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Internet Engineering Task Force (IETF)                       J. KorhonenRequest for Comments: 6097                        Nokia Siemens NetworksCategory: Informational                                   V. DevarapalliISSN: 2070-1721                                          Vasona Networks                                                           February 2011Local Mobility Anchor (LMA) Discovery for Proxy Mobile IPv6Abstract   Large Proxy Mobile IPv6 deployments would benefit from a   functionality where a Mobile Access Gateway could dynamically   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 document describes several possible   dynamic Local Mobility Anchor discovery solutions.Status of This Memo   This document is not an Internet Standards Track specification; it is   published for informational purposes.   This document is a product of the Internet Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Not all documents   approved by the IESG are a candidate for any level of Internet   Standard; seeSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc6097.Korhonen & Devarapalli        Informational                     [Page 1]

RFC 6097                      LMA Discovery                February 2011Copyright Notice   Copyright (c) 2011 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (http://trustee.ietf.org/license-info) in effect on the date of   publication of this document.  Please review these documents   carefully, as they describe your rights and restrictions with respect   to this document.  Code Components extracted from this document must   include Simplified BSD License text as described in Section 4.e of   the Trust Legal Provisions and are provided without warranty as   described in the Simplified BSD License.Table of Contents1. Introduction ....................................................22. AAA-Based Discovery Solutions ...................................3      2.1. Receiving the LMA Address during Network Access           Authentication .............................................4      2.2. Receiving the LMA FQDN during Network Access           Authentication .............................................43. Discovery Solutions Based on Data from Lower Layers .............53.1. Constructing the LMA FQDN from a Mobile Node Identity ......53.2. Receiving the LMA FQDN or IP Address from Lower Layers .....53.3. Constructing the LMA FQDN from a Service Name ..............64. Handover Considerations .........................................65. Recommendations .................................................76. Security Considerations .........................................87. Acknowledgements ................................................88. References ......................................................98.1. Normative References .......................................98.2. Informative References .....................................91.  Introduction   A Proxy Mobile IPv6 (PMIPv6) [RFC5213] deployment would benefit from   a functionality where a Mobile Access Gateway (MAG) can 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 an LMA include LMA   load balancing solutions and selecting an LMA based on desired   services (i.e., allowing service-specific routing of traffic)   [RFC5149].  This document describes several possible dynamic LMA   discovery approaches and makes a recommendation of the preferred one.Korhonen & Devarapalli        Informational                     [Page 2]

RFC 6097                      LMA Discovery                February 2011   The following list briefly introduces solution approaches that will   be discussed in this document.  The approaches discussed do not   include all possible discovery mechanisms, but are limited to those   considered to fit most simply into the PMIPv6 environment.   o  LMA Address is retrieved from the Authentication, Authorization,      and Accounting (AAA) infrastructure during the network access      authentication procedure when the MN attaches to the MAG.   o  LMA Fully Qualified Domain Name (FQDN) is retrieved from the AAA      infrastructure during the network access authentication, followed      by a Domain Name System (DNS) lookup.   o  LMA FQDN is 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 is received from the lower layers during      the network attachment.  The reception of an FQDN from the lower      layers is followed by a DNS lookup.   o  LMA FQDN is derived from the service selection indication received      from lower layers during the network attachment, followed by a DNS      lookup.   When an 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 in the new MAG   should be able to return the information of 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 an LMA discovery solution that requires a MAG   to be connected to an AAA infrastructure (as described in [RFC5779],   for instance).  The AAA infrastructure is also assumed to be aware of   PMIPv6.  An MN attaching to a PMIPv6 domain is typically required to   provide authentication for network access and to be authorized for   mobility services before the MN is allowed to send or receive any IP   packets or even complete its IP level configuration.Korhonen & Devarapalli        Informational                     [Page 3]

