Internet Engineering Task Force (IETF)                      M. Boucadair
Request for Comments: 8983                                        Orange
Updates: 7296                                              February 2021
Category: Standards Track
ISSN: 2070-1721


 Internet Key Exchange Protocol Version 2 (IKEv2) Notification Status
                   Types for IPv4/IPv6 Coexistence

Abstract

  This document specifies new Internet Key Exchange Protocol Version 2
  (IKEv2) notification status types to better manage IPv4 and IPv6
  coexistence by allowing the responder to signal to the initiator
  which address families are allowed.

  This document updates RFC 7296.

Status of This Memo

  This is an Internet Standards Track document.

  This document is a product of the Internet Engineering Task Force
  (IETF).  It represents the consensus of the IETF community.  It has
  received public review and has been approved for publication by the
  Internet Engineering Steering Group (IESG).  Further information on
  Internet Standards is available in Section 2 of RFC 7841.

  Information about the current status of this document, any errata,
  and how to provide feedback on it may be obtained at
  https://www.rfc-editor.org/info/rfc8983.

Copyright Notice

  Copyright (c) 2021 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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  the Trust Legal Provisions and are provided without warranty as
  described in the Simplified BSD License.

Table of Contents

  1.  Introduction
  2.  Terminology
  3.  Why Not INTERNAL_ADDRESS_FAILURE?
  4.  IP6_ALLOWED and IP4_ALLOWED Status Types
  5.  Update to RFC 7296
  6.  Security Considerations
  7.  IANA Considerations
  8.  References
    8.1.  Normative References
    8.2.  Informative References
  Acknowledgements
  Author's Address

1.  Introduction

  As described in [RFC7849], if the subscription data or network
  configuration allows only one IP address family (IPv4 or IPv6), the
  cellular host must not request a second PDP-Context (Section 3.2 of
  [RFC6459]) to the same Access Point Name (APN) for the other IP
  address family (AF).  The Third Generation Partnership Project (3GPP)
  network informs the cellular host about allowed Packet Data Protocol
  (PDP) types by means of Session Management (SM) cause codes.  In
  particular, the following cause codes can be returned:

  cause #50 "PDP type IPv4 only allowed":  This cause code is used by
     the network to indicate that only PDP type IPv4 is allowed for the
     requested Public Data Network (PDN) connectivity.

  cause #51 "PDP type IPv6 only allowed":  This cause code is used by
     the network to indicate that only PDP type IPv6 is allowed for the
     requested PDN connectivity.

  cause #52 "single address bearers only allowed":  This cause code is
     used by the network to indicate that the requested PDN
     connectivity is accepted with the restriction that only single IP
     version bearers are allowed.

  If the requested IPv4v6 PDP-Context is not supported by the network
  but IPv4 and IPv6 PDP types are allowed, then the cellular host will
  be configured with an IPv4 address or an IPv6 prefix by the network.
  It must initiate another PDP-Context activation of the other address
  family in addition to the one already activated for a given APN.  The
  purpose of initiating a second PDP-Context is to achieve dual-stack
  connectivity (that is, IPv4 and IPv6 connectivity) by means of two
  PDP-Contexts.

  When the User Equipment (UE) attaches to the 3GPP network using a
  non-3GPP access network (e.g., Wireless Local Area Network (WLAN)),
  there are no equivalent IKEv2 capabilities [RFC7296] notification
  codes for the 3GPP network to inform the UE why an IP address family
  is not assigned or whether that UE should retry with another address
  family.

  This document fills that void by introducing new IKEv2 notification
  status types for the sake of deterministic UE behaviors (Section 4).

  These notification status types are not specific to 3GPP
  architectures but can be used in other deployment contexts.  Cellular
  networks are provided as an illustration example.

2.  Terminology

  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.

  This document makes use of the terms defined in [RFC7296].  In
  particular, readers should be familiar with "initiator" and
  "responder" terms used in that document.

