Internet DRAFT - draft-link-v6ops-claton

draft-link-v6ops-claton







IPv6 operations                                               J. Linkova
Internet-Draft                                                    Google
Updates: 8585 (if approved)                                    T. Jensen
Intended status: Informational                                 Microsoft
Expires: 31 August 2024                                 28 February 2024


       464 Customer-side Translator (CLAT): Node Recommendations
                       draft-link-v6ops-claton-02

Abstract

   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).  This document provides recommendations on when a
   node shall enable or disable CLAT.

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
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   This Internet-Draft will expire on 31 August 2024.

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
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   Please review these documents carefully, as they describe your rights
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   provided without warranty as described in the Revised BSD License.



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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Multiple Interfaces Considerations  . . . . . . . . . . . . .   3
   5.  Enabling CLAT . . . . . . . . . . . . . . . . . . . . . . . .   4
     5.1.  Detecting IPv4 Presence . . . . . . . . . . . . . . . . .   4
   6.  CLAT Addresses Considerations . . . . . . . . . . . . . . . .   4
     6.1.  CLAT IPv4 Addresses . . . . . . . . . . . . . . . . . . .   4
     6.2.  CLAT IPv6 Addresses . . . . . . . . . . . . . . . . . . .   6
   7.  Disabling CLAT  . . . . . . . . . . . . . . . . . . . . . . .   7
   8.  Updates to RFC8585  . . . . . . . . . . . . . . . . . . . . .   7
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   10. Privacy Considerations  . . . . . . . . . . . . . . . . . . .   9
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     12.1.  Normative References . . . . . . . . . . . . . . . . . .   9
     12.2.  Informative References . . . . . . . . . . . . . . . . .  10
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   464XLAT is widely deployed in 3GPP networks (as described in
   Section 4.2 of [RFC6877]) where a mobile phone performs the CLAT
   function, providing a private IPv4 address and IPv4 default route for
   the applications and tethered devices.  Enabling 464XLAT allowed
   mobile operators to migrate User Equipment (UE) devices (also known
   as mobile phones) to IPv6-only mode, where those devices are only
   assigned IPv6 addresses.

   Until recently, IPv6-only hosts were rather uncommon outside of
   mobile networks and datacenters.  Even if the network provides PLAT
   in the form of NAT64, hosts like desktops and laptops still need the
   network to provide IPv4 addresses, as otherwise IPv4-only
   applications fail.  However, as more and more operating systems
   outside of the 3GPP world support CLAT, it becomes possible to
   migrate those devices to IPv6-only mode.  Networks such as public Wi-
   Fi, enterprise networks, or even home networks can deploy 464XLAT as
   described in Section 4.2 of [RFC6877]:

   *  PLAT functions are performed by NAT64 network devices.

   *  CLAT is performed by the host itself.






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   Another 464XLAT deployment model is a Wireline one (section 4.1 of
   [RFC6877]), when a CPE router is connected to an IPv6-only network
   and provides CLAT functions for IPv4-enabled downstream devices.
   [RFC8585] specifies 464XLAT support requirements for such devices.

   For both scenarios to work, the node performing CLAT (such as a host
   or a CPE router) need to enable the CLAT when connecting to an
   IPv6-only network.  This document complements [RFC6877] by providing
   recommendations for the node developers on enabling and disabling
   CLAT functions.

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

   *  IPv6-only network: A network that does not assign IPv4 addresses
      to hosts and facilitates connectivity to IPv4-only destinations
      using NAT64 (([RFC6146]).  In this document, the term "IPv6-only
      network" specifically refers to networks that provide NAT64 as
      it's required by the 464XLAT architecture ([RFC6877]).

   *  CLAT Node: a node (a host or a router) which performs CLAT
      functions by running one or multiple CLAT instances (e.g. one CLAT
      instance per interface).

4.  Multiple Interfaces Considerations

   A node may have multiple IPv6-only interfaces (for example, a mobile
   phone can be connected to an IPv6-only Wi-Fi network and to an
   IPv6-only mobile network).  In that case the node SHOULD run an
   independent, dedicated CLAT instance on each interface connected to a
   network equipped with PLAT.  Consequently, each CLAT instance SHOULD
   install a separate default IPv4 route on each CLAT-enabled interface.
   The metrics of IPv4 routes SHOULD be consistent with the metrics of
   IPv6 default routes.










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5.  Enabling CLAT

   To enable CLAT, the node needs to discover the PLAT-side translation
   IPv6 prefix, also known as the NAT64 prefix (see Section 6.3 of
   [RFC6877]).  The PREF64 Router Advertisement option ([RFC8781])
   provides that information and can be used as a strong indication that
   the network supports NAT64 (PLAT) functionality.  Therefore the node
   SHOULD enable CLAT if it receives an Router Advertisement containing
   PREF64 option.

