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Network Working Group                                    F. Templin, Ed.
Internet-Draft                              Boeing Research & Technology
Intended status: Standards Track                        January 14, 2010
Expires: July 18, 2010


                   Virtual Enterprise Traversal (VET)
                    draft-templin-intarea-vet-06.txt

Abstract

   Enterprise networks connect hosts and routers over various link
   types, and may also connect to provider networks and/or the global
   Internet.  Enterprise network nodes require a means to automatically
   provision IP addresses/prefixes and support internetworking operation
   in a wide variety of use cases including Small Office, Home Office
   (SOHO) networks, Mobile Ad hoc Networks (MANETs), ISP networks,
   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.  VET can also be
   considered as version 2 of the Intra-Site Automatic Tunnel Addressing
   Protocol (i.e., "ISATAPv2").

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
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   Drafts.

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   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on July 18, 2010.

Copyright Notice



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   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   the Trust Legal Provisions and are provided without warranty as
   described in the BSD License.







































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  6
   3.  Enterprise Characteristics . . . . . . . . . . . . . . . . . . 11
   4.  Autoconfiguration  . . . . . . . . . . . . . . . . . . . . . . 12
     4.1.  Enterprise Router (ER) Autoconfiguration . . . . . . . . . 12
     4.2.  Enterprise Border Router (EBR) Autoconfiguration . . . . . 14
       4.2.1.  VET Interface Initialization . . . . . . . . . . . . . 14
       4.2.2.  PRL Discovery and Enterprise Identification  . . . . . 15
       4.2.3.  Provider-Aggregated (PA) EID Prefix
               Autoconfiguration  . . . . . . . . . . . . . . . . . . 16
       4.2.4.  Provider-Independent (PI) EID Prefix
               Autoconfiguration  . . . . . . . . . . . . . . . . . . 17
     4.3.  Enterprise Border Gateway (EBG) Autoconfiguration  . . . . 17
     4.4.  VET Host Autoconfiguration . . . . . . . . . . . . . . . . 18
   5.  Internetworking Operation  . . . . . . . . . . . . . . . . . . 18
     5.1.  Routing Protocol Participation . . . . . . . . . . . . . . 19
     5.2.  Address Selection  . . . . . . . . . . . . . . . . . . . . 19
     5.3.  VET interface Neighbor Discovery . . . . . . . . . . . . . 19
       5.3.1.  Router and Prefix Discovery  . . . . . . . . . . . . . 20
       5.3.2.  Next Hop Determination . . . . . . . . . . . . . . . . 22
       5.3.3.  Redirect Function  . . . . . . . . . . . . . . . . . . 23
       5.3.4.  Neighbor Unreachability Detection  . . . . . . . . . . 24
       5.3.5.  Reverse Path Forwarding Checks . . . . . . . . . . . . 25
       5.3.6.  IPv4 Neighbor Discovery  . . . . . . . . . . . . . . . 25
     5.4.  Generating Errors  . . . . . . . . . . . . . . . . . . . . 25
     5.5.  Processing Errors  . . . . . . . . . . . . . . . . . . . . 26
     5.6.  Mobility and Multihoming Considerations  . . . . . . . . . 27
     5.7.  Multicast  . . . . . . . . . . . . . . . . . . . . . . . . 28
     5.8.  Service Discovery  . . . . . . . . . . . . . . . . . . . . 29
     5.9.  Enterprise Partitioning  . . . . . . . . . . . . . . . . . 29
     5.10. EBG Prefix State Recovery  . . . . . . . . . . . . . . . . 29
     5.11. Support for Legacy ISATAP Services . . . . . . . . . . . . 29
     5.12. SEAL Encapsulation . . . . . . . . . . . . . . . . . . . . 29
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 30
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 30
   8.  Related Work . . . . . . . . . . . . . . . . . . . . . . . . . 31
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 32
   10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 32
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 33
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 33
     11.2. Informative References . . . . . . . . . . . . . . . . . . 34
   Appendix A.  Duplicate Address Detection (DAD) Considerations  . . 38
   Appendix B.  Link-Layer Multiplexing and Traffic Engineering . . . 39
   Appendix C.  Anycast Services  . . . . . . . . . . . . . . . . . . 41
   Appendix D.  Change Log  . . . . . . . . . . . . . . . . . . . . . 42
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 43



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1.  Introduction

   Enterprise networks [RFC4852] connect hosts and 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.  ISP networks are another
   example use case that fits well with the VET enterprise network
   model.  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 scenarios.

   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 specified.



























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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
   IP in IP encapsulation.  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) addressing.  This is
   especially true for enterprise scenarios that involve mobility and
   multihoming.  Also in scope are ingress filtering for multihomed
   sites, adaptation based on authenticated ICMP feedback from on-path
   routers, effective tunnel path MTU mitigations, and routing scaling
   suppression as required in many enterprise network scenarios.  The



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   VET specification provides adaptable mechanisms that address these
   and other issues in a wide variety of enterprise network use cases.

