Network Working Group                                    F. Templin, Ed.
Internet-Draft                                                S. Russert
Intended status: Informational                                     S. Yi
Expires: February 20, 2009                          Boeing Phantom Works
                                                         August 19, 2008

    MANET Autoconfiguration using Virtual Enterprise Traversal (VET)

Status of this Memo

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   Mobile Ad-hoc Networks (MANETs) connect routers on links with
   asymmetric reachability characteristics, and may also connect to
   other networks including the Internet.  Routers in MANETs must have a
   way to automatically provision IP addresses/prefixes and other
   information.  This document specifies a Virtual Enterprise Traversal
   (VET) abstraction for autoconfiguration and operation of routers in

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  MANET Characteristics  . . . . . . . . . . . . . . . . . . . .  6
   4.  MANET Router Autoconfiguration . . . . . . . . . . . . . . . .  7
     4.1.  MANET Interface Autoconfiguration  . . . . . . . . . . . .  8
     4.2.  VET Interface Autoconfiguration  . . . . . . . . . . . . .  9
     4.3.  MANET Gateway List Discovery and MANET Identification  . . 10
     4.4.  Site-interior Interface Autoconfiguration  . . . . . . . . 10
       4.4.1.  Autoconfiguration of IPv4 Addresses/Prefixes . . . . . 10
       4.4.2.  Autoconfiguration of IPv6 Addresses/Prefixes . . . . . 11
       4.4.3.  Prefix and Route Maintenance . . . . . . . . . . . . . 12
     4.5.  Portable and Self-Configured IP Prefixes . . . . . . . . . 12
     4.6.  Separation of IP Addressing Domains  . . . . . . . . . . . 13
   5.  Post-Autoconfiguration Operation . . . . . . . . . . . . . . . 13
     5.1.  Forwarding Packets to Off-MANET Destinations . . . . . . . 13
     5.2.  MANET-Local Communications . . . . . . . . . . . . . . . . 14
     5.3.  Multicast  . . . . . . . . . . . . . . . . . . . . . . . . 14
     5.4.  Service Discovery  . . . . . . . . . . . . . . . . . . . . 14
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 15
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 15
   8.  Related Work . . . . . . . . . . . . . . . . . . . . . . . . . 15
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15
   10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 15
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 16
     11.2. Informative References . . . . . . . . . . . . . . . . . . 16
   Appendix A.  Duplicate Address Detection (DAD) Considerations  . . 18
   Appendix B.  Change Log  . . . . . . . . . . . . . . . . . . . . . 19
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 22
   Intellectual Property and Copyright Statements . . . . . . . . . . 23

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1.  Introduction

   Mobile Ad-hoc Networks (MANETs) connect MANET Routers (MNRs) on links
   with asymmetric reachability characteristics (see: [RFC4861], Section
   2.2).  From the standpoint of IP autoconfiguration, MANETs share
   properties with enterprise networks [RFC4852] except that their
   topologies may change dynamically over time and there may be
   little/no active management by (centralized) network operation
   authorities.  These specialized characteristics require careful
   considerations for MANET router autoconfiguration and operation,
   however the same principles apply equally to enterprise network
   scenarios that may be neither mobile nor ad-hoc.

   MANET autoconfiguration entails the configuration of addresses/
   prefixes and other information on routers in MANETs, where addresses
   of different scopes may be assigned on various types of interfaces
   with diverse properties.  The different types of interfaces that may
   occur on a MANET router are defined, and the autoconfiguration
   mechanisms used for each type are specified.  (Out of scope for this
   document is the autoconfiguration of Internet-facing interfaces,
   which must be coordinated in a manner specific to the service
   provider's network.)  Figure 1 below depicts the conceptual model for
   a MANET Router:

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                               Internet-facing Interfaces
                                    x   x        x
                                    |   |        |
             |                      |   |        |          |    M
             |                      |   |  ....  |          |    A
             |                  +---+---+--------+---+      |    N
             |                  |   +--------+      /|      |    E
             |   I  V  I   x----+   |  Host  |   I /*+------+--< T
             |   n  i  n        |   |Function|   n|**|      |
             |   t  r  t        |   +--------+   t|**|      |    I
             |   e  t  e   x----+              V e|**+------+--< n
             |   r  u  r      . |              E r|**|  .   |    t
             |   n  a  f      . |              T f|**|  .   |    e
             |   a  l  a      . |   +--------+   a|**|  .   |    r
             |   l     c      . |   | Router |   c|**|  .   |    f
             |         e   x----+   |Function|   e \*+------+--< a
             |         s        |   +--------+      \|      |    c
             |                  +---+---+--------+---+      |    e
             |                      |   |  ....  |          |    s
             |                      |   |        |          |
                                    |   |        |
                                    x   x        x
                               Site-Interior Interfaces

                          Figure 1: MANET Router

   This document specifies a Virtual Enterprise Traversal (VET)
   abstraction for MANET autoconfiguration and operation with multilink
   subnet avoidance; both IPv4 [RFC0791] and IPv6 [RFC2460] are
   discussed within this context.  The use of standard DHCP
   [RFC2131][RFC3315] and neighbor discovery [RFC0826][RFC4861]
   mechanisms is assumed unless otherwise specified.

