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Versions: 00 01 02 03 04 05 06 07 rfc5679                               
MIPSHOP WG                                                     G. Bajko
Internet Draft                                                    Nokia
Intended Status: Proposed Standard                         June 4, 2009
Expires: December 3, 2009

            Locating IEEE 802.21 Mobility Servers using DNS

   Status of this Memo

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

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   This Internet-Draft will expire on December 3, 2009.

   Copyright and License 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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   This document defines application service tags that allow service
   location without relying on rigid domain naming conventions, and DNS
   procedures for discovering servers which provide IEEE 802.21
   [IEEE802.21] defined Mobility Services. Such Mobility Services are
   used to assist a Mobile Node (MN) supporting IEEE 802.21
   [IEEE802.21], in handover preparation (network discovery) and

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   handover decision (network selection). The services addressed by
   this document are the Media Independent Handover Services defined in

Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   this document are to be interpreted as described in RFC-2119.

Terminology and abbreviations used in this document

   Mobility Services: comprises of a set of different services provided
   by the network to mobile nodes to facilitate handover preparation
   and handover decision, as described in [IEEE802.21].

   Mobility Server: a network node providing IEEE 802.21 Mobility

   MIH: Media Independent Handover, as defined in [IEEE802.21].

   MIH Service: IS, ES or CS type of service, as defined in

   Application service:  is a generic term for some type of
   application, independent of the protocol that may be used to offer
   it. Each application service will be associated with an IANA-
   registered tag.

   Application protocol: is used to implement the application service.
   These are also associated with IANA-registered tags.

Table of Content

   1. Introduction....................................................2
   2. Discovering a Mobility Server...................................3
        2.1 Selecting a Mobility Service..............................4
        2.2 Selecting the transport protocol..........................4
        2.3 Determining the IP address and port.......................6
   3. IANA Considerations.............................................6
   4. Security Considerations.........................................7
   5. Normative References............................................8
   6. Informative References..........................................8
   7. Author's Address................................................9

1. Introduction

   IEEE 802.21 [IEEE802.21] defines three distinct service types to
   facilitate link layer handovers across heterogeneous technologies:

   a) Information Services (IS)

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        IS provides a unified framework to the higher layer entities
        across the heterogeneous network environment to facilitate
        discovery and selection of multiple types of networks existing
        within a geographical area, with the objective to help the
        higher layer mobility protocols to acquire a global view of the
        heterogeneous networks and perform seamless handover across
        these networks.

   b) Event Services (ES)
        Events may indicate changes in state and transmission behavior
        of the physical, data link and logical link layers, or predict
        state changes of these layers. The Event Service may also be
        used to indicate management actions or command status on the
        part of the network or some management entity.

   c) Command Services (CS)
        The command service enables higher layers to control the
        physical, data link, and logical link layers. The higher layers
        may control the reconfiguration or selection of an appropriate
        link through a set of handover commands.

   In IEEE terminology these services are called Media Independent
   Handover (MIH) services.
   While these services may be co-located, the different pattern and
   type of information they provide does not necessitate the co-

   "Service Management" service messages, i.e., MIH registration, MIH
   capability discovery and MIH event subscription messages, are
   considered as ES and CS when transporting MIH messages over L3

   An MN may make use of any of these MIH service types separately or
   any combination of them.

   It is anticipated that a Mobility Server will not necessarily host
   all three of these MIH Services together, thus there is a need to
   discover the MIH Service types separately.

   This document defines a number of application service tags that
   allow service location without relying on rigid domain naming

2. Discovering a Mobility Server

   The Dynamic Delegation Discovery System (DDDS) [RFC3401] is used to
   implement lazy binding of strings to data, in order to support
   dynamically configured delegation systems.  The DDDS functions by
   mapping some unique string to data stored within a DDDS Database by
   iteratively applying string transformation rules until a terminal
   condition is reached. When DDDS uses DNS as a distributed database
   of Rules, these Rules are encoded using the Naming Authority Pointer

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   (NAPTR) Resource Record (RR). One of these Rules is the First Well
   Known Rule, which says where the process starts.

   In current specifications, the First Well Known Rule in a DDDS
   application [RFC3403] is assumed to be fixed, ie the domain in the
   tree where the lookups are to be routed to, is known. This document
   proposes the input to the First Well Known Rule to be dynamic, based
   on the search path the resolver discovers or is configured with.

   The search path of the resolver can either be pre-configured,
   discovered using DHCP or learned from a previous MIH Information
   Service (IS) query [IEEE802.21] as described in

   When the MN needs to discover Mobility Services in its home domain,
   the input to the First Well Known Rule MUST be the MN's home domain,
   which is assumed to be pre-configured in the MN.

