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Versions: (draft-devarapalli-mip4-mobike-connectivity) 00 01 02 03 RFC 5266

MIP4 Working Group                                        V. Devarapalli
Internet-Draft                                           Azaire Networks
Intended status: Best Current                                  P. Eronen
Practice                                                           Nokia
Expires: September 3, 2007                                 March 2, 2007


     Secure Connectivity and Mobility using Mobile IPv4 and MOBIKE
               draft-ietf-mip4-mobike-connectivity-03.txt

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Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   Enterprise users require mobility and secure connectivity when they
   roam and connect to the services offered in the enterprise.  Secure
   connectivity is required when the user connects to the enterprise
   from an untrusted network.  Mobility is beneficial when the user
   moves, either inside or outside the enterprise network, and acquires
   a new IP address.  This document describes a solution using Mobile
   IPv4 and mobility extensions to IKEv2 (MOBIKE) to provide secure



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   connectivity and mobility.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Solution Overview  . . . . . . . . . . . . . . . . . . . . . .  5
     3.1.  Access modes . . . . . . . . . . . . . . . . . . . . . . .  7
       3.1.1.  Access mode: 'h' . . . . . . . . . . . . . . . . . . .  7
       3.1.2.  Access mode: 'c' . . . . . . . . . . . . . . . . . . .  7
       3.1.3.  Access mode: 'f' . . . . . . . . . . . . . . . . . . .  7
       3.1.4.  Access mode: 'mc'  . . . . . . . . . . . . . . . . . .  7
     3.2.  Mobility within the enterprise . . . . . . . . . . . . . .  8
     3.3.  Mobility when outside the enterprise . . . . . . . . . . .  8
     3.4.  Crossing Security Boundaries . . . . . . . . . . . . . . .  8
       3.4.1.  Operation when moving from an untrusted network  . . .  9
       3.4.2.  Operation when moving from a trusted network . . . . . 10
   4.  NAT Traversal  . . . . . . . . . . . . . . . . . . . . . . . . 10
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 11
   7.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 11
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 12
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 12
   Appendix A.  Applicability to a Mobile Operator Network  . . . . . 13
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
   Intellectual Property and Copyright Statements . . . . . . . . . . 15























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1.  Introduction

   A typical enterprise network consists of users connecting to the
   services from a trusted network (intranet), and from an untrusted
   network (Internet).  The trusted and untrusted networks are typically
   separated by a demilitarized zone (DMZ).  Access to the intranet is
   controlled by a firewall and a VPN gateway in the DMZ.

   Enterprise users, when roaming on untrusted networks, most often have
   to authenticate themselves to the VPN gateway and set up a secure
   tunnel in order to access the intranet.  The use of IPsec VPNs is
   very common to enable such secure connectivity to the intranet.  When
   the user is on the trusted network, VPNs are not used.  However, the
   users benefit tremendously when session mobility between subnets,
   through the use of Mobile IPv4, is available.

   There has been some work done on using Mobile IPv4 and IPsec VPNs to
   provide roaming and secure connectivity to an enterprise [6] [7].
   The solution described in [6] was designed with certain restrictions,
   including requiring no modifications to the VPN gateways and involves
   the use of two layers of MIPv4, with one home agent inside the
   intranet and one in the Internet or in the DMZ before the VPN
   gateway.  The per-packet overhead is very high in this solution.  It
   is also challenging to implement and have two instances of MIPv4
   active at the same time on a mobile node.  However, the solution
   described here is only applicable when IKEv2 IPsec VPNs are used.

   This document describes an alternate solution that does not require
   two layers of MIPv4.  The solution described in this document uses
   Mobile IPv4 when the mobile node is on the trusted network and MOBIKE
   capable IPsec VPNs when mobile node is on the untrusted network.  The
   mobile node uses the tunnel inner address (TIA) given out by the
   IPsec VPN gateway as the co-located CoA for MIPv4 registration.  This
   eliminates the need for using an external MIPv4 home agent and the
   need for encapsulating the VPN tunnel inside a MIPv4 tunnel.

