MOBIKE Working Group                                      P. Eronen, Ed.
Internet-Draft                                                     Nokia
Expires: April 2, 10, 2006                                September 29,                                  October 7, 2005

            IKEv2 Mobility and Multihoming Protocol (MOBIKE)

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Copyright Notice

   Copyright (C) The Internet Society (2005).


   This document describes the MOBIKE protocol, a mobility and
   multihoming extension to Internet Key Exchange (IKEv2).  MOBIKE
   allows hosts to update the (outer) IP addresses associated with IKEv2
   and IPsec Security Associations.  A mobile VPN client could use
   MOBIKE to keep the connection with the VPN gateway active while
   moving from one address to another.  Similarly, a multihomed host
   could use MOBIKE to move the traffic to a different interface if, for
   instance, the one currently being used one stops working.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology and Notation . . . . . . . . . . . . . . . . . . .  3
   3.  Protocol Overview  . . . . . . . . . . . . . . . . . . . . . .  4
     3.1.  Basic Operation  . . . . . . . . . . . . . . . . . . . . .  4
     3.2.  Example Protocol Runs  . . . . . . . . . . . . . . . . . .   5
     3.3  6
     3.3.  MOBIKE and Network Address Translation (NAT) . . . . . . .  8
     3.4.  Limitations  . . . . . . . . . . . . . . . . . . . . . . .  8
   4.  Protocol Exchanges . . . . . . . . . . . . . . . . . . . . . .  9
     4.1.  Signaling Support for MOBIKE . . . . . . . . . . . . . . .  9
     4.2.  Initial Tunnel Header Addresses  . . . . . . . . . . . . .  9
     4.3.  Additional Addresses . . . . . . . . . . . . . . . . . . .  9
     4.4.  Changing Addresses in IPsec SAs  . . . . . . . . . . . . . 11
     4.5.  Updating Additional Addresses  . . . . . . . . . . . . . . 14
     4.6.  Return Routability Check . . . . . . . . . . . . . . . . . 15
     4.7.  Changes in NAT Mappings  . . . . . . . . . . . . . . . . .  16
     4.8 15
     4.8.  NAT Prohibition  . . . . . . . . . . . . . . . . . . . . . 16
     4.9.  Path Testing . . . . . . . . . . . . . . . . . . . . . . . 17
     4.10. Failure Recovery and Timeouts  . . . . . . . . . . . . . . 17
   5.  Payload Formats  . . . . . . . . . . . . . . . . . . . . . .  19
     5.1 . 18
     5.1.  MOBIKE_SUPPORTED Notify Payload  . . . . . . . . . . . . .  19
     5.2 18
     5.2.  ADDITIONAL_IP4/6_ADDRESS Notify Payloads . . . . . . . . .  19
     5.3 18
     5.3.  NO_ADDITIONAL_ADDRESSES Notify Payload . . . . . . . . . .  19
     5.4 18
     5.4.  UPDATE_SA_ADDRESSES Notify Payload . . . . . . . . . . . .  19
     5.5 18
     5.5.  UNACCEPTABLE_ADDRESSES Notify Payload  . . . . . . . . . .  20
     5.6 19
     5.6.  COOKIE2 Notify Payload . . . . . . . . . . . . . . . . . .  20
     5.7 19
     5.7.  NO_NATS_ALLOWED Notify Payload . . . . . . . . . . . . . .  20
     5.8 19
     5.8.  UNEXPECTED_NAT_DETECTED Notify Payload . . . . . . . . . .  20 19
   6.  Security Considerations  . . . . . . . . . . . . . . . . . .  21
     6.1 . 20
     6.1.  Traffic Redirection and Hijacking  . . . . . . . . . . . .  21
     6.2 20
     6.2.  IPsec Payload Protection . . . . . . . . . . . . . . . . .  21
     6.3 20
     6.3.  Denial-of-Service Attacks Against Third Parties  . . . . .  22
     6.4 21
     6.4.  Spoofing Network Connectivity Indications  . . . . . . . .  23
     6.5 22
     6.5.  Address and Topology Disclosure  . . . . . . . . . . . . .  23 22
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . .  24 . 23
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . .  25 . 24
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . .  25
     9.1 . 24
     9.1.  Normative References . . . . . . . . . . . . . . . . . . .  25
     9.2 24
     9.2.  Informative References . . . . . . . . . . . . . . . . . .  26
        Author's Address 25
   Appendix A.  Changelog . . . . . . . . . . . . . . . . . . . . . .  27
   A.   Changelog 26
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . .  27 29
   Intellectual Property and Copyright Statements . . . . . . . . . . 30

1.  Introduction

   IKEv2 is used for performing mutual authentication and establishing
   and maintaining IPsec Security Associations (SAs).  In the current
   specifications, the IPsec and IKE SAs are created implicitly between
   the IP addresses that are used when the IKE_SA is established.  These
   IP addresses are then used as the outer (tunnel header) addresses for
   tunnel mode IPsec packets.  Currently, it is not possible to change
   these addresses after the IKE_SA has been created.

   There are scenarios where these IP addresses might change.  One
   example is mobility: a host changes its point of network attachment,
   and receives a new IP address.  Another example is a multihoming host
   that would like to change to a different interface if, for instance,
   the currently used interface stops working for some reason.

   Although the problem can be solved by creating new IKE and IPsec SAs
   when the addresses need to be changed, this may not be optimal for
   several reasons.  In some cases, creating a new IKE_SA may require
   user interaction for authentication (entering a code from a token
   card, for instance).  Creating new SAs often also involves expensive
   calculations and possibly a large number of roundtrips.  Due to round-trips.  For these
   reasons, a mechanism for updating the IP addresses of existing IKE
   and IPsec SAs is needed.  The MOBIKE protocol described in this
   document provides such a mechanism.

   The main scenario for MOBIKE is making it possible for enabling a remote access VPN user to
   move from one address to another without re-
   establishing re-establishing all security
   associations with the VPN gateway.  For instance, a user could start
   from fixed Ethernet in the office, and then disconnect the laptop and
   move to office wireless LAN.  When leaving the office the laptop
   could start using GPRS, and switch to a different wireless LAN when
   the user arrives home.  MOBIKE updates only the outer (tunnel header)
   addresses of IPsec SAs, and the addresses and others traffic
   selectors used inside the tunnel stay unchanged.  Thus, mobility can
   be (mostly) invisible to applications and their connections using the

   MOBIKE also supports more complex scenarios where the VPN gateway
   also has several network interfaces: these interfaces could be
   connected to different networks or ISPs, they may have may be a mix
   of IPv4 and IPv6 addresses, and the addresses may change over time.
   Furthermore, both parties could be VPN gateways relaying traffic for
   other parties.

