Network Working Group                                         V. Smyslov
Internet-Draft                                                ELVIS-PLUS
Updates: 4555 (if approved)                            November 15, 2021
Intended status: Standards Track
Expires: May 19, 2022

           Responder Initiated IP Addresses Update in MOBIKE


   IKEv2 Mobility and Multihoming Protocol (MOBIKE), defined in
   [RFC4555] allows peers to update their IP addresses without re-
   establishing IKE and IPsec Security Associations (SAs).  In the
   MOBIKE protocol it is the initiator of the IKE SA, who is responsible
   for selecting new SA addresses and for initiating the IP addresses
   update procedure.  This document presents an extension to the MOBIKE
   protocol that allows the responder to initiate IP address update.
   The document updates [RFC4555].

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on May 19, 2022.

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   to this document.  Code Components extracted from this document must
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology and Notation  . . . . . . . . . . . . . . . . . .   3
   3.  Protocol Overview . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Protocol Description  . . . . . . . . . . . . . . . . . . . .   4
     4.1.  Capability Advertising  . . . . . . . . . . . . . . . . .   4
     4.2.  Responder Initiated IP Address Update . . . . . . . . . .   5
   5.  Payload Formats . . . . . . . . . . . . . . . . . . . . . . .   7
     5.1.  MOBIKE_SUPPORTED Notification . . . . . . . . . . . . . .   7
     5.2.  SWITCH_TO_IP_ADDRESS Notification . . . . . . . . . . . .   7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   The Internet Key Exchange protocol version 2 (IKEv2), specified in
   [RFC7296], is a key part of the IP Security (IPsec) architecture.  It
   allows peers to perform authenticated key exchange, which results in
   establishing IKE Security Association (IKE SA) and to create a data
   protection channels called IPsec Security Associations (IPsec SAs).
   In original IKEv2 the IKE and IPsec SAs are established between the
   IP addresses used in IKEv2 negotiation.  The IKEv2 Mobility and
   Multihoming Protocol (MOBIKE), specified in [RFC4555], extends the
   IKEv2 functionality by allowing peers to dynamically change IP
   addresses of the established SAs without the need to re-establish
   these SAs.

   The main use case for the MOBIKE protocol is a remote access user
   that travels and moves from one IP address to another without re-
   establishing existing SAs with the VPN gateway.  However, the MOBIKE
   also supports more complex scenarios when VPN gateway is multihomed
   and its addresses may change over time.

   In the MOBIKE it is the original initiator of the IKE SA (e.g. the
   remote access client) who is responsible for detecting the working IP
   addresses pairs and for deciding which pair to use.  In other words,
   the responder (e.g. the VPN gateway) plays a passive role and could
   neither initiate the IP address update process nor tell the initiator

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   which IP address is preferred to use.  This limitation makes use of
   complex scenarios less efficient and decreases the value of MOBIKE

   For example, if the VPN gateway is a load sharing cluster where each
   node has its own IP address, then the cluster must be able to move SA
   between nodes depending on their current load.  Currently Redirect
   Mechanism for IKEv2 [RFC5685] can accomplish this task, however it
   requires new IKE SA to be established, that is very inefficient.
   Another possible solution is to use IKE SA Cloning along with the
   MOBIKE (see [RFC7791] for scenario description), but the limitation
   of the MOBIKE protocol makes this problematic.  Obviously, the client
   has insufficient information to choose when and to which of cluster
   IP addresses to move an SA to and the VPN gateway has no means to
   provide the client with this information.

   This specification extends the MOBIKE protocol by adding ability for
   the responder to ask the initiator for IP address update and to
   provide it with the new IP address to use.

2.  Terminology and Notation

   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.

   In this document the term "initiator" means the party who originally
   initiated the first IKE SA (in a series of possibly several rekeyed
   IKE SAs), and "responder" means the other party.  This is consistent
   with a way these terms are used in [RFC4555].  Note, that in
   [RFC7296] the terms "original initiator" and "original responder"
   mean the party, who initiated (or responded to) the latest IKE SA in
   a series of possibly several rekeyed IKE SAs.