   When the MN needs to discover Mobility Services in a local (visited)
   domain, it SHOULD use DHCP as described in [ID.ietf-mipshop-mos-
   dhcp-options] to discover the IP address of the server hosting the
   desired service, and use it in SRV queries. In some instances, the
   discovery may result in a per protocol/application list of domain
   names which are then to be used as starting points for the
   subsequent NAPTR lookups. If neither IP address or domain name can
   be discovered with the above procedure, the MN MAY request for a
   domain search list, as described in [RFC3397] and [RFC3646], and use
   it as input to the DDDS application.

   The MN may also have a list of cached domain names of Service
   Providers, learned from a previous MIH Information Service (IS)
   query [IEEE802.21]. If the cache entries have not expired, they can
   be used as input to the DDDS application.

   When the MN does not find valid domain names using the procedures
   above, it MUST stop any attempt to discover MIH Services.

   The dynamic rule described above SHOULD NOT be used for discovering
   services other than MIH Services described in this document, unless
   stated otherwise by a future specification.

   The procedures defined here result in an IP address, port and
   transport protocol where the MN can contact the Mobility Server
   which hosts the service the MN is looking for.

2.1 Selecting a Mobility Service

   The MN should know the characteristics of the Mobility Services
   defined in [IEEE802.21] and based on that it should be able to
   select the service it wants to use to facilitate its handover. The
   services it can choose from are:
           - Information Service (MIHIS)

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           - Event Service (MIHES)
           - Command Service (MIHCS)

   The service identifiers for the services are "MIHIS", "MIHES", and
   "MIHCS" respectively.
   The server supporting any of the above services MUST support at
   least UDP and TCP as transport, as described in [ID.ietf-mipshop-
   mstp-solution]. SCTP and other transport protocols MAY also be

2.2 Selecting the transport protocol

   After the desired service has been chosen, the client selects the
   transport protocol it prefers to use. Note, that transport selection
   may impact the handover performance.

   The services relevant for the task of transport protocol selection
   are those with NAPTR service fields with values "ID+M2X", where ID
   is the service identifier defined in the previous section and X is a
   letter that corresponds to a transport protocol supported by the
   domain. This specification defines M2U for UDP, M2T for TCP and M2S
   for SCTP.   This document also establishes an IANA registry for
   NAPTR service name to transport protocol mappings.

   These NAPTR [RFC3403] records provide a mapping from a domain to the
   SRV [RFC2782] record for contacting a server with the specific
   transport protocol in the NAPTR services field. The resource record
   will contain an empty regular expression and a replacement value,
   which indicates the domain name where the SRV record for that
   particular transport protocol can be found. If the server supports
   multiple transport protocols, there will be multiple NAPTR records,
   each with a different service value.  As per [RFC3403], the client
   discards any records whose services fields are not applicable.

   The MN MUST discard any service fields that identify a resolution
   service whose value is not "M2X", for values of X that indicate
   transport protocols supported by the client.  The NAPTR processing
   as described in RFC 3403 will result in the discovery of the most
   preferred transport protocol of the server that is supported by the
   client, as well as an SRV record for the server.

   As an example, consider a client that wishes to find MIHIS service
   in the example.com domain. The client performs a NAPTR query for
   that domain, and the following NAPTR records are returned:

           order pref flags  service     regexp       replacement
   IN NAPTR  50   50   "s"  "MIHIS+M2T"    ""  _MIHIS._tcp.example.com
   IN NAPTR  90   50   "s"  "MIHIS+M2U"    ""  _MIHIS._udp.example.com

   This indicates that the domain does have a server providing MIHIS
   services over TCP and UDP, in that order of preference. Since the
   client supports TCP and UDP, TCP will be used, targeted to a host

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   determined by an SRV lookup of _MIHIS._tcp.example.com.  That lookup
   would return:

   ;;          Priority  Weight    Port        Target
        IN  SRV    0        1      XXXX   server1.example.com
        IN  SRV    0        2      XXXX   server2.example.com

   If no NAPTR records are found, the client constructs SRV queries for
   those transport protocols it supports, and does a query for each.
   Queries are done using the service identifier "_MIHIS" for the MIH
   Information Service, "_MIHES" for the MIH Event Service and "_MIHCS"
   for the MIH Command Service. A particular transport is supported if
   the query is successful.  The client MAY use any transport protocol
   it desires which is supported by the server.

   Note, that the regexp field in the NAPTR example above is empty.
   This document discourages the use of this field as its usage can be
   complex and error prone; and the discovery of the MIH services do
   not require the flexibility provided by this field over a static
   target present in the TARGET field.

