Network Working Group                                    F. Templin, Ed.
Internet-Draft                                      Boeing Phantom Works
Intended status: Informational                          October 28, 2008
Expires: May 1, 2009


                   Virtual Enterprise Traversal (VET)
                   draft-templin-autoconf-dhcp-19.txt

Status of this Memo

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   This Internet-Draft will expire on May 1, 2009.

Abstract

   Enterprise networks connect routers over various link types, and may
   also connect to provider networks and/or the global Internet.
   Routers in enterprise networks must have a way to automatically
   provision IP addresses/prefixes and other information, and must also
   support post-autoconfiguration operations even for highly-dynamic
   networks.  This document specifies a Virtual Enterprise Traversal
   (VET) abstraction for autoconfiguration and operation of routers in
   enterprise networks.







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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Enterprise Characteristics . . . . . . . . . . . . . . . . . .  7
   4.  Autoconfiguration  . . . . . . . . . . . . . . . . . . . . . .  8
     4.1.  Enterprise Interior Router (EIR) Autoconfiguration . . . .  8
     4.2.  Enterprise Border Router (EBR) Autoconfiguration . . . . . 10
       4.2.1.  VET Interface Autoconfiguration  . . . . . . . . . . . 10
       4.2.2.  Enterprise Border Gateway Discovery and Enterprise
               Identification . . . . . . . . . . . . . . . . . . . . 11
       4.2.3.  Inner IP Address/Prefix Delegation and Maintenance . . 11
       4.2.4.  Portable Inner IP Addresses/Prefixes . . . . . . . . . 13
       4.2.5.  Enterprise-edge Interface Autoconfiguration  . . . . . 13
     4.3.  Enterprise Border Gateway (EBG) Autoconfiguration  . . . . 13
   5.  Post-Autoconfiguration Operation . . . . . . . . . . . . . . . 13
     5.1.  Forwarding Packets to Destinations Outside of the
           Enterprise . . . . . . . . . . . . . . . . . . . . . . . . 14
     5.2.  Enterprise-Local Communications  . . . . . . . . . . . . . 14
     5.3.  Multicast  . . . . . . . . . . . . . . . . . . . . . . . . 15
     5.4.  Service Discovery  . . . . . . . . . . . . . . . . . . . . 15
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 15
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 15
   8.  Related Work . . . . . . . . . . . . . . . . . . . . . . . . . 16
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16
   10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 16
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 17
     11.2. Informative References . . . . . . . . . . . . . . . . . . 17
   Appendix A.  Duplicate Address Detection (DAD) Considerations  . . 19
   Appendix B.  Change Log  . . . . . . . . . . . . . . . . . . . . . 20
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 23
   Intellectual Property and Copyright Statements . . . . . . . . . . 24


















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1.  Introduction

   Enterprise networks [RFC4852] connect routers over various link types
   (see: [RFC4861], Section 2.2).  Certain Mobile Ad-hoc Networks
   (MANETs) [RFC2501] can be considered as a challenging example of an
   enterprise network, in that their topologies may change dynamically
   over time and that they may employ little/no active management by a
   centralized network administrative authority.  These specialized
   characteristics for MANETs require careful consideration, but the
   same principles apply equally to other enterprise network scenarios.

   This document specifies a Virtual Enterprise Traversal (VET)
   abstraction for autoconfiguration and runtime operation of enterprise
   routers over various interface types, where addresses of different
   scopes may be assigned on various types of interfaces with diverse
   properties.  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.