   If RAs received by the node do not contain a PREF64 option, the node
   MAY use other mechanisms to detect the PLAT presence and obtain the
   NAT64 prefix (such as [RFC7050]).  In that case, the node SHOULD
   enable CLAT after discovering the NAT64 prefix, unless by that time
   the node has already obtained an IPv4 address.

   The node MUST follow recommendations from Section 4 of [RFC7335] to
   avoid IPv4 address space conflicts.

5.1.  Detecting IPv4 Presence

   From a performance perspective, native IPv4 connectivity is
   preferrable over 464XLAT, so CLAT SHOULD NOT be enabled if the node
   has IPv4 connectivity over the given interface.  However, SLAAC might
   complete faster than DHCPv4.  The node SHOULD NOT wait for an
   explicit (DHCPv4 Option 108, [RFC8925]) or an implicit (DHCPv4
   timeouts) indication that native IPv4 connectivity is not available.
   Such delay would be impactful for IPv4-only applications, as such
   applications cannot benefit from 464XLAT until CLAT is operational.
   Therefore, the node SHOULD enable CLAT as soon as network support for
   PLAT is detected while IPv4 connectivity is not yet detected.
   Clients SHOULD then disable CLAT if native IPv4 connectivity is
   established whether or not PLAT support from the network remains
   available.

6.  CLAT Addresses Considerations

6.1.  CLAT IPv4 Addresses

   There are two different models in 464xlat deployments:











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   *  A dedicated prefix model, which Section 4.1 of [RFC6877] calls
      "wireline network architecture".  In that case, the node
      performing CLAT functions also extends the network downstream and
      provides network connectivity services to other connected systems.
      Those systems can be physical (e.g. various clients connected to a
      CPE router), or logical (e.g. virtual systems running on a node,
      while the host system acts as a router and performs CLAT).  In all
      those cases, systems behind the CLAT node usually use [RFC1918]
      addresses.

   *  A single-address model, which section 4.2 of [RFC6877] calls
      "wireless network architecture".  In that case, the CLAT instance
      provides an IPv4 address and the default route to the local node's
      network stack only.  It should be noted that [RFC6877] implies
      that the second deployment scenario is limited to 3GPP cases,
      while currently it is also deployed in other types of networks,
      such as enterprise and public Wi-Fi networks, where hosts (as
      mobile phones, laptops and desktops) use CLAT to provide
      connectivity to IPv4-only local applications.  Despite the word
      "wireless" in the name, this architecure is applicable for wired
      networks as well (e.g. desktops or servers using wired
      connections).

   In the latter case, the CLAT instance needs a single IPv6 and a
   single IPv4 address only.  The node providing CLAT functions to local
   applications SHOULD use IPv4 addresses from the dedicated
   192.0.0.0/29 range ([RFC7335]), reserved for IPv4 continuity
   solutions including but not limited to 464XLAT.  If the node runs
   multiple CLAT instances (see Section 4), the node SHOULD use
   different local IPv4 addresses for each CLAT instance.  This means
   that it is not possible to run more than 8 CLAT instances per node.
   The node MUST NOT send packets on wire from the local CLAT address.

   The host SHOULD use 255.255.255.255 as a netmask for the CLAT
   address.  That allows all 8 addresses from 192.0.0.0/29 to be used,
   if needed.

   It should be noted that 192.0.0.0/29 is shared between multiple IPv4
   continuity solutions such as 464XLAT and DS-Lite (see [RFC7335].  For
   example, Section 10 of [RFC6333] reserves 192.0.0.1 for the Dual-
   Stack Lite default router.  However, as per Section 4 of [RFC7335],
   the host MUST NOT enable two active IPv4 continuity solutions
   simultaneously in a way that would cause a node to have overlapping
   192.0.0.0/29 address space.  Therefore, as long as the host is not
   using DS-Lite, it MAY use 192.0.0.1 as a CLAT address.






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6.2.  CLAT IPv6 Addresses

   Section 6.3 of [RFC6877] recommends that the CLAT instance acquires a
   dedicated /64 for translating between IPv4 and IPv6, and only uses a
   single interface IPv6 address if a dedicated prefix is not available
   via DHCPv6-PD.  However, deployments where each node can obtain a
   dedicated /64 just for CLAT are rather uncommon, to say the least.
   In most cases, the CLAT instance uses a single IPv6 address as a
   source for all IPv4 traffic translated bt CLAT.