   This work is related to activites of the IETF autoconf, dhc, ipv6,
   manet and v6ops working groups.

2.  Terminology

   The terms "inner" and "outer" are used throughout this document to
   respectively refer to the innermost IP {address, protocol, header,
   packet, etc.} *before* encapsulation, and the outermost IP {address,
   protocol, header, packet, etc.} *after* encapsulation.  (There may
   also be "mid-layer" encapsulations between the inner and outer
   layers, including IPSec [RFC4301], the Subnetwork Encapsulation and
   Adaptation Layer (SEAL) [I-D.templin-seal], etc.)

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   The terminology in [I-D.ietf-autoconf-manetarch] and the normative
   references apply.  The following terms are defined within the scope
   of this document:

      the same as defined in [RFC3819].

   Mobile Ad-hoc Network (MANET)
      a connected network region of MANET routers that maintain a
      routing structure among themselves over asymmetric reachability
      links (see: [RFC4861], Section 2.2).  Further information on
      MANETs can be found in [RFC2501] and

   MANET Router (MNR)
      a mobile router that forwards packets over MANET interfaces.  For
      the purpose of this specification, an MNR comprises a router
      function, a host function, one or more MANET interfaces and zero
      or more internal virtual, site-interior, Internet-facing and VET

   MANET Border Router (MNBR)
      an MNR that connects other networks to the MANET and/or connects
      the MANET to other networks, including the Internet.  MNBRs also
      configure a seperate VET interface (used for automatic tunneling)
      for each distinct MANET they connect to.  All MNBRs are also MNRs.

   MANET Gateway (MNGW)
      a MNBR that connects the MANET to the Internet via Internet-facing
      interfaces and can delegate addresses/prefixes to other MNBRs.
      All MNGWs are also MNBRs.

   Internal Virtual Interface
      a MNBR's attachment to an internal virual link (e.g., a loopback
      ).  Internal virtual interfaces are also considered as site-
      interior interfaces.

   Site-interior Interface
      a MNBR's attachment to a link (e.g., an ethernet, a wireless
      personal area network, etc.) that it connects to the MANET and/or
      the Internet.

   Internet-facing Interface
      a MNBR's attachment to the Internet, or to a provider network
      outside of the MANET via which the Internet can be reached.

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   MANET Interface
      a MNR's attachment to a link in a MANET.  A MANET interface is
      "neutral" in its orientation, i.e., it is inherently neither site-
      interior nor Internet-facing.  In particular, a packet may need to
      be forwarded over several MANET interfaces before it is forwarded
      via either a site-interior or Internet-facing interface.

   MANET Local Address (MLA)
      a MANET-scoped IP address (e.g., an IPv6 Unique Local Address
      [RFC4193], an IPv4 privacy address [RFC1918], etc.) that is
      assigned to a MANET interface and unique within the MANET.  MLAs
      are used as identifiers for operating the routing protocol and/or
      locators for packet forwarding within the scope of the MANET; MLAs
      are also used as *outer* IP addresses during encapsulation.

   Virtual Enterprise Traversal (VET)
      an abstraction that uses IP-in-IP encapsulation to span a multi-
      link network (e.g., a MANET) in a single (inner) IP hop.

   VET interface
      a MNBR's interface used for virtual enterprise traversal.  The
      MNBR configures a VET interface over a set of underlying MANET
      interface(s) belonging to the same MANET.  The VET interface
      encapsulates each inner IP packet in any mid-layer headers plus an
      outer IP header then forwards it on an underlying MANET interface
      such that the TTL/Hop Limit in the inner header is not decremented
      as the packet traverses the MANET.  The VET interface presents an
      automatic tunneling abstraction that represents the MANET as a
      single IP hop.