                             Provider-edge Interfaces
                                  x   x        x
                                  |   |        |
             +--------------------+---+--------+----------+    E
             |                    |   |        |          |    n
             |    I               |   |  ....  |          |    t
             |    n           +---+---+--------+---+      |    e
             |    t           |   +--------+      /|      |    r
             |    e  I   x----+   |  Host  |   I /*+------+--< p  I
             |    r  n        |   |Function|   n|**|      |    r  n
             |    n  t        |   +--------+   t|**|      |    i  t
             |    a  e   x----+              V e|**+------+--< s  e
             |    l  r      . |              E r|**|  .   |    e  r
             |       f      . |              T f|**|  .   |       f
             |    V  a      . |   +--------+   a|**|  .   |    I  a
             |    i  c      . |   | Router |   c|**|  .   |    n  c
             |    r  e   x----+   |Function|   e \*+------+--< t  e
             |    t  s        |   +--------+      \|      |    e  s
             |    u           +---+---+--------+---+      |    r
             |    a               |   |  ....  |          |    i
             |    l               |   |        |          |    o
             +--------------------+---+--------+----------+    r
                                  |   |        |
                                  x   x        x
                           Enterprise-edge Interfaces

                 Figure 1: Enterprise Router Architecture




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   Figure 1 above depicts the architectural model for an enterprise
   router.  As shown in the figure, an enterprise router may have a
   variety of interface types including enterprise-edge, enterprise-
   interior, provider-edge, internal-virtual, as well as VET interfaces
   used for encapsulation of inner IP packets within outer IP headers.
   The different types of interfaces are defined, and the
   autoconfiguration mechanisms used for each type are specified.  This
   architecture applies equally for MANET routers, in which enterprise-
   interior interfaces correspond to the wireless multihop radio
   interfaces typically associated with MANETs.  Out of scope for this
   document is the autoconfiguration of provider interfaces, which must
   be coordinated in a manner specific to the service provider's
   network.

   The VET specification represents a functional superset of 6over4
   [RFC2529] and ISATAP [RFC5214], and further supports additional
   encapsulations such as IPsec [RFC4301], SEAL [I-D.templin-seal], etc.

   The VET principles can be either directly or indirectly traced to the
   deliberations of the ROAD group in January 1992, and likely also to
   still earlier works.  [RFC1955] captures the high-level architectural
   aspects of the ROAD group deliberations in a "New Scheme for Internet
   Routing and Addressing [ENCAPS] for IPNG".

   VET is related to the present-day activites of the IETF autoconf,
   dhc, ipv6, manet and v6ops working groups.


2.  Terminology

   The mechanisms within this document build upon the fundamental
   principles of IP-within-IP encapsulation.  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.  VET also supports the inclusion
   of "mid-layer" encapsulations between the inner and outer layers,
   including IPSec [RFC4301], the Subnetwork Encapsulation and
   Adaptation Layer (SEAL) [I-D.templin-seal], etc.

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

   subnetwork
      the same as defined in [RFC3819].






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   enterprise
      the same as defined in [RFC4852].

   site
      a logical and/or physical grouping of interfaces that connect a
      topological area less than or equal to the enterprise in scope.  A
      site within an enterprise can be considered as an enterprise unto
      itself.

   Mobile Ad-hoc Network (MANET)
      a connected topology of mobile or fixed routers that maintain a
      routing structure among themselves over asymmetric reachability
      links (see: [RFC4861], Section 2.2), where a wide variety of
      MANETs share common properties with enterprise networks.  Further
      information on MANETs can be found in [RFC2501].

   enterprise/site/MANET
      throughout the remainder of this document, the term "enterprise"
      is used to collectively refer to any of enterprise/site/MANET,
      i.e., the VET mechanisms and operational principles apply equally
      to enterprises, sites and MANETs.

   enterprise router
      an Enterprise Interior Router, Enterprise Border Router, or
      Enterprise Border Gateway.  For the purose of this specification,
      an enterprise router comprises a router function, a host function,
      one or more enterprise-interior interfaces and zero or more
      internal virtual, enterprise-edge, provider-edge and VET
      interfaces.

   Enterprise Interior Router (EIR)
      a fixed or mobile enterprise router that forwards packets over a
      set of enterprise-interior interfaces connected to the same
      enterprise.

   Enterprise Border Router (EBR)
      an EIR that connects edge networks to the enterprise, and/or
      connects multiple enterprises together.  An EBR configures a
      seperate VET interface over each set of enterprise-interior
      interfaces that connect the EBR to each distinct enterprise, i.e.,
      an EBR may configure mulitple VET interfaces - one for each
      distinct enterprise.  All EBRs are also EIRs.

