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Versions: (draft-korhonen-netlmm-lma-discovery) 00 01 02 03 04 05 06 07 08 RFC 6097

Network-based Localized Mobility                             J. Korhonen
Management (NetLMM)                               Nokia Siemens Networks
Internet-Draft                                            V. Devarapalli
Intended status: Informational                                  WiChorus
Expires: March 6, 2010                                 September 2, 2009


                  LMA Discovery for Proxy Mobile IPv6
                 draft-ietf-netlmm-lma-discovery-02.txt

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on March 6, 2010.

Copyright Notice

   Copyright (c) 2009 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   Please review these documents carefully, as they describe your rights
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Abstract

   Large Proxy Mobile IPv6 deployments would benefit from a
   functionality, where a Mobile Access Gateway could dynamically



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   discover a Local Mobility Anchor for a Mobile Node attaching to a
   Proxy Mobile IPv6 domain.  The purpose of the dynamic discovery
   functionality is to reduce the amount of static configuration in the
   Mobile Access Gateway.  This specification describes a number of
   possible dynamic Local Mobility Anchor discovery solutions.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  AAA-based Discovery Solutions  . . . . . . . . . . . . . . . .  3
     2.1.  Receiving LMA Address during the Network Access
           Authentication . . . . . . . . . . . . . . . . . . . . . .  4
     2.2.  Receiving LMA FQDN during the Network Access
           Authentication . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Lower Layers based Discovery Solutions . . . . . . . . . . . .  5
     3.1.  Constructing the LMA FQDN from a mobile node Identity  . .  5
     3.2.  Receiving LMA FQDN or IP Address from Lower Layers . . . .  6
     3.3.  Constructing the LMA FQDN from a Service Name  . . . . . .  6
   4.  Domain Name System Considerations  . . . . . . . . . . . . . .  6
   5.  Handover Considerations  . . . . . . . . . . . . . . . . . . .  7
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  8
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  8
   9.  Informative References . . . . . . . . . . . . . . . . . . . .  9
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10

























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1.  Introduction

   Large Proxy Mobile IPv6 (PMIPv6) [RFC5213] deployments would benefit
   from a functionality, where a Mobile Access Gateway (MAG) could
   dynamically discover a Local Mobility Anchor (LMA) for a Mobile Node
   (MN) attaching to a PMIPv6 domain.  The purpose of the dynamic
   discovery functionality is to reduce the amount of static
   configuration in the MAG.  Other drivers for the dynamic discovery of
   a LMA include LMA load balancing solutions and selecting LMA based on
   desired services (i.e. allowing service-specific routing of traffic).
   This document describes a number of possible dynamic LMA discovery
   solutions.

   There are a number of different ways for dynamically discovering the
   LMA at the MAG.  The following list briefly introduces solutions that
   will be discussed in this specification:

   o  LMA Address from AAA during the network access authentication
      procedure when the MN attaches to the MAG.

   o  LMA FQDN from AAA during the network access authentication,
      followed by a Domain Name System (DNS) lookup.

   o  LMA FQDN derived from the MN identity received from the lower
      layers during the network attachment, followed by a DNS lookup.

   o  LMA FQDN or IP address received from the lower layers during the
      network attachment followed by an optional DNS lookup.

   o  LMA FQDN derived from the service selection indication received
      from lower layers during the network attachment, followed by a DNS
      lookup.

   When a MN performs a handover from one MAG to another, the new MAG
   must use the same LMA that the old MAG was using.  This is required
   for session continuity.  The LMA discovery mechanism used by the new
   MAG should be able to return the information about the same LMA that
   was being used by the old MAG.  This document also discusses
   solutions for LMA discovery during a handover.


2.  AAA-based Discovery Solutions

   This section presents a LMA discovery solution that requires a MAG to
   be connected to an AAA infrastructure.  The AAA infrastructure is
   also assumed to be aware of and support PMIPv6 functionality.  A MN
   attaching to a PMIPv6 domain is typically required to authenticate to
   the network access and to be authorized for the mobility services



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   before the MN is allowed to send or receive any IP packets or even
   complete its IP level configuration.

   The AAA-based LMA discovery solution hooks into the network access
   authentication and authorization procedure.  The MAG has also the
   role of a Network Access Server (NAS) at this step.  While the MN is
   attaching to the network, the PMIPv6 related parameters are
   bootstrapped at the same time the MN is authenticated for the network
   access and authorized for the mobility services using the AAA
   infrastructure.  The PMIPv6 parameters bootstrapping involves the
   Policy Profile download over the AAA infrastructure to the MAG.  The
   procedure for the Policy Profile download resembles largely the
   client Mobile IPv6 Integrated Scenario bootstrapping [RFC5447].