   The following additional abbreviations are used throughout the

   CGA - Cryptographically Generated Address
   DHCP[v4,v6] - the Dynamic Host Configuration Protocol
   IP[v4,v6] - the Internet Protocol
   ISATAP - Intra-Site Automatic Tunnel Addressing Protocol
   ND - Neighbor Discovery
   PIO - Prefix Information Option
   RIO - Route Information Option
   RS/RA - IPv6 Neighbor Discovery Router Solicitation/Advertisement
   SEAL - Subnetwork Encapsulation and Adaptation Layer
   SLAAC - IPv6 StateLess Address AutoConfiguation

3.  MANET Characteristics

   MNRs typically participate in a routing protocol over MANET

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   interfaces to discover routes across the MANET using multiple Layer-2
   or Layer-3 forwarding hops if necessary.  MANETs may also connect to
   other networks via MANET Border Routers (MNBRs) and connect to the
   Internet via MANET Gateways (MNGWs).  A MANET may be as simple as a
   small collection of MNRs (and their attached networks); a MANET may
   also contain other MANETs and/or be a subnetwork of a larger MANET.

   MANETs that comprise homogeneous link types within a single IP subnet
   can configure the routing protocol to operate as a sub-IP layer
   mechanism such that IP 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 without IP layer encapsulation.

   MANETs that comprise heterogeneous link types and/or multiple IP
   subnets must also provide a routing service that operates as an IP
   layer mechanism, e.g., to accommodate 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
   such that specific autoconfiguration procedures are necessary to
   avoid multilink subnet issues [RFC4903].  In particular, we describe
   herein the use of IP-in-IP encapsulation to span the MANET in a
   single (inner) IP hop in order to avoid the multilink subnet issues
   that arise when MANET interfaces are used directly by applications.

   Conceptually, a MNR embodies both a host function and router
   function.  The host function enables the MNR to generate and receive
   packets over any of its non-MANET interfaces according to the weak
   end system model [RFC1122].  The router function connects the MNR's
   attached networks to MANETs via MANET interfaces and/or connects the
   MANET to other networks including the Internet (see: Figure 1).

   MNBRs also configure a VET interface that views all routers in the
   MANET as single-hop neighbors, where the MANET can also appear as a
   single IP hop within another MANET.  MNBRs configure a seperate VET
   interface for each distinct MANET to which they connect, and discover
   a list of MNBRs for each VET interface that can be used for
   forwarding packets to off-MANET destinations.  The following sections
   present the Virtual Enterprise Traversal approach for MANET

4.  MANET Router Autoconfiguration

   MNRs configure one or more MANET interfaces and engage in any MANET
   routing protocols over those interfaces.  They also configure zero or
   more Internet-facing interfaces that connect the MANET to the
   Internet, and zero or more site-interior interfaces (including
   internal virtual interfaces such as a loopback interface) that attach

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   other networks to the MANET.

   MNRs that configure site-interior/Internet-facing interfaces also act
   as MNBRs, and configure a VET interface over a set of underlying
   MANET interfaces belonging to the same MANET.  (Note that a MNBR may
   connect to multiple distinct MANETs, in which case it would configure
   multiple VET interfaces.)  MNRs obtain addresses/prefixes and other
   autoconfiguration information using the mechanisms specified in the
   following sections.

4.1.  MANET Interface Autoconfiguration

   When a MNR joins a MANET, it first configures a unique IPv6 link-
   local address on each MANET interface that requires an IPv6 link-
   local capability and an IPv4 link-local address on each MANET
   interface that requires an IPv4 link-local capability.  IPv6 link-
   local address generation mechanisms that provide sufficient
   uniqueness include Cryptographically Generated Addresses (CGAs)
   [RFC3972], StateLess Address AutoConfiguration (SLAAC) using EUI-64
   interface identifiers [RFC4862], etc.  The mechanisms specified in
   [RFC3927] provide an IPv4 link-local address generation capability.

   Next, the MNR configures a MANET Local Address (MLA) of the outer IP
   protocol version on each of its MANET interfaces and engages in any
   MANET routing protocols on those interfaces.  The MNR can configure
   an MLA via explicit management, DHCP autoconfiguration, pseudo-random
   self-generation from a suitably large address pool, or through an
   alternate autoconfiguration mechanism.

   DHCP configuration of MLAs may require support from relays within the
   MANET that have already autoconfigured an MLA as well as a MANET-wide
   multicast forwarding capability.  For DHCPv6, relays that do not
   already know the MLA of a server relay requests to the
   'All_DHCP_Servers' site-scoped IPv6 multicast group.  For DHCPv4,
   relays that do not already know the MLA of a server relay requests to
   the site-scoped IPv4 multicast group address TBD (see: Section 6).
   DHCPv4 servers that delegate MLAs join the TBD multicast group and
   service any DHCPv4 messages received for that group.