3.  Protocol Overview

   The MOBIKE protocol is designed in such a way, that it is the IKE SA
   initiator, who is responsible for performing the actions concerned
   with the selecting of a working IP addresses pair and for initiating
   an IP addresses update exchange.  Usually the initiator selects an IP
   addresses pair by periodically probing different pairs and choosing
   the working one.  If several pairs work then the choice between them
   is arbitrary.  The responder cannot influence the process of
   selecting and cannot ask the client to immediately switch to a
   particular gateway's address.  As a result the process of selection a

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   new pair takes substantial time and may ends up with a suboptimal

   Obviously, this limitation comes from the fact that there might be
   middleboxes on the path like Network Address Translators (NAT) or
   firewalls, that might disallow IP packets to come from VPN gateway to
   the client unless the client first contacts the VPN gateway.  For
   example, the client might reside behind a dynamic NAT that creates a
   mapping when IP packet first comes from the client to the gateway.
   If the gateway tries to send an IP packet to the client from
   different IP address, the packet would be dropped since the NAT box
   has no corresponding mapping.

   This specification provides the following solution to the described
   problem.  When the responder decides that its end of existing SA
   should be switched from its original IP address IP_R1 to a new IP
   address IP_R2, it initiates an INFORMATIONAL exchange containing a
   new notification SWITCH_TO_IP_ADDRESS, that contains IP_R2.  Once the
   initiator completes an exchange containing SWITCH_TO_IP_ADDRESS
   notification, it immediately initiates standard MOBIKE procedure for
   updating SA addresses by starting the INFORMATIONAL exchange
   containing UPDATE_SA_ADDRESSES notification.

4.  Protocol Description

4.1.  Capability Advertising

   According to [RFC4555], the peers must exchange MOBIKE_SUPPORTED
   notifications in the IKE_AUTH exchange before they can use the MOBIKE
   protocol.  If the initiator supports this specification and is
   willing to use it, then it MUST include a single octet 0x52 ('R') in
   the notification data of the MOBIKE_SUPPORTED notification sent to
   the responder.  There is no need for the initiator to know whether
   the responder supports this specification or not, so the
   MOBIKE_SUPPORTED notification sent by the responder has an empty
   notification data.

   Note, that [RFC4555] specifies that MOBIKE_SUPPORTED notification
   must contains no data when sending and the content of the
   notification data must be ignored while parsing.  So, if the
   responder doesn't support this specification, it will just ignore the
   content of the MOBIKE_SUPPORTED notification and will use MOBIKE
   without this extension.

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   (IP_I1:500 -> IP_R1:500)  -->
   HDR, SAi1, KEi, Ni,

                             <--  (IP_R1:500 -> IP_I1:500)
                                  HDR, SAr1, KEr, Nr,

   (IP_I1:4500 -> IP_R1:4500)  -->
        SAi2, TSi, TSr,
        N(MOBIKE_SUPPORTED('R')) }

                             <--  (IP_R1:4500 -> IP_I1:4500)
                                  HDR, SK { IDr, CERT, AUTH,
                                       SAr2, TSi, TSr,
                                       N(ADDITIONAL_IP4_ADDRESS) }

4.2.  Responder Initiated IP Address Update

   If the initiator advertised its support for this specification during
   the initial exchange as described in Section 4.1, then the responder
   is free to initiate IP Address Update request at any time.  If the
   initiator doesn't indicate its support for this extension, then the
   responder MUST NOT initiate IP Address Update request.  The IP
   Address Update request NUST NOT be initiated by the initiator, the
   responder MUST NOT take any action if it receives such a request
   (apart from sending an empty response message to complete the

   It is up to the responder to decide when to initiate an IP Address
   Update request and what new address to include into it.  Some of the
   possible reasons are:

   o  the responder is multihomed and wishes to switch an SA to a
      different IP address

   o  the responder is a cluster and wishes to move an SA to a different
      node having its own IP address

   The responder requests the initiator to update SA address by
   initiating the INFORMATIONAL exchange containing a new status type
   notification SWITCH_TO_IP_ADDRESS.  Its notification data contains a
   new IP address the responder requests the initiator to use for the
   IKE SA and its Child SAs.  In the example below the SA was

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   established using IP_I1 and IP_R1 addresses for the initiator and
   responder respectively, and the responder wishes to change the
   address of its end of the SA to IP_R2.  So, it initiates the
   INFORMATIONAL exchange from IP_R1 address containing the
   SWITCH_TO_IP_ADDRESS notification with IP_R2 address.