   The following assumptions are made for the solution described in this
   document.

   o  IKEv2 [4] and IPsec [5] are used to set up the VPN tunnels between
      the mobile node and the VPN gateway.
   o  The VPN gateway and the mobile node support MOBIKE extensions as
      defined in [3].
   o  When the mobile node is on the trusted network, traffic should not
      go through the DMZ.  Current deployments of firewalls and DMZs
      consider the scenario where only a small amount of the total
      enterprise traffic goes through the DMZ.  Routing through the DMZ
      typically involves stateful inspection of each packet by the



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      firewalls in the DMZ.  Moreover, the DMZ architecture assumes that
      the DMZ is less secure than the internal network.  Therefore the
      DMZ based architecture allows the least amount of traffic to
      traverse the DMZ, that is, only traffic between the trusted
      network and the external network.  Requiring all normal traffic to
      the mobile nodes to traverse the DMZ would negate this
      architecture.
   o  When the mobile node is on the trusted network and uses a wireless
      access technology, confidentiality protection of the data traffic
      is provided by the particular access technology.  In some
      networks, confidentiality protection MAY be available between the
      mobile node and the first hop access router, in which case it is
      not required at layer 2.

   This document also presents a solution for the mobile node to detect
   when it is on a trusted network, so that the IPsec tunnel can be
   dropped and the mobile node can use Mobile IP in the intranet.

   IPsec VPN gateways that use IKEv1 [13] are not addressed in this
   document.


2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [1].

   Many of the following terms are defined in [6], but are repeated here
   to make this document self-contained.

   FA:  Mobile IPv4 foreign agent

   CCoA:  co-located Care-of address

   FA-CoA:  Foreign Agent Care-of address

   FW:  Firewall

   i-FA:  Mobile IPv4 foreign agent residing in the trusted (intranet)
      network

   i-HA:  Mobile IPv4 home agent residing in the trusted (intranet)
      network







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   i-MIP:  The mobile node uses the home agent in the internal network

   VPN TIA:  VPN tunnel inner address.  This address is given out by the
      VPN gateway during IKE negotiation and is routable in the trusted
      network

   mVPN:  VPN with MOBIKE functionality

   The following access modes are used in explaining the protocol.  The
   access modes are explained in more detail in [6].
   f: i-MIP with FA-CoA
   c: i-MIP with CCoA
   mc:  mobile enhanced VPN, i-MIP with VPN TIA as CCoA


3.  Solution Overview

   The mobile node is configured with a home address that remains the
   same irrespective of whether the mobile node is inside or outside the
   enterprise network.  The mobile node is also reachable at the same
   home address irrespective of its current point of attachment.  When
   the mobile node is connected to the intranet directly, it uses Mobile
   IP for internal mobility.

   When the mobile node roams and connects to an untrusted network
   outside the enterprise, it sets up a VPN tunnel to the VPN gateway.
   However, it still maintains a valid binding cache entry at the i-HA.
   It uses the VPN TIA, allocated by the VPN gateway, as the co-located
   CoA for registration with the i-HA.  If the VPN TIA changes or if the
   mobile node moves and connects to another VPN gateway, then it sends
   a Registration Request to the i-HA using the new co-located CoA.

   If the mobile node moves while outside the enterprise and its access
   network changes, it uses the MOBIKE protocol to update the VPN
   gateway of its current address.  The internal home agent is not aware
   of the mobile node's movement as long as the mobile node is attached
   to the same VPN gateway and the TIA remains the same.

   Figure 1 depicts the network topology assumed for the solution.  It
   also shows the possible mobile node locations and access modes.