   Enterprise Border Gateway (EBG)
      an EBR that either directly or indirectly connects the enterprise
      to provider networks and can delegate addresses/prefixes to other
      EBRs within the enterprise.  All EBGs are also EBRs.




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   internal-virtual interface
      a virtual interface that is a special case of either an
      enterprise-edge or an enterprise-interior interface.  Internal-
      virtual interfaces that are also enterprise-edge interfaces are
      often loopback interfaces of some form.  Internal-virtual
      interfaces that are also enterprise-interior interfaces are often
      tunnel interfaces of some form configured over another enterprise-
      interior interface.

   enterprise-edge interface
      an EBR's attachment to a link (e.g., an ethernet, a wireless
      personal area network, etc.) on an arbitrarily-complex edge
      network that the EBR connects to an enterprise and/or to provider
      networks.

   provider-edge interface
      an EBR's attachment to the Internet, or to a provider network
      outside of the enterprise via which the Internet can be reached.

   enterprise-interior Interface
      a EIR's attachment to a link within an enterprise.  An enterprise-
      interior interface is "neutral" in its orientation, i.e., it is
      inherently neither an enterprise-edge nor provider-edge interface.
      In particular, a packet may need to be forwarded over several
      enterprise-interior interfaces before it is forwarded via either
      an enterprise-edge or provider-edge interface.

   Enterprise Local Address (ELA)
      an enterprise-scoped IP address (e.g., an IPv6 Unique Local
      Address [RFC4193], an IPv4 privacy address [RFC1918], etc.) that
      is assigned to an enterprise-interior interface and unique within
      the enterprise.  ELAs are used as identifiers for operating the
      routing protocol and/or locators for packet forwarding within the
      scope of the enterprise; ELAs 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 enterprise in a single (inner) IP hop.

   VET interface
      an EBR's Non-Broadcast, Multiple Access interface used for Virtual
      Enterprise Traversal.  The EBR configures a VET interface over a
      set of underlying enterprise-interior interface(s) belonging to
      the same enterprise.  When there are multiple distinct enterprises
      (each with their own distinct set of enterprise-interior
      interfaces), the EBR configures a separate VET interface over each
      set of enterprise-interior interfaces, i.e., the EBR configures



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      multiple VET interfaces.

      The VET interface encapsulates each inner IP packet in any mid-
      layer headers plus an outer IP header then forwards it on an
      underlying enterprise-interior interface such that the TTL/Hop
      Limit in the inner header is not decremented as the packet
      traverses the enterprise.  The VET interface presents an automatic
      tunneling abstraction that represents the enterprise as a single
      IP hop.

   The following additional acronyms are used throughout the document:

   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.  Enterprise Characteristics

   Enterprises consist of links that are connected by enterprise routers
   as depicted in Figure 1.  All enterprise routers are also Enterprise
   Interior Routers (EIRs) that typically participate in a routing
   protocol over enterprise-interior interfaces to discover routes that
   may include multiple Layer-2 or Layer-3 forwarding hops.  Enterprise
   Border Routers (EBRs) are EIRs that connect edge networks and/or join
   multiple enterprises together, while Enterprise Border Gateways
   (EBGs) are EBRs that either directly or indirectly connect
   enterprises to provider networks.  An enterprise may be as simple as
   a small collection of enterprise routers (and their attached edge
   networks); an enterprise may also contain other enterprises/sites
   and/or be a subnetwork of a larger enterprise.  An enterprise may
   further encompass a set of branch offices connected to a home office
   over one or several service providers, e.g., through Virtual Private
   Network (VPN) tunnels.

   Enterprises 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 enterprise 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 enterprise without IP
   layer encapsulation.



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   Enterprises 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
   enterprise 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
   enterprise in a single (inner) IP hop in order to avoid the multilink
   subnet issues that arise when enterprise-interior interfaces are used
   directly by applications.