2.  Terminology and Notation
   When messages containing IKEv2 payloads are described, optional
   payloads are shown in brackets (for instance, "[FOO]"), and a plus
   sign indicates that a payload can be repeated one or more times (for
   instance, "FOO+").  In some cases, the diagrams also show what
   payloads defined in [IKEv2] would be typically included in, for
   instance, the IKE_AUTH exchange.  These payloads are shown for
   illustrative purposes only; see [IKEv2] for an authoritative

   When this document talks about updating the source/destination
   addresses of an IPsec SA, it means updating IPsec-related state so
   that outgoing ESP/AH packets use those addresses in the tunnel
   header.  Depending on how the nominal division between Security
   Association Database (SAD), Security Policy Database (SPD), and Peer
   Authorization Database (PAD) described in [IPsecArch] is actually
   implemented, an implementation can have several different places that
   have to be updated.

   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); "responder" is the other peer.  During the lifetime of the
   IKE_SA, both parties may initiate INFORMATIONAL or CREATE_CHILD_SA
   exchanges; in this case, the terms "exchange initiator" and "exchange
   responder" are used.  The term "original initiator" (which in [IKEv2]
   refers to the party who started the latest IKE_SA rekeying) is not
   used in this document.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [KEYWORDS].

3.  Protocol Overview


3.1.  Basic Operation

   MOBIKE allows both parties to have several addresses, and there are
   up to N*M pairs of IP addresses that could potentially be used.  The
   decision of which of these pairs to use has to take into account
   several factors.  First, the parties have may have preferences about which
   interface should be used, due to performance and cost reasons, for
   instance.  Second, the decision is constrained by the fact that some
   of the pairs may not work at all due to incompatible IP versions,
   outages somewhere in the network, problems at the local link at
   either end, and so on.

   MOBIKE solves this problem by taking a simple approach: the party
   that initiated the IKE_SA (the "client" in a remote access VPN
   scenario) is responsible for deciding which address pair is used for
   the IPsec SAs, and for collecting the information it needs to make
   this decision (such as determining which address pairs work or do not
   work).  The other party (the "gateway" in a remote access VPN
   scenario) simply tells the initiator what addresses it has, but does
   not update the IPsec SAs until it receives a message from the
   initiator to do so.

   Making the decision at the initiator is consistent with how normal
   IKEv2 works: the initiator decides which addresses it uses when
   contacting the responder.  It also makes sense sense, especially when the
   initiator is the mobile node: it is in a better position to decide
   which of its network interfaces should be used for both upstream and
   downstream traffic.

   The details of exactly how the initiator makes the decision, what
   information is used in making it, how the information is collected,
   how preferences affect the decision, and when a decision needs to be
   changed, are largely beyond the scope of MOBIKE.  This does not mean
   that these details are unimportant: on the contrary, they are likely
   to be crucial in any real system.  However, MOBIKE is concerned with
   these details only to the extent that they are visible in IKEv2/IPsec
   messages exchanged between the peers (and thus need to be
   standardized to ensure interoperability).


   Also, many of these issues are also not specific to MOBIKE, but are common
   with the use of existing hosts in dynamic environments or with
   mobility protocols such as Mobile IP [MIP4] [MIP6].  A number of
   mechanisms already exist or are being developed to deal with these
   issues.  For instance, link layer and IP layer mechanisms can be used
   to track the status of connectivity within the local link [RFC2461], [RFC2461];
   movement detection is being specified in for both IPv4 and IPv6 [DNA4] in
   [DNA4], [DNA6], and so on.


   Naturally, updating the addresses of IPsec SAs naturally has to take into
   account several security considerations.  MOBIKE includes two
   features designed to address these considerations.  First, a "return
   routability" check can be used to verify the addresses provided by
   the peer.  This makes it more difficult to flood third parties with
   large amounts of traffic.  Second, a "NAT prohibition" feature
   ensures that IP addresses have not been modified by NATs, IPv4/IPv6
   translation agents, or other similar devices.  This feature is mainly
   intended for site-to-site VPNs where the administrators may know
   beforehand that NATs are not present, and thus any modification to
   the packet can be considered to be an attack.


3.2.  Example Protocol Runs

   A simple MOBIKE exchange in a mobile scenario is illustrated below:

      Initiator                  Responder
     -----------                -----------
   1) HDR, SAi1, KEi, Ni,
           N(NAT_DETECTION_*_IP)  -->

                            <--  HDR, SAr1, KEr, Nr,

   2) HDR, SK { IDi, CERT, AUTH,
                SAi2, TSi, TSr,
                N(MOBIKE_SUPPORTED) }  -->

                            <--  HDR, SK { IDr, CERT, AUTH,
                                           SAr2, TSi, TSr,
                                           N(MOBIKE_SUPPORTED) }

   (Initiator gets information from lower layers that its attachment
   point and address has changed.)

                N(NAT_DETECTION_*_IP) }  -->

                            <--  HDR, SK { N(NAT_DETECTION_*_IP) }

   (Responder verifies that the initiator has given it
   a correct IP address.)

   4)                       <--  HDR, SK { N(COOKIE2) }

      HDR, SK { N(COOKIE2) }  -->

   Step 1 is the normal IKE_INIT exchange.  In step 2, the peers inform
   each other that they support MOBIKE.  In step 3, the initiator
   notices a change in its own address, and informs the responder about
   this.  At this point, it also starts to use the new address as a
   source address in its own outgoing ESP traffic.  The responder
   records the new address, and if so required by policy, performs a
   return routability check of the address.  When this check completes,
   the responder starts to use the new address as the destination for
   its outgoing ESP traffic.

   Another protocol run in a multihoming scenario is illustrated below.