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                                                {h} (MN)   [i-HA]
                                                      \     /
                                                     .-+---+-.
                                                    (         )
                                   [mVPN]            `--+----'
                                     !                  !
                                  .--+--.              [R]
                                 (  DMZ  )              !
           .-+-------+--.         `--+--'         .-----+------.
          (              )           !           (              )
          ( external net +---[R]----[FW]----[R]--+ internal net )
          (              )                       (              )
           `--+---------'                         `---+---+----'
             /                                       /     \
   [DHCP]  [R]                              [DHCP] [R]     [R]    [i-FA]
      \    /                                   \   /         \    /
      .+--+---.                               .-+-+--.     .--+--+-.
     (         )                             (        )   (         )
      `---+---'                               `--+---'     `---+---'
          !                                      !             !
         (MN) {mc}                             (MN) {c}      (MN) {f}

             Figure 1: Network Topology using MIPv4 and MOBIKE

   The solution described above results in a Mobile IP tunnel inside an
   IPsec tunnel.  The Mobile IP tunnel is between the mobile node and
   the home agent and the IPsec tunnel is between the MN and the mVPN
   gateway.  The mobile node MUST reverse tunnel through the home agent
   [8] when the Mobile IP tunnel is inside an IPsec tunnel.

   The overhead of running a Mobile IP tunnel inside an IPsec tunnel can
   be avoided by having the Mobile IP foreign agent functionality on the
   VPN gateway.  This is out of scope for this document and is further
   described in [9].

   Whenever the mobile node attaches to a new link, it may encounter a
   foreign agent.  The mobile node MUST not use the foreign agent
   care-of address with the i-HA when attached to an untrusted access
   network.  The default behavior for the mobile node is to always
   configure an address from the access link using DHCP.  The mobile
   node then checks if it is attached to a trusted access network by
   sending a registration request to the i-HA in the co-located care-of
   address mode.  If the mobile node discovers that it is attached to a
   trusted access network, then it MAY start using foreign agent care-of
   address with the i-HA.  In order to do this, the mobile node has to
   perform a new registration with the i-HA.

   The mobile node can use a foreign agent on a untrusted access



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   network, if there is an external home agent that the mobile node is
   able to use.  The use of an external home agent in the untrusted
   access network and a home agent in the trusted access network at the
   same time is described in detail in [6].

   Some IPsec VPN implementations allow a host to send traffic directly
   to the Internet when attached to an untrusted network.  This traffic
   bypasses the IPsec tunnel with the VPN gateway.  This document does
   not prevent such traffic from being sent out from the host, but there
   will be no mobility or session continuity for the traffic.  Any data
   traffic that is sent through the Mobile IP tunnel with the home agent
   is always sent through the VPN gateway.

3.1.  Access modes

   The following access modes are used in the solution described in this
   document.

3.1.1.  Access mode: 'h'

   This access mode is standard Mobile IPv4 [2] when the mobile node is
   attached to its home link.  The mobile node must detect that it is
   connected to home link before using this mode.

3.1.2.  Access mode: 'c'

   This access mode is standard Mobile IPv4 [2] with a co-located
   care-of address.  The mobile node must detect that it is connected to
   an internal trusted network before using this mode.  The co-located
   care-of address is assigned by the access network to which the mobile
   node is attached to.

3.1.3.  Access mode: 'f'

   This access mode is standard Mobile IPv4 [2] with a foreign agent
   care-of address.  The mobile node can use this mode only when it
   detects that it is connected to an internal trusted network and also
   detects a foreign agent on the access network.

3.1.4.  Access mode: 'mc'

   This access mode involves using both Mobile IPv4 and a MOBIKE enabled
   IPsec VPN gateway, resulting in a Mobile IP tunnel inside an IPsec
   tunnel.  The mobile node uses the VPN TIA as the co-located CoA for
   registering with the home agent.  This mode is used only when the
   mobile node is attached to an untrusted network and is required to
   set up an IPsec tunnel with a VPN gateway to gain access to the
   trusted network.