   Conceptually, an enterprise router (i.e, an EIR/EBR/EBG) embodies
   both a host function and router function.  The host function supports
   global-scoped communications over any of the enterprise router's non-
   enterprise-interior interfaces according to the weak end system model
   [RFC1122] and also supports enterprise-local-scoped communications
   over its enterprise-interior interfaces.  The router function
   connects the enterprise router's attached edge networks to the
   enterprise and/or connects the enterprise to other networks including
   the Internet (see: Figure 1).

   In addition to other interface types, EBRs configure VET interfaces
   that view all other EBRs in an enterprise as single-hop neighbors,
   where the enterprise can also appear as a single IP hop within
   another enterprise.  EBRs configure a separate VET interface for each
   distinct enterprise to which they connect, and discover a list of
   EBRs for each VET interface that can be used for forwarding packets
   to off-enterprise destinations.  The following sections present the
   Virtual Enterprise Traversal approach.


4.  Autoconfiguration

   EIRs configure enterprise-interior interfaces.  An EBR is an EIR that
   also configures enterprise-edge and VET interfaces.  An EBG is an EBR
   that also either directly or indirectly connects the enterprise to a
   provider network.  EIRs, EBRs and EBGs configure themselves for
   operation according to the following subsections:

4.1.  Enterprise Interior Router (EIR) Autoconfiguration

   EIRs configure enterprise-interior interfaces and engage in routing
   protocols over those interfaces.

   When an EIR joins an enterprise, it first configures a unique IPv6
   link-local address on each enterprise-interior interface that
   requires an IPv6 link-local capability and an IPv4 link-local address



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

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

   Self-generation of ELAs for IPv6 can be from a large IPv6 local-use
   address range, e.g., IPv6 Unique Local Addresses [RFC4193].  Self-
   generation of ELAs for IPv4 can be from a large IPv4 private address
   range, e.g., [I-D.fuller-240space].  When self-generation is used
   alone, the EIR must continuously monitor the ELAs 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").

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




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4.2.  Enterprise Border Router (EBR) Autoconfiguration

   EBRs are EIRs that configure enterprise-edge interfaces, and also
   configure a VET interface over a set of underlying enterprise-
   interior interfaces belonging to the same enterprise.  Note that an
   EBR may connect to multiple distinct enterprises, in which case it
   would configure multiple VET interfaces over multiple distinct sets
   of enterprise-interior interfaces.  EBRs perform the following
   autoconfiguration operations:

4.2.1.  VET Interface Autoconfiguration

   EBRs configure a VET interface over a set of underlying enterprise-
   interior interfaces belonging to the same enterprise, where the VET
   interface presents a virtual view of all EBRs in the enterprise 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
   enterprise-interior interface.  Further encapsulation details are
   specified in Section 5.

   When IPv6 and IPv4 are used as the inner/outer protocols
   (respectively), the EBR 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 link-local address embeds an IPv4 ELA assigned to an
   underlying enterprise-interior interface, and need not be checked for
   uniqueness since the IPv4 ELA 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 EBR configures a VET interface, it can communicate with
   other EBRs as single-hop neighbors.  It can also confirm reachability
   of other EBRs through Neighbor Discovery (ND) and/or DHCP exchanges
   over the VET interface, or through other means such as information
   conveyed in the routing protocol.

   The EBR must be able to detect and recover from the loss of VET
   interface neighbors due to e.g., enterprise network 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,
   etc. can be used according to the particular deployment scenario.





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4.2.2.  Enterprise Border Gateway Discovery and Enterprise
        Identification

   After the EBR configures its VET interfaces, it next discovers a list
   of EBGs for each distinct enterprise 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
   EBR can discover the list of EBGs by resolving an identifying name
   for the enterprise using an Enterprsie-local name resolution service
   (e.g., using LLMNR [RFC4759] over the VET interface).  In the absence
   of other identifying names, the EBR can resolve either the hostname
   "6over4" or the FQDN "6over4.example.com" (i.e., if an enterprise-
   specific suffix "example.com" is known) for multicast-capable
   enterprises.  For non-multicast enterprises, the EBR can instead
   resolve the hostname "isatap" or the FQDN "isatap.example.com".

