Network Working Group                                    F. Templin, Ed.
Internet-Draft                            Boeing Research and Technology
Intended status: Informational                         February 17, 2009
Expires: August 21, 2009

                   Virtual Enterprise Traversal (VET)

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   Enterprise networks connect routers over various link types, and may
   also connect to provider networks and/or the global Internet.

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   Enterprise network nodes require a means to automatically provision
   IP addresses/prefixes and support internetworking operation in a wide
   variety of use cases including SOHO networks, Mobile Ad-hoc Networks
   (MANETs), multi-organizational corporate networks and the interdomain
   core of the global Internet itself.  This document specifies a
   Virtual Enterprise Traversal (VET) abstraction for autoconfiguration
   and operation of nodes in enterprise networks.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  6
   3.  Enterprise Characteristics . . . . . . . . . . . . . . . . . . 10
   4.  Autoconfiguration  . . . . . . . . . . . . . . . . . . . . . . 11
     4.1.  Enterprise Router (ER) Autoconfiguration . . . . . . . . . 11
     4.2.  Enterprise Border Router (EBR) Autoconfiguration . . . . . 13
       4.2.1.  VET Interface Autoconfiguration  . . . . . . . . . . . 13
       4.2.2.  Provider-Aggregated (PA) Prefix Autoconfiguration  . . 14
       4.2.3.  Provider-Independent (PI) Prefix Autoconfiguration . . 15
     4.3.  Enterprise Border Gateway (EBG) Autoconfiguration  . . . . 15
     4.4.  VET Host Autoconfiguration . . . . . . . . . . . . . . . . 16
   5.  Internetworking Operation  . . . . . . . . . . . . . . . . . . 16
     5.1.  Routing Protocol Participation . . . . . . . . . . . . . . 16
     5.2.  IPv6 Router Discovery and Prefix Registration  . . . . . . 16
       5.2.1.  IPv6 Default Router Discovery  . . . . . . . . . . . . 17
       5.2.2.  IPv6 PA Prefix Registration  . . . . . . . . . . . . . 17
       5.2.3.  IPv6 PI Prefix Registration  . . . . . . . . . . . . . 18
       5.2.4.  IPv6 Next-Hop EBR Discovery  . . . . . . . . . . . . . 19
     5.3.  IPv4 Router Discovery and Prefix Registration  . . . . . . 21
     5.4.  Forwarding Packets . . . . . . . . . . . . . . . . . . . . 22
     5.5.  SEAL Encapsulation . . . . . . . . . . . . . . . . . . . . 22
     5.6.  Generating Errors  . . . . . . . . . . . . . . . . . . . . 23
     5.7.  Processing Errors  . . . . . . . . . . . . . . . . . . . . 23
     5.8.  Mobility and Multihoming Considerations  . . . . . . . . . 24
     5.9.  Enterprise-Local Communications  . . . . . . . . . . . . . 25
     5.10. Multicast  . . . . . . . . . . . . . . . . . . . . . . . . 25
     5.11. Service Discovery  . . . . . . . . . . . . . . . . . . . . 26
     5.12. Enterprise Partitioning  . . . . . . . . . . . . . . . . . 27
     5.13. EBG Prefix State Recovery  . . . . . . . . . . . . . . . . 27
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 27
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 28
   8.  Related Work . . . . . . . . . . . . . . . . . . . . . . . . . 28
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 29
   10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 29
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 29
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 29
     11.2. Informative References . . . . . . . . . . . . . . . . . . 31
   Appendix A.  Duplicate Address Detection (DAD) Considerations  . . 33
   Appendix B.  Change Log  . . . . . . . . . . . . . . . . . . . . . 34
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 38

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1.  Introduction

   Enterprise networks [RFC4852] connect routers over various link types
   (see: [RFC4861], Section 2.2).  The term "enterprise network" in this
   context extends to a wide variety of use cases and deployment
   scenarios.  For example, an "enterprise" can be as small as a SOHO
   network, as complex as a multi-organizational corporation, or as
   large as the global Internet itself.  Certain Mobile Ad-hoc Networks
   (MANETs) [RFC2501] can also 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

   This document specifies a Virtual Enterprise Traversal (VET)
   abstraction for autoconfiguration and internetworking operation,
   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][RFC1256][RFC4861] mechanisms is assumed unless otherwise

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                             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 (ER) Architecture

   Figure 1 above depicts the architectural model for an Enterprise
   Router (ER).  As shown in the figure, an ER 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.

   Enterprise networks must have a means for supporting both Provider-
   Independent (PI) and Provider-Aggregated (PA) IP prefixes for global-
   scope communications.  This is especially true for enterprise
   scenarios that involve mobility and multihoming.  Also in scope are
   ingress filtering for multi-homed sites, adaptation based on
   authenticated ICMP feedback from on-path routers, effective tunnel
   path MTU mitigations and routing scaling suppression as required in

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   many enterprise network scenarios.  Recognizing that one size does
   not fit all, the VET specification provides adaptable mechanisms that
   address these issues and more in a wide variety of enterprise network
   use cases.

   VET 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.  As a result, VET
   provides a map-and-encaps architecture using IP-in-IP tunneling based
   on both IP routing and mapping service resolution (defined herein).

   The VET principles can be either directly or indirectly traced to the
   deliberations of the ROAD group in January 1992, and also to still
   earlier works including NIMROD [RFC1753], the Catenet model for
   internetworking [CATENET][IEN48][RFC2775], etc.  [RFC1955] captures
   the high-level architectural aspects of the ROAD group deliberations
   in a "New Scheme for Internet Routing and Addressing [ENCAPS] for

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

2.  Terminology

   The mechanisms within this document build upon the fundamental
   principles of IP-within-IP encapsulation.  The terms "inner" and
   "outer" are used 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 allows for 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:

      the same as defined in [RFC3819].

      the same as defined in [RFC4852].  An enterprise is also
      understood to refer to a cooperative networked collective with a
      commonality of business, social, political, etc. interests.
      Minimally, the only commonality of interest in some enterprise
      network scenarios may be the cooperative provisioning of

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      connectivity itself.

      a logical and/or physical grouping of interfaces that connect a
      topological area less than or equal to an enterprise in scope.  A
      site within an enterprise can in some sense 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 dynamic links, where a
      wide variety of MANETs share common properties with enterprise
      networks.  Characteristics of MANETs are defined in [RFC2501],
      Section 3.

      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 can be applied
      to enterprises, sites and MANETs of any size or shape.

   Enterprise Router (ER)
      As depicted in Figure 1, an Enterprise Router (ER) is a fixed or
      mobile router that 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.  At a minimum, an ER forwards packets over one or more
      sets of enterprise-interior interfaces, where each set connects to
      a distinct enterprise.