   In this scenario scenario, the initiator has one address but the responder has

      Initiator                  Responder
     -----------                -----------
   1) HDR, SAi1, KEi, Ni,
           N(NAT_DETECTION_*_IP)  -->

                            <--  HDR, SAr1, KEr, Nr,

   2) HDR, SK { IDi, CERT, AUTH,
                SAi2, TSi, TSr,
                N(MOBIKE_SUPPORTED) }  -->

                            <--  HDR, SK { IDr, CERT, AUTH,
                                           SAr2, TSi, TSr,
                                           N(ADDITIONAL_IPV4_ADDRESS) }

   (The initiator suspects a problem in the currently used address pair,
   and probes its liveness.)

   3) HDR, SK { N(NAT_DETECTION_*_IP) }  -->

                            <--  HDR, SK { N(NAT_DETECTION_*_IP) }

   (The initiator gives up on the current address pair, and tests the
   other available address pair.)

                N(COOKIE2) }  -->

                            <--  HDR, SK { N(NAT_DETECTION_*_IP),
                                           N(COOKIE2) }

   (This worked, and the initiator requests the peer to switch to new

                N(NAT_DETECTION_*_IP) }  -->

                            <--  HDR, SK { N(NAT_DETECTION_*_IP) }


3.3.  MOBIKE and Network Address Translation (NAT)

   In some MOBIKE scenarios the network may contain NATs or stateful
   packet filters (for brevity, the rest of this document talks simply
   about NATs).  The NAT Traversal feature specified in [IKEv2] allows
   IKEv2 to work through NATs in many cases, and MOBIKE can leverage
   this functionality: when the addresses used for IPsec SAs are
   changed, MOBIKE can enable or disable IKEv2 NAT Traversal as needed.

   Nevertheless, there are some limitations since because NATs usually
   introduce an asymmetry in the network: only packets coming from the
   "inside" cause state to be created.  This asymmetry leads to
   restrictions on what MOBIKE can do.  To give a concrete example,
   consider a situation where both peers have only a single address, and
   the initiator is behind a NAT.  If the responder's address now
   changes, it needs to send a packet to the initiator using its new
   address.  However, if the NAT is, for instance, of the common
   "restricted cone" type (see [STUN] for one description of different
   NAT types), this is not possible: the NAT will drop packets sent from
   the new address (unless the initiator has previously sent a packet to
   that address -- which it cannot do until it knows the address).

   For simplicity, MOBIKE does not attempt to handle all possible NAT-
   related scenarios.  Instead, MOBIKE assumes that if NATs are present,
   the initiator is the party "behind" the NAT, and does not fully
   support the case where the responder's addresses change.

   "Does not fully support" means that no special effort is made to
   support this functionality.  However, if the alternative is losing
   connectivity completely, the responder can still attempt to proceed
   with the change, and depending on, e.g., the exact type of NAT, it
   may succeed.  However, analyzing the exact circumstances when this
   will or will not work is not done in this document.


3.4.  Limitations

   This document focuses on the main scenario outlined in Section 1, and
   supports only tunnel mode.

   The base version of the MOBIKE protocol may not cover all potential
   future use scenarios, such as transport mode, application to securing
   SCTP, or optimizations desirable in specific circumstances.  Future
   extensions may be defined later to support additional requirements.

4.  Protocol Exchanges


4.1.  Signaling Support for MOBIKE

   Implementations that wish to use MOBIKE for a particular IKE_SA MUST
   include a MOBIKE_SUPPORTED notification in the IKE_AUTH exchange (in
   case of multiple IKE_AUTH exchanges, in the message containing the SA

   The format of the MOBIKE_SUPPORTED notification is described in
   Section 5.


4.2.  Initial Tunnel Header Addresses

   When an IPsec SA is created, the tunnel header IP addresses (and port
   port, if doing UDP encapsulation) are taken from the IKE_SA, not the
   IP header of the IKEv2 message requesting the IPsec SA.  The
   addresses in the IKE_SA are initialized as follows: If the
   IKE_SA_INIT request contains the NAT_DETECTION_*_IP notifications and
   the responder supports NAT Traversal, the values are initialized from
   the IP header of the first IKE_AUTH request.  Otherwise, the values
   are initialized from the IP header of the IKE_SA_INIT request.

   The addresses are taken from the IKE_AUTH request when NAT Traversal
   is being used because IKEv2 requires changing from port 500 to 4500
   if a NAT is discovered.  To simplify things, implementations that
   support both this specification and NAT Traversal MUST change to port
   4500 if the correspondent also supports both, even if no NAT was
   detected between them (this way, there is no need to change the ports


4.3.  Additional Addresses

   Both the initiator and responder MAY include one or more
   the IKE_AUTH exchange (in case of multiple IKE_AUTH exchanges, in the
   message containing the SA payload).

      Initiator                  Responder
     -----------                -----------
      HDR, SK { IDi, [CERT], [IDr], AUTH,
                SAi2, TSi, TSr,
                [N(ADDITIONAL_*_ADDRESS)+] }  -->

                            <--  HDR, SK { IDr, [CERT], AUTH,
                                           SAr2, TSi, TSr,
                                           [N(ADDITIONAL_*_ADDRESS)+] }

   The recipient stores this information, but no other action is taken
   at this time.

   Although both the initiator and responder maintain a set of peer
   addresses (logically associated with the IKE_SA), it is important to
   note that they use this information for slightly different purposes.

   The initiator uses the set of responder addresses as an input to its
   address selection policy; it may may, at some later point point, decide to move
   the IPsec traffic to one of these addresses using the procedure
   described in Section 4.4.  The responder normally does not use the
   set of initiator addresses for anything: the addresses are used only
   when the responder's own addresses change (see Section 4.5).

   The set of addresses available to the peers can change during the
   lifetime of the IKE_SA.  The procedure for updating this information
   is described in Section 4.5.

   Note that if some of the initiator's interfaces are behind a NAT
   (from the responder's point of view), the addresses received by the
   responder will be incorrect.  This means the procedure for changing
   responder addresses described in Section 4.5 does not fully work when
   the initiator is behind a NAT.  For the same reason, the peers also
   SHOULD NOT use this information for any other purposes than what is
   explicitly described in this document.


4.4.  Changing Addresses in IPsec SAs

   In MOBIKE, the initiator decides what addresses are used in the IPsec
   SAs.  That is, the responder usually never updates any IPsec SAs
   without receiving an explicit UPDATE_SA_ADDRESSES request from the
   initiator.  (As described below, the responder can, however, update
   the IKE_SA in some circumstances.)