RFC 6097                      LMA Discovery                February 2011   The AAA-based LMA discovery solution hooks into the network access   authentication and authorization process.  The MAG also has 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 in parallel with authentication for the network access   and authorization for the mobility services.  The bootstrapping of   PMIPv6 parameters involves the policy profile download over the AAA   infrastructure to the MAG (seeAppendix A of [RFC5213]).2.1.  Receiving the LMA Address during Network Access Authentication   After the MN has been successfully authenticated for network access   and authorized for the mobility service, the MAG receives the LMA IP   address from the AAA server over the AAA infrastructure.  The LMA IP   address information would be part of the AAA message that ends the   successful authentication and authorization portion of the AAA   exchange.   Once the MAG receives the LMA IP address, it sends a Proxy Binding   Update (PBU) message for the newly authenticated and authorized MN.   The MAG expects 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 one the MN already has a mobility   session set up with.2.2.  Receiving the LMA FQDN during Network Access Authentication   This solution is similar to the procedure described inSection 2.1.   The difference is that the MAG receives an 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 name for a PMIPv6 domain that   resolves to one or more LMAs in the PMIPv6 domain.  Alternatively,   the LMA FQDN might be resolved to exactly one LMA within the PMIPv6   domain.  The latter approach would obviously be useful if a new   target MAG, after a handover, resolved the LMA FQDN to the LMA IP   address where the MN mobility session is already located.   The procedures described in this section and inSection 2.1 may also   be used together.  For example, the AAA server might return a generic   LMA FQDN during the MN's initial attachment, and once the LMA gets   selected, return the LMA IP address during the subsequent attachments   to other 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 policy store   update using the AAA infrastructure once it receives the initial PBU   from the MAG for the new mobility session.Korhonen & Devarapalli        Informational                     [Page 4]

RFC 6097                      LMA Discovery                February 20113.  Discovery Solutions Based on Data from Lower Layers   The following section discusses solutions where a MAG acquires   information from layers below the IP layer.  Based on this   information, the MAG is able to determine which LMA to contact when   the MN attaches to the MAG.  The lower layers discussed here are not   explicitly defined but include different radio access technologies   and tunneling solutions such as an Internet Key Exchange version 2   (IKEv2) [RFC5996] IPsec tunnel [RFC4303].3.1.  Constructing the LMA FQDN from a Mobile Node Identity   A MAG acquires an MN identity from lower layers.  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 that can be used to uniquely identify   the entity hosting and operating the LMA for the MN.  Examples of   such MN identities are the International Mobile Subscriber Identity   (IMSI) and the Globally Unique Temporary User Equipment Identity   (GUTI) [3GPP.23.003].  These MN identities contain information that   can uniquely identify the operator to whom the subscription belongs.3.2.  Receiving the LMA FQDN or IP Address from Lower Layers   The solution described here is similar to the solution discussed inSection 3.1.  A MAG receives an LMA FQDN or an IP address from lower   layers, for example, as a part of the normal lower-layer signaling   when the MN attaches to the network.  IKEv2 could be an existing   example of such lower-layer signaling where IPsec is the "lower   layer" for the MN [3GPP.24.302].  IKEv2 has an IKEv2   Identification - Responder (IDr) payload, which is used by the IKEv2   initiator (i.e., the MN in this case) to specify which of the   responder's identities (i.e., the LMA in this case) it wants to talk   to.  And here the responder identity could be an FQDN or an IP   address of the LMA (as the IKEv2 identification payload can be an IP   address or an FQDN).  Another existing example is the Access Point   Name Information Element (APN IE) [3GPP.24.008] used in 3GPP radio   network access signaling and capable of carrying an FQDN.  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 does not associate the information with any   LMA function.Korhonen & Devarapalli        Informational                     [Page 5]

RFC 6097                      LMA Discovery                February 20113.3.  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 [3GPP.24.302]   [RFC5996].  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., seeSection 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 [3GPP.23.003] 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 a service or external   network name is the Access Point Name (APN) [3GPP.23.003] that   contains the information of the operator providing the access to the   given service or the external network.  For example, an FQDN for an   "ims" APN could be "ims.apn.epc.mnc015.mcc234.3gppnetwork.org".4.  Handover Considerations   Whenever an 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 [RFC5949].  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 inSection 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 regulations (such as inter-operator   roaming consortium agreements), the situation might not be this   desperate.  For example, a MAG might be able to synthesize an   LMA-specific FQDN (e.g., out of an MN identity or some otherKorhonen & Devarapalli        Informational                     [Page 6]