   Enterprise Border Router (EBR)
      an ER 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.  In
      particular, an EBR may configure mulitple VET interfaces - one for
      each distinct enterprise.  All EBRs are also ERs.

   Enterprise Border Gateway (EBG)
      an EBR that connects VET interfaces configured over child
      enterprises to a provider network - either directly via a
      provider-edge interface, or indirectly via another VET interface
      configured over a parent enterprise.  EBRs may act as EBGs on some
      VET interfaces and as ordinary EBRs on other VET interfaces.  All
      EBGs are also EBRs.

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   enterprise-interior interface
      a ER's attachment to a link within an enterprise.  Packets sent
      over enterprise-interior interfaces may be forwarded over multiple
      additional enterprise-interior interfaces within the enterprise
      before they are forwarded via an enterprise-edge interface,
      provider-edge interface or a VET interface configured over a
      different enterprise.

   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

   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.

   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 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 used as the *outer* IP
      addresses during encapsulation, and can also be used as addresses
      for enterprise-internal communications that do not require

   Provider-Independent (PI) prefix
      an IPv6 or IPv4 prefix (e.g., 2001:DB8::/48, 192.0.2/24, etc.)
      that is routable within a limited scope and may also appear in a
      global mapping table.  PI prefixes that can appear in a global
      mapping table are typically delegated to an EBR by a registry, but
      are not aggregated by a provider network.  Local-use IPv6 and IPv4
      prefixes (e.g., FD00::/8, 192.168/16, etc.) are another example of
      a PI prefix, but these typically do not appear in a global mapping

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   Provider Aggregated (PA) prefix
      an IPv6 or IPv4 prefix that is either derived from a PI prefix or
      delegated directly to a provider network by a registry.

   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 (NBMA) 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 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 therefore presents an
      automatic tunneling abstraction that represents the enterprise as
      a single IP hop.

   VET host
      any node (host or router) that configures a VET interface for host
      operation only.  Note that a single node may configure some of its
      VET interfaces as host interfaces and others as router interfaces.

   VET node
      any node that configures and uses a VET interface.

   The following additional acronyms are used throughout the document:

   CGA - Cryptographically Generated Address
   DHCP[v4,v6] - the Dynamic Host Configuration Protocol
   FIB - Forwarding Information Base
   ISATAP - Intra-Site Automatic Tunnel Addressing Protocol
   NBMA - Non-Broadcast, Multiple Access
   ND - Neighbor Discovery
   PA - Provider Aggregated
   PI - Provider Independent
   PIO - Prefix Information Option
   PRL - Potential Router List
   PRLNAME - Identifying name for the PRL (default is "isatap")
   RIO - Route Information Option

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   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
   (ERs) as depicted in Figure 1.  ERs 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 ERs that connect edge networks
   to the enterprise and/or join multiple enterprises together.
   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 ERs and their
   attached edge networks; an enterprise may also contain other
   enterprises and/or be a subnetwork of a larger enterprise.  An
   enterprise may further encompass a set of branch offices and/or
   nomadic hosts connected to a home office over one or several service
   providers, e.g., through Virtual Private Network (VPN) tunnels.

   Enterprises that comprise link types with sufficiently similar
   properties (e.g., Layer-2 (L2) address formats, maximum transmission
   units (MTUs), etc.) can configure a sub-IP layer routing service 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.

   Enterprises that comprise link types with diverse properties and/or
   configure multiple IP subnets must also provide a routing service
   that operates as an IP layer mechanism.  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 ER embodies both a host function and router
   function.  The host function supports global-scoped communications
   over any of the ER'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 engages in the enterprise-interior routing
   protocol, connects any of the ER's edge networks to the enterprise
   and may also connect the enterprise to provider networks (see:

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   Figure 1).

   In addition to other interface types, VET nodes configure VET
   interfaces that view all other VET nodes in an enterprise as single-
   hop neighbors attached to an imaginary Non-Broadcast, Multiple Access
   (NBMA) link, where the enterprise can also appear as a single IP hop
   within another enterprise.  VET nodes configure a separate VET
   interface for each distinct enterprise to which they connect, and
   discover other EBRs on each VET interface that can be used for
   forwarding packets to off-enterprise destinations.

   For each distinct enterprise, an enterprise trust basis must be
   established and consistently applied.  For example, in enterprises in
   which EBRs establish symmetric security associations, mechanisms such
   as IPsec [RFC4301] can be used to assure authentication and
   confidentiality.  In other enterprise network scenarios, asymmetric
   securing mechanisms such as SEcure Neighbor Discovery (SEND)
   [RFC3971] may be necessary to authenticate exchanges based on trust

   Finally, in enterprises with a centralized management structure
   (e.g., a corporate campus network), the enterprise name service and a
   synchronized set of EBGs can provide infrastructure support for
   virtual enterprise traversal.  In that case, the EBGs can provide a
   "default mapper" [I-D.jen-apt] service used for short term packet
   forwarding until EBR neighbor relationships can be established.  In
   enterprises with a distributed management structure (e.g., a large
   MANET), peer-to-peer coordination between the EBRs themselves may be
   required.  Recognizing that various use cases will entail a continuum
   between a fully-distributed and fully-centralized approach, the
   following sections present the mechanisms of Virtual Enterprise
   Traversal as they apply to a wide variety of scenarios.

4.  Autoconfiguration

   ERs, EBRs, EBGs, and VET hosts configure themselves for operation as
   specified in the following subsections:

4.1.  Enterprise Router (ER) Autoconfiguration

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

   When an ER 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
   on each enterprise-interior interface that requires an IPv4 link-

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   local capability.  IPv6 link-local address generation mechanisms that
   provide sufficient uniqueness include Cryptographically Generated
   Addresses (CGAs) [RFC3972], IPv6 Privacy Addresses [RFC4941],
   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 ER 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 ER 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.  In some enterprise use cases (e.g., highly dynamic
   MANETs), assignment of ELAs as singleton addresses (i.e., as /32s for
   IPv4 and /128s for IPv6) may be necessary to avoid multilink subnet

   ERs that configure ELAs using DHCP may require relay support from
   other ERs within the enterprise; the ER can alternatively configure
   both a DHCP client and relay that are connected, e.g., via a pair of
   back-to-back connected ethernet interfaces, a tun/tap interface, a
   loopback interface, inter-process communication, etc.  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 'All_DHCPv4_Servers'
   (see: Section 6).  DHCPv4 servers that delegate ELAs join the
   'All_DHCPv4_Servers' 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., [RFC1918]).  When self-generation is used alone, the ER
   must continuously monitor the ELAs for uniqueness, e.g., by
   monitoring the routing protocol, but care must be taken in the
   interaction of this monitoring with existing mechanisms.