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3.2.  Mobility within the enterprise

   When the mobile node is inside the enterprise network and attached to
   the intranet, it uses Mobile IPv4 [2] for subnet mobility.  The
   mobile node always configures a care-of address address through DHCP
   on the access link and uses it as the co-located care-of address.
   The mobile node MAY use a foreign agent care-of address, if a foreign
   agent is available.  However, the foreign agent care-of address is
   used only when the mobile node is attached to the trusted access
   network.  The mobile node attempts Foreign Agent discovery and CoA
   address acquisition through DHCP simultaneously in order to avoid the
   delay in discovering a foreign agent when there is no foreign agent
   available.  The mobile node maintains a valid binding cache entry at
   all times at the home agent mapping the the home address to the
   current CoA.  Whenever the mobile node moves, it sends a Registration
   Request to update the binding cache entry.

   The Mobile IP signaling messages between the mobile node and the home
   agent are authenticated as described in [2].

   The mobile node maintains a valid binding cache entry at the home
   agent even when it is outside the enterprise network.

3.3.  Mobility when outside the enterprise

   When the mobile node is attached to an untrusted network, it sets up
   an IPsec VPN tunnel with the VPN gateway to gain access to the
   enterprise network.  If the mobile node moves and its IP address
   changes, it initiates the MOBIKE protocol [3] to update the address
   on the VPN gateway.

   The mobile node maintains a binding at the home agent even when it is
   outside the enterprise network.  If the TIA changes due to the mobile
   node re-connecting to the VPN gateway or attaching to a different VPN
   gateway, the mobile node should send a Registration Request to its
   home agent to update the binding cache with the new TIA.

3.4.  Crossing Security Boundaries

   Security boundary detection is based on the reachability of the i-HA
   from the mobile node's current point of attachment.  Whenever the
   mobile node detects a change in network connectivity, it sends a
   Registration Request to the i-HA without any VPN encapsulation.  If
   the mobile node receives a Registration Reply, then it assumes that
   it is on a trusted network.  The mobile node MUST check that the
   Registration Reply is integrity protected using the mobile node-home
   agent mobility security association before concluding it is attached
   to a trusted network.  This security boundary detection is based on



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   the mechanism described in [6] to detect attachment to the internal
   trusted network.  The mobile node should re-transmit the Registration
   Request if it does not receive the Registration Reply within a
   timeout period.  The number of times the mobile node should re-
   transmit the Registration Request and the timeout period for
   receiving the Registration Reply are configurable on the mobile node.

   When the mobile node is attached to an untrusted network and is using
   an IPsec VPN to the enterprise network, the ability to send a
   Registration Request to the i-HA without VPN encapsulation would
   require some interaction between the IPsec and MIPv4 modules on the
   mobile node.  This is local to the mobile node and out of scope for
   this document.

   If the mobile node has an existing VPN tunnel to its VPN gateway, it
   MUST send a MOBIKE message at the same time as the registration
   request to the i-HA whenever the IP address changes.  If the mobile
   node receives a response from the VPN gateway, but not from the i-HA,
   it assumes it is outside the enterprise network.  If it receives a
   response from the i-HA, then it assumes it is inside the enterprise
   network.

   There could also be some out-of-band mechanisms that involve
   configuring the wireless access points with some information which
   the mobile node can recognize as access points that belong to the
   trusted network in an enterprise network.  Such mechanisms are beyond
   the scope of this document.

   The mobile node should not send any normal traffic while it is trying
   to detect whether it is attached to the trusted or untrusted network.
   This is described in more detail in [6].

3.4.1.  Operation when moving from an untrusted network

   When the mobile node is outside the enterprise network and attached
   to an untrusted network, it has an IPsec VPN tunnel with its mobility
   aware VPN gateway, and a valid registration with a home agent on the
   intranet with the VPN TIA as the care-of address.

   If the mobile nodes moves and its IP address changes, it performs the
   following steps:

   1a.  Initiate an IKE mobility exchange to update the VPN gateway with
      the current address.  If the new network is also untrusted, this
      will be enough for setting up the connectivity.  If the new
      network is trusted, and if the VPN gateway is reachable, this
      exchange will allow the mobile node to keep the VPN state alive
      while on the trusted side.  If the VPN gateway is not reachable



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      from inside, then this exchange will fail.
   1b.  At the same time as step 1, send a Mobile IPv4 Registration
      Request to the internal home agent without VPN encapsulation.
   2. If the mobile node receives a Registration Reply to the request
      sent in step 1b, then the current subnet is a trusted subnet, and
      the mobile node can communicate without VPN tunneling.  The mobile
      node MAY tear down the VPN tunnel.