   Identifying names along with addresses of EBGs and/or the prefixes
   they aggregate serve as an identifier for the enterprise.

4.2.3.  Inner IP Address/Prefix Delegation and Maintenance

   EBRs acquire inner IP protocol addresses and/or prefix delegations
   through autoconfiguration exchanges via EBGs over VET interfaces, as
   discussed in the following sections:

4.2.3.1.  IPv4 Addresses/Prefix Delegation

   When IPv4 is used as the inner IP protocol, the EBR coordinates with
   EBGs to acquire IPv4 prefixes for sub-delegation and/or assignment on
   its enterprise-edge interfaces.  This coordination can be through
   explicit management, or through an unspecified automated prefix
   delegation exchange.  The EBR can also obtain /32 prefixes the same
   as for any IPv4 prefix.

4.2.3.2.  IPv6 Addresses/Prefix Delegation

   When IPv6 is used as the inner protocol, the EBR sends unicast IPv6
   Router Solicitation (RS) messages to an EBG over a VET interface to
   receive Router Advertisements (RAs) with Prefix Information Options
   (PIOs) and/or with the M/O flags set to signify whether DHCPv6
   autoconfiguration is available; the EBR may also perform RS/RA
   exchanges with multiple EBGs.  When the EBR 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



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   addresses are autoconfigured and assigned as ISATAP addresses the
   same as specified in [RFC5214].)

   When the EBR receives an RA with the M/O flags set to 1, the EBG that
   sent the RA also hosts a DHCPv6 relay/server.  If the RA also
   contains PIOs with the 'L' bit set to 0, the EBR can use them as
   hints of prefixes the server is willing to delegate (see:
   Section 4.3).  Whether or not such hints are available, the EBR
   (acting as a requesting router) can use DHCPv6 prefix delegation
   [RFC3633] over the VET interface to obtain IPv6 prefixes from the
   server (acting as a delegating router).  The EBR can then use the
   delegated prefixes for sub-delegation and/or assignment on its
   enterprise-edge interfaces.

   The EBR 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 EBR's host function forwards a
   Solicit message with an IA_PD option to a DHCPv6 relay associated
   with its router function, i.e., the EBR acts as both client and
   relay.  The relay then forwards the message over the VET interface to
   the server via the EBG.  The forwarded Solicit message will elicit a
   Reply from the server containing IPv6 prefix delegations.

   The EBR 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 EBR if it was able
   to perform the delegation.  The EBR can use mechanisms such as CGAs
   [RFC3972], IPv6 privacy address [RFC4941], etc. to self-generate
   addresses in conjunction with prefix delegation.

4.2.3.3.  Prefix and Route Maintenance

   When DHCP prefix delegation is used, the DHCP server ensures that the
   delegations are unique and that the EBG's router function will
   forward IP packets over the VET interface to the EBR to which the
   prefix was delegated.  The prefix delegation remains active as long
   as the EBR 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 EBR and
   DHCP server is disrupted for a period of time (e.g., due to an
   enterprise network partition) before being reestablished (e.g., due
   to an enterprise network merge).  EBRs can also sub-delegate inner IP
   prefixes to requesting routers on networks connected on their
   enterprise-edge interfaces as well as to EBRs in other enterprises.

   Since the DHCP client and relay are co-resident on the same EBR, no
   special coordination is necessary for the EBG to maintain routing



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   information.  The EBG simply retains forwarding information base
   entries that identify the EBR as the next-hop toward the prefix over
   the VET interface, and issues ordinary redirects over the VET
   interface when necessary .

4.2.4.  Portable Inner IP Addresses/Prefixes

   Independent of any inner IP addresses/prefix delegations (see:
   Section 4.2.3), an EBR can also use portable IP addresses/prefixes
   (e.g., taken from a home network) and/or self-configured IP
   addresses/prefixes (e.g., IPv6 Unique Local Addresses (ULAs)
   [RFC4193][I-D.ietf-ipv6-ula-central]).  The EBR can continue to use
   these addresses/prefixes as it travels between visited enterprise
   networks as long as it coordinates in some fashion with a mapping
   agent, prefix aggregation authority, etc.  EBRs can also sub-delegate
   portable (and other self-configured) prefixes to requesting routers
   on networks connected on their enterprise-edge interfaces as well as
   to EBRs in other enterprises.