   The reasons why the initiator wishes to change the addresses are
   largely beyond the scope of MOBIKE.  Typically  Typically, triggers include
   information received from lower layers, such as changes in IP
   addresses or link-down indications.  Some of this information can be
   unreliable: for instance, ICMP messages could be spoofed by an
   attacker.  Unreliable information itself MUST NOT be used to conclude
   than an update is needed: instead, the initiator SHOULD trigger dead
   peer detection (that is, send an INFORMATIONAL request).

   Changing addresses can also be triggered by events within IKEv2.  At
   least the following events can cause the initiator to re-evaluate its
   local address selection policy, possibly leading to changing the

   o  An IKEv2 request has been re-transmitted several times, but no
      valid reply has been received.  This suggests the current path is
      no longer working.

   o  An INFORMATIONAL request containing ADDITIONAL_IP4/6_ADDRESS
      notifications is received.  This means the peer's addresses may
      have changed.

   o  An UNACCEPTABLE_ADDRESSES notification is received as a response
      to address update request (described below).

   o  The initiator receives a NAT_DETECTION_DESTINATION_IP notification
      that does not match the previous UPDATE_SA_ADDRESSES response (see
      Section 4.7 for a more detailed description).

   The description in the rest of this section assumes that the
   initiator has already decided what the new addresses should be.  When
   this decision has been made, the initiator:

   o  Updates the IKE_SA with the new addresses, and sets the
      "pending_update" flag in the IKE_SA.

   o  Updates the IPsec SAs associated with this IKE_SA with the new
      addresses (unless the initiator's policy requires a return
      routability check before updating the IPsec SAs, and the check has
      not been done for this responder address yet).

   o  If the IPsec SAs were updated in the previous step: If NAT
      Traversal is not enabled, and the responder supports NAT Traversal
      (as indicated by NAT detection payloads in the IKE_SA_INIT
      exchange), and the initiator either suspects or knows that a NAT
      is likely to be present, enables NAT Traversal.

   o  If there are outstanding IKEv2 requests (requests for which the
      initiator has not yet received a reply), continues retransmitting
      them using the addresses in the IKE_SA (the new addresses).

   o  When the window size allows, sends an INFORMATIONAL request
      containing the UPDATE_SA_ADDRESSES notification (which does not
      contain any data), and clears the "pending_update" flag.  The
      request will be as follows:

      Initiator                  Responder
     -----------                -----------
                [N(COOKIE2)] } -->

   o  If a new address change occurs while waiting for the response,
      starts again from the first step (and ignores responses to this
      UPDATE_SA_ADDRESSES request).

   When processing an INFORMATIONAL request containing the
   UPDATE_SA_ADDRESSES notification, the responder:

   o  Determines whether it has already received a newer
      UPDATE_SA_ADDRESSES request than this one (if the responder uses a
      window size greater than one, it is possible that requests are
      received out of order).  If it has, a normal response message
      (described below) is sent, but no other action is taken.

   o  If the NO_NATS_ALLOWED notification is present, processes it as
      described in Section 4.8.

   o  Checks that the (source IP address, destination IP address) pair
      in the IP header is acceptable according to local policy.  If it
      is not, replies with a message containing the
      UNACCEPTABLE_ADDRESSES notification (and possibly COOKIE2).

   o  Updates the IP addresses in the IKE_SA with the values from the IP
      header.  (Using the address from the IP header is consistent with
      normal IKEv2, and allows IKEv2 to work with NATs without needing
      unilateral self-address fixing [UNSAF].)
   o  Replies with an INFORMATIONAL response:

      Initiator                  Responder
     -----------                -----------
                            <--  HDR, SK { [N(NAT_DETECTION_*_IP)],
                                           [N(COOKIE2)] }

   o  If necessary, initiates a return routability check for the new
      initiator address (see Section 4.6) and waits until the check is

   o  Updates the IPsec SAs associated with this IKE_SA with the new

   o  If NAT Traversal is supported and NAT detection payloads were
      included, enables or disables NAT Traversal.

   When the initiator receives the reply, it: reply:

   o  If an address change has occurred after the request was first
      sent, no MOBIKE processing is done for the reply message, since message because a
      new UPDATE_SA_ADDRESSES is going to be sent (or has already been
      sent, if window size greater than one is in use).

   o  If the response contains the UNEXPECTED_NAT_DETECTED notification,
      it processes the response as described in Section 4.8.

   o  If the response contains an UNACCEPTABLE_ADDRESSES notification,
      the initiator MAY select another addresses and retry the exchange,
      keep on using the current addresses, or disconnect.

   o  Updates  It updates the IPsec SAs associated with this IKE_SA with the new
      addresses (unless this was already done before sending the

   o  If NAT Traversal is supported and NAT detection payloads were
      included, it enables or disables NAT Traversal.

   There is one exception to the rule that the responder never updates
   any IPsec SAs without receiving an UPDATE_SA_ADDRESSES request.  If
   the source address that the responder is currently using becomes
   unavailable (i.e., sending packets using that source address is no
   longer possible), the responder is allowed to update the IPsec SAs to
   use some other address (in addition to initiating the procedure
   described in the next section).


4.5.  Updating Additional Addresses

   As described in Section 4.3, both the initiator and responder can
   send a list of additional addresses in the IKE_AUTH exchange.  This
   information can be updated by sending an INFORMATIONAL exchange
   request message that contains either one or more ADDITIONAL_IP4/
   6_ADDRESS notifications or the NO_ADDITIONAL_ADDRESSES notification.
   The message exchange will look as follows:

      Initiator                  Responder
     -----------                -----------
                [N(COOKIE2)] }  -->

                            <--  HDR, SK { [N(COOKIE2)] }

   When a request containing ADDITIONAL_*_ADDRESS or
   NO_ADDITIONAL_ADDRESSES notification is received, the exchange

   o  Determines whether it has already received a newer request to
      update the addresses (if a window size greater than one is used,
      it is possible that the requests are received out of order).  If
      it has, a response message is sent, but the address set is not

   o  If the NO_NATS_ALLOWED notification is present, processes it as
      described in Section 4.8.

   o  Updates the set of peer addresses based on the IP header and

   o  Sends a response.

   The initiator MAY include these notifications in the same request as

   If the request to update the addresses is retransmitted using several
   different source addresses, a new INFORMATIONAL request MUST be sent.

