IPv6 operations                                             D. Lamparter
Internet-Draft                                              NetDEF, Inc.
Updates: 7915 (if approved)                                   J. Linkova
Intended status: Standards Track                                  Google
Expires: 15 April 2025                                   12 October 2024


Using Dummy IPv4 Address and Node Identification Extensions for IP/ICMP
                          translators (XLATs)
           draft-equinox-v6ops-icmpext-xlat-v6only-source-00

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 15 April 2025.




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Copyright Notice

   Copyright (c) 2024 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
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   4
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Translation Behavior  . . . . . . . . . . . . . . . . . . . .   4
     4.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .   4
     4.2.  Adding Node Identification Extension Object . . . . . . .   4
       4.2.1.  Order of Operations and Translating ICMPv6 Packet Too
               Big . . . . . . . . . . . . . . . . . . . . . . . . .   5
       4.2.2.  Adding New ICMP Extension Structure . . . . . . . . .   5
       4.2.3.  Adding Node Identification Extension Object to Existing
               ICMP Extension Structure  . . . . . . . . . . . . . .   6
   5.  Updates to RFC7915  . . . . . . . . . . . . . . . . . . . . .   6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   7.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .   7
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

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].



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   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.

   [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.







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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.

   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:



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   *  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.

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.

4.2.2.  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.







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   *  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.

4.2.3.  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:

   *  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

5.  Updates to RFC7915

   This document makes the following changes to Section 5.1 of
   [RFC7915]:

   The text in RFC7915 is as follows:

   |  Source Address: Mapped to an IPv4 address based on the algorithms
   |  presented in Section 6.

   This document updates the text as follows:









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   |  Source Address: Mapped to an IPv4 address based on the algorithms
   |  presented in Section 6.  When translating ICMPv4 error messages to
   |  ICMPv6 error messages and the valid IPv6 source address in the
   |  outermost IPv6 header does not match the prefix used in
   |  algorithmic mapping, the translator SHOULD follow the
   |  recommendations in draft-equinox-intarea-icmpext-xlat-source.

   This document also adds the following paragraph before the very last
   paragraph of Section 5.2 of [RFC7915] (before "Error payload:"):

   |  If valid IPv6 source address in the outermost IPv6 header of the
   |  ICMPv6 messages does not match the prefix used in algorithmic
   |  mapping, the translator SHOULD follow the recommendations in
   |  draft-equinox-intarea-icmpext-xlat-source.

6.  Security Considerations

   TBD.

7.  Privacy Considerations

   This document does not introduce any privacy considerations.

8.  IANA Considerations

   This memo includes no request to IANA.

9.  References

9.1.  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>.






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   [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>.

   [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, "Extending ICMP for Node
              Identification", Work in Progress, Internet-Draft, draft-
              ietf-intarea-extended-icmp-nodeid-00, 30 September 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-intarea-
              extended-icmp-nodeid-00>.

9.2.  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>.

   [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 Darren Dukes, Bill Fenner for their
   feedback, comments and guidance.



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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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