   Self-generation of MLAs for IPv6 can be from a large IPv6 local-use
   address range, e.g., IPv6 Unique Local Addresses [RFC4193].  Self-
   generation of MLAs for IPv4 can be from a large IPv4 private address
   range, e.g., 240/4 [I-D.fuller-240space].  When self-generation is
   used alone, the MNR must continuously monitor the MLAs for
   uniqueness, e.g., by monitoring the routing protocol, sending
   beacons, etc.  (This continuous monitoring process is sometimes known
   as "in-service duplicate address detection").

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   A combined approach using both DHCP and self-generation is also
   possible.  In this combined approach, the MNR first self-generates a
   temporary MLA which it will use only for the purpose of procuring an
   actual MLA from a DHCP server.  Acting as a combined client/relay,
   the MNR then uses the temporary MLA to engage in the routing protocol
   and performs a relay-server exchange using the temporary MLA as an
   address for the relay.  When the DHCP server delegates an actual MLA,
   the MNR abandons the temporary MLA, assigns the actual MLA to the
   MANET interface and re-engages in the routing protocol.  Note that
   the range of MLAs delegated by a DHCP server must be disjoint from
   the range of MLAs used by the MNR for self-generation.

4.2.  VET Interface Autoconfiguration

   MNBRs configure a VET interface over a set of underlying MANET
   interfaces belonging to the same MANET, where the VET interface sees
   all MNBRs in the MANET as single hop neighbors.  Inner IP packets
   forwarded over the VET interface are encapsulated in any mid-layer
   headers (e.g., IPsec, the SEAL header, etc.) followed by an outer IP
   header, then submitted to the outer IP forwarding engine for
   transmission on an underlying MANET interface (further encapsulation
   details are specified in Section 5.)

   When IPv6 and IPv4 are used as the inner/outer protocols
   (respectively), the MNBR autoconfigures an ISATAP link-local address
   ([RFC5214], Section 6.2) on the VET interface to support packet
   forwarding and operation of the IPv6 neighbor discovery protocol.
   The ISATAP address embeds an IPv4 MLA assigned to an underlying MANET
   interface, and need not be checked for uniqueness since the IPv4 MLA
   itself was already determined to be unique.  Link-local address
   configuration for other inner/outer IP protocol combinations is
   through administrative configuration or through an unspecified
   alternate method.

   After the MNBR configures a VET interface, it can communicate with
   other MNBRs as single-hop neighbors, i.e., it can confirm
   reachability of other MNBRs through Neighbor Discovery (ND) and/or
   DHCP exchanges over the VET interface.  (The MNBR can also confirm
   reachability through information conveyed in the MANET routing
   protocol or through some other means associated with the specific
   MANET subnetwork technology.)

   The MNBR must be able to detect and recover from the loss of VET
   interface neighbors due to e.g., MANET partitions, node failures,
   etc.  Mechanisms specified outside of this document such as
   monitoring the routing protocol, ND beaconing/polling, DHCP renewals/
   leasequeries, upper layer protocol hints of forward progress,
   bidirectional forward detection, detection of network attachment,

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   etc. can be used according to the particular deployment scenario.

4.3.  MANET Gateway List Discovery and MANET Identification

   After the MNBR configures its VET interfaces, it next discovers a
   list of MNGWs for each distinct MANET to which it connects.  The list
   can be discovered through information conveyed in the routing
   protocol or through the discovery mechanisms outlined in [RFC5214],
   Section 8.3.2.

   In particular, whether or not routing information is available the
   MNBR can discover the list of MNGWs by resolving an identifying name
   for the MANET using a MANET-local name resolution service (such as
   LLMNR [RFC4759] over the VET interface).  In the absence of other
   identifying names, the MNBR can resolve either the hostname
   "isatapv2" or the FQDN "" (i.e., if a MANET-
   specific suffix "" is known) for multicast-capable MANETs.
   For non-multicast MANETs, the MNBR can instead resolve the hostname
   "isatap" or the FQDN "".

   Identifying names, addresses of MNGWs and/or the prefixes they
   aggregate serve as an identifier for the MANET.

4.4.  Site-interior Interface Autoconfiguration

   MNBRs can acquire addresses and/or prefix delegations for assignment
   on site-interior interfaces through autoconfiguration exchanges with
   MNGWs over the VET interface.  Site-interior interface
   autoconfiguration considerations are discussed in the following

4.4.1.  Autoconfiguration of IPv4 Addresses/Prefixes

   When IPv4 is used as the inner protocol, the MNBR discovers the
   addresses of one or more MNGWs that delegate IPv4 prefixes then
   performs a DHCPv4 prefix delegation exchange
   [I-D.ietf-dhc-subnet-alloc] over the VET interface to obtain IPv4
   prefixes for assignment and/or sub-delegation on its site-interior

   To perform the DHCPv4 prefix delegation exchange, a DHCPv4 client
   associated with the MNBR's host function forwards a DHCPDISCOVER
   message with a Subnet Allocation option to a DHCPv4 relay associated
   with its router function, i.e., the MNBR acts as both client and
   relay.  The relay then forwards the message over the VET interface to
   the DHCPv4 server on a MNGW.  The forwarded DHCPDISCOVER will elicit
   a DHCPOFFER from the server containing IPv4 prefix delegations, and
   the MNBR completes the delegation through a DHCPREQUEST/DHCPACK

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   exchange (again using the combined client/relay approach).