   There is one additional complication: when the responder wants to
   update the address set, the currently used addresses may no longer
   work.  In this case, the responder uses the additional address list
   received from the initiator initiator, and the list of its own addresses addresses, to
   determine which addresses to use for sending the INFORMATIONAL
   request.  This is the only time the responder uses the additional
   address list received from the initiator.

   Note that both peers can have their own policies about what addresses
   are acceptable to use.  A minimal "mobile client" could have a policy
   that says that only the responder's address specified in local
   configuration is acceptable.  This kind of client does not have to
   send or process ADDITIONAL_*_ADDRESS notifications.  Similarly, a
   simple "VPN gateway" that has only a single address, and is not going
   to change it, does not need to send or understand
   ADDITIONAL_*_ADDRESS notifications.


4.6.  Return Routability Check

   Both parties can optionally verify that the other party can actually
   receive packets at the claimed address.  This "return routability
   check" can be done before updating the IPsec SAs, immediately after
   updating them, or continuously during the connection.

   By default, the return routability check SHOULD be done before
   updating the IPsec SAs.  In environments where the peer is expected
   to be
   well-behaving well-behaved (many corporate VPNs, for instance), or the
   address can be verified by some other means (e.g., the address is
   included in the peer's certificate), the return routability check MAY
   be omitted or postponed until after the IPsec SAs have been updated.

   Any INFORMATIONAL exchange can be used for return routability
   purposes (with
   purposes, with one exception, described below): exception: when a valid response is received, we
   know the other party can receive packets at the claimed address.

   To ensure that the peer cannot generate the correct INFORMATIONAL
   response without seeing the request, a new payload is added to
   INFORMATIONAL messages.  The sender of an INFORMATIONAL request MAY
   include a COOKIE2 notification, and if included, the recipient of an
   INFORMATIONAL request MUST copy the notification as-is to the
   response.  When processing the response, the original sender MUST
   verify that the value is the same one as sent.  If the values do not
   match, the IKE_SA MUST be closed.

   If the same INFORMATIONAL request has been sent to several different
   addresses (i.e., the destination address in the IKE_SA has been
   updated after the request was first sent), receiving the
   INFORMATIONAL response does not tell which address is the working
   one.  In this case, a new INFORMATIONAL request needs to be sent to
   check return routability.


4.7.  Changes in NAT Mappings

   IKEv2 performs Dead Peer Detection (DPD) if there has recently been
   only outgoing traffic on all of the SAs associated with the IKE_SA.

   In MOBIKE, these messages can also be used to detect if NAT mappings
   have changed (for example, if the keepalive internal is too long, or
   the NAT box is rebooted).  More specifically, if both peers support
   both this specification and NAT Traversal, NAT_DETECTION_*_IP
   notifications MAY be included in any INFORMATIONAL request; if the
   request includes them, the responder MUST also include them in the
   response (but no other action is taken, unless otherwise specified).

   When the initiator is behind a NAT (as detected earlier using
   NAT_DETECTION_*_IP notifications), it SHOULD include these
   notifications in DPD messages, and compare the received
   NAT_DETECTION_DESTINATION_IP notifications with the value from the
   previous UPDATE_SA_ADDRESSES response (or the IKE_SA_INIT response).
   If the values do not match, the IP address and/or port seen by the
   responder has changed, and the initiator SHOULD send
   UPDATE_SA_ADDRESSES as described in Section 4.4.

   When MOBIKE is in use, the dynamic updates specified in [IKEv2]
   Section 2.23 (where the peer address and port are updated from the
   last valid authenticated packet) work in a slightly different
   fashion.  The host not behind a NAT MUST NOT use these dynamic
   updates for IKEv2 packets, but MAY use them for ESP packets.  This
   ensures that an INFORMATIONAL exchange that does not contain
   UPDATE_SA_ADDRESSES does not cause any changes, allowing it to be
   used for, e.g., testing whether a particular path works.


4.8.  NAT Prohibition

   Basic IKEv2/IPsec without NAT Traversal support may work across some
   types of one-to-one "basic" NATs and IPv4/IPv6 translation agents in
   tunnel mode.  This is because the IKEv2 integrity checksum does not
   cover the addresses in the IP header.  This may be considered a
   problem in some circumstances, since because in some sense any modification
   of the IP addresses can be considered to be an attack.

   This specification addresses the issue by protecting the IP addresses
   when NAT Traversal has not been explicitly enabled.  This means that
   MOBIKE without NAT Traversal support will not work if the paths
   contain NATs, IPv4/IPv6 translation agents, or other nodes that
   modify the addresses in the IP header.  This feature is mainly
   intended for site-to-site VPN cases, where the administrators may
   know beforehand that NATs are not present, and thus any modification
   to the packet can be considered to be an attack.

   More specifically, when NAT Traversal is not enabled, all messages
   that can update the addresses associated with the IKE_SA and/or IPsec
   SAs (the IKE_SA_INIT request and all INFORMATIONAL requests that
   notifications) MUST also include a NO_NATS_ALLOWED notification.  The
   exchange responder MUST verify that the contents of the
   NO_NATS_ALLOWED notification match the addresses in the IP header.
   If they do not match, a response containing an
   UNEXPECTED_NAT_DETECTED notification is sent (and in the case of the
   IKE_SA_INIT exchange, no state is created at the responder).  The
   response message is sent to the address and port that the
   corresponding request came from, not to the address contained in the
   NO_NATS_ALLOWED notification.

   If the exchange initiator receives an UNEXPECTED_NAT_DETECTION
   notification in response to its request, it SHOULD retry the
   operation several times using new IKE_SA_INIT/INFORMATIONAL requests.
   This ensures that an attacker who is able to modify only a single
   packet does not unnecessarily cause a path to remain unused.

   If an UNEXPECTED_NAT_DETECTED notification is sent, the exchange
   responder MUST NOT use the contents of the NO_NATS_ALLOWED
   notification for any other purpose than possibly logging the
   information for troubleshooting purposes.


4.9.  Path Testing

   IKEv2 Dead Peer Detection allows the peers to detect if the currently
   used path has stopped working.  However, if either of the peers has
   several addresses, Dead Peer Detection alone does not tell which of
   the other paths might work.

   If required by its address selection policy, the initiator can use
   normal IKEv2 INFORMATIONAL request/response messages to test whether
   a certain path works.  Implementations MAY do path testing even if
   the currenly used path currently being used is working to, for example, detect when
   a better (but previously unavailable) path becomes available.