   If the client is already configured with the information about which
   transport protocol is used for a mobility service in a particular
   domain, it can directly perform an SRV query for that specific
   transport using the service identifier of the Mobility Service. For
   example, if the client knows that it should be using TCP for MIH IS
   service, it can perform a SRV query directly for

2.3 Determining the IP address and port

   Once the server providing the desired service and the transport
   protocol has been determined, the next step is to determine the IP
   address and port.

   If TARGET is a numeric IP address, the MN uses that IP address and
   the already chosen transport to contact the server providing the
   desired service.

   If the TARGET was not a numeric IP address, then the MN performs an
   A and/or AAAA record lookup of the domain name, as appropriate. The
   result will be a list of IP addresses, each of which can be
   contacted using the transport protocol determined previously.

   If the result of the SRV query contains a port number, then the MN
   SHOULD contact the server at that port number. If the SRV record did
   not contain a port number then the MN SHOULD contact the server at
   the default port number of that particular service. A default port
   number for MIH services is requested from IANA in [ID.ietf-mipshop-

3. IANA considerations

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   The usage of NAPTR records described here requires well known values
   for the service fields for each transport supported by Mobility
   Services. The table of mappings from service field values to
   transport protocols is to be maintained by IANA.

   The registration in the RFC MUST include the following information:

        Service Field: The service field being registered.

        Protocol: The specific transport protocol associated with that
        service field.  This MUST include the name and acronym for the
        protocol, along with reference to a document that describes the
        transport protocol.

        Name and Contact Information: The name, address, email address
        and telephone number for the person performing the

   The following values have been placed into the registry:

   Service Fields                    Protocol
      MIHIS+M2T                        TCP
      MIHIS+M2U                        UDP
      MIHIS+M2S                       SCTP
      MIHES+M2T                        TCP
      MIHES+M2U                        UDP
      MIHES+M2S                       SCTP
      MIHCS+M2T                        TCP
      MIHCS+M2U                        UDP
      MIHCS+M2S                       SCTP

   New Service Fields are to be added via Standards Action as defined
   in [RFC5226].
   New entries to the table that specify additional transport protocols
   for the existing Service Fields may be registered by IANA on a First
   Come First Served' basis [RFC5226].

4. Security considerations

   A list of known threats to services using DNS is documented in
   [RFC3833]. For most of those identified threats, the DNS Security
   Extensions [RFC4033] does provide protection. It is therefore
   recommended to consider the usage of DNSSEC [RFC4033] and the
   aspects of DNSSEC Operational Practices [RFC4641] when deploying
   IEEE 802.21 Mobility Services.

   In deployments where DNSSEC usage is not feasible, measures should
   be taken to protect against forged DNS responses and cache poisoning
   as much as possible. Efforts in this direction are documented in

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5. Normative References

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

   [RFC3403] Mealling, M., "Dynamic Delegation Discovery System (DDDS)
       Part Three: The Domain Name System (DNS) Database", RFC 3403,
       October 2002.

   [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
       Rose, "DNS Security Introduction and Requirements", RFC 4033,
       March 2005.

   [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
       IANA Considerations Section in RFCs", BCP 26, RFC 5226, May
   [RFC3397] B. Aboba and S. Cheshire, "DHCP Domain Search Option", RFC
       3397, November 2002.

   [RFC3646] R. Droms, "DNS Configuration options for DHCPv6", RFC
       3646, December 2003.

6. Informative References

   [IEEE802.21] IEEE 802.21 Standard for Local and Metropolitan Area
       Networks: Media Independent Handover Services

   [RFC4641] Kolkman, O. and R. Gieben, "DNSSEC Operational Practices",
       RFC 4641, September 2006.

   [RFC3401] M. Mealling, "Dynamic Delegation Discovery System (DDDS)
       Part One: The Comprehensive DDDS", RFC 3401, October 2002.

   [RFC3833] Atkins, D. and R. Austein, "Threat Analysis of the Domain
       Name System (DNS)", RFC 3833, August 2004.

   [ID.ietf-mipshop-mstp-solution] Mobility Services Transport Protocol
       Design, Melia et al, April 2008, work in progress

   [ID.ietf-mipshop-mos-dhcp-options] DHCP Options for IEEE 802.21
       Mobility Services (MoS) Discovery, Bajko et al, May 2009, work
       in progress

   [ID.ietf-dnsext-forgery-resilience] Measures for making DNS more
       resilient against forged answers, Hubert et al, August 2008,
       work in progress

7. Author's Addresses

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   Gabor Bajko

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