unreachable to ICMPv4 Destination Unreachable
* ICMPv6 Time Exceeded to ICMPv4 Time Exceeded.
* ICMPv6 Packet Too Big to ICMPv4 Destination Unreachable.
and the IPv6 source address in the outermost IPv6 header is
untranslatable.
When adding the Node Identification Extension Object, the translator
MUST include the IP Address Sub-Object containing the original IPv6
source address of the packet.
This document doesn't prescribe the exact algorith for adding the
Node Identification Extension Object when translating ICMPv6 messages
to ICMPv4. Section 11.1 describes one possible approach, but the
choice is left to implementors, as long as the following requirements
are met:
* The resulting ICMPv6 message contains the Node Identification
Extension Object with the IP Address Sub-Object.
* The checksum field of the Extension Header (Section 7 of
[RFC4884]) is updated accordingly.
* The resulting ICMPv6 packet size doesn't exceed the minimum IPv6
MTU.
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4.2.1. Order of Operations and Translating ICMPv6 Packet Too Big
This specification does not prescribe whether the Node Identification
Extension Object is added before or after translating an ICMPv6
message to ICMPv4. This choice is up to the implementation. However
ICMP Extensions can not be added to ICMPv6 Packet Too Big messages
(see Section 4.6 of [RFC4884]). Therefore in order to be able to add
the Node Identification Extension Object and preserve the original
untranslatable IPv6 address, the translator needs to add the object
to the resulting ICMPv4 packet after it's been translated from
ICMPv6. The translator MAY choose not to append the Node
Identification Extension Object when translating ICMPv6 Packet Too
Big to ICMPv4 Destination Unreachable. Such implementations SHOULD
still translate ICMPv6 Packet Too Big from untranslatable sources
using 192.0.0.8 as an IPv4 source address and SHOULD NOT drop those
packets.
5. Previous Work
[RFC6791] proposes using the Interface Information Object and
Interface IP Address Sub-Object defined in [RFC5837] to preserve the
information about untranslatable IPv6 addresses. However it should
be noted that Section 4.2 of [RFC5837] suggests that an IPv4 packet
MUST only contain an IP Interface Sub-Object representint an IPv4
address.
The solution proposes in this document has a number of benefits:
* No changes to processing of the Interface Information Object is
required.
* Using a dedicated IPV4 dummy address 192.0.0.8 might be benefitial
to indicate to the user that it's not an actual IPv4 address of
the intermediate node.
Therefore this document deprecates [RFC6791].
6. Updates to RFC7915
This document makes the following changes to Section 5.1 of
[RFC7915]:
OLD TEXT
| Source Address: Mapped to an IPv4 address based on the algorithms
| presented in Section 6.
NEW TEXT
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| Source Address: Mapped to an IPv4 address based on the algorithms
| presented in Section 6. When translating ICMPv6 error messages to
| ICMPv4 error messages and the valid IPv6 source address in the
| outermost IPv6 header can not be mapped to an IPv4 address (the
| address does not match the prefix used in algorithmic mapping and
| there are no static or stateful entries for that address), the
| translator SHOULD follow the recommendations in draft-equinox-
| intarea-icmpext-xlat-source.
This document also updates the very last paragraph of Section 5.2 of
[RFC7915] ("Error payload:") as follows:
OLD TEXT:
| For extensions not defined in [RFC4884], the translator passes the
| extensions as opaque bit strings and any IPv6 address literals
| contained therein will not be translated to IPv4 address literals;
| this may cause problems with processing of those ICMP extensions.
NEW TEXT:
| For extensions not defined in [RFC4884], the translator passes the
| extensions as opaque bit strings and any IPv6 address literals
| contained therein will not be translated to IPv4 address literals;
| this may cause problems with processing of those ICMP extensions.
| If valid IPv6 source address in the outermost IPv6 header of the
| ICMPv6 messages can not be mapped to an IPv4 address (the address
| does not match the prefix used in algorithmic mapping and there
| are no static or stateful entries for that address), the
| translator SHOULD follow the recommendations in draft-equinox-
| intarea-icmpext-xlat-source.
7. Applicability Considerations
The mechanism described in this document necessitates that the
translator distinguish between ICMPv6 packets originating from
untranslatable addresses requiring translation (triggered by an IPv4
packet translated to IPv6) and native IPv6 traffic that does not.
When the translator employs dedicated IPv6 address(es) for IPv4
translation (e.g., a CLAT instance acquiring dedicated address(es) or
a dedicated /64), this differentiation is straightforward.
However, if the same IPv6 address is used for both IPv4 translation
and native IPv6 traffic, the translator may require more complex
techniques to differentiate. These techniques could include
maintaining state and/or analyzing the invoking packet header within
the ICMPv6 message body to determine if the invoking packet was
translated
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8. Security Considerations
This document does not introduce new security considerations.
9. Privacy Considerations
This document does not introduce any privacy considerations.
10. IANA Considerations
This memo includes no request to IANA.