   A combined approach using both DHCP and self-generation is also
   possible in which the ER first self-generates a temporary ELA used
   only for the purpose of procuring an actual ELA taken from a disjoint
   addressing range.  The ER then assigns the temporary ELA to an
   enterprise-interior interface, engages in the routing protocol and
   performs a DHCP client/relay exchange using the temporary ELA as the
   address of the relay.  When the DHCP server delegates an actual ELA,
   the ER abandons the temporary ELA, assigns the actual ELA to the
   enterprise-interior interface and re-engages in the routing protocol.

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4.2.  Enterprise Border Router (EBR) Autoconfiguration

   EBRs are ERs that configure VET interfaces over distinct sets of
   underlying enterprise-interior interfaces; an EBR can connect to
   multiple enterprises, in which case it would configure multiple VET
   interfaces.  EBRs perform the following autoconfiguration operations:

4.2.1.  VET Interface Autoconfiguration

   VET interface autoconfiguration entails: 1) interface initialization,
   2) EBG discovery and enterprise identification, and 3) IPv6 stateless
   address autoconfiguration.  These functions are specified in the
   following sections:  Interface Initialization

   EBRs configure a VET interface over a set of underlying enterprise-
   interior interfaces belonging to the same enterprise, where the VET
   interface presents a Non-Broadcast, Multiple Access (NBMA)
   abstraction in which all EBRs in the enterprise appear as single hop
   neighbors through the use of IP-in-IP encapsulation.

   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 checked (see:
   Section 4.1).  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 VET nodes as single-hop neighbors from the viewpoint of the
   inner IP protocol.  Enterprise Border Gateway Discovery

   The EBR next discovers a list of EBGs for each of its VET interfaces.
   The list can be discovered through information conveyed in the
   routing protocol and/or through the Potential Router List (PRL)
   discovery mechanisms outlined in ([RFC5214], Section 8.3.2).  In
   multicast-capable enterprises, EBRs can also listen for
   advertisements on the 'rasadv' [RASADV] IPv4 multicast group address.

   In particular, whether or not routing information is available the
   EBR can discover the list of EBGs by resolving an identifying name

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   for the PRL ('PRLNAME') formed as 'hostname.domainname', where
   'hostname' is an enterprise-specific name string and 'domainname' is
   an enterprise-specific DNS suffix.  The EBR discovers 'PRLNAME'
   through manual configuration, a DHCP option, 'rasadv' protocol
   advertisements, link-layer information (e.g., an IEEE 802.11 SSID) or
   through some other means specific to the enterprise.  In the absence
   of other information, the EBR sets the 'hostname' component of
   'PRLNAME' to "isatap" and sets the 'domainname' component only if an
   enterprise-specifc DNS suffix "" is known (e.g., as

   The global Internet interdomain routing core represents a specific
   example of an enterprise network scenario, albeit on an enormous
   scale.  The 'PRLNAME' assigned to the global Internet interdomain
   routing core is "".

   After discovering 'PRLNAME', the EBR can discover the list of EBGs by
   resolving 'PRLNAME' to a list of IPv4 addresses through a name
   service lookup.  For centrally-managed enterprises, the EBR resolves
   'PRLNAME' using an enterprise-local name service (e.g., the
   enterprise-local DNS).  For enterprises with a distributed management
   structure, the EBR resolves 'PRLNAME' using LLMNR [RFC4759] over the
   VET interface.  In that case, all EBGs in the PRL respond to the
   LLMNR query, and the EBR accepts the union of all responses.  Enterprise Identification

   Each distinct enterprise must have a unique identity that EBRs can
   use to discern their enterprise affiliations.  'PRLNAME' as well as
   the ELAs of EBGs and the IP prefixes the EBGs aggregate serve as an
   identifier for the enterprise.

4.2.2.  Provider-Aggregated (PA) Prefix Autoconfiguration

   EBRs can acquire Provider-Aggregated (PA) prefixes through
   autoconfiguration exchanges with EBGs over VET interfaces, where each
   EBG may be configured as either a DHCP relay or DHCP server.

   When IPv4 is used as the inner IP protocol, the EBR acquires PA
   prefixes via an unspecified automated IPv4 prefix delegation
   exchange, explicit management, etc.

   When IPv6 is used as the inner IP protocol, the EBR acquires PA
   prefixes via IPv6 Neighbor Discovery and DHCPv6 Prefix Delegation
   exchanges.  In particular, the EBR (acting as a requesting router)
   can use DHCPv6 prefix delegation [RFC3633] over the VET interface via
   an EBG to obtain PA IPv6 prefixes from the server (acting as a
   delegating router).

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   The EBR obtains prefixes using either a 2-message or 4-message DHCPv6
   exchange [RFC3315].  For example, to perform the 2-message exchange
   the EBR's DHCPv6 client forwards a Solicit message with an IA_PD
   option to its DHCPv6 relay, i.e., the EBR acts as a combined client/
   relay (see: Section 4.1).  The relay then forwards the message over
   the VET interface to the EBG, which either services the request or
   relays it further.  The forwarded Solicit message will elicit a reply
   from the server containing PA IPv6 prefix delegations.

   The EBR can 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.

   After the EBR receives PA prefix delegations, it can provision the
   prefixes on its enterprise-edge interfaces as well as on other VET
   interfaces for which it is configured as an EBG.

4.2.3.  Provider-Independent (PI) Prefix Autoconfiguration

   Independent of any PA prefixes, EBRs can acquire and use Provider-
   Independent (PI) prefixes that are either self-configured
   [RFC4193][I-D.ietf-ipv6-ula-central] or delegated by a registration
   authority.  When an EBR acquires a PI prefix, it must also obtain
   credentials (e.g., from a certification authority) that it can use to
   prove prefix ownership when it registers the prefixes with EBGs
   within an enterprise (see: Section 5.2 and Section 5.3).

   The minimum-sized IPv6 PI prefix that an EBR may acquire is a /56.

   The minimum-sized IPv4 PI prefix that an EBR may acquire is a /24.

4.3.  Enterprise Border Gateway (EBG) Autoconfiguration

   EBGs are EBRs that connect child enterprises to a provider network
   via ordinay provider-edge interfaces and/or VET interfaces configured
   over parent enterprises.  EBGs autoconfigure provider-edge interfaces
   in a manner that is specific to their provider connections, and
   autoconfigure VET interfaces as specified in Section 4.2.1.  EBGs
   that support PA prefix delegation also configure a DHCP relay/server.

   For each VET interface on which it is configured as an EBG, the EBG
   must arrange to add its enterprise-interior interface addresses
   (i.e., its ELAs) to the PRL (see: Section, and must maintain
   these resource records in accordance with ([RFC5214], Section 9).  In
   particular, for each such VET interface the EBG adds its ELAs to name
   service resource records for 'PRLNAME'.  To avoid looping, EBGs MUST

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   NOT configure a default route over a VET interface on which it is
   configured as an EBG.