2.1.  Receiving LMA Address during the Network Access Authentication

   After the MN has successfully authenticated for the network access
   and authorized for the mobility service, the MAG receives the LMA IP
   address(es) from the AAA server over the AAA infrastructure.  The LMA
   IP address information would be part of the AAA message(s) that ends
   the successful authentication and authorization AAA exchange.

   Once the MAG receives the LMA IP address(es), it sends Proxy Binding
   Update (PBU) message for the newly authenticated and authorized MN.
   The MAG trusts that the LMA returned by the AAA server is able to
   provide mobility session continuity for the MN, i.e. after a handover
   the LMA would be the same the MN already has a mobility session set
   up with.

2.2.  Receiving LMA FQDN during the Network Access Authentication

   This solution is identical to the procedure described in Section 2.1.
   The difference is that the MAG receives a Fully Qualified Domain Name
   (FQDN) of the LMA instead of the IP address(es).  The MAG has to
   query the DNS infrastructure in order to resolve the FQDN to the LMA
   IP address(es).

   The LMA FQDN might be a generic to a PMIPv6 domain resolving to one
   or more LMAs in the said domain.  Alternatively the LMA FQDN might
   resolve to exactly one LMA within the PMIPv6 domain.  The latter
   approach would obviously be useful if a new target MAG after a
   handover should resolve the LMA FQDN to the LMA IP address where the
   MN mobility session is already located.

   The procedures described in this section and in Section 2.1 may also
   be used together.  For example, the AAA server might return a generic
   LMA FQDN during the MN initial attach and once the LMA gets selected,
   return the LMA IP address during the subsequent attachments to other



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   MAGs in the PMIPv6 domain.  In order for this to work, the resolved
   and selected LMA IP address must be updated to the remote Policy
   Store.  For example, the LMA could perform the update once it
   receives the initial PBU from the MAG for the new mobility session.


3.  Lower Layers based Discovery Solutions

   The following section discusses solutions, where the MAG receives
   information from lower layers below the IP layer when the MN attaches
   to the MAG.  Based on this information, the MAG is then able to
   determine which LMA to contact.  These solution could essentially
   allow large PMIPv6 deployments without the AAA infrastructure.  The
   lower layers discussed here are not explicitly defined but could
   include different radio access technologies and tunneling solutions
   such as IKEv2 [RFC4306] IPsec tunnel [RFC4303].

3.1.  Constructing the LMA FQDN from a mobile node Identity

   Depending on the actual network access technology, the MAG may be
   able to receive a MN identity (or actually the subscription identity
   but from now on we assume that the MN identity equals to the
   subscription identity, which is a rather broad simplification) as a
   result of the network access attachment procedure.  The MN may signal
   its identity as part of the attachment signaling or alternatively the
   MAG receives the MN identity from a remote policy store.

   Once the MAG has acquired the MN identity, the MAG can use the
   information embedded in the identity to construct a generic LMA FQDN
   (based on some pre-configured formatting rules) and then proceed to
   resolve the LMA IP address(es) using the DNS.  Obviously, the MN
   identity must embed information elements that can be extracted and at
   minimum used to determine the entity hosting and operating the LMA
   for the MN.  Thus the MN identity in this solution cannot be a "flat"
   identity without any structure and "clear text" parts containing the
   hosting entity information.  Examples of such identities are the
   International Mobile Subscriber Identity (IMSI) or Globally Unique
   Temporary User Equipment Identity (GUTI) [3GPP.23.003] that both
   contain information of the operator owning the given subscription.

   The solution discussed in this section has issues if MN's identity
   does not embed enough information.  In a case the MN identity does
   not embed any LMA hosting entity information, the MAG might use a
   local database to map MN identities to corresponding LMAs.  However,
   this solution is unlikely to scale outside a limited PMIPv6 domain.






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3.2.  Receiving LMA FQDN or IP Address from Lower Layers

   The solution described in this section is similar to the solution
   discussed in Section 3.1.  Instead of deriving the LMA FQDN from the
   MN identity, the MAG receives a LMA FQDN or an IP address information
   from lower layers, for example, as a part of the normal lower layer
   signaling when the MN attaches to the network.  One existing example
   of such lower layer functionality is the Access Point Name
   Information Element (APN IE) in 3GPP radio's network access signaling
   capable of carrying a FQDN [3GPP.24.008].  However, in general this
   means the MN is also the originator of the LMA information.  The LMA
   information content as such can be transparent to the MN, meaning the
   MN has no knowledge it being anything LMA related.