4.2.5.  Enterprise-edge Interface Autoconfiguration

   After the EBR receives inner IP address/prefix delegations (see:
   Section 4.2.3), it can assign them on enterprise-edge interfaces
   only; it does not assign them on provider-edge, VET, or enterprise-
   interior interfaces (see: [RFC3633], Section 12.1).  Similarly, the
   EBR can assign portable and/or self-configured addresses/prefixes
   (see: Section 4.2.4) on enterprise-edge interfaces.

4.3.  Enterprise Border Gateway (EBG) Autoconfiguration

   EBGs are EBRs that connect an enterprise to a service provider either
   directly via provider-edge interfaces or indirectly via another
   enterprise.  EBGs configure provider-edge interfaces in a manner that
   is specific to its provider connections.

   For IPv6, EBGs send RAs over VET interfaces on enterprises for which
   they are gateways with the M/O flags set to indicate whether they
   configure a DHCP relay/server.  EBGs can also include PIOs with the
   'L' bit set to '0' and with a prefix such as 2001:DB8::/48 as a hint
   of an aggregated prefix from which it is willing to delegate longer
   prefixes.


5.  Post-Autoconfiguration Operation

   After an EIR has been autoconfigured, it participates in any routing
   protocols over enterprise-interior interfaces and forwards outer IP
   packets within the enterprise as for any ordinary router.



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   EBRs can additionally engage in any inner IP routing protocols over
   enterprise-edge, provider-edge and VET interfaces interfaces, and can
   use those interfaces for forwarding inner IP packets to off-
   enterprise destinations.  Note that these inner IP routing protocols
   are separate and distinct from any enterprise-interior routing
   protocols.

   The following sections discuss post-autoconfiguration operations:

5.1.  Forwarding Packets to Destinations Outside of the Enterprise

   EBRs consult the inner IP forwarding table to determine the next hop
   address (e.g., the VET interface address of another EBR) for
   forwarding packets to destinations outside of the enterprise.  When
   there is no forwarding information available, the EBR can discover
   the next-hop through FQDN or reverse lookup using the same name
   resolution services as for EBG discovery (see: Section 4.2.2).

   For forwarding to next-hop addresses over VET interfaces that use
   IPv6-in-IPv4 encapsulation, EBRs 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
   method.

   EBRs 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 EBR.  After default
   and/or more-specific routes are discovered, the EBR can forward IP
   packets via a specific EBR as the next-hop router on the VET
   interface.  When multiple default routers are available, the EBR can
   use default router preferences, routing protocol information, traffic
   engineering configurations, etc. to select the best exit router.

   Note that the EBR only accepts PIOs, M/O flag settings and default
   router preferences in RAs that are received from EBGs (i.e., it does
   not accept them from ordinary EBRs).

5.2.  Enterprise-Local Communications

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



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5.3.  Multicast

   In multicast-capable deployments, EIRs provide an enterprise-wide
   multicasting service such as Simplified Multicast Forwarding (SMF)
   [I-D.ietf-manet-smf] over their enterprise-interior interfaces such
   that outer IP multicast messages of site- or greater scope will be
   propagated across the enterprise.  For such deployments, EBRs 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.

   EBRs 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
   method.

   For multicast-capable enterprises, 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 enterprise-wide
   flooding.  Therefore, EBRs should use unicast ND services over the
   VET interface instead of multicast whenever possible.

5.4.  Service Discovery

   EIRs can peform enterprise-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
   enterprise-interior interface.  More scalable and efficient service
   discovery mechanisms are for further study.


6.  IANA Considerations

   A Site-Local Scope IPv4 multicast group (TBD) for DHCPv4 server
   discovery is requested.  The allocation should be taken from the
   239.255.000.000-239.255.255.255 Site-Local Scope range in the IANA
   'multicast-addresses' registry.