   For enterprises with a distributed management structure, EBGs respond
   to LLMNR queries for 'PRLNAME'.

4.4.  VET Host Autoconfiguration

   Nodes that cannot be attached via an EBR's enterprise-edge interface
   (e.g., nomadic laptops that connect to a home office via a Virtual
   Private Network (VPN)) can instead be configured for operation as a
   simple host connected to the VET interface.  Such VET hosts perform
   the same VET interface autoconfiguration procedures as specified for
   EBRs in Section 4.2.1, but they configure their VET interfaces as
   host interfaces (and not router interfaces).  VET hosts can then send
   packets to other hosts on the VET interface, or to off-enterprise
   destinations via a next-hop EBR.

   Note that a node may be configured as a host on some VET interfaces
   and as an EBR/EBG on other VET interfaces.

5.  Internetworking Operation

   Following the autoconfiguration procedures specified in Section 4,
   ERs, EBRs, EBGs and VET hosts engage in normal internetworking
   operations as discussed in the following sections:

5.1.  Routing Protocol Participation

   Following autoconfiguration, ERs engage in any routing protocols over
   their enterprise-interior interfaces and forward outer IP packets
   within the enterprise as for any ordinary router.

   EBRs can additionally engage in any inner IP routing protocols over
   enterprise-edge, provider-edge and VET 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.

5.2.  IPv6 Router Discovery and Prefix Registration

   The following sections discuss router and prefix discovery
   considerations for the case of IPv6 as the inner IP protocol:

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5.2.1.  IPv6 Default Router Discovery

   EBGs follow the router and prefix discovery procedures specified in
   ([RFC5214], Section 8.2).  They send solicited RAs over VET
   interfaces for which they are configured as gateways with default
   router lifetimes, with PIOs that contain PA prefixes for SLAAC, and
   with any other required options/parameters.  EBGs must set the 'M'
   flag in RAs to 0, since the use of DHCPv6 for address configuration
   on VET interfaces is undefined.  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
   PA prefixes.

   VET nodes follow the router and prefix discovery procedures specified
   in ([RFC5214], Section 8.3).  They discover EBGs within the
   enterprise as specified in Section, then perform RS/RA
   exchanges with the EBGs to establish and maintain default routes.  In
   particular the VET node sends unicast RS messages to EBGs over its
   VET interface(s) to receive RAs.  Depending on the enterprise network
   trust basis, VET nodes may be required to use SEND to secure the
   RS/RA exchanges.

   When the VET node receives an RA, it authenticates the message then
   configures a default route based on the Router Lifetime.  If the RA
   contains Prefix Information Options (PIOs) with the 'A' and 'L' bits
   set to 1, the VET node also autoconfigures IPv6 addresses from the
   advertised prefixes using SLAAC and assigns them to the VET
   interface.  Thereafter, the VET node accepts packets that are
   fowarded by EBGs for which it has current default routing information
   (i.e., ingress filtering is based on the default router trust
   relationship rather than a prefix-specific ingress filter entry).

5.2.2.  IPv6 PA Prefix Registration

   After an EBR discovers default routes, it can use DHCP prefix
   delegation to obtain PA prefixes via an EBG as specified in
   Section 4.2.2.  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 correct EBR.  In particular, the EBG
   must register and track the PA prefixes that are delegated to each

   The PA prefix registrations remain active in the EBGs as long as the
   EBR continues to issue DHCP renewals over the VET interface before
   lease lifetimes expire.  The lease lifetime also keeps the delegation
   state active even if communications between the EBR and DHCP server
   are disrupted for a period of time (e.g., due to an enterprise
   network partition) before being reestablished (e.g., due to an

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   enterprise network merge).

5.2.3.  IPv6 PI Prefix Registration

   After an EBR discovers default routes, it must register its PI
   prefixes by sending RAs to a set of one or more EBGs with Route
   information Options (RIOs) [RFC4191] that contain the EBR's PI
   prefixes.  Each RA must include the ELA of an EBG as the outer IP
   destination address and an ISATAP link-local address derived from the
   ELA as the inner IP destination address.  For enterprises that use
   SEND, the RAs also include a CGA link-local inner source address
   along with SEND credentials plus any certificates needed to prove
   ownership of the PI prefixes.  The EBR additionally tracks the set of
   EBGs that it sends RAs to so that it can send subsequent RAs to the
   same set.

   When the EBG receives the RA, it first authenticates the message; if
   the authentication fails, the EBG discards the RA.  Otherwise, the
   EBG installs the PI prefixes with their respective lifetimes in its
   Forwarding Information Base (FIB) and configures them for both
   ingress filtering [RFC3704] and forwarding purposes.  In particular,
   the EBG configures the FIB entries as ingress filter rules to accept
   packets received on the VET interface that have a source address
   taken from the PI prefixes.  It also configures the FIB entries to
   forward packets received on other interfaces with a destination
   address taken from the PI prefixes to the EBR that registered the
   prefixes on the VET interface.

   The EBG then publishes the PI prefixes in a distributed database
   (e.g., in a private instance of a routing protocol in which only EBGs
   participate, via an automated name service update mechanism
   [RFC3007], etc.).  For enterprises that are managed under a
   centralized administrative authority, the EBG also publishes the PI
   prefixes in the enterprise-local name service (e.g., the enterprise-
   local DNS [RFC1035]).

   In particular, the EBG publishes each /56 prefix taken from the PI
   prefixes as a seperate FQDN that consists of a sequence of 14 nibbles
   in reverse order (i.e., the same as in [RFC3596], Section 2.5)
   followed by the string 'ip6' followed by the string 'PRLNAME'.  For
   example, when 'PRLNAME' is "", the EBG publishes
   the prefix '2001:DB8::/56' as:
   ''.  The EBG
   includes the outer IPv4 source address of the RA (e.g., in a DNS A
   resource record) in each prefix publication.  For enterprises that
   use SEND, the EBG also includes the inner IPv6 CGA source address
   (e.g., in a DNS AAAA record) in each prefix publication.  If the
   prefix was already installed in the distributed database, the EBG

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   instead adds the outer IPv4 source address (e.g., in an additional
   DNS A records) to the pre-existing publication to support PI prefixes
   that are multihomed.  For enterprises that use SEND, this latter
   provision requires all EBRs of a multihomed site that advertise the
   same PI prefixes in RAs to use the same CGA and the same SEND

   After the EBG authenticates the RA and publishes the PI prefixes, it
   next acts as a Neighbor Discovery proxy (NDProxy) [RFC4389] on the
   VET interfaces configured over any of its parent enterprises and
   relays a proxied RA to the EBGs on those interfaces.  (For
   enterprises that use SEND, the EBG additionally acts as a SEcure
   Neighbor Discovery Proxy (SENDProxy) [I-D.ietf-csi-proxy-send].)
   EBGs in parent enterprises that receive the proxied RAs in turn act
   as NDProxys/SENDProxys to relay the RAs to EBGs on their parent
   enterprises, etc.  The RA proxying and PI prefix publication recurses
   in this fashion and ends when an EBR attached to an interdomain
   routing core is reached.

