Network Working Group                                         F. Templin
Internet-Draft                                                S. Russert
Intended status: Informational                               I. Chakeres
Expires: August 11, 2007                                           S. Yi
                                                    Boeing Phantom Works
                                                        February 7, 2007

                        MANET Autoconfiguration

Status of this Memo

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Copyright Notice

   Copyright (C) The IETF Trust (2007).


   Mobile Ad-hoc Networks (MANETs) consist of routers operating over
   wireless links and may or may not connect to other networks.  Routers
   in MANETs that connect to the Internet must have a way to
   automatically provision globally routable and unique IP addresses/
   prefixes.  This document specifies mechanisms for MANET
   autoconfiguration.  Both IPv4 and IPv6 are discussed.

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1.  Introduction

   Mobile Ad-hoc Networks (MANETs) comprise links with asymmetric
   reachability characteristics (see: [RFC2461], Section 2.2) that
   connect MANET Routers (MRs).  MRs participate in a routing protocol
   such that packets can be forwarded via multiple hops across the MANET
   if necessary.  MANETs may connect to other networks via MANET Border
   Routers (MBRs), and MRs may be multiple IP hops away from their
   nearest MBR in some scenarios.  A MANET may be as large as an
   Autonomous System (AS) or as small as an individual site, and may
   contain other MANETs and/or fixed networks.  MRs with hosts on
   downstream-attached links that require global Internet access must
   have a means to automatically provision global IP addresses/prefixes
   and/or other configuration information.

   Conceptually, MRs comprise a router entity and a host entity that are
   connected via a virtual point-to-point interface configured over an
   imaginary shared link for the MANET.  The imaginary shared link
   provides the conceptual model of a fully-connected shared link to
   which all MRs attach (i.e., a "virtual ethernet") that is identified
   by the set of MBRs in the MANET.  An MR (and its downstream-attached
   links) is a "site" unto itself, and a MANET is therefore a "site-of-

   MANETs that comprise homogeneous link types can configure the routing
   protocol to operate as a sub-IP layer mechanism such that IP (i.e.,
   Layer-3) sees the MANET as an ordinary shared link the same as for a
   (bridged) campus LAN.  In that case, a single IP hop is sufficient to
   traverse the MANET.

   MANETs that comprise heterogeneous link types must configure the
   routing protocol to operate as a Layer-3 mechanism such that routing
   protocol operation is based on MANET-Local Addresses (MLAs) or other
   Layer-3 identifiers that are unique within the MANET to avoid issues
   associated with bridging media types with dissimilar Layer-2 address
   formats and maximum transmission units (MTUs).  In that case,
   multiple IP hops may be necessary to traverse the MANET.

   This document specifies mechanisms and operational practices for
   MANET autoconfiguration.  Operation using standard BOOTP/DHCP
   [RFC0951][RFC2131][RFC3315][RFC3633] and neighbor discovery
   [RFC0826][RFC1256][RFC2461][RFC2462] mechanisms is assumed unless
   otherwise specified.  Both IPv4 [RFC0791] and IPv6 [RFC2460] are

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2.  Terminology

   The terminology in the normative references apply; the following
   terms are defined within the scope of this document:

   Mobile Ad-hoc Network (MANET)
      a connected network region that comprises MANET routers that
      maintain a routing structure among themselves in a relatively
      arbitrary fashion over links with asymmetric reachability
      characteristics (see: [RFC2461], Section 2.2).  MANETs may be
      large as an Autonomous System (AS) or as small as an individual
      site.  Further information on the characteristics of MANETs can be
      found in [RFC2501].

   MANET Interface
      a MANET router's attachment to an underlying link within the

   virtual ethernet
      an imaginary shared link that connects all MRs in a MANET.  A MR's
      interface to the virtual ethernet is configured over the
      underlying MANET interface(s) and has both "raw" and "cooked"
      access methods.  Packets sent using the raw access method are
      transmitted on the underlying MANET interface without further
      encapsulation and may require multiple Layer 3 hops to traverse
      the MANET, i.e., the raw access method sees the MANET as a
      multilink site.  Packets sent using the cooked access method are
      encapsulated in an outer IP header such that all MRs appear to be
      single-hop neighbors at Layer 3, i.e., the cooked access method
      sees the MANET as a unified link.