   When the MNBR receives IPv4 prefix delegations, it assigns the
   prefixes on site-interior interfaces; it does not assign them on the
   VET interface or on MANET interfaces.  The MNBR can also obtain /32
   prefixes using DHCPv4 prefix delegation the same as for any IPv4
   prefix, and can assign them as IPv4 addresses with /32 netmasks on
   site-interior interfaces.

4.4.2.  Autoconfiguration of IPv6 Addresses/Prefixes

   When IPv6 is used as the inner protocol, the MNBR sends unicast IPv6
   Router Solicitation (RS) messages to MNGWs over the VET interface to
   receive Router Advertisements (RAs) with Prefix Information Options
   (PIOs) and/or with the 'M' flag set to signify whether DHCPv6
   autoconfiguration is available.  When the MNBR receives an RA
   containing PIOs with the 'A' and 'L' bits set to 1, it autoconfigures
   IPv6 addresses from the prefixes using SLAAC and assigns them to the
   VET interface.  (When IPv4 is used as the outer IP protocol, the
   addresses are autoconfigured and assigned as ISATAP addresses the
   same as specified in [RFC5214].)

   When the MNBR receives an RA with the 'M' flag set to 1, the MNGW
   that sent the RA also hosts a DHCPv6 server capable of delegating
   IPv6 prefixes (support for the MNGW acting as a DHCPv6 relay may be
   considered in the future).  If the RA also contains PIOs with the 'L'
   bit set to 0, the MNBR can use them as hints of prefixes the server
   is willing to delegate.  For example, a MNGW can include a PIO with a
   prefix such as 2001::DB8::/48 as a hint of an aggregated prefix from
   which it is willing to delegate longer prefixes.  Whether or not such
   hints are available, the MNBR (acting as a requesting router) can use
   DHCPv6 prefix delegation [RFC3633] over the VET interface to obtain
   IPv6 prefixes from the MNGW (acting as a delegating router).  The
   MNBR can then use the delegated prefixes for assignment and/or sub-
   delegation on its site-interior interfaces.

   The MNBR obtains prefixes using either a 2-message or 4-message
   DHCPv6 exchange [RFC3315].  For example, to perform the 2-message
   exchange a DHCPv6 client associated with the MNBR's host function
   forwards a Solicit message with an IA_PD option to a DHCPv6 relay
   associated with its router function, i.e., the MNBR acts as both
   client and relay.  The relay then forwards the message over the VET
   interface to the DHCPv6 server.  The forwarded Solicit message will
   elicit a Reply from the server containing IPv6 prefix delegations.
   When the MNBR receives IPv6 prefix delegations, it assigns the
   prefixes on site-interior interfaces only; it does not assign them on
   Internet-facing, VET, or MANET interfaces (see: [RFC3633], Section

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   The MNBR can also propose a specific prefix to the DHCPv6 server per
   Section 7 of [RFC3633], e.g., if a prefix delegation hint is
   available.  The server will check the proposed prefix for consistency
   and uniqueness, then return it in the reply to the MNBR if it was
   able to perform the delegation.  The MNBR can use mechanisms such as
   CGAs [RFC3972], IPv6 privacy address [RFC4941], etc. to self-generate
   addresses in conjunction with prefix delegation.

4.4.3.  Prefix and Route Maintenance

   When DHCP prefix delegation is used, the MNGW's DHCP server ensures
   that the delegations are unique within the MANET and that its router
   function will forward IP packets over the VET interface to the MNBR
   to which the prefix was delegated.  The prefix delegation remains
   active as long as the MNBR continues to issue renewals over the VET
   interface before the lease lifetime expires.  The lease lifetime also
   keeps the delegation state active even if communications between the
   MNBR and MNGW is disrupted for a period of time (e.g., due to a MANET
   partition) before being reestablished (e.g., due to a MANET merge).

   Since the DHCP client and relay are co-resident on the same MNBR, no
   special coordination is necessary for the MNGW to maintain routing
   information.  The MNGW simply retains forwarding information base
   entries that identify the MNBR as the next-hop toward the prefix via
   the VET interface, and issues ordinary redirects over the VET
   interface when necessary .