   After the initial PI prefix registration, the EBR that owns the
   prefix(es) must periodically send additional RAs to its set of EBGs
   to refresh prefix lifetimes.  Each such EBG tracks the set of EBGs in
   parent enterprises that it relays the proxied RAs to, and should
   relay subsequent RAs to the same set.

   This procedure has a direct analogy in the Teredo method of
   maintaining state in network middleboxes through the periodic
   transmission of "bubbles" [RFC4380].

5.2.4.  IPv6 Next-Hop EBR Discovery

   VET nodes discover destination-specific next-hop EBRs within the
   enterprise by querying the name service for the /56 IPv6 PI prefix
   taken from a packet's destination address, by forwarding packets via
   a default route to an EBG, or by some other inner IP to outer IP
   address mapping mechansim.  For example, for the IPv6 destination
   address '2001:DB8:1:2::1' and 'PRLNAME' "" the VET
   node can lookup the domain name:
   ''.  If the name
   service lookup succeeds, it will return IPv4 addresses (e.g., in DNS
   A records) that correspond to the ELAs assigned to enterprise
   interior interfaces of next-hop EBRs to which the VET node can
   forward packets.  (In enterprises that use SEND, it will also return
   an IPv6 CGA address, e.g., in a DNS AAAA record.)

   Name service lookups in enterprises with a centralized management
   structure use an infrastructure-based service, e.g., an enterprise-
   local DNS.  Name service lookups in enterprises with a distributed

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   management structure and/or that lack an infrastructure-based name
   service instead use LLMNR over the VET interface.  When LLMNR is
   used, the EBR that performs the lookup sends an LLMNR query (with the
   /56 prefix taken from the IP destination address encoded in dotted-
   nibble format as shown above) and accepts the union of all replies it
   receives from other EBRs on the VET interface.  When an EBR receives
   an LLMNR query, it responds to the query IFF it aggregates an IP
   prefix that covers the prefix in the query.

   Alternatively, in enterprises with a stable and highly-available set
   of EBGs, the VET node can simply forward an initial packet via a
   default route to an EBG.  The EBG will forward the packet to a next-
   hop EBR on the VET interface and return an ICMPv6 Redirect [RFC4861]
   (using SEND, if necessary).  If the packet's source address is on-
   link on the VET interface, the EBG returns an ordinary "router-to-
   host" redirects with the source address of the packet as its
   destination.  If the packet's source address is not on-link, the EBG
   instead returns a "router-to-router" redirect with the link-local
   ISATAP address of the previous-hop EBR as its destination.  The EBG
   also includes in the redirect one or more IPv6 Link-Layer Address
   Options (LLAOs) that contain the IPv4 ELAs of potential next-hop EBRs
   arranged in order from highest to lowest priority (i.e., the first
   LLAO contains the highest priority ELA and the final LLAO option
   contains the lowest priority).  The LLAOs are formatted using a
   modified version of the form specified in ( [RFC2529], Section 5) as
   shown in Figure 2:

   | Type  |Length |      TTL      |        IPv4 Address           |

              Figure 2: VET Link-Layer Address Option Format

   For each LLAO, the Type is set to 2 (for Target Link-Layer Address
   Option), Length is set to 1, and IPv4 Address is set to the IPv4 ELA
   of the next-hop EBR.  TTL is set to the time in seconds that the
   recipient may cache the ELA, where the value 65535 represents
   infinity and the value 0 suspends forwarding through this ELA.

   When a VET host receives an ordinay "router-to-host" redirect, it
   processes the redirect exacly as specified in [RFC4861], Section 8.
   When an EBR receives a "router-to-router" redirect, it discovers the
   IPv4 ELA addresses of potential next-hop EBRs by examining the LLAOs
   included in the redirect.  The EBR then installs a FIB entry that
   contains the /56 prefix of the destination address encoded in the
   redirect and the list of IPv4 ELAs of potential next-hop EBRs.  The
   EBR then enables the FIB entry for forwarding to next-hop EBRs but
   DOES NOT enable it for ingress filtering acceptance of packets from

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   next-hop EBRs (i.e., the forwarding determination is unidirectional).

   In enterprises in which spoofing is possible, after discovering
   potential next-hop EBRs (either through name service lookup or ICMP
   redirect) the EBR must send authenticating credentials before
   forwarding packets via the next-hops.  To do so, the EBR must send
   RAs over the VET interface (using SEND, if necessary) to one or more
   of the potential next-hop EBRs with a link-local ISATAP address that
   embeds a next-hop EBR IPv4 ELA as the destination.  The RAs must
   include a Route Information Option (RIO) [RFC4191] that contains the
   /56 PI prefix of the original packet's source address.  After sending
   the RAs, the EBR can either enable the new FIB entry for forwarding
   immediately or delay until it receives an explicit acknowledgement
   that a next-hop EBR received the RA (e.g., using the SEAL explicit
   acknowledgement mechanism - see: Section 5.5).

   When a next-hop EBR receives the RA, it authenticates the message
   then performs a name service lookup on the prefix in the RIO if
   further authenticating evidence is required.  If the name service
   returns resource records that are consistent with the inner and outer
   IP addresses of the RA, the next-hop EBR then installs the prefix in
   the RIO in its FIB and enables the FIB entry for ingress filtering
   but DOES NOT enable it for forwarding purposes.  After an EBR sends
   initial RAs following a redirect, it should send periodic RAs to
   refresh the next-hop EBR's ingress filter prefix lifetimes as long as
   traffic is flowing.

   EBRs retain the FIB entrys created as result of an ICMP redirect
   until all ELA TTLs expire, or until no hints of forward progress
   through any of the associated ELAs are received.  In this way, ELA
   liveness detection exactly parallels IPv6 Neighbor Unreachability
   Detection ([RFC4861], Section 3).

5.3.  IPv4 Router Discovery and Prefix Registration

   When IPv4 is used as the inner IP protocol, router discovery and
   prefix registration exactly parallels the mechanisms specified for
   IPv6 in Section 5.2.  To support this, modifications to the ICMPv4
   Router Advertisement [RFC1256] function to include SEND constructs,
   and modifications to the ICMPv4 Redirect [RFC0792] function to
   support router-to-router redirects will be specified in a future
   document.  Additionally, publications for IPv4 prefixes will be in
   dotted-nibble format in the '' domain.  For
   example, the IPv4 prefix 192.0.2/24 would be represented as:

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5.4.  Forwarding Packets

   VET nodes forward packets by consulting the FIB to determine a
   specific EBR/EBG as the next-hop router on a VET interface.  When
   multiple next-hop routers are available, VET nodes can use default
   router preferences, routing protocol information, traffic engineering
   configurations, etc. to select the best exit router.  When there is
   no FIB information other than ::/0 available, VET nodes can discover
   the next-hop EBR/EBG through the mechanisms specified in Section 5.2.