   MANET Router (MR)
      a node that participates in a routing protocol over its MANET
      interface(s) and forwards packets on behalf of its downstream-
      attached nodes and other MRs.  Conceptually, an MR comprises a
      router entity and a host entity connected via a virtual point-to-
      point interface configured over the MANET's virtual ethernet.  An
      MR (and its downstream-attached links) is a "site" unto itself,
      and a MANET is therefore a "site-of-sites".  For the purpose of
      this specification, an MR's host entity configures a DHCP client
      and its router entity configures a DHCP relay.

   MANET Border Router (MBR)
      an MR that connects the MANET to other networks.  For the purpose
      of this specification, MBRs are assumed to configure a DHCP relay
      and/or a DHCP server.

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   MANET Local Address (MLA)
      a Layer-3 unicast address/prefix configured by an MR that is used
      for intra-MANET communications, i.e., routable only within the
      scope of the MANET.  For IPv6, Unique Local Addresses (ULAs)
      [RFC4193][I-D.jelger-autoconf-mla] provide a natural MLA

   Extended Router Advertisement/Solicitation (ERA/ERS)
      an IP Router Advertisement/Solicitation (RA/RS) message [RFC1256]
      [RFC2461] associated with the MANET's virtual ethernet and
      transmitted according to one of the two virtual ethernet access
      methods (both methods are considered as functional equivalents):

      In the "raw" access method, ERA/ERS messages are transmitted
      unencapsulated over the underlying MANET link as for ordinary
      RA/RS, except with an MLA source address and with destination
      address set to an MLA or a site-scoped multicast address.

      In the "cooked" access method, ERA/ERS messages are constructed by
      encapsulating ordinary RA/RS in an outer IP header then
      transmitted over the underlying MANET link, e.g., as specified for
      ISATAP [RFC4214].

3.  MANET Autoconfiguration

   The following sections specify autoconfiguration mechanisms and
   operational practices that allow MRs to participate in the routing
   protocol and obtain addresses/prefixes for Intra-MANET and global
   Internet communications.

3.1.  MANET Router (MR) Operation

   Each MR configures MLAs on each of its MANET interfaces.  For IPv6,
   MLAs are generated using Unique Local Addresses
   [RFC4193][I-D.jelger-autoconf-mla] with interface identifiers that
   are either managed for uniqueness (e.g., per [RFC4291], Appendix A)
   or self-generated using a suitable random interface identifier
   generation mechanism that is compatible with EUI-64 format (e.g.,
   Cryptographically Generated Addresses (CGAs) [RFC3972]).  For IPv4,
   MLAs are generated using a corresponding unique local address
   configuration mechanism.

   Each MR next engages in the routing protocol and discovers the set of
   MBRs that identify the virtual ethernet that connects all MRs.  The
   set of MBRs is discovered the same as for the ISATAP Potential Router
   List (PRL) initialization procedure (see: [RFC4214], Sections 8.3.2
   and 9); if the set of MBRs is NULL, an alternate identifier (e.g.,

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   the IEEE MAC address of an ordinary MR) can instead be used to
   provide a name for the MANET.  MRs can then confirm reachability of
   MBRs (and, in the case of IPv6, discover prefixes associated with the
   MANET's virtual ethernet) by sending ERSs and/or receiving ERAs, via
   an out-of-band service discovery protocol, via information conveyed
   in the routing protocol itself, or through some other means
   associated with the particular link technology.

   After a MR discovers MBRs, the DHCP client associated with its host
   function forwards a DHCP DISCOVER (DHCPv4) or Solicit (DHCPv6)
   request to the DHCP relay associated with its router function to
   request global IP address and/or prefix delegations (see also:
   Section 3.6).  The relay function then forwards the request to one or
   more MBRs, to other known DHCP servers, or to a site-scoped "All-
   DHCP-Servers" multicast address.

   For DHCPv4, the MR's relay function writes an MLA from the MANET
   interface over which it will forward the request in the 'giaddr'
   field and also includes the MLA in a DHCPv4 MLA option (see:
   Section 3.4).  If necessary to identify the MR's downstream-attached
   host function, the relay also includes a link selection sub-option
   [RFC3527] with an address from the prefix associated with the virtual
   ethernet (if a prefix is available).

   For DHCPv6, the MR's relay function writes an MLA from the outgoing
   MANET interface in the "peer-address" field and also writes an
   address from the prefix associated with the virtual ethernet in the
   "link-address" field (if a prefix is available).  The MR can also use
   DHCP prefix delegation [RFC3633] to obtain prefixes for further sub-
   delegation to nodes on its downstream-attached links.