3.4.2.  Operation when moving from a trusted network

   When the mobile node is inside the enterprise and attached to the
   intranet, it does not use a VPN tunnel for data traffic.  It has a
   valid binding cache entry at its home agent.  If the VPN gateway is
   reachable from the trusted network, the mobile node MAY have valid
   IKEv2 security associations with its VPN gateway.  The IPsec security
   associations can be created when required.  The mobile node may have
   to re-negotiate the IKEv2 security associations to prevent them from
   expiring.

   If the mobile node moves and its IP address changes, it performs the
   following steps:

   1.  Initiate an IKE mobility exchange to update the VPN gateway with
       the current address, or if there is no VPN connection, then
       establish a VPN tunnel with the gateway from the new local IP
       address.  If the new network is trusted, and if the VPN gateway
       is reachable, this exchange will allow the mobile node to keep
       the VPN state alive, while in the trusted side.  If the new
       network is trusted and if the VPN gateway is not reachable from
       inside, then this exchange will fail.
   2.  At the same time as step 1, send a Mobile IPv4 Registration
       Request to the internal home agent without VPN encapsulation.
   3.  If the mobile node receives a Registration Reply to the request
       sent in step 2, then the current subnet is a trusted subnet, and
       the mobile node can communicate without VPN tunneling, using only
       Mobile IP with the new care-of address.
   4.  If the mobile node didn't receive the response in step 3, and if
       the VPN tunnel is successfully established and registered in step
       1, then the mobile node sends a Registration Request over the VPN
       tunnel to the internal home agent.  After receiving a
       Registration Reply from the home agent, the mobile node can start
       communicating over the VPN tunnel with the Mobile IP home
       address.


4.  NAT Traversal

   There could be a NAT device between the mobile node and the home



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   agent in any of the access modes, 'c', 'f' and 'mc', and between the
   mobile node and the VPN gateway in the access mode 'mc'.  Mobile IPv4
   NAT traversal, as described in [10] should be used by the mobile node
   and the home agent in access modes 'c' or 'f', when there is a NAT
   device present.  When using access mode, 'mc', IPsec NAT traversal
   [11] [12] should be used by the mobile node and the VPN gateway, if
   there is a NAT device present.  Typically, the TIA would be a
   routable address inside the enterprise network.  But in some cases,
   the TIA could be from a private address space associated with the VPN
   gateway.  In such a case, Mobile IPv4 NAT traversal should be used in
   addition to IPsec NAT traversal in the 'mc' mode.


5.  Security Considerations

   Enterprise connectivity typically requires very strong security, and
   the solution described in this document was designed keeping this in
   mind.

   Security concerns related to the mobile node detecting that it is on
   a trusted network and thereafter dropping the VPN tunnel are
   described in [6].

   When the mobile node sends a registration request to the i-HA from an
   untrusted network that does not go through the IPsec tunnel, it will
   reveal the i-HA's address, its own identity including the NAI and the
   home address, and the Authenticator value in the authentication
   extensions to the untrusted network.  This may be a concern in some
   deployments.

   Please see [3] for MOBIKE-related security considerations, and [10],
   [11] for security concerns related to the use of NAT traversal
   mechanisms for Mobile IPv4 and IPsec.


6.  IANA Considerations

   This document requires no action from IANA.


7.  Acknowledgments

   The authors would like to thank Henry Haverinen, Sandro Grech, Dhaval
   Shah and John Cruz for their participation in developing this
   solution.

   The authors would also like to thank Henrik Levkowetz, Jari Arkko, TJ
   Kniveton, Vidya Narayanan, Yaron Sheffer, Hans Sjostrand, Jouni



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   Korhonen and Sami Vaarala for reviewing the document.


8.  References

8.1.  Normative References

   [1]   Bradner, S., "Key words for use in RFCs to Indicate Requirement
         Levels", BCP 14, RFC 2119, March 1997.