3.3.  Constructing the LMA FQDN from a Service Name

   Some network access technologies (including tunneling solutions)
   allow the MN to signal the service name that identifies a particular
   service or the external network it wants to access.  If the MN
   originated service name also embeds the information of the entity
   hosting the service or the hosting information can be derived from
   other information available at the same time (e.g., see Section 3.1),
   then the MAG can construct a generic LMA FQDN (e.g., based on some
   pre-defined formatting rules) providing an access to the service or
   the external network.  The pre-defined formatting rules are usually
   agreed on among operators that belong to the same inter-operator
   roaming consortium or by network infrastructure vendors defining an
   open networking system architecture.

   Once the MAG has the FQDN it can proceed to resolve the LMA IP
   address(es) using the DNS.  An example of such service or external
   network name is the Access Point Name (APN) [3GPP.23.003] that
   contain information of the operator providing the access to the given
   service or the external network.


4.  Domain Name System Considerations

   A number of LMA discovery solutions described in Section 2 and
   Section 3 eventually depend on the DNS.  This section discusses
   impacts of the DNS response caching and issues related to the Dynamic
   DNS [RFC2136] updates.

   The caching (positive or negative) properties of the DNS [RFC2308]
   and the fact that updates to the DNS take time to propagate globally,
   need to be considered when applying DNS-based solutions to the PMIPv6
   domain.  First, the caching of DNS responses effectively delay the
   propagation of up to date FQDN to IP address mappings (after both



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   addition and deletion).  Hosts in the PMIPv6 domain keep using the
   stale cached DNS response (positive or negative) until they give up
   or the caching times out.  The delay can be in order of hours in the
   worst case.  On the other hand, DNS administrators can lower the
   resource record caching time (the Time To Live (TTL) value).
   Obviously, too low TTL values increase the number of DNS queries
   considerably.  Second, the secondary DNS servers do not get
   immediately updated when the masters do.  These updates are also
   periodic, usually in order of several hours, and may cause
   considerable delay on global propagation of the updated naming
   information.  Third, some DNS resolvers ignore low TTLs, replacing
   them with a higher default value.  This could lead to outdated LMA
   information being around for longer than desired.

   The above considerations are valid when, for example, the PMIPv6
   domain LMA availability or load information is dynamically updated
   into the DNS.  There are incentives for doing so, however, the
   concerns described above need to be understood clearly in that case.


5.  Handover Considerations

   Whenever a MN moves and attaches to a new MAG in a PMIPv6 domain, all
   the MAGs that the MN attaches to, should use the same LMA.  If there
   is only one LMA per PMIPv6 domain, then there is no issue.  If there
   is a context transfer mechanism available between the MAGs, then the
   new MAG knows the LMA information from the old MAG.  Such a mechanism
   is described in [I-D.ietf-mipshop-pfmipv6].  If the MN related
   context is not transferred between the MAGs, then a mechanism to
   deliver the current LMA information to the new MAG is required.

   Relying on DNS during handovers is not generally a working solution
   if the PMIPv6 domain has more than one LMA, unless the DNS
   consistently assigns a specific LMA for each given MN.  In most cases
   described in Section 3, where the MAG derives the LMA FQDN, there is
   no prior knowledge whether the LMA FQDN resolves to one or more LMA
   IP address(es) in the PMIPv6 domain.  However, depending on the
   deployment and deployment related regulation (such as inter-operator
   roaming consortium agreements) the situation might not be this
   desperate.  For example, a MAG might be able to synthesize a LMA
   specific FQDN (e.g. out of MN identity or some other service specific
   parameters).  Another alternative could that MAG uses, for example, a
   MN identity as an input to an algorithm that deterministically
   assigns the same LMA out of a pool of LMAs (assuming the MAG has e.g.
   learned a group of LMA FQDNs via SRV [RFC2782] query).  These
   approaches would guarantee that DNS returns always the same LMA
   Address to the MAG.