3.  Why Not INTERNAL_ADDRESS_FAILURE?

  The following address assignment failures may be encountered when an
  initiator requests assignment of IP addresses/prefixes:

  *  An initiator asks for IPvx, but IPvx address assignment is not
     supported by the responder.

  *  An initiator requests both IPv4 and IPv6 addresses, but only IPv4
     address assignment is supported by the responder.

  *  An initiator requests both IPv4 and IPv6 addresses, but only IPv6
     prefix assignment is supported by the responder.

  *  An initiator asks for both IPv4 and IPv6 addresses, but only one
     address family can be assigned by the responder for policy
     reasons.

  Section 3.15.4 of [RFC7296] defines a generic notification error type
  (INTERNAL_ADDRESS_FAILURE) that is related to a failure to handle an
  address assignment request.  The responder sends
  INTERNAL_ADDRESS_FAILURE only if no addresses can be assigned.  This
  behavior does not explicitly allow an initiator to determine why a
  given address family is not assigned, nor whether it should try using
  another address family.  INTERNAL_ADDRESS_FAILURE is a catch-all
  error type when an address-related issue is encountered by an IKEv2
  responder.

  INTERNAL_ADDRESS_FAILURE does not provide sufficient hints to the
  IKEv2 initiator to adjust its behavior.

4.  IP6_ALLOWED and IP4_ALLOWED Status Types

  IP6_ALLOWED and IP4_ALLOWED notification status types (see Section 7)
  are defined to inform the initiator about the responder's address
  family assignment support capabilities and to report to the initiator
  the reason why an address assignment failed.  These notification
  status types are used by the initiator to adjust its behavior
  accordingly (Section 5).

  No data is associated with these notifications.

5.  Update to RFC 7296

  If the initiator is dual stack (i.e., supports both IPv4 and IPv6),
  it MUST include configuration attributes for both address families in
  its configuration request (absent explicit policy/configuration
  otherwise).  More details about IPv4 and IPv6 configuration
  attributes are provided in Section 3.15 of [RFC7296].  These
  attributes are used to infer the requested/assigned AFs listed in
  Table 1.

  The responder MUST include the IP6_ALLOWED and/or IP4_ALLOWED
  notification status type in a response to an address assignment
  request as indicated in Table 1.

   +=============+==============+=============+=====================+
   | Requested   | Supported    | Assigned    | Returned            |
   | AF(s)       | AF(s)        | AF(s)       | Notification Status |
   | (Initiator) | (Responder)  | (Responder) | Type(s) (Responder) |
   +=============+==============+=============+=====================+
   | IPv4        | IPv6         | None        | IP6_ALLOWED         |
   +-------------+--------------+-------------+---------------------+
   | IPv4        | IPv4         | IPv4        | IP4_ALLOWED         |
   +-------------+--------------+-------------+---------------------+
   | IPv4        | IPv4 and     | IPv4        | IP4_ALLOWED,        |
   |             | IPv6         |             | IP6_ALLOWED         |
   +-------------+--------------+-------------+---------------------+
   | IPv6        | IPv6         | IPv6        | IP6_ALLOWED         |
   +-------------+--------------+-------------+---------------------+
   | IPv6        | IPv4         | None        | IP4_ALLOWED         |
   +-------------+--------------+-------------+---------------------+
   | IPv6        | IPv4 and     | IPv6        | IP4_ALLOWED,        |
   |             | IPv6         |             | IP6_ALLOWED         |
   +-------------+--------------+-------------+---------------------+
   | IPv4 and    | IPv4         | IPv4        | IP4_ALLOWED         |
   | IPv6        |              |             |                     |
   +-------------+--------------+-------------+---------------------+
   | IPv4 and    | IPv6         | IPv6        | IP6_ALLOWED         |
   | IPv6        |              |             |                     |
   +-------------+--------------+-------------+---------------------+
   | IPv4 and    | IPv4 and     | IPv4 and    | IP4_ALLOWED,        |
   | IPv6        | IPv6         | IPv6        | IP6_ALLOWED         |
   +-------------+--------------+-------------+---------------------+
   | IPv4 and    | IPv4 or IPv6 | IPv4 or     | IP4_ALLOWED,        |
   | IPv6        | (policy      | IPv6        | IP6_ALLOWED         |
   |             | based)       |             |                     |
   +-------------+--------------+-------------+---------------------+