4.5.  Portable and Self-Configured IP Prefixes

   Independent of any MNGW-aggregated addresses/prefixes (see:
   Section 4.4), a MNBR can retain portable IP prefixes (e.g., prefixes
   taken from a home network, IPv6 Unique Local Addresses (ULAs)
   [RFC4193][I-D.ietf-ipv6-ula-central], etc.) as it travels between
   visited networks as long it coordinates in some fashion, e.g., with a
   mapping agent, prefix aggregation authority, etc.  MNBRs can sub-
   delegate portable (and other self-configured) prefixes on networks
   connected on their site-interior interfaces.

   Portable prefixes are not aggregated, redistributed or advertised by
   MNGWs and can therefore travel with the MNBR as it moves to new
   visited networks and/or configures peering arrangements with other
   nodes.  Generation and coordination of portable (and other self-
   configured) prefixes can therefore occur independently of any other
   autoconfiguration considerations.

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4.6.  Separation of IP Addressing Domains

   When the inner and outer IP protocols are different (i.e., IPv6-in-
   IPv4 or IPv4-in-IPv6), the MNBR's dual-stack orientation provides a
   natural separation between the inner and outer IP addressing domains,
   and separate default routes can be configured for each domain.

   When the inner and outer IP protocols are the same (i.e., IPv4-in-
   IPv4 or IPv6-in-IPv6) separation between inner and outer IP
   addressing domains can only be determined through the examination of
   IP prefixes.  In that case, special configurations/mechanisms may be
   necessary to support unambiguous determination of when to encapsulate
   using the VET interface vs when to forward using a MANET interface.

5.  Post-Autoconfiguration Operation

   After a MNR has been autoconfigured, it participates in any MANET
   routing protocols over MANET interfaces and forwards outer IP packets
   within the MANET as for any ordinary router.  MNBRs can additionally
   participate in any inner IP routing protocols over non-MANET
   interfaces and forward inner IP packets to off-MANET destinations.
   The following sections discuss post-autoconfiguration operations:

5.1.  Forwarding Packets to Off-MANET Destinations

   MNBRs consult the inner IP forwarding table to determine the next hop
   address (e.g., the VET interface address of another MNBR) for
   forwarding packets to off-MANET destinations.  When there is no
   forwarding information available, the MNBR can discover the next-hop
   through FQDN or reverse lookup using the same name resolution
   services as for MNGW discovery (see Section 4.3).

   For forwarding to next-hop addresses over VET interfaces that use
   IPv6-in-IPv4 encapsulation, MNBRs determine the outer destination
   address through static extraction of the IPv4 address embedded in the
   next-hop ISATAP address.  For other IP-in-IP encapsulations,
   determination of the outer destination address is through
   administrative configuration or through an unspecified alternate

   MNBRs that use IPv6 as the inner protocol can discover default router
   preferences and more-specific routes [RFC4191] by sending an RS over
   the VET interface to elicit an RA from another MNBR.  After default
   and/or more-specific routes are discovered, the MNBR can forward IP
   packets via a specific MNBR as the next-hop router on the VET
   interface.  When multiple default routers are available, the MNBR can
   use default router preferences, routing protocol information, traffic

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   engineering configurations, etc. to select the best exit router.

5.2.  MANET-Local Communications

   When permitted by policy, pairs of MNRs that configure the endpoints
   of a communications session can avoid VET interface encapsulation by
   directly invoking the outer IP protocol using MLAs assigned to their
   MANET interfaces.  For example, when the outer protocol is IPv4 a
   pair of communicating MNRs can use IPv4 MLAs for direct
   communications over their MANET interfaces without using the VET

5.3.  Multicast

   In multicast-capable deployments, MNRs provide a MANET-wide
   multicasting service such as Simplified Multicast Forwarding (SMF)
   [I-D.ietf-manet-smf] over their MANET interfaces such that outer IP
   multicast messages of site- or greater scope will be propagated
   across the MANET.  For such deployments, MNBRs can also provide an
   inner IP multicast/broadcast capability over their VET interfaces
   through mapping of the inner IP multicast address space to the outer
   IP multicast address space.

   MNBRs encapsulate inner IP multicast messages sent over the VET
   interface in any mid-layer headers (e.g., IPsec, SEAL, etc.) plus an
   outer IP header with a site-scoped outer IP multicast address as the
   destination.  For the case of IPv6 and IPv4 as the inner/outer
   protocols (respectively), [RFC2529] provides mappings from the IPv6
   multicast address space to the IPv4 multicast address space.  For
   other IP-in-IP encapsulations, mappings are established through
   administrative configuration or through an unspecified alternate

   For multicast-capable MANETs, use of the inner IP multicast service
   for operating the ND protocol over the VET interface is available but
   should be used sparingly to minimize MANET-wide flooding.  Therefore,
   MNBRs should use unicast ND services over the VET interface instead
   of multicast whenever possible.