7.  Security Considerations

   Security considerations for MANETs are found in [RFC2501].



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   Security considerations with tunneling that apply also to VET are
   found in [RFC2529][RFC5214].


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.
   As for this document, these architectural principles also follow from
   earlier works articulated by the ROAD group deliberations of 1992.

   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.

   [I-D.ietf-v6ops-tunnel-security-concerns] discusses security concerns
   regarding tunneling mechanisms that may subvert security through
   Network Address Translator (NAT) traversal.

   An automated IPv4 prefix delegation mechanism is proposed in
   [I-D.ietf-dhc-subnet-alloc].


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, 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

   The following individuals have contributed to this document:

   Eric Fleischman (eric.fleischman@boeing.com)
   Thomas Henderson (thomas.r.henderson@boeing.com)
   Steven Russert (steven.w.russert@boeing.com)
   Seung Yi (seung.yi@boeing.com)

   Ian Chakeres (ian.chakeres@gmail.com) contributed to earlier versions
   of the document.




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11.  References

11.1.  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.

   [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

   [I-D.cheshire-dnsext-multicastdns]
              Cheshire, S. and M. Krochmal, "Multicast DNS",
              draft-cheshire-dnsext-multicastdns-07 (work in progress),
              September 2008.

   [I-D.fuller-240space]



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

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

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

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

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

   [I-D.ietf-v6ops-tunnel-security-concerns]
              Hoagland, J., Krishnan, S., and D. Thaler, "Security
              Concerns With IP Tunneling",
              draft-ietf-v6ops-tunnel-security-concerns-01 (work in
              progress), October 2008.

   [I-D.templin-seal]
              Templin, F., "The Subnetwork Encapsulation and Adaptation
              Layer (SEAL)", draft-templin-seal-23 (work in progress),
              August 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.

   [RFC1955]  Hinden, R., "New Scheme for Internet Routing and
              Addressing (ENCAPS) for IPNG", RFC 1955, June 1996.

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



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   [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.,
              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 ELA assigned on an enterprise-interior interface (such as
   specified in [RFC4862]) would require either flooding the entire



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   enterprise or somehow discovering a link in the enterprise 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 an enterprise-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 ELAs on enterprise-interior interfaces and employ a
   passive in-service DAD (e.g., one that monitors routing protocol
   messages for duplicate assignments).

   Pseudo-random IPv6 ELAs can be generated with mechanisms such as
   CGAs, IPv6 privacy addresses, etc. with very small probability of
   collision.  Pseudo-random IPv4 ELAs 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 EBG-
   aggregated addresses/prefixes, while statistical properties for
   pseudo-random address self-generation can assure uniqueness for the
   ELAs assigned on an EIR's enterprise-interior interfaces.  Still, an
   ELA delegation authority should be used when available, while a
   passive in-service DAD mechanism should be used to detect ELA
   duplications when there is no ELA delegation authority.


Appendix B.  Change Log

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

   Changes from -17 to 18:

   o  adjusted section headings to group autoconf operations under EIR/
      EBR/EBG.

   o  clarified M/O bits

   o  clarified EBG roles

   Changes from -15 to 17:

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

   o  changed document focus from MANET-centric to the much-broader
      Enterprise-centric, where "Enterprise" is understood to also cover
      a wide range of MANET types.

   Changes from -14 to 15:



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   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:

   o  removed the transparent/opaque VET portal abstractions.

   o  removed routing header as an option for MANET exit router
      selection.

   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.



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   Changes from -07 to -08:

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

   o  revised MANET Router diagram.

   o  introduced RFC3753 terminology for Mobile Router; ingress/egress
      interface.

   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

   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




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   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
      considerations.

   o  various editorial changes


Author's Address

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

   Email: fltemplin@acm.org

















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Full Copyright Statement

   Copyright (C) The IETF Trust (2008).

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   contained in BCP 78, and except as set forth therein, the authors
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