   The DHCP request will elicit a DHCP reply from a server with IP
   address/prefix delegations.  When addresses are delegated, the MR
   assigns the resulting addresses to the virtual point-to-point
   interface that connects its host and router functions, i.e., the
   addresses are *not* assigned on the upstream MANET interface.  When
   prefixes are delegated, the MR can assign and/or further sub-delegate
   the prefixes to its downstream-attached links, including physical
   links and virtual links of the MR itself.  If the MANET uses a
   proactive routing protocol, the MR can advertise the delegated
   addresses/prefixes into the routing protocol during the duration of
   the delegation lifetimes.

   The DHCP server ensures unique IP address/prefix delegations.  By
   assigning global IP addresses/prefixes only on downstream-attached
   interfaces (and not the upstream MANET interface) there is no
   requirement for the MR to perform Duplicate Address Detection (DAD)
   for global addresses on its MANET interfaces.  See Appendix A for

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   further DAD considerations.

   After the MR configures global IP addresses/prefixes, it can send IP
   packets with global IP source addresses to off-MANET destinations
   either by using any available MBRs as egress gateways or by selecting
   specific MBRs on a per-packet basis.  For MANETs in which MBRs can
   advertise a 'default' route that propagates throughout the routing
   protocol, the MR can send IP packets without encapsulation using the
   virtual ethernet "raw" access method at the expense of extra TTL
   (IPv4) or Hop Limit (IPv6) decrementation.  For MANETs in which the
   routing protocol cannot propagate a default route, or when the MR
   wishes to select as specific MBR as the egress gateway, the MR can
   either: a) send packets using the virtual ethernet "cooked" access
   method with an MLA for an MBR as the destination address in the outer
   header (i.e., tunnels the packets to the MBR), or b) send packets
   using the "raw" access method with an IPv4 source routing header
   (likewise IPv6 routing header) to ensure that the packets will be
   forwarded through a specific MBR.

3.2.  MANET Border Router Operation

   MBRs send periodic and/or solicited ERAs which (for IPv6) can include
   prefixes associated with the MANET's virtual ethernet.  Such prefixes
   should be advertised as not to be used for on-link determination or
   StateLess Address AutoConfiguration (SLAAC) [RFC2462] by setting the
   'A', 'L' bits in Prefix Information Options to 0.  (See: Appendix B
   for further considerations on using SLAAC for MANET

   MBRs act as BOOTP/DHCP relays and/or servers for a MR's DHCP
   requests/replies.  For DHCPv4, when a MBR acting as a relay forwards
   a DHCP request that includes an MLA option, it writes its own address
   in the 'giaddr' field, i.e., it overwrites the value that was written
   into 'giaddr' by the MR's relay function.

3.3.  DHCP Server Extensions

   No MANET autoconfiguration-specific extensions are required for
   DHCPv6 servers.

   DHCPv4 servers examine DHCPv4 requests for a DHCPv4 MLA option (see:
   Section 3.4).  If a DHCPv4 MLA option is present, the DHCPv4 server
   copies the option into the corresponding DHCPv4 reply message(s).

3.4.  MLA Encapsulation

   For DHCPv6, the MLA is encoded directly in the "peer-address" field
   of DHCPv6 requests/replies.

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   For DHCPv4, a new DHCPv4 option [RFC2132] called the 'MLA option' is
   required to encode an MLA for DHCP transactions that will traverse a
   MBR, i.e., so that the MBR has a MANET-relevant address to direct
   DHCPv4 replies to the correct MR, which may be multiple Layer-3 hops
   away.  The format of the DHCPv4 MLA option is given below:

     Code  Len   Ether Type      MLA
   | TBD |  n  |    type   |  a1 |  a2 | ...

      a one-octet field that identifies the option type (see:
      Section 5).

      a one-octet field that encodes the remaining option length.

   Ether Type
      a type value from the IANA "ethernet-numbers" registry.

      a variable-length MANET Local Address (MLA).

3.5.  MANET Flooding

   When multicast service discovery is required, Layer-3 MANETs that
   implement this specification must use a MANET flooding mechanism
   (e.g., Simplified Multicast Forwarding (SMF) [I-D.ietf-manet-smf]) so
   that site-scoped multicast messages can be propagated across multiple
   Layer-3 hops.

3.6.  Self-Generated Addresses

   MR's can self-generate an address (e.g., an IPv6 Cryptographically-
   Generated Address (CGA) [RFC3972]) then propose the address to the
   DHCP server.  If the DHCP server determines that the self-generated
   address is unique, it will delegate the address for the MR's use.