   VET interfaces encapsulate inner IP packets in any mid-layer headers
   followed by an outer IP header according to the specific
   encapsulation type (e.g., [RFC4301][RFC5214][I-D.templin-seal]); they
   next submit the encapsulated packet to the outer IP forwarding engine
   for transmission on an underlying enterprise-interior interface.

   For forwarding to next-hop addresses over VET interfaces that use
   IPv6-in-IPv4 encapsulation, VET nodes determine the outer destination
   address (i.e., the IPv4 ELA of the next-hop EBR) 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.  When there are multiple
   candidate destination ELAs available, the VET node should only select
   an ELA for which there is current forwarding information in the outer
   IP protocol FIB.

5.5.  SEAL Encapsulation

   VET nodes should use SEAL encapsulation [I-D.templin-seal] in
   conjunction with packet forwarding over VET interfaces to accommdate
   path MTU diversity, to defeat source address spoofing, and to monitor
   next-hop EBR reachability.  SEAL encapsulation maintains a
   unidirectional and monotonically-incrementing per-packet
   identification value known as the 'SEAL_ID'.  When a VET node that
   uses SEAL encapsulation sends a SEND-protected Router Advertisement
   (RA) or Router Solicitation (RS) message to another VET node, both
   nodes cache the new SEAL_ID as per-tunnel state used for maintaining
   a window of unacknowledged SEAL_IDs.

   In terms of security, when a VET node receives an ICMP message, it
   can confirm that the packet-in-error within the ICMP message
   corresponds to one of its recently-sent packets by examining the
   SEAL_ID along with source and destination addresses, etc.
   Additionally, a next-hop EBR can track the SEAL_ID in packets
   received from EBRs for which there is an ingress filter entry and
   discard packets that have SEAL_ID values outside of the current

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   In terms of next-hop reachability, an EBR can set the SEAL
   "Acknowledgement Requested" bit in messages to receive confirmation
   that a next-hop EBR is reachable (see also Section 5.2.4.  Setting
   the "Acknowledgement Requested" bit is also used as the method for
   maintaining the window of outstanding SEAL_ID's.

5.6.  Generating Errors

   When an EBR receives a packet over a VET interface and there is no
   matching ingress filter entry, it drops the packet and returns an
   ICMPv6 [RFC4443] "Destination Unreachable; Source address failed
   ingress/egress policy" message to the previous hop EBR subject to
   rate limiting.

   When an EBR receives a packet over a VET interface, and there is no
   longest-prefix-match FIB entry for the destination, it returns an
   ICMPv6 "Destination Unreachable; No route to destination" message to
   the previous hop EBR subject to rate limiting.

   When an EBR receives a packet over a VET interface and the longest-
   prefix-match FIB entry for the destination is configured over the
   same VET interface the packet arrived on, the EBR forwards the packet
   then (if the FIB prefix is longer than ::/0) sends a router-to-router
   ICMPv6 Redirect message (using SEND, if necessary) to the previous
   hop EBR as specified in Section 5.2.4.

   Generation of other ICMPv6 messages (e.g., ICMPv6 "Packet Too Big")
   is the same as for any IPv6 interface.

5.7.  Processing Errors

   When an EBR receives an ICMPv6 "Destination Unreachable; Source
   address failed ingress/egress policy" message from a next-hop EBR,
   and there is a longest-prefix-match FIB entry for the original
   packet's destination that is more-specific than ::/0, the EBR
   discards the message and marks the FIB entry for the destination as
   "forwarding suspended" for the ELA taken from the source address of
   the ICMPv6 message.  The EBR should then allow subsequent packets to
   flow through different ELAs associated with the FIB entry until it
   forwards a new RA to the suspended ELA.  If the EBR receives
   excessive ICMPv6 ingress policy errors through multiple ELAs
   associated with the same FIB entry, it should delete the FIB entry
   and allow subsequent packets to flow through an EBG if supported in
   the specific enterprise scenario.

   When a VET node receives an ICMPv6 "Destination Unreachable; No route
   to destination" message from a next-hop EBR, it forwards the ICMPv6
   message to the source of the original packet as normal.  If the EBR

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   has longest-prefix-match FIB entry for the original packet's
   destination that is more-specific than ::/0, the EBR also deletes the
   FIB entry.

   When an EBR receives an authentic ICMPv6 Redirect, it processes the
   packet as specified in Section 5.2.4.

   When an EBG receives new mapping information for a specific
   destination prefix, it can propagate the update to other EBRs/EBGs by
   sending an ICMPv6 redirect message to the 'All Routers' link-local
   multicast address with a LLAO with the TTL for the unreachable LLAO
   set to zero, and with a NULL packet in error.

   Additionally, a VET node may receive ICMPv4 [RFC0792] "Destination
   Unreachable; net / host unreachable" messages from an ER indicating
   that the path to a VET neighbor may be failing.  The EBR should first
   check authenticating information in the message (e.g., the SEAL_ID,
   IPsec sequence number, source address of the original packet if
   available, etc.) before accepting it, then should mark the longest-
   prefix-match FIB entry for the destination as "forwarding suspended"
   for the ELA destination address of the ICMPv4 packet-in-error.  If
   the EBR receives excessive ICMPv4 unreachable errors through multiple
   ELAs associated with the same FIB entry, it should delete the FIB
   entry and allow subsequent packets to flow through a different route.

5.8.  Mobility and Multihoming Considerations

   EBRs that travel between distinct enterprise networks must either
   abandon their PA prefixes that are relative to the "old" enterprise
   and obtain new ones relative to the "new" enterprise, or somehow
   coordinate with a "home" enterprise to retain ownership of the
   prefixes.  In the first instance, the EBR would be required to
   coordinate a network renumbering event using the new PA prefixes
   [RFC4192].  In the second instance, an ancillary mobilitiy management
   mechanism must be used.

   EBRs can retain their PI prefixes as they travel between distinct
   enterprise networks as long as they register the prefixes with new
   EBGs and (preferrably) withdraw the prefixes from old EBGs prior to
   departure.  Prefix registration with new EBGs is coordinated exactly
   as specified in Section 5.2.3; prefix withdrawl from old EBGs is
   simply through re-announcing the PI prefixes with zero lifetimes.