5.4.  Service Discovery

   MNRs can peform MANET-wide service discovery using a suitable name-
   to-address resolution service.  Examples of flooding-based services
   include the use of LLMNR [RFC4759] over the VET interface or mDNS
   [I-D.cheshire-dnsext-multicastdns] over an underlying MANET
   interface.  More scalable and efficient service discovery mechanisms
   for MANETs are for further study.

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6.  IANA Considerations

   A site-scoped IPv4 multicast group (TBD) for DHCPv4 server discovery
   is requested.

7.  Security Considerations

   Security considerations for MANETs are found in
   [RFC2501][I-D.ietf-autoconf-manetarch] and apply also to the
   mechanisms and procedures specified in this document.

   Security considerations for MANET routing protocols that may be used
   within this context are found in their respective specifications.

8.  Related Work

   The authors acknowledge the work done by Brian Carpenter and Cyndi
   Jung in [RFC2529] that introduced the concept of intra-site automatic
   tunneling.  This concept was later called: "Virtual Ethernet" and
   investigated by Quang Nguyen under the guidance of Dr. Lixia Zhang.

   Telcordia has proposed DHCP-related solutions for the CECOM MOSAIC
   program.  The Naval Research Lab (NRL) Information Technology
   Division uses DHCP in their MANET research testbeds.  Various
   proposals within the IETF have suggested similar mechanisms.

9.  Acknowledgements

   The following individuals gave direct and/or indirect input that was
   essential to the work: Jari Arkko, Teco Boot, Emmanuel Bacelli, James
   Bound, Thomas Clausen, Eric Fleischman, Bob Hinden, Joe Macker,
   Thomas Narten, Alexandru Petrescu, John Spence, Jinmei Tatuya, Dave
   Thaler, Michaela Vanderveen and others in the IETF AUTOCONF and MANET
   working groups.  Many others have provided guidance over the course
   of many years.

10.  Contributors

   Thomas Henderson ( contributed to this
   document.  Ian Chakeres ( contributed to
   earlier versions of the document.

11.  References

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11.1.  Normative References

              Johnson, R., "Subnet Allocation Option",
              draft-ietf-dhc-subnet-alloc-07 (work in progress),
              July 2008.

   [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.

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

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

   [RFC4191]  Draves, R. and D. Thaler, "Default Router Preferences and
              More-Specific Routes", RFC 4191, November 2005.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              September 2007.

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862, September 2007.

   [RFC5214]  Templin, F., Gleeson, T., and D. Thaler, "Intra-Site
              Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214,
              March 2008.

11.2.  Informative References

              Cheshire, S. and M. Krochmal, "Multicast DNS",
              draft-cheshire-dnsext-multicastdns-06 (work in progress),

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              August 2006.

              Fuller, V., "Reclassifying 240/4 as usable unicast address
              space", draft-fuller-240space-02 (work in progress),
              March 2008.

              Chakeres, I., Macker, J., and T. Clausen, "Mobile Ad hoc
              Network Architecture", draft-ietf-autoconf-manetarch-07
              (work in progress), November 2007.

              Hinden, R., "Centrally Assigned Unique Local IPv6 Unicast
              Addresses", draft-ietf-ipv6-ula-central-02 (work in
              progress), June 2007.

              Macker, J. and S. Team, "Simplified Multicast Forwarding
              for MANET", draft-ietf-manet-smf-07 (work in progress),
              February 2008.

              Templin, F., "The Subnetwork Encapsulation and Adaptation
              Layer (SEAL)", draft-templin-seal-22 (work in progress),
              June 2008.

   [RFC1122]  Braden, R., "Requirements for Internet Hosts -
              Communication Layers", STD 3, RFC 1122, October 1989.

   [RFC1918]  Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
              E. Lear, "Address Allocation for Private Internets",
              BCP 5, RFC 1918, February 1996.

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

   [RFC2529]  Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4
              Domains without Explicit Tunnels", RFC 2529, March 1999.

   [RFC3056]  Carpenter, B. and K. Moore, "Connection of IPv6 Domains
              via IPv4 Clouds", RFC 3056, February 2001.

   [RFC3753]  Manner, J. and M. Kojo, "Mobility Related Terminology",
              RFC 3753, June 2004.

   [RFC3819]  Karn, P., Bormann, C., Fairhurst, G., Grossman, D.,

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              Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L.
              Wood, "Advice for Internet Subnetwork Designers", BCP 89,
              RFC 3819, July 2004.