4.  Operation with Multiple MBRs

   For a set of MANETs and MBRs that attach to the same backbone
   network, MRs can retain their global IP address/prefix delegations as
   they move if the backbone network participates with the MBRs and MRs
   in a localized mobility management scheme, e.g., see:

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   For a set of MBRs that attach to different backbone networks and/or
   serve different global IP prefixes from within the same network, MRs
   must configure new global IP addresses/prefixes as they change
   between different MBRs unless inter-MBR tunnels and routing protocol
   exchanges are supported, e.g., see:
   [I-D.templin-autoconf-netlmm-dhcp], Appendix A.

   Global mobility management mechanisms for MRs that configure new
   global IP addresses/prefixes as they move between different MBRs are
   beyond the scope of this document.

5.  IANA Considerations

   A new DHCP option code is requested for the DHCP MLA Option in the
   IANA "bootp-dhcp-parameters" registry.

6.  Security Considerations

   Threats relating to MANET routing protocols also apply to this

7.  Related Work

   Telcordia has proposed DHCP-related solutions for the CECOM MOSAIC
   program.  The virtual ethernet model was proposed by Quang Nguyen
   under the guidance of Dr. Lixia Zhang.  Various IETF AUTOCONF working
   group proposals have suggested similar mechanisms.

8.  Acknowledgements

   The Naval Research Lab (NRL) Information Technology Division uses
   DHCP in their MANET research testbeds.  Many of the ideas on this
   document originated from IETF AUTOCONF working group discussions on
   various aspects of autoconfiguration for MANETs.

   Thomas Henderson provided valuable input; Jinmei Tatuya reminded that
   address duplication can occur when multiple mechanisms (i.e. manual
   configuration, stateless and DHCP) are used within the same network.

9.  References

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9.1.  Normative References

   [RFC0791]  Postel, J., "Internet Protocol", STD 5, RFC 791,
              September 1981.

   [RFC0826]  Plummer, D., "Ethernet Address Resolution Protocol: Or
              converting network protocol addresses to 48.bit Ethernet
              address for transmission on Ethernet hardware", STD 37,
              RFC 826, November 1982.

   [RFC0951]  Croft, B. and J. Gilmore, "Bootstrap Protocol", RFC 951,
              September 1985.

   [RFC1256]  Deering, S., "ICMP Router Discovery Messages", RFC 1256,
              September 1991.

   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol",
              RFC 2131, March 1997.

   [RFC2132]  Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
              Extensions", RFC 2132, March 1997.

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, December 1998.

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

   [RFC2462]  Thomson, S. and T. Narten, "IPv6 Stateless Address
              Autoconfiguration", RFC 2462, December 1998.

   [RFC3315]  Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
              and M. Carney, "Dynamic Host Configuration Protocol for
              IPv6 (DHCPv6)", RFC 3315, July 2003.

   [RFC3633]  Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
              Host Configuration Protocol (DHCP) version 6", RFC 3633,
              December 2003.

   [RFC4214]  Templin, F., Gleeson, T., Talwar, M., and D. Thaler,
              "Intra-Site Automatic Tunnel Addressing Protocol
              (ISATAP)", RFC 4214, October 2005.

9.2.  Informative References

              Macker, J., "Simplified Multicast Forwarding for MANET",

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Internet-Draft           MANET Autoconfiguration           February 2007

              draft-ietf-manet-smf-03 (work in progress), October 2006.

              Jelger, C., "MANET Local IPv6 Addresses",
              draft-jelger-autoconf-mla-01 (work in progress),
              October 2006.

              Templin, F., "Network Localized Mobility Management using
              DHCP", draft-templin-autoconf-netlmm-dhcp-04 (work in
              progress), October 2006.

              Thaler, D., "Multi-Subnet MANETs",
              draft-thaler-autoconf-multisubnet-manets-00 (work in
              progress), February 2006.

              Thaler, D., "Issues With Protocols Proposing Multilink
              Subnets", draft-thaler-intarea-multilink-subnet-issues-00
              (work in progress), March 2006.

   [RFC2501]  Corson, M. and J. Macker, "Mobile Ad hoc Networking
              (MANET): Routing Protocol Performance Issues and
              Evaluation Considerations", RFC 2501, January 1999.

   [RFC3527]  Kinnear, K., Stapp, M., Johnson, R., and J. Kumarasamy,
              "Link Selection sub-option for the Relay Agent Information
              Option for DHCPv4", RFC 3527, April 2003.