4.10.  Failure Recovery and Timeouts

   In MOBIKE, the initiator is responsible for detecting and recovering
   from most failures.

   To give the initiator enough time to detect the error, the responder
   SHOULD use relatively long timeout intervals when, for instance,
   retransmitting IKEv2 requests or deciding whether to initiate dead
   peer detection.  While no specific timeout lengths are required, it
   is suggested that responders continue retransmitting IKEv2 requests
   for at least five minutes before giving up.

5.  Payload Formats


5.1.  MOBIKE_SUPPORTED Notify Payload

   The MOBIKE_SUPPORTED notification is included in the IKE_AUTH
   exchange to indicate that the implementation supports this

   The Notify Message Type for MOBIKE_SUPPORTED is TBD-BY-IANA1.  The
   Protocol ID and SPI Size fields are set to zero.  There is no data
   associated with this Notify type.


5.2.  ADDITIONAL_IP4/6_ADDRESS Notify Payloads

   Both parties can include ADDITIONAL_IP4_ADDRESS and/or
   ADDITIONAL_IP6_ADDRESS notifications in the IKE_AUTH exchange and
   INFORMATIONAL exchange request messages; see Section 4.3 and
   Section 4.5 for more detailed description.

   The Notify Message Types for ADDITIONAL_IP4_ADDRESS and
   respectively.  The Protocol ID and SPI Size fields are set to zero.
   The data associated with these Notify types is either a four-octet
   IPv4 address or a 16-octet IPv6 address.



   The NO_ADDITIONAL_ADDRESSES notification can be included in an
   INFORMATIONAL exchange request messages message to indicate that the exchange
   initiator does not have addresses beyond the one used in the exchange
   (see Section 4.5 for more detailed description).

   The Notify Message Type for NO_ADDITIONAL_ADDRESSES is TBD-BY-IANA4.
   The Protocol ID and SPI Size fields are set to zero.  There is no
   data associated with this Notify type.


5.4.  UPDATE_SA_ADDRESSES Notify Payload

   This notification is included in INFORMATIONAL exchange requests sent
   by the initiator to update addresses of the IKE_SA and IPsec SAs (see
   Section 4.4).

   The Notify Message Type for UPDATE_SA_ADDRESSES is TBD-BY-IANA5.  The
   Protocol ID and SPI Size fields are set to zero.  There is no data
   associated with this Notify type.



   The responder can include this notification in an INFORMATIONAL
   exchange response to indicate that the address change in the
   corresponding request message (which contained an UPDATE_SA_ADDRESSES
   notification) was not carried out.

   The Notify Message Type for UNACCEPTABLE_ADDRESSES is TBD-BY-IANA6.
   The Protocol ID and SPI Size fields are set to zero.  There is no
   data associated with this Notify type.


5.6.  COOKIE2 Notify Payload

   This notification MAY be included in any INFORMATIONAL request for
   return routability check purposes (see Section 4.6).  If the
   INFORMATIONAL request includes COOKIE2, the exchange responder MUST
   copy the notification to the response message.

   The data associated with this notification MUST be between 8 and 64
   octets in length (inclusive), and MUST be chosen by the exchange
   initiator in a way that is unpredictable to the exchange responder.
   The Notify Message Type for this message is TBD-BY-IANA7.  The
   Protocol ID and SPI Size fields are set to zero.


5.7.  NO_NATS_ALLOWED Notify Payload

   See Section 4.8 for a description of this notification.

   The data field of this notification contains the following
   information: the IP address and port from which the packet was sent,
   and the IP address and port to which the packet was sent.  The Notify
   Message Type for this message is TBD-BY-IANA8.  The Protocol ID and
   SPI Size fields are set to zero.



   See Section 4.8 for a description of this notification.

   The Notify Message Type for UNEXPECTED_NAT_DETECTED is TBD-BY-IANA9.
   The Protocol ID and SPI Size fields are set to zero.  There is no
   data associated with this Notify type.

6.  Security Considerations

   The main goals of this specification are to not reduce the security
   offered by usual IKEv2 procedures and to counter mobility related mobility-related
   threats in an appropriate manner.  This section describes new
   security considerations introduced by MOBIKE.  See [IKEv2] for
   security considerations for IKEv2 in general.


6.1.  Traffic Redirection and Hijacking

   MOBIKE payloads relating to updating addresses are encrypted,
   integrity protected, and replay protected using the IKE_SA.  This
   assures that no one except the participants can, for instance, give a
   control message to change the addresses.

   However, just like with normal IKEv2, the actual IP addresses in the
   IP header are not covered by the integrity protection.  This means
   that a NAT between the parties (or an attacker acting as a NAT) can
   modify the addresses and cause incorrect tunnel header (outer) IP
   addresses to be used for IPsec SAs.  The scope of this attack is
   limited mainly to denial-of-service, since denial-of-service because all traffic is protected
   using IPsec.

   This attack can only be launched by on-path attackers that are
   capable of modifying IKEv2 messages carrying NAT detection payloads
   (such as Dead Peer Detection messages).  By modifying the IP header
   of these packets, the attackers can lead the peers to believe a new
   NAT or a changed NAT binding exists between them.  The attack can
   continue as long as the attacker is on the path, modifying the IKEv2
   messages.  If this is no longer the case, IKEv2 and MOBIKE mechanisms
   designed to detect NAT mapping changes will eventually recognize that
   the intended traffic is not getting through, and will update the
   addresses appropriately.

   MOBIKE introduces the NO_NATS_ALLOWED notification that is used to
   detect modification modification, by outsiders, of the addresses in the IP header by outsiders. header.
   When this notification is used, communication through NATs and other
   address translators is impossible, so it is sent only when not doing
   NAT Traversal.  This feature is mainly intended for site-to-site VPN
   cases, where the administrators may know beforehand that valid NATs
   are not present, and thus any modification to the packet can be
   considered to be an attack.


6.2.  IPsec Payload Protection

   The use of IPsec protection on payload traffic protects the
   participants against disclosure of the contents of the traffic,
   should the traffic end up in an incorrect destination or be
   eavesdropped along the way.

   However, security associations originally created for the protection
   of a specific flow between specific addresses may be updated by
   MOBIKE later on.  This has to be taken into account if the level of
   required protection depends on, for instance, the current location of
   the VPN client.

   It is recommended that security policies policies, for peers that are allowed
   to use MOBIKE MOBIKE, are configured in a manner that takes into account
   that a single security association can be used at different times
   through paths of varying security properties at different times.