RFC 6097                      LMA Discovery                February 2011   service-specific parameters).  Alternatively, the MAG could use (for   example), an 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 an SRV   [RFC2782] query).  These approaches would guarantee that DNS always   returns the same LMA Address to the MAG.   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 [RFC5779].  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 server delivers the existing LMA information to the new   MAG as part of the authentication and authorization procedure as   described inSection 2.1.5.  Recommendations   This document discussed several solution approaches for a dynamic LMA   discovery.  All discussed solution approaches actually require   additional functionality or infrastructure support that the base   PMIPv6 specification [RFC5213] does not require.   Solutions inSection 3 all depend on lower layers being able to   provide information that a MAG can then use to query the DNS and   discover a suitable LMA.  The capabilities of the lower layers and   the interactions with them are generally out of scope of the IETF,   and specific to a certain system and architecture.   Solutions inSection 2 depend on the existence of an AAA   infrastructure, which is able to provide to a MAG either an LMA IP   address or an LMA FQDN.  While there can be system- and architecture-   specific details regarding the AAA interactions and the use of DNS,   the dynamic LMA discovery can be implemented in an access- and   technology-agnostic manner, and work in the same way across   heterogeneous environments.  Therefore, using AAA-based LMA discovery   solutions is recommended by this document.  Furthermore, following   the guidance inSection 4, Paragraph 4.1 of [RFC1958], the use of   FQDNs should be preferred over IP addresses in the context of   AAA-based LMA discovery solutions.Korhonen & Devarapalli        Informational                     [Page 7]

RFC 6097                      LMA Discovery                February 20116.  Security Considerations   The use of DNS for obtaining the IP address of a mobility agent   carries certain security risks.  These are explained in detail inSection 9.1 of [RFC5026].  However, the risks described in [RFC5026]   are mitigated to a large extent in this document, since the MAG and   the LMA 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.   [RFC5213] specifies the use of IKEv2 between the MAG and the LMA to   authenticate each other and set up 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-AAA-   server communication relies on the security properties of the   intermediate AAA brokers and AAA proxies.7.  Acknowledgements   The authors would like to thank Julien Laganier, Christian Vogt,   Ryuji Wakikawa, Frank Xia, Behcet Sarikaya, Charlie Perkins, Qin Wu,   Jari Arkko, and Xiangsong Cui for their comments, extensive   discussions, and suggestions on this document.Korhonen & Devarapalli        Informational                     [Page 8]

RFC 6097                      LMA Discovery                February 20118.  References8.1.  Normative References   [RFC5213]  Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury, K.,              and B. Patil, "Proxy Mobile IPv6",RFC 5213, August 2008.8.2.  Informative References   [3GPP.23.003]              3GPP, "Numbering, addressing and identification", 3GPP              TS 23.003 v10.0.0, December 2010.   [3GPP.24.008]              3GPP, "Mobile radio interface Layer 3 specification", 3GPP              TS 24.008 v10.1.0, December 2010.   [3GPP.24.302]              3GPP, "Access to the 3GPP Evolved Packet Core (EPC) via              non-3GPP access networks", 3GPP TS 24.302 v10.2.0,              December 2010.   [RFC1958]  Carpenter, B., Ed., "Architectural Principles of the              Internet",RFC 1958, June 1996.   [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.   [RFC5026]  Giaretta, G., Ed., Kempf, J., and V. Devarapalli, Ed.,              "Mobile IPv6 Bootstrapping in Split Scenario",RFC 5026,              October 2007.   [RFC5149]  Korhonen, J., Nilsson, U., and V. Devarapalli, "Service              Selection for Mobile IPv6",RFC 5149, February 2008.   [RFC5779]  Korhonen, J., Ed., Bournelle, J., Chowdhury, K., Muhanna,              A., and U. Meyer, "Diameter Proxy Mobile IPv6: Mobile              Access Gateway and Local Mobility Anchor Interaction with              Diameter Server",RFC 5779, February 2010.Korhonen & Devarapalli        Informational                     [Page 9]

RFC 6097                      LMA Discovery                February 2011   [RFC5949]  Yokota, H., Chowdhury, K., Koodli, R., Patil, B., and F.              Xia, "Fast Handovers for Proxy Mobile IPv6",RFC 5949,              September 2010.   [RFC5996]  Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen,              "Internet Key Exchange Protocol Version 2 (IKEv2)",RFC 5996, September 2010.Authors' Addresses   Jouni Korhonen   Nokia Siemens Networks   Linnoitustie 6   FIN-02600 Espoo   Finland   EMail: jouni.nospam@gmail.com   Vijay Devarapalli   Vasona Networks   EMail: dvijay@gmail.comKorhonen & Devarapalli        Informational                    [Page 10]