                         <--  (IP_R1:4500 -> IP_I1:4500)
                              HDR, SK { N(SWITCH_TO_IP_ADDRESS(IP_R2)) }
   (IP_I1:4500 -> IP_R1:4500)  -->
   HDR, SK {}

   Upon receiving the SWITCH_TO_IP_ADDRESS notification the initiator
   extracts its content and makes a decision whether the received IP
   address is appropriate for the SA.  If the received IP address is
   among the addresses previously received from the responder in
   it is appropriate for the SA.  Otherwise local policy must be
   consulted to decide whether the received IP is appropriate.  If the
   address is considered inappropriate, then the initiator MUST current
   address.  It is RECOMMENDED that the initiator immediately initiates
   Liveness Check exchange to ensure that the responder is able to
   operate using its current address.

   If the initiator makes a decision that the received address is
   appropriate the initiator initiates an IP address update procedure
   according to the MOBIKE specification by sending an INFORMATIONAL
   exchange request message containing the UPDATE_SA_ADDRESSES
   notification.  See [RFC4555] for details.  As a result, the remote IP
   address of the SA is changed from IP_R1 to IP_R2.  Note that only the
   IP address is changed, the port remains the same.

   (IP_I1:4500 -> IP_R2:4500)  -->
        N(COOKIE2) }

                             <--  (IP_R2:4500 -> IP_I1:4500)
                                  HDR, SK { N(NAT_DETECTION_SOURCE_IP),
                                       N(COOKIE2) }

   The responder MUST NOT change IP addresses of the SA until it
   receives the UPDATE_SA_ADDRESSES notification from the initiator.

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5.  Payload Formats

5.1.  MOBIKE_SUPPORTED Notification

   The MOBIKE_SUPPORTED Notification is defined in [RFC4555],
   Section 4.2.1 with the Notify Message Type 16396.  This definition
   requires the notification data to be empty while sending and to be
   ignored when notification is received.

   This document updates the definition from [RFC4555].  Exchange
   initiator sets the notification data of the MOBIKE_SUPPORTED
   Notification to a single octet 0x52 ('R') to indicate that this
   specification is supported.

5.2.  SWITCH_TO_IP_ADDRESS Notification

   The Notify Message Type for this notification is <TBA by IANA>.  The
   notification data contains new responder's IP address.

   For IPv4, the notification data is 4 octets long and is defined as

                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |                 New Responder's IPv4 Address                  |

   For IPv6, the notification data is 16 octets long and is defined as

                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |                                                               |
   |                 New Responder's IPv6 Address                  |
   |                                                               |
   |                                                               |

   The Protocol ID and SPI Size fields are set to zero.

6.  Security Considerations

   This specification is an extension of the MOBIKE protocol, so the
   Security Considerations described in [RFC4555] are applied.

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7.  IANA Considerations

   This document defines new Notify Message Types in the "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,

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <>.

   [RFC4555]  Eronen, P., "IKEv2 Mobility and Multihoming Protocol
              (MOBIKE)", RFC 4555, DOI 10.17487/RFC4555, June 2006,

   [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, <>.

8.2.  Informative References

   [RFC5685]  Devarapalli, V. and K. Weniger, "Redirect Mechanism for
              the Internet Key Exchange Protocol Version 2 (IKEv2)",
              RFC 5685, DOI 10.17487/RFC5685, November 2009,

   [RFC7791]  Migault, D., Ed. and V. Smyslov, "Cloning the IKE Security
              Association in the Internet Key Exchange Protocol Version
              2 (IKEv2)", RFC 7791, DOI 10.17487/RFC7791, March 2016,

Author's Address

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   Valery Smyslov
   PO Box 81
   Moscow (Zelenograd)  124460
   Russian Federation

   Phone: +7 495 276 0211

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