6.3 properties.

6.3.  Denial-of-Service Attacks Against Third Parties

   Traffic redirection may be performed not just to gain access to the
   traffic (not very interesting since because it is encrypted) or to deny
   service to the peers, but also to cause a denial-of-service attack
   for a third party.  For instance, a high-speed TCP session or a
   multimedia stream may be redirected towards a victim host, causing
   its communications capabilities to suffer.

   The attackers in this threat can be either outsiders or even one of
   the IKEv2 peers.  In usual VPN usage scenarios, attacks by the peers
   can be easily dealt with if the authentication performed in the
   initial IKEv2 negotiation can be traced to persons who can be held
   responsible for the attack.  This may not be the case in all
   scenarios, particularly with opportunistic approaches to security.


   Normally, such attacks would expire in a short time frame due to the
   lack of responses (such as transport layer acknowledgements) from the
   victim.  However, as described in [Aura02], malicious participants
   would typically be able to spoof such acknowledgements and maintain
   the traffic flow for an extended period of time.  For instance, if
   the attacker opened the TCP stream itself before redirecting it to
   the victim, the attacker becomes aware of the sequence number space
   used in this particular session.

   It should also be noted, as shown in [Bombing], that without ingress
   filtering in the attacker's network network, such attacks are already
   possible simply by sending spoofed packets from the attacker to the
   victim directly.  Furthermore, if the attacker's network has ingress
   filtering, this attack is largely prevented for MOBIKE as well.
   Consequently, it makes little sense to protect against attacks of
   similar nature in MOBIKE.  However, it still makes sense to limit the
   amplification capabilities provided to attackers, so that they cannot
   use stream redirection to send a large number of packets to the
   victim by sending just a few packets themselves.

   This specification includes return routability tests to limit the
   duration of any "third party bombing" attacks by off-path (relative
   to the victim) attackers.  The tests are authenticated messages that
   the peer has to respond to, and can be performed either before the
   address change takes effect, immediately afterwards, or even
   periodically during the session.  The tests contain unpredictable
   data, and only someone who has the keys associated with the IKE SA
   and has seen the request packet can properly respond to the test.


6.4.  Spoofing Network Connectivity Indications

   Attackers may spoof various indications from lower layers and the
   network in an effort to confuse the peers about which addresses are
   or are not working.  For example, attackers may spoof link-layer
   error messages in an effort to cause the parties to move their
   traffic elsewhere or even to disconnect.  Attackers may also spoof
   information related to network attachments, router discovery, and
   address assignments in an effort to make the parties believe they
   have Internet connectivity when when, in reality reality, they do not.

   This may cause use of non-preferred addresses or even denial-of-

   MOBIKE does not provide any protection of its own for indications
   from other parts of the protocol stack.  These vulnerabilities can be
   mitigated through the use of techniques specific to the other parts
   of the stack, such as validation of ICMP errors [ICMPAttacks], link
   layer security, or the use of [SEND] to protect IPv6 Router and
   Neighbor Discovery.


   Ultimately, MOBIKE depends on the delivery of IKEv2 messages to
   determine which paths can be used.  If IKEv2 messages sent using a
   particular source and destination addresses reach the recipient and a
   reply is received, MOBIKE will usually consider the path working; if
   no reply is received even after retransmissions, MOBIKE will suspect
   the path is broken.  An attacker who can consistently control the
   delivery or non-delivery of the IKEv2 messages in the network can
   thus influence which addresses actually get used.


6.5.  Address and Topology Disclosure

   MOBIKE address updates and ADDITIONAL_IP4/6_ADDRESS notifications
   reveal information about which networks the peers are connected to.

   For example, consider a host A with two network interfaces: a
   cellular connection and a wired Ethernet connection to a company LAN.
   If host A now contacts host B using IKEv2/MOBIKE and sends
   ADDITIONAL_IP4/6_ADDRESS notifications, host B receives additional
   information it might not otherwise know.  If host A used the cellular
   connection for the IKEv2/MOBIKE traffic, host B can also see the
   company LAN address (and perhaps further guess that host A is used by
   an employee of that company).  If host A used the company LAN to make
   the connection, host B can see that host A has a subscription from
   this particular cellular operator.

   These additional addresses can also disclose more accurate location
   information than just a single address.  Suppose that host A uses its
   cellular connection for IKEv2/MOBIKE traffic, but also sends an
   ADDITIONAL_IP4_ADDRESS notification containing an IP address
   corresponding to, say, a wireless LAN at a particular coffee shop
   location.  It is likely that host B can now make a much better guess
   at A's location than would be possible based on the cellular IP
   address alone.

   Furthermore, as described in Section 4.3, some of the addresses could
   also be private addresses behind a NAT.

   In many environments, disclosing address information is not a problem
   (and indeed it cannot be avoided if the hosts wish to use those
   addresses for IPsec traffic).  For instance, a remote access VPN
   client could consider the corporate VPN gateway sufficiently
   trustworthy for this purpose.

   However, if MOBIKE is used in some more opportunistic approach, it
   can be desirable to limit the information that is sent.  The  Naturally,
   the peers
   naturally do not have to disclose any addresses they do not want to
   use for IPsec traffic.  Also, as noted in Section 4.5, an initiator
   whose policy is to always use the locally configured responder
   address does not have to send any ADDITIONAL_IP4/6_ADDRESS payloads.

7.  IANA Considerations

   This document does not create any new namespaces to be maintained by
   IANA, but it requires new values in namespaces that have been defined
   in the IKEv2 base specification [IKEv2].

   This document defines several new IKEv2 notifications whose values
   are to be allocated from the "IKEv2 Notify Message Types" namespace.

      Notify Message               Value
      ---------------------------  -----
      MOBIKE_SUPPORTED             TBD-BY-IANA1 (16396..40959)
      ADDITIONAL_IP4_ADDRESS       TBD-BY-IANA2 (16396..40959)
      ADDITIONAL_IP6_ADDRESS       TBD-BY-IANA3 (16396..40959)
      NO_ADDITIONAL_ADDRESSES      TBD-BY-IANA4 (16396..40959)
      UPDATE_SA_ADDRESSES          TBD-BY-IANA5 (16396..40959)
      COOKIE2                      TBD-BY-IANA7 (16396..40959)
      NO_NATS_ALLOWED              TBD-BY-IANA8 (16396..40959)

   These notifications are described in Section 5.