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

   [3]   Eronen, P., "IKEv2 Mobility and Multihoming Protocol (MOBIKE)",
         RFC 4555, June 2006.

   [4]   Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
         RFC 4306, December 2005.

   [5]   Kent, S. and K. Seo, "Security Architecture for the Internet
         Protocol", RFC 4301, December 2005.

   [6]   Vaarala, S. and E. Klovning, "Mobile IPv4 Traversal Across
         IPsec-based VPN Gateways",
         draft-ietf-mip4-vpn-problem-solution-02 (work in progress),
         November 2005.

8.2.  Informative References

   [7]   Adrangi, F. and H. Levkowetz, "Problem Statement: Mobile IPv4
         Traversal of Virtual Private Network (VPN) Gateways", RFC 4093,
         August 2005.

   [8]   Montenegro, G., "Reverse Tunneling for Mobile IP, revised",
         RFC 3024, January 2001.

   [9]   Sahasrabudhe, M. and V. Devarapalli, "Optimizations to Secure
         Connectivity and Mobility",
         draft-meghana-mip4-mobike-optimizations-01 (work in progress),
         October 2006.

   [10]  Levkowetz, H. and S. Vaarala, "Mobile IP Traversal of Network
         Address Translation (NAT) Devices", RFC 3519, May 2003.

   [11]  Kivinen, T., Swander, B., Huttunen, A., and V. Volpe,
         "Negotiation of NAT-Traversal in the IKE", RFC 3947,
         January 2005.




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

   [13]  Harkins, D. and D. Carrel, "The Internet Key Exchange (IKE)",
         RFC 2409, November 1998.


Appendix A.  Applicability to a Mobile Operator Network

   The solution described in this document can also be applied to a
   Mobile Operator's network when the Operator deploys heterogeneous
   access networks and some of the access networks are considered as
   trusted networks and others as untrusted networks.  Figure 2
   illustrates such a network topology.


                                          +----------------------+
                                          |            +----+    |
                     +----------------+   |            |i-HA|    |
                     |                |   |            +----+    |
             (MN)----+    trusted     +---+                      |
                     | access network |   |   internal network   |
                     +----------------+   |                      |
                                          |                      |
                                          +----------+-----------+
                                                     |
                                                     |
                                                     |
                                                   [mVPN]
                     +----------------+              |
                     |                |              |
             (MN)----+   untrusted    +--------------+
             {mc}    | access network |
                     +----------------+

     Figure 2: Network Topology of a Mobile Operator with trusted and
                            untrusted networks

   An IPsec VPN gateway provides secure connectivity to the Operator's
   internal network for mobile nodes attached to an untrusted access
   network.  The VPN gateway supports MOBIKE extensions so that the
   IPsec tunnels survive any IP address change when the mobile node
   moves while attached to the untrusted access networks.

   When the mobile node is attached to the trusted access network it
   uses Mobile IP with the i-HA.  It uses the IP address obtained from
   the trusted access network as the co-located care-of address to



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   register with the i-HA.  If a foreign agent is available in the
   trusted access network, the mobile node may use foreign agent care-of
   address.  If the mobile node moves and attaches to an untrusted
   access network, it sets up an IPsec tunnel with the VPN gateway to
   access the Operator's internal network.  It uses the IPsec TIA as the
   co-located care-of address to register with the i-HA thereby creating
   a Mobile IP tunnel inside an IPsec tunnel.

   When the mobile node is attached to the trusted access network, it
   can either by attached to a foreign link in the trusted network or to
   the home link directly.  This document does not impose any
   restrictions.


Authors' Addresses

   Vijay Devarapalli
   Azaire Networks
   3121 Jay Street
   Santa Clara, CA  95054
   USA

   Email: vijay.devarapalli@azairenet.com


   Pasi Eronen
   Nokia Research Center
   P.O. Box 407
   FIN-00045 Nokia Group
   Finland

   Email: pasi.eronen@nokia.com



















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