RFC 8983

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


   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

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction
   2.  Terminology
   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

   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

   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

   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",
   "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.


   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

   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

   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,

   [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,

   [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,


   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
   35000 Rennes

   Email: mohamed.boucadair@orange.com