8.  Acknowledgements

   This document is a collaborative effort of the entire MOBIKE WG.  We
   would particularly like to thank Jari Arkko, Francis Dupont, Paul
   Hoffman, Tero Kivinen, and Hannes Tschofenig.  This document also
   incorporates ideas and text from earlier MOBIKE protocol proposals,
   including [AddrMgmt], [Kivinen], [MOPO], and [SMOBIKE], and the
   MOBIKE design document [Design].

9.  References


9.1.  Normative References

   [IKEv2]    Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
              draft-ietf-ipsec-ikev2-17 (work in progress),
              October 2004.

              Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", draft-ietf-ipsec-rfc2401bis-06 (work
              in progress), March 2005.

              Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", RFC 2119, March 1997.

              Huttunen, A., Swander, B., Volpe, V., DiBurro, L., and M.
              Stenberg, "UDP Encapsulation of IPsec ESP Packets",
              RFC 3948, January 2005.


9.2.  Informative References

              Dupont, F., "Address Management for IKE version 2",
              draft-dupont-ikev2-addrmgmt-07 (work in progress),
              May 2005.

   [Aura02]   Aura, T., Roe, M., and J. Arkko, "Security of Internet
              Location Management",  Proc. 18th Annual Computer Security
              Applications Conference (ACSAC), December 2002.

   [Bombing]  Dupont, F., "A note about 3rd party bombing in Mobile
              IPv6", draft-dupont-mipv6-3bombing-02 (work in progress),
              June 2005.

   [DNA4]     Aboba, B., "Detecting Network Attachment (DNA) in IPv4",
              draft-ietf-dhc-dna-ipv4-15 (work in progress),
              August 2005.

   [DNA6]     Narayanan, S., Daley, G., and N. Montavont, "Detecting
              Network Attachment in IPv6 - Best Current Practices for
              hosts", draft-ietf-dna-hosts-01 (work in progress),
              June 2005.

   [Design]   Kivinen, T. and H. Tschofenig, "Design of the MOBIKE
              protocol", draft-ietf-mobike-design-02 (work in progress),
              February 2005.

              Gont, F., "ICMP attacks against TCP",
              draft-gont-tcpm-icmp-attacks-03 (work in progress),
              December 2004.

   [Kivinen]  Kivinen, T., "MOBIKE protocol",
              draft-kivinen-mobike-protocol-00 (work in progress),
              February 2004.

   [MIP4]     Perkins, C., "IP Mobility Support for IPv4", RFC 3344,
              August 2002.

   [MIP6]     Johnson, D., Perkins, C., and J. Arkko, "Mobility Support
              in IPv6", RFC 3775, June 2004.

   [MOPO]     Eronen, P., "Mobility Protocol Options for IKEv2 (MOPO-
              IKE)", draft-eronen-mobike-mopo-02 (work in progress),
              February 2005.

   [RFC2461]  Narten, T., Nordmark, E., and W. Simpson, "Neighbor
              Discovery for IP Version 6 (IPv6)", RFC 2461,
              December 1998.

   [SEND]     Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
              Neighbor Discovery (SEND)", RFC 3971, March 2005.

   [SMOBIKE]  Eronen, P. and H. Tschofenig, "Simple Mobility and
              Multihoming Extensions for IKEv2 (SMOBIKE)",
              draft-eronen-mobike-simple-00 (work in progress),
              March 2004.

   [STUN]     Rosenberg, J., Weinberger, J., Huitema, C., and R. Mahy,
              "STUN - Simple Traversal of User Datagram Protocol (UDP)
              Through Network Address Translators (NATs)", RFC 3489,
              March 2003.

   [UNSAF]    Daigle, L., "IAB Considerations for UNilateral Self-
              Address Fixing (UNSAF) Across Network Address
              Translation", RFC 3424, November 2002.

Author's Address

   Pasi Eronen (editor)
   Nokia Research Center
   P.O. Box 407
   FIN-00045 Nokia Group


Appendix A.  Changelog

   (This section should be removed by the RFC editor.)

   Changes from -03 to -04:

   o  Copy-editing done by the RFC editor.

   Changes from -02 to -03:

   o  Editorial fixes and clarifications (issues 42 and 43).

   o  Clarified IANA considerations (issue 42).

   o  Added security considerations about address and topology
      disclosure (issue 42).

   o  Added a suggestion about retransmission timeout (issue 42).

   o  Change dynamic address updates: MUST NOT do them based on IKEv2
      packets, MAY do based on ESP (issue 34).

   o  Mandate NAT prohibition if not doing NAT traversal (issue 41).

   o  Clarified security considerations related to NATs (issue 41).

   o  Don't use SHA-1 in NO_NATS_ALLOWED, just send the addresses (issue

   o  Added a short section about path testing.

   o  Added an example protocol run in Section 1.

   Changes from -01 to -02:

   o  Moved MOBIKE_SUPPORTED from IKE_SA_INIT to IKE_AUTH (issues 35,

   o  Changed terminology related to NAT prohibition (issues 22, 24).

   o  Rewrote much of the ADDITIONAL_*_ADDRESS text, added
      NO_ADDITIONAL_ADDRESSES notification.

   o  Use NAT detection payloads to detect changes in NAT mappings
      (issue 34).

   o  Removed separate PATH_TEST message (issue 34).

   o  Clarified processing of UNACCEPTABLE_ADDRESSES when request has
      been sent using several different addresses (issue 36).

   o  Clarified changing of ports 500/4500 (issue 33).

   o  Updated security considerations (issues 27 and 28).

   o  No need to include COOKIE2 in non-RR messages (issue 32).

   o  Many editorial fixes and clarifications (issue 38, 40).

   o  Use the terms initiator and responder more consistently.

   o  Clarified that this document does not solve all problems in MOBIKE
      WG charter (issue 40).

   Changes from -00 to -01:

   o  Editorial fixes and small clarifications (issues 21, 25, 26, 29).

   o  Use Protocol ID zero for notifications (issue 30).

   o  Separate ADDITIONAL_*_ADDRESS payloads for IPv4 and IPv6 (issue

   o  Use the word "path" only in senses that include the route taken
      (issue 29).

Author's Address

   Pasi Eronen (editor)
   Nokia Research Center
   P.O. Box 407
   FIN-00045 Nokia Group


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