   [RFC3927]  Cheshire, S., Aboba, B., and E. Guttman, "Dynamic
              Configuration of IPv4 Link-Local Addresses", RFC 3927,
              May 2005.

   [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.

   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, December 2005.

   [RFC4759]  Stastny, R., Shockey, R., and L. Conroy, "The ENUM Dip
              Indicator Parameter for the "tel" URI", RFC 4759,
              December 2006.

   [RFC4852]  Bound, J., Pouffary, Y., Klynsma, S., Chown, T., and D.
              Green, "IPv6 Enterprise Network Analysis - IP Layer 3
              Focus", RFC 4852, April 2007.

   [RFC4903]  Thaler, D., "Multi-Link Subnet Issues", RFC 4903,
              June 2007.

   [RFC4941]  Narten, T., Draves, R., and S. Krishnan, "Privacy
              Extensions for Stateless Address Autoconfiguration in
              IPv6", RFC 4941, September 2007.

Appendix A.  Duplicate Address Detection (DAD) Considerations

   A-priori uniqueness determination (also known as "pre-service DAD")
   for an MLA assigned on a MANET interface (such as specified in
   [RFC4862]) would require either flooding the entire MANET or somehow
   discovering a link in the MANET on which a node that configures a
   duplicate address is attached and performing a localized DAD exchange
   on that link.  But, the control message overhead for such a MANET-
   wide DAD would be substantial and prone to false-negatives due to
   packet loss and intermittent connectivity.  An alternative to pre-
   service DAD is to autoconfigure pseudo-random MLAs on MANET
   interfaces and employ a passive in-service DAD (e.g., one that
   monitors routing protocol messages for duplicate assignments).

   Pseudo-random IPv6 MLAs can be generated with mechanisms such as

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   CGAs, IPv6 privacy addresses, etc. with very small probability of
   collision.  Pseudo-random IPv4 MLAs can be generated through random
   assignment from a suitably large IPv4 prefix space, e.g., the soon-
   to-be-reclassified 240/4 space [I-D.fuller-240space].

   Consistent operational practices can assure uniqueness for MNGW-
   aggregated addresses/prefixes, while statistical properties for
   pseudo-random address self-generation can assure uniqueness for the
   MLAs assigned on a MNR's MANET interfaces.  Still, an MLA delegation
   authority should be used when available, while a passive in-service
   DAD mechanism should be used to detect MLA duplications when there is
   no MLA delegation authority.

Appendix B.  Change Log

   (Note to RFC editor - this section to be removed before publication
   as an RFC.)

   Changes from -14 to 15:

   o  title change to "Virtual Enterprise Traversal (VET) for MANETs".

   o  Address review comments

   Changes from -12 to 14:

   o  title change to "The MANET Virtual Ethernet Abstraction".

   o  Minor section rearrangement.

   o  Clartifications on portable and self-configured prefixes.

   o  Clarifications on DHCPv6 prefix delegation procedures.

   Changes from -11 to 12:

   o  title change to "MANET Autoconfiguration using Virtual Ethernet".

   o  DHCP prefix delegation for both IPv4 and IPv6 as primary address
      delegation mechanism.

   o  IPv6 SLAAC for address autoconfiguration on the VET interface.

   o  fixed editorials based on comments received.

   Changes from -10 to 11:

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   o  removed the transparent/opaque VET portal abstractions.

   o  removed routing header as an option for MANET exit router

   o  included IPv6 SLAAC as an endorsed address configuration mechanism
      for the VET interface.

   Changes from -08 to -09:

   o  Introduced the term "VET".

   o  Changed address delegation language to speak of "MNBR-aggregated"
      instead of global/local.

   o  Updated figures 1-3.

   o  Explained why a MANET interface is "neutral".

   o  Removed DHCPv4 "MLA Address option".  Now, MNBRs can only be
      DHCPv4 servers; not relays.

   Changes from -07 to -08:

   o  changed terms "unenhanced" and "enhanced" to "transparent" and

   o  revised MANET Router diagram.

   o  introduced RFC3753 terminology for Mobile Router; ingress/egress

   o  changed abbreviations to "MNR" and "MNBR".

   o  added text on ULAs and ULA-Cs to "Self-Generated Addresses".

   o  rearranged Section 3.1.

   o  various minor text cleanups

   Changes from -06 to -07:

   o  added MANET Router diagram.

   o  added new references

   o  various minor text cleanups

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   Changed from -05 to -06:

   o  Changed terms "raw" and "cooked" to "unenhanced" and "enhanced".

   o  minor changes to preserve generality

   Changed from -04 to -05:

   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 (editor)
   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


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


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Full Copyright Statement

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