   Since EBRs can move about independently of one another, stale FIB
   entry state may be left in VET nodes when a neighboring EBR departs.
   Additionally, EBRs can lose state for various reasons, e.g., power
   failure, machine reboot, etc.  For this reason, EBRs are advised to
   set relatively short PI prefix lifetimes in RIO options, and to send

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   additional RAs to refresh lifetimes before they expire.  (EBRs should
   place conservative limits on the RAs they send to reduce congestion,

   EBRs may register their PI prefixes with multiple EBGs for
   multihoming purposes.  EBRs should only forward packets via EBGs with
   which it has registered its PI prefixes, since other EBGs may drop
   the packets and return ICMPv6 "Destination Unreachable; Source
   address failed ingress/egress policy" messages.

   EBRs can also act as delegating routers to sub-delegate portions of
   their PI prefixes to requesting routers on their enterprise edge
   interfaces and on VET interfaces for which they are configured as
   EBGs.  In this sense, the sub-delegations of an EBR's PI prefixes
   become the PA prefixes for downstream-dependent nodes.  Downstream-
   dependent nodes that travel with a mobile provider EBR can continue
   to use addresses configured from PA prefixes; downstream-dependent
   nodes that move away from their provider EBR must perform address/
   prefix renumbering when they assocate with a new provider.

   The EBGs of a multi-homed enterprise should participate in a private
   inner IP routing protocol instance between themselves (possibly over
   an alternate topology) to accommodate enterprise partitions/merges as
   well as intra-enterprise mobility events.  These peer EBGs should
   accept packets from one another without respect to the destination
   (i.e., ingress filtering is based on the peering relationship rather
   than a prefix-specific ingress filter entry).

5.9.  Enterprise-Local Communications

   When permitted by policy, end systems that configure the endpoints of
   enterprise-local communications 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, end systems can use IPv4 ELAs for enterprise-local
   communications over their enterprise-interior interfaces without
   using encapsulation.

5.10.  Multicast

   In multicast-capable deployments, ERs provide an enterprise-wide
   multicasting service (e.g., Simplified Multicast Forwarding (SMF)
   [I-D.ietf-manet-smf], PIM routing, DVMRP routing, etc.) 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, VET nodes 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

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   multicast address space.  In that case, operation of link- or greater
   scoped inner IP multicasting services (e.g., a link-scoped neighbor
   discovery protocol) over the VET interface is available, but link-
   scoped services should be used sparingly to minimize enterprise-wide

   VET nodes 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 a site-scoped IPv4 multicast address space
   (for other IP-in-IP encapsulations, mappings are established through
   administrative configuration or through an unspecified alternate
   static mapping).

   Multicast mapping for inner IP multicast groups over outer IP
   multicast groups can be accommodated, e.g. through VET interface
   snooping of inner multicast group membership and routing protocol
   control messages.  To support inner-to-outer IP multicast mappinging,
   the VET interface acts as a virtual outer IP multicast host connected
   to its underlying enterprise-interior interfaces.  When the VET
   interface detects inner IP multicast group joins or leaves, it
   forwards corresponding outer IP multicast group membership reports
   for each enterprise-interior interface over which the VET interface
   is configured.  If the VET node is configured as an outer IP
   multicast router on the underlying enterprise-interior interfaces,
   the VET interface forwards locally looped-back group membership
   reports to the outer IP multicast routing process.  If the VET node
   is configued as a simple outer IP multicast host, the VET interface
   instead fowards actual group membership reports (e.g., IGMP messages)
   directly over each of the underlying enterprise-interior interfaces.

   Since inner IP multicast groups are mapped to site-scoped outer IP
   multicast groups, the VET node must ensure that the site-scope outer
   IP multicast messages received on the enterprise-interior interfaces
   for one VET interface do not "leak out" to the enterprise-interior
   interfaces of another VET interface.  This is accomodated through
   normal site-scoped outer IP multicast group filtering at enterprise-
   interior interface boundaries.

5.11.  Service Discovery

   VET nodes 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

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   efficient service discovery mechanisms are for further study.

5.12.  Enterprise Partitioning

   EBGs can physically partition an enterprise by configuring multiple
   VET interfaces over multiple distinct sets of underlying interfaces.
   In that case, each partition (i.e., each VET interface) must
   configure its own distinct 'PRLNAME' (e.g.,
   '', '', etc.).

   EBGs can logically partition an enterprise using a single VET
   interface by sending RAs with PIOs containing different IPv6 PA
   prefixes to group nodes into different logical partitions.  EBGs can
   identify partitions, e.g., by examining IPv4 ELA prefixes, observing
   the interfaces over which RSs are received, etc.  In that case, a
   single 'PRLNAME' can cover all partitions.

5.13.  EBG Prefix State Recovery

   EBGs must retain explicit state that tracks the inner IP prefixes
   owned by EBRs within the enterprise, e.g., so that packets are
   delivered to the correct EBRs and not incorrectly "leaked out" of the
   enterprise via a default route.  For PA prefixes the state is
   maintained via an EBR's DHCP prefix delegation lease renewals, while
   for PI prefixes the state is maintained via an EBR's periodic prefix
   registration RAs.

   When an EBG loses some or all of its state (e.g., due to a power
   failure), it must recover the state before allowing packets to flow
   over incorrect routes.  If the EBG aggregates PA prefixes from which
   the IP prefixes of all EBRs in the enterprise are sub-delegated, then
   the EBG can recover state through DHCP prefix delegation lease
   renewals, through bulk lease queries, or through on-demand name
   service lookups based due to IP packet forwarding.  If the EBG serves
   as an anchor for PI prefixes, however, care must be taken to avoid
   looping while state is recovered through prefix registration RAs from
   EBRs.  In that case, when the EBG that is recovering state forwards
   an IP packet for which it has no explicit route other than ::/0, it
   must first perform an on-demand name service lookup to refresh state.

6.  IANA Considerations

   A Site-Local Scope IPv4 multicast group ('All_DHCPv4_Servers') for
   DHCPv4 server discovery is requested.  The allocation should be taken
   from the Site-Local Scope range in
   the IANA 'multicast-addresses' registry.

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7.  Security Considerations

   Security considerations for MANETs are found in [RFC2501].

   Security considerations with tunneling that apply also to VET are
   found in [RFC2529][RFC5214].  In particular, VET nodes must verify
   that the outer IP source address of a packet received on a VET
   interface is correct for the inner IP source address using the
   procedures specified in ([RFC5214], Section 7.3) in conjunction with
   the ingress filtering mechanisms specified in this document.

   SEND [RFC3971], IPsec [RFC4301] and SEAL Section 5.5 provide
   additional securing mitigations to detect source address spoofing and
   bogus RA messages sent by rogue routers.

   Rogue routers can send bogus RA messages with spoofed ELA source
   addresses that can consume network resources and cause EBGs to
   perform extra work.  Nonetheless, EBGs should not "blacklist" such
   ELAs, as that may result in a denial of service to the ELAs'
   legitimate owners.