   The CLAT instance SHOULD obtain a dedicated IPv6 address used
   exclusively for CLAT functions.  This is required as when the node
   receives a packet from a NAT64 source, the node needs to
   differentiate between native IPv6 traffic and traffic which needs to
   be passed to the CLAT instance.  For example, an ICMPv6 Echo Reply
   packet from 64:ff9b::203.0.113.1 can be a response to either an IPv6
   ping to 64:ff9b::203.0.113.1, or an IPv4 ping to 203.0.113.1,
   translated by CLAT.  Using a dedicated IPv6 source address for CLAT
   traffic allows the node to make that distinction without keeping
   state and operate in the stateless mode (see Section 1.3 of
   [RFC6145].

   In accordance with Section 5.4 of [RFC4862], the node MUST perform
   Duplicate Address Detection for each dedicated CLAT address.

   If the dedicated CLAT address is obtained via SLAAC, the CLAT
   instance SHOULD ensure that the address is checksum-neutral for the
   given local IPv4 CLAT address and the NAT64 prefix (this means that
   the local IPv4 address needs to be assigned/known before the IPv6 one
   is configured).  Using a checksum-neutral CLAT address provides the
   following benefits:

   *  Better performance as CLAT doesn't need to recalculate the
      checksum.

   *  If a protocol uses the standard IP checksum, CLAT doesn't need to
      recalculate the checksum.  That improves the chances of the
      protocol working via CLAT even if CLAT is not aware of the
      protocol's semantics.

   The node SHOULD generate a different interface id for the CLAT
   address when connecting to different networks, even if the NAT64
   prefix and the local IPv4 CLAT address do not change.  To achieve
   that, the node SHOULD generate a random checksum-neutral CLAT address
   every time.






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7.  Disabling CLAT

   The node MAY choose to turn CLAT off if an IPv4 address becomes
   available after CLAT has started.  However, turning it off would
   affect all applications and traffic flows already utilizing CLAT.

8.  Updates to RFC8585

   This document makes the following changes to Section 3.2.1 of
   [RFC8585]:

   OLD TEXT:

   ===

   464XLAT requirements:

   ===

   NEW TEXT:

   ===

   464XLAT requirements:

   464XLAT-0: The IPv6 Transition CE Router SHOULD follow
   recommendations provided in draft-link-v6ops-claton.

   ===

   OLD TEXT:

   ===

   464XLAT-4: The IPv6 Transition CE Router MUST implement [RFC7050]
   ("Discovery of the IPv6 Prefix Used for IPv6 Address Synthesis") in
   order to discover the provider-side translator (PLAT) translation
   IPv4 and IPv6 prefix(es)/suffix(es).

   464XLAT-5: If PCP is implemented, the IPv6 Transition CE Router MUST
   follow [RFC7225] ("Discovering NAT64 IPv6 Prefixes Using the Port
   Control Protocol (PCP)") in order to learn the PLAT-side translation
   IPv4 and IPv6 prefix(es)/suffix(es) used by an upstream PCP-
   controlled NAT64 device.

   464XLAT-6: If the network provides several choices for the discovery/
   learning of the NAT64 prefix, the priority to use one or the other
   MUST follow this order: 1) [RFC7225] and 2) [RFC7050].



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   The NAT64 prefix could be discovered by means of the method defined
   in [RFC7050] only if the service provider uses DNS64 [RFC6147].  It
   may be the case that the service provider does not use or does not
   trust DNS64 [RFC6147] because the DNS configuration at the CE (or
   hosts behind the CE) can be modified by the customer.  In that case,
   the service provider may opt to configure the NAT64 prefix by means
   of the option defined in [RFC7225].  This can also be used if the
   service provider uses DNS64 [RFC6147].

   ===

   NEW TEXT

   ===

   464XLAT-4: The IPv6 Transition CE Router MUST implement [RFC8781]
   ("Discovering PREF64 in Router Advertisements") and [RFC7050]
   ("Discovery of the IPv6 Prefix Used for IPv6 Address Synthesis") in
   order to discover the provider-side translator (PLAT) translation
   IPv4 and IPv6 prefix(es)/suffix(es).

   464XLAT-5: If PCP is implemented, the IPv6 Transition CE Router MUST
   follow [RFC7225] ("Discovering NAT64 IPv6 Prefixes Using the Port
   Control Protocol (PCP)") in order to learn the PLAT-side translation
   IPv4 and IPv6 prefix(es)/suffix(es) used by an upstream PCP-
   controlled NAT64 device.

   464XLAT-6: If the network provides several choices for the discovery/
   learning of the NAT64 prefix, the priority to use one or the other
   MUST follow this order: 1)[RFC7225] 2)[RFC8781] and 3) [RFC7050].