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   Once the MN completes its initial attachment to a PMIPv6 domain, the
   information about the LMA that is selected to serve the MN is stored
   in the Policy Store (or the AAA server).  The LMA information is
   conveyed to the policy store by the LMA after the initial attachment
   is completed [I-D.ietf-dime-pmip6].  Typically AAA infrastructure is
   used for exchanging information between the LMA and the Policy Store.

   When the MN moves and attaches to another MAG in the PMIPv6 domain,
   then the AAA servers delivers the existing LMA information to the new
   MAG as part of the authentication and authorization procedure as
   described in Section 2.1


6.  Security Considerations

   The use of DNS for obtaining the IP address of a mobility agent
   carries certain security risks.  These are explained in detail in
   Section 9.1 of RFC 5026 [RFC5026].  However, the risks described in
   RFC 5026 are mitigated to a large extent in this document, since the
   MAG and the LMA belong belong to the same PMIPv6 domain.  The DNS
   server that the MAG queries is also part of the same PMIPv6 domain.
   Even if the MAG obtains the IP address of a bogus LMA from a bogus
   DNS server, further harm is prevented since the MAG and the LMA
   should authenticate each other before exchanging PMIPv6 signaling
   messages.  RFC 5213 [RFC5213] specifies the use of IKEv2 [RFC4306]
   between the MAG and the LMA to authenticate each other and setup
   IPsec security associations for protecting the PMIPv6 signaling
   messages.

   The AAA infrastructure may be used to transport the LMA discovery
   related information between the MAG and the AAA server via one or
   more AAA brokers and/or AAA proxies.  In this case the MAG to the AAA
   server communication relies on the security properties of the
   intermediate AAA brokers and AAA proxies.


7.  IANA Considerations

   This specification has no actions for IANA.


8.  Acknowledgements

   The authors would like to thank Julien Laganier, Christian Vogt,
   Ryuji Wakikawa, Frank Xia, Behcet Sarikaya and Xiangsong Cui for
   their comments, extensive discussions and suggestions on this
   document.




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9.  Informative References

   [3GPP.23.003]
              3GPP, "Numbering, addressing and identification", 3GPP
              TS 23.003 8.2.0, September 2008.

   [3GPP.24.008]
              3GPP, "Mobile radio interface Layer 3 specification", 3GPP
              TS 24.008 8.6.0, June 2009.

   [I-D.ietf-dime-pmip6]
              Korhonen, J., Bournelle, J., Chowdhury, K., Muhanna, A.,
              and U. Meyer, "Diameter Proxy Mobile IPv6: Mobile Access
              Gateway and Local Mobility Anchor  Interaction with
              Diameter Server", draft-ietf-dime-pmip6-03 (work in
              progress), August 2009.

   [I-D.ietf-mipshop-pfmipv6]
              Yokota, H., Chowdhury, K., Koodli, R., Patil, B., and F.
              Xia, "Fast Handovers for Proxy Mobile IPv6",
              draft-ietf-mipshop-pfmipv6-08 (work in progress),
              July 2009.

   [RFC2136]  Vixie, P., Thomson, S., Rekhter, Y., and J. Bound,
              "Dynamic Updates in the Domain Name System (DNS UPDATE)",
              RFC 2136, April 1997.

   [RFC2308]  Andrews, M., "Negative Caching of DNS Queries (DNS
              NCACHE)", RFC 2308, March 1998.

   [RFC2782]  Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
              specifying the location of services (DNS SRV)", RFC 2782,
              February 2000.

   [RFC4303]  Kent, S., "IP Encapsulating Security Payload (ESP)",
              RFC 4303, December 2005.

   [RFC4306]  Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
              RFC 4306, December 2005.

   [RFC5026]  Giaretta, G., Kempf, J., and V. Devarapalli, "Mobile IPv6
              Bootstrapping in Split Scenario", RFC 5026, October 2007.

   [RFC5213]  Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury, K.,
              and B. Patil, "Proxy Mobile IPv6", RFC 5213, August 2008.

   [RFC5447]  Korhonen, J., Bournelle, J., Tschofenig, H., Perkins, C.,
              and K. Chowdhury, "Diameter Mobile IPv6: Support for



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              Network Access Server to Diameter Server Interaction",
              RFC 5447, February 2009.


Authors' Addresses

   Jouni Korhonen
   Nokia Siemens Networks
   Linnoitustie 6
   FIN-02600 Espoo
   Finland

   Email: jouni.nospam@gmail.com


   Vijay Devarapalli
   WiChorus
   3950 North First Street
   San Jose, CA 95134
   USA

   Email: vijay@wichorus.com





























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