11. Appendix
11.1. Adding Node Identification Extension Object: Suggested Algorithm
11.1.1. Adding New ICMP Extension Structure
If the original ICMPv6 message does not contain an ICMP Extension
Structure (as defined in Section 7 of [RFC4884]), the translator
SHOULD append a new ICMP Extension Structure to the ICMP message.
When adding the new Extension Structure, the translator MUST:
* Create a new ICMP Extension Structure, containing one Extension
Header and one Node Identification Extension object. The Node
Identification Extension object MUST contain a IP Address Sub-
Object, carrying the IPv6 source address of the ICMPv6 message
being translated.
* Append that Extension Structure to the ICMP message.
* If the resulting packet size exceeds the minimum IPv6 MTU:
truncate the embedded invoking packet by removing the trailing 28
octets (to accommodate for 4 octets of the extension header and 24
octets of the extension object).
* Set the length field of the ICMP message to the length of the
padded "original datagram" field, measured in 32-bit words.
11.1.2. Adding Node Identification Extension Object to Existing ICMP
Extension Structure
If the original ICMPv6 message already contains an ICMP Extension
Structure, the translator SHOULD append a Node Identification
Extension object containing the IP Address Sub-Object to that
structure. When appending the object, the translator MUST:
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* Create a Node Identification Extension object containing the IP
Address Sub-Object. The IP Address Sub-Object MUST contain the
original source IPv6 address of the ICMPv6 message being
translated.
* Append Node Identification Extension object to the Extension
Structure.
* Update the checksum field of the Extension Header accordingly.
* If the resulting packet size exceeds the minimum IPv6 MTU:
truncate the embedded invoking packet by removing the trailing 24
octets (to accommodate for 24 octets of the extension object) and
update the length field of the ICMP message
12. References
12.1. Normative References
[RFC0792] Postel, J., "Internet Control Message Protocol", STD 5,
RFC 792, DOI 10.17487/RFC0792, September 1981,
<https://www.rfc-editor.org/info/rfc792>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet
Control Message Protocol (ICMPv6) for the Internet
Protocol Version 6 (IPv6) Specification", STD 89,
RFC 4443, DOI 10.17487/RFC4443, March 2006,
<https://www.rfc-editor.org/info/rfc4443>.
[RFC4884] Bonica, R., Gan, D., Tappan, D., and C. Pignataro,
"Extended ICMP to Support Multi-Part Messages", RFC 4884,
DOI 10.17487/RFC4884, April 2007,
<https://www.rfc-editor.org/info/rfc4884>.
[RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052,
DOI 10.17487/RFC6052, October 2010,
<https://www.rfc-editor.org/info/rfc6052>.
[RFC7915] Bao, C., Li, X., Baker, F., Anderson, T., and F. Gont,
"IP/ICMP Translation Algorithm", RFC 7915,
DOI 10.17487/RFC7915, June 2016,
<https://www.rfc-editor.org/info/rfc7915>.
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[RFC6791] Li, X., Bao, C., Wing, D., Vaithianathan, R., and G.
Huston, "Stateless Source Address Mapping for ICMPv6
Packets", RFC 6791, DOI 10.17487/RFC6791, November 2012,
<https://www.rfc-editor.org/info/rfc6791>.
[RFC6877] Mawatari, M., Kawashima, M., and C. Byrne, "464XLAT:
Combination of Stateful and Stateless Translation",
RFC 6877, DOI 10.17487/RFC6877, April 2013,
<https://www.rfc-editor.org/info/rfc6877>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[I-D.ietf-intarea-extended-icmp-nodeid]
Fenner, B. and R. Thomas, "Adding Extensions to ICMP
Errors for Originating Node Identification", Work in
Progress, Internet-Draft, draft-ietf-intarea-extended-
icmp-nodeid-01, 28 February 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-intarea-
extended-icmp-nodeid-01>.
12.2. Informative References
[RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
NAT64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146,
April 2011, <https://www.rfc-editor.org/info/rfc6146>.
[RFC5837] Atlas, A., Ed., Bonica, R., Ed., Pignataro, C., Ed., Shen,
N., and JR. Rivers, "Extending ICMP for Interface and
Next-Hop Identification", RFC 5837, DOI 10.17487/RFC5837,
April 2010, <https://www.rfc-editor.org/info/rfc5837>.
[RFC7755] Anderson, T., "SIIT-DC: Stateless IP/ICMP Translation for
IPv6 Data Center Environments", RFC 7755,
DOI 10.17487/RFC7755, February 2016,
<https://www.rfc-editor.org/info/rfc7755>.
Acknowledgements
This document is the result of discussions with Thomas Jensen. The
authors would like to thank Lorenzo Colitti, Darren Dukes, Bill
Fenner, Tobias Fiebig for their feedback, comments and guidance. The
authors would like to particularly thank Tore Anderson for pointing
out the existence and relevance of [RFC6791].
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Authors' Addresses
David 'equinox' Lamparter
NetDEF, Inc.
San Jose,
United States of America
Email: equinox@diac24.net, equinox@opensourcerouting.org
Jen Linkova
Google
1 Darling Island Rd
Pyrmont NSW 2009
Australia
Email: furry13@gmail.com, furry@google.com
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