   [RFC8781] allows the service provider to signal NAT64 prefix
   independently from DNS64 presence.  At the same time the NAT64 prefix
   could be discovered by means of the method defined in [RFC7050] only
   if the service provider uses DNS64 [RFC6147].  It may be the case
   that the service provider does not use or does not trust DNS64
   [RFC6147] because the DNS configuration at the CE (or hosts behind
   the CE) can be modified by the customer.  In that case, the service
   provider may opt to configure the NAT64 prefix by means of the option
   defined in [RFC7225].  This can also be used if the service provider
   uses DNS64 [RFC6147].

   ===








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9.  Security Considerations

   If a malicious actor spoofs PLAT presence signals (such as an RA with
   PREF64 option) or DNS responses for DNS-based NAT64 prefix detection
   ([RFC7050]), traffic of IPv4-only applications using CLAT can be
   affected:

   *  if there is no PLAT (NAT64) devices, traffic to NAT64 destinations
      would be dropped.

   *  If the attacker intercepts traffic for the NAT64 prefix (e.g. by
      providing the victim with a bogus NAT64 prefix and steering
      traffic for those destinations towards themselves), the attacker
      might be able to perform man-in-the-middle attacks.

   Using the PREF64 RA option to detect PLAT presence and the NAT64
   prefix is less prone to such attacks, as the attacker needs to be on-
   link and be able to bypass layer-2 security features such as RA
   Guard.

10.  Privacy Considerations

   This document does not introduce any privacy considerations.

11.  IANA Considerations

   This memo does not introduce any requests to IANA.

12.  References

12.1.  Normative References

   [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>.

   [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>.

   [RFC6333]  Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
              Stack Lite Broadband Deployments Following IPv4
              Exhaustion", RFC 6333, DOI 10.17487/RFC6333, August 2011,
              <https://www.rfc-editor.org/info/rfc6333>.





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   [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>.

   [RFC7050]  Savolainen, T., Korhonen, J., and D. Wing, "Discovery of
              the IPv6 Prefix Used for IPv6 Address Synthesis",
              RFC 7050, DOI 10.17487/RFC7050, November 2013,
              <https://www.rfc-editor.org/info/rfc7050>.

   [RFC7335]  Byrne, C., "IPv4 Service Continuity Prefix", RFC 7335,
              DOI 10.17487/RFC7335, August 2014,
              <https://www.rfc-editor.org/info/rfc7335>.

   [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>.

   [RFC8781]  Colitti, L. and J. Linkova, "Discovering PREF64 in Router
              Advertisements", RFC 8781, DOI 10.17487/RFC8781, April
              2020, <https://www.rfc-editor.org/info/rfc8781>.

   [RFC8585]  Palet Martinez, J., Liu, H. M.-H., and M. Kawashima,
              "Requirements for IPv6 Customer Edge Routers to Support
              IPv4-as-a-Service", RFC 8585, DOI 10.17487/RFC8585, May
              2019, <https://www.rfc-editor.org/info/rfc8585>.

   [RFC8925]  Colitti, L., Linkova, J., Richardson, M., and T.
              Mrugalski, "IPv6-Only Preferred Option for DHCPv4",
              RFC 8925, DOI 10.17487/RFC8925, October 2020,
              <https://www.rfc-editor.org/info/rfc8925>.

12.2.  Informative References

   [RFC1918]  Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.
              J., and E. Lear, "Address Allocation for Private
              Internets", BCP 5, RFC 1918, DOI 10.17487/RFC1918,
              February 1996, <https://www.rfc-editor.org/info/rfc1918>.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              DOI 10.17487/RFC4861, September 2007,
              <https://www.rfc-editor.org/info/rfc4861>.

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862,
              DOI 10.17487/RFC4862, September 2007,
              <https://www.rfc-editor.org/info/rfc4862>.



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   [RFC6145]  Li, X., Bao, C., and F. Baker, "IP/ICMP Translation
              Algorithm", RFC 6145, DOI 10.17487/RFC6145, April 2011,
              <https://www.rfc-editor.org/info/rfc6145>.

   [RFC7225]  Boucadair, M., "Discovering NAT64 IPv6 Prefixes Using the
              Port Control Protocol (PCP)", RFC 7225,
              DOI 10.17487/RFC7225, May 2014,
              <https://www.rfc-editor.org/info/rfc7225>.

Acknowledgements

   Thanks to Ondrej Caletka, Lorenzo Colitti, Ted Lemon, Jordi Palet,
   Dieter Siegmund for the discussions, the input and all contribution.

Authors' Addresses

   Jen Linkova
   Google
   1 Darling Island Rd
   Pyrmont NSW 2009
   Australia
   Email: furry13@gmail.com, furry@google.com


   Tommy Jensen
   Microsoft
   Email: tojens@microsoft.com
























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