              Table 1: Returned Notification Status Types

  If the initiator only receives one single IP4_ALLOWED or IP6_ALLOWED
  notification from the responder, the initiator MUST NOT send a
  subsequent request for an alternate address family not supported by
  the responder.

  If a dual-stack initiator requests only an IPv6 prefix (or an IPv4
  address) but only receives an IP4_ALLOWED (or IP6_ALLOWED)
  notification status type from the responder, the initiator MUST send
  a request for IPv4 address(es) (or IPv6 prefix(es)).

  If a dual-stack initiator requests both an IPv6 prefix and an IPv4
  address but receives an IPv6 prefix (or an IPv4 address) only with
  both IP4_ALLOWED and IP6_ALLOWED notification status types from the
  responder, the initiator MAY send a request for the other AF (i.e.,
  IPv4 address (or IPv6 prefix)).  In such case, the initiator MUST
  create a new IKE Security Association (SA) and request another
  address family using the new IKE SA.

  For other address-related error cases that have not been covered by
  the aforementioned notification status types, the responder/initiator
  MUST follow the procedure defined in Section 3.15.4 of [RFC7296].

6.  Security Considerations

  Since the IPv4/IPv6 capabilities of a node are readily determined
  from the traffic it generates, this document does not introduce any
  new security considerations compared to the ones described in
  [RFC7296], which continue to apply.

7.  IANA Considerations

  IANA has updated the "IKEv2 Notify Message Types - Status Types"
  registry (available at <https://www.iana.org/assignments/
  ikev2-parameters/>) with the following status types:

         +=======+================================+===========+
         | Value | NOTIFY MESSAGES - STATUS TYPES | Reference |
         +=======+================================+===========+
         | 16439 | IP4_ALLOWED                    | RFC 8983  |
         +-------+--------------------------------+-----------+
         | 16440 | IP6_ALLOWED                    | RFC 8983  |
         +-------+--------------------------------+-----------+

           Table 2: Updates to "IKEv2 Notify Message Types -
                         Status Types" Registry

8.  References

8.1.  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>.

  [RFC7296]  Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
             Kivinen, "Internet Key Exchange Protocol Version 2
             (IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October
             2014, <https://www.rfc-editor.org/info/rfc7296>.

  [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>.

8.2.  Informative References

  [RFC6459]  Korhonen, J., Ed., Soininen, J., Patil, B., Savolainen,
             T., Bajko, G., and K. Iisakkila, "IPv6 in 3rd Generation
             Partnership Project (3GPP) Evolved Packet System (EPS)",
             RFC 6459, DOI 10.17487/RFC6459, January 2012,
             <https://www.rfc-editor.org/info/rfc6459>.

  [RFC7849]  Binet, D., Boucadair, M., Vizdal, A., Chen, G., Heatley,
             N., Chandler, R., Michaud, D., Lopez, D., and W. Haeffner,
             "An IPv6 Profile for 3GPP Mobile Devices", RFC 7849,
             DOI 10.17487/RFC7849, May 2016,
             <https://www.rfc-editor.org/info/rfc7849>.

Acknowledgements

  Many thanks to Christian Jacquenet for the review.

  Thanks to Paul Wouters, Yaov Nir, Valery Smyslov, Daniel Migault,
  Tero Kivinen, and Michael Richardson for the comments and review.

  Thanks to Benjamin Kaduk for the AD review.

  Thanks to Murray Kucherawy, Éric Vyncke, and Robert Wilton for the
  IESG review.

Author's Address

  Mohamed Boucadair
  Orange
  35000 Rennes
  France

  Email: [email protected]

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