   [RFC3972]  Aura, T., "Cryptographically Generated Addresses (CGA)",
              RFC 3972, March 2005.

   [RFC4193]  Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
              Addresses", RFC 4193, October 2005.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, February 2006.

Appendix A.  IPv6 Neighbor Discovery (ND) and Duplicate Address
             Detection (DAD)

   In terms of ND, [RFC2461][RFC4291] require that a node configure a
   link-local address on each of its IPv6-enabled interfaces, and the
   primary requirement for link-locals seems to be for the purpose of
   uniquely identifying routers on the link.  But, it is for further
   study as to whether MRs should send RAs on MANET interfaces at all,

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   since the MANET is a peering point between distinct sites and not the
   link of a single site with a clear set of serving routers and
   dependent end-hosts.  In particular, since MANET interfaces configure
   MLAs which already provide a statistically-unique identifier, the use
   link-local addresses may only be practical for environments in which
   link-local address assignments are specifically managed for
   uniqueness, e.g., ISATAP link-local addresses [RFC4214].

   In terms of DAD, pre-service DAD for an address assigned on a MANET
   link (such as specified in [RFC2462]) would require either flooding
   the entire MANET or somehow discovering a targeted region of the
   MANET on which a node that configures a duplicate address resides and
   sending a directed DAD message toward that region.  But, the control
   message overhead for such a MANET-wide DAD would be substantial and
   prone to false-negatives due to packet loss.  Note also that link-
   local addresses using Cryptographically Generated Addresses (CGAs)
   [RFC3972] provide random generation only in 59 bits of the lower 64
   bits of the IPv6 address, while MLAs using CGAs also use 40/56 bits
   of random generation in the upper 64 bits of the IPv6 address.  Since
   such MLAs are highly unlikely to collide, pre-service DAD can be
   avoided and a passive in-service DAD (e.g., one that monitors routing
   protocol messages) can be used instead.

   Statistical properties can assure uniqueness for the MLAs assigned on
   a MR's MANET interfaces, and careful operational practices can assure
   uniqueness for the global addresses/prefixes assigned on a MR's
   downstream-attached links (since the DHCP server assures unique
   assignments).  However, a passive in-service DAD mechanism should
   still be used to detect duplicates that were assigned via other
   means, e.g., manual configuration.

Appendix B.  IPv6 StateLess Address AutoConfiguration (SLAAC)

   For IPv6, the use of StateLess Address AutoConfiguration (SLAAC)
   [RFC2462] could be indicated by prefix information options in ERAs
   with the 'A' bit set to 1.  MRs that receive such ERAs could then
   self-generate an address from the prefix and assign it to the virtual
   point-to-point interface configured over the MANET's virtual
   ethernet, then use a passive in-service DAD approach to detect
   duplicates within the MANET.  But, if the MANET partitions, DAD might
   not be able to monitor the routing exchanges occurring in other
   partitions and address duplication could result.

Appendix C.  Change Log

   Changed from -04 to -05:

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   o  introduced conceptual "virtual ethernet" model.

   o  support "raw" and "cooked" modes as equivalent access methods on
      the virutal ethernet.

   Changed from -03 to -04:

   o  introduced conceptual "imaginary shared link" as a representation
      for a MANET.

   o  discussion of autonomous system and site abstractions for MANETs

   o  discussion of autoconfiguration of CGAs

   o  new appendix on IPv6 StateLess Address AutoConfiguration

   Changes from -02 to -03:

   o  updated terminology based on RFC2461 "asymmetric reachability"
      link type; IETF67 MANET Autoconf wg discussions.

   o  added new appendix on IPv6 Neighbor Discovery and Duplicate
      Address Detection

   o  relaxed DHCP server deployment considerations allow DHCP servers
      within the MANET itself

   Changes from -01 to -02:

   o  minor updates for consistency with recent developments

   Changes from -00 to -01:

   o  new text on DHCPv6 prefix delegation and multilink subnet

   o  various editorial changes

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Authors' Addresses

   Fred L. Templin
   Boeing Phantom Works
   P.O. Box 3707 MC 7L-49
   Seattle, WA  98124


   Steven W. Russert
   Boeing Phantom Works
   P.O. Box 3707 MC 7L-49
   Seattle, WA  98124


   Ian D. Chakeres
   Boeing Phantom Works
   P.O. Box 3707 MC 7L-49
   Seattle, WA  98124


   Seung Yi
   Boeing Phantom Works
   P.O. Box 3707 MC 7L-49
   Seattle, WA  98124


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