8.  Related Work

   Brian Carpenter and Cyndi Jung introduced the concept of intra-site
   automatic tunneling in [RFC2529]; this concept was later called:
   "Virtual Ethernet" and investigated by Quang Nguyen under the
   guidance of Dr. Lixia Zhang.  Subsequent works by these authors and
   their colleagues have motivated a number of foundational concepts on
   which this work is based.

   Telcordia has proposed DHCP-related solutions for MANETs through the
   CECOM MOSAIC program.

   The Naval Research Lab (NRL) Information Technology Division uses
   DHCP in their MANET research testbeds.

   [I-D.ietf-v6ops-tunnel-security-concerns] discusses security concerns
   pertaining to tunneling mechanisms.

   An automated IPv4 prefix delegation mechanism is proposed in

   MANET link types are discussed in [I-D.clausen-manet-linktype].

   Various proposals within the IETF have suggested similar mechanisms.

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9.  Acknowledgements

   The following individuals gave direct and/or indirect input that was
   essential to the work: Jari Arkko, Teco Boot, Emmanuel Bacelli, Scott
   Brim, Brian Carpenter, James Bound, Thomas Clausen, Claudiu Danilov,
   Dino Farinacci, Vince Fuller, Thomas Goff, Joel Halpern, Bob Hinden,
   Sapumal Jayatissa, Dan Jen, Darrel Lewis, Tony Li, Joe Macker, David
   Meyer, Thomas Narten, Pekka Nikander, Dave Oran, Alexandru Petrescu,
   John Spence, Jinmei Tatuya, Dave Thaler, Ole Troan, Michaela
   Vanderveen, Lixia Zhang 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 (
   Thomas Henderson (
   Steven Russert (
   Seung Yi (

   Ian Chakeres ( contributed to earlier versions
   of the document.

11.  References

11.1.  Normative References

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

   [RFC0792]  Postel, J., "Internet Control Message Protocol", STD 5,
              RFC 792, 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.

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, November 1987.

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

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

   [RFC3007]  Wellington, B., "Secure Domain Name System (DNS) Dynamic
              Update", RFC 3007, November 2000.

   [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.

   [RFC3596]  Thomson, S., Huitema, C., Ksinant, V., and M. Souissi,
              "DNS Extensions to Support IP Version 6", RFC 3596,
              October 2003.

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

   [RFC3971]  Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
              Neighbor Discovery (SEND)", RFC 3971, March 2005.

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

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

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

   [RFC4443]  Conta, A., Deering, S., and M. Gupta, "Internet Control
              Message Protocol (ICMPv6) for the Internet Protocol
              Version 6 (IPv6) Specification", RFC 4443, March 2006.

   [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.

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11.2.  Informative References

   [CATENET]  Pouzin, L., "A Proposal for Interconnecting Packet
              Switching Networks", May 1974.

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

              Clausen, T., "The MANET Link Type",
              draft-clausen-manet-linktype-00 (work in progress),
              October 2008.

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

              Krishnan, S., Laganier, J., and M. Bonola, "Secure Proxy
              ND Support for SEND", draft-ietf-csi-proxy-send-00 (work
              in progress), November 2008.

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

              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-08 (work in progress),
              November 2008.

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

              Jen, D., Meisel, M., Massey, D., Wang, L., Zhang, B., and

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              L. Zhang, "APT: A Practical Transit Mapping Service",
              draft-jen-apt-01 (work in progress), November 2007.

              Templin, F., "The Subnetwork Encapsulation and Adaptation
              Layer (SEAL)", draft-templin-seal-23 (work in progress),
              August 2008.

   [IEN48]    Cerf, V., "The Catenet Model for Internetworking",
              July 1978.

   [RASADV]   Microsoft, "Remote Access Server Advertisement (RASADV)
              Protocol Specification", October 2008.

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

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

   [RFC1753]  Chiappa, J., "IPng Technical Requirements Of the Nimrod
              Routing and Addressing Architecture", RFC 1753,
              December 1994.

   [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.

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

   [RFC2775]  Carpenter, B., "Internet Transparency", RFC 2775,
              February 2000.

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

   [RFC3704]  Baker, F. and P. Savola, "Ingress Filtering for Multihomed
              Networks", BCP 84, RFC 3704, March 2004.

   [RFC3753]  Manner, J. and M. Kojo, "Mobility Related Terminology",

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              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.

   [RFC4192]  Baker, F., Lear, E., and R. Droms, "Procedures for
              Renumbering an IPv6 Network without a Flag Day", RFC 4192,
              September 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.

   [RFC4380]  Huitema, C., "Teredo: Tunneling IPv6 over UDP through
              Network Address Translations (NATs)", RFC 4380,
              February 2006.

   [RFC4389]  Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery
              Proxies (ND Proxy)", RFC 4389, April 2006.

   [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 would require

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   either flooding the entire 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.

   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 ER'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 -33 to 34:

   o  Enterprise management models described

   o  Enterprise security models described

   o  Clarification of mechanisms based on enterprise management/
      security models

   Changes from -32 to 33::

   o  Secure Neighbor Discovery Proxy

   Changes from -28 to 29:

   o  Updates on processing/receiving errors.

   Changes from -27 to 28:

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   o  Introduced concept of a default mapper.

   Changes from -26 to 27:

   o  Introduced new model for PI prefix management.

   o  Teredo mechanisms used in conjunction with ISATAP ("teratap"?

   Changes from -25 to 26:

   o  Clarifications on Router Discovery and Ingress FIltering.

   o  Mechanisms for detecting locator liveness

   o  Mechanisms for avoiding state synchonization requirements.

   Changes from -23 to 24:

   o  Clarifications on router discovery.

   Changes from -22 to 23:

   o  Clarifications on prefix mapping.

   Changes from -21 to 22:

   o  Using SEAL to secure VET

   Changes from -20 to 21:

   o  Enterprise partitioning.

   o  Mapping and name service management.

   Changes from -18 to 20:

   o  Added support for simple hosts.

   o  Added EBG name service maintenace procedures

   o  Added router and prefix maintenace procedures

   Changes from -17 to 18:

   o  adjusted section headings to group autoconf operations under EIR/

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   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:

   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

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

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   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

   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:

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   o  introduced conceptual "virtual ethernet" model.

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

   Changed from -03 to -04:

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

   o  discussion of autonomous system and site abstractions for MANETs

   o  discussion of autoconfiguration of CGAs

   o  new appendix on IPv6 StateLess Address AutoConfiguration

   Changes from -02 to -03:

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

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

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

   Changes from -01 to -02:

   o  minor updates for consistency with recent developments

   Changes from -00 to -01:

   o  new text on DHCPv6 prefix delegation and multilink subnet

   o  various editorial changes

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Author's Address

   Fred L. Templin (editor)
   Boeing Research and Technology
   P.O. Box 3707 MC 7L-49
   Seattle, WA  98124


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