   VET represents a functional superset of 6over4 [RFC2529] and the
   Intra-Site Automatic Tunnel Addressing Protocol (ISATAP) [RFC5214],
   and can be considered as version 2 of the ISATAP protocol (i.e.,
   "ISATAPv2").  VET works in conjunction with the Subnetwork
   Encapsulation and Adaptation Layer (SEAL) [I-D.templin-intarea-seal],
   and is also compatible with additional encapsulations such as IPsec
   [RFC4301].  VET further defines mechanisms that are very similar in
   nature to those specified for IPv6 operation over Non-Broadcast
   Multiple Access (NBMA) networks [RFC2491].

   VET and its associated technologies serve as functional building
   blocks for a new Internetworking architecture known as Routing and
   Addressing in Next Generation EnteRprises [I-D.templin-ranger]
   [I-D.russert-rangers].  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] and
   the Catenet model for internetworking [CATENET] [IEN48] [RFC2775].
   [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 activities of the IETF INTAREA,
   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 in 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 uses the Subnetwork Encapsulation and
   Adaptation Layer (SEAL) [I-D.templin-intarea-seal] as a "mid-layer"
   encapsulation between the inner and outer IP headers, and also allows
   for inclusion of other mid-layer encapsulations including IPSec
   [RFC4301].

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







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   Virtual Enterprise Traversal (VET)
      an abstraction that uses IP in IP encapsulation to create overlays
      for traversing enterprise networks.  VET can be considered as
      version 2 of the ISATAP protocol (i.e., "ISATAPv2").

   enterprise
      the same as defined in [RFC4852].  An enterprise is also
      understood to refer to a cooperative networked collective of
      devices within a common IP routing and addressing region and 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
      connectivity itself.

   subnetwork
      the same as defined in [RFC3819].

   site
      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.  The
      characteristics of MANETs are defined in [RFC2501], Section 3, and
      a wide variety of MANETs share common properties with enterprise
      networks.

   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 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 outer IP packets over
      one or more sets of enterprise-interior interfaces, where each set
      connects to a distinct enterprise.







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   Enterprise Border Router (EBR)
      an ER that connects edge networks to the enterprise and/or
      connects multiple enterprises together.  An EBR is a tunnel
      endpoint router, and it configures a separate VET interface over
      each set of enterprise-interior interfaces that connect the EBR to
      each distinct enterprise.  In particular, an EBR may configure
      multiple 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.

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

   VET node
      any node (host or router) that configures and uses a VET
      interface.

   enterprise-interior interface
      an 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-interior interfaces connect
      laterally within the IP network hierarchy.

   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 provider
      network.  Enterprise-edge interfaces connect to lower levels
      within the IP network hierarchy.

   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.
      Provider-edge interfaces connect to higher levels within the IP
      network hierarchy.




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   internal-virtual interface
      an interface that is internal to an EBR and does not in itself
      directly attach to a tangible physical link, e.g., an Ethernet
      cable.  Examples include a loopback interface, a virtual private
      network interface, or some form of tunnel interface.

   VET link
      a virtual link that uses automatic tunneling to create an overlay
      network that spans an enterprise-interior routing region.  VET
      links can be segmented (e.g., by IP in IP protocol filtering
      gateways) into multiple distinct segments that can be joined
      together by bridges or IP routers the same as for any link.
      Bridging would view the multiple (bridged) segments as a single
      VET link, whereas IP routing would view the multiple segments as
      multiple distinct VET links.  VET link segments can further be
      partitioned into multiple logical areas, where each area is
      identified by a distinct set of EBGs.

      VET links in non-multicast enterprises are Non-Broadcast, Multiple
      Access (NBMA); VET links in enterprises that support multicast are
      multicast capable.

   VET interface
      a VET node's attachment to a VET link.  VET nodes configure each
      VET interface over a set of underlying interfaces that connect to
      an enterprise-interior routing region spanned by a single VET
      link.  When there are multiple distinct VET links (each with their
      own distinct set of underlying interfaces), the VET node
      configures separate VET interfaces for each link.

      The VET interface encapsulates each inner IP packet in any mid-
      layer headers followed by an outer IP header, then forwards the
      packet on an underlying interface such that the Time to Live (TTL)
      - Hop Limit in the inner header is not decremented as the packet
      traverses the link.  The VET interface therefore presents an
      automatic tunneling abstraction that represents the link as a
      single IP hop.

   VET address
      an IPv6 address assigned to a VET interface that embeds an IPv4
      address within the IPv6 address interface identifier.  VET
      addresses are formed exactly as specified for ISATAP addresses in
      Sections 6.1 and 6.2 of [RFC5214].

   Provider-Independent (PI) prefix
      an IPv6 prefix (e.g., 2001:DB8::/48) or IPv4 prefix (e.g.,
      192.0.2/24) that is either self-generated by an EBR or delegated
      to an EBR by a registry.



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   Provider Aggregated (PA) prefix
      an IPv6 or IPv4 prefix that is delegated to an EBR by a provider
      network.

   Routing Locator (RLOC)
      a non-link-local IPv4 or IPv6 address taken from a PI/PA prefix
      that can appear in enterprise-interior and/or interdomain routing
      tables.  Global-scope RLOC prefixes are delegated to specific
      enterprises and routable within both the enterprise-interior and
      interdomain routing regions.  Enterprise-local-scope RLOC prefixes
      (e.g., IPv6 Unique Local Addresses [RFC4193], IPv4 privacy
      addresses [RFC1918], etc.) are self-generated by individual
      enterprises and routable only within the enterprise-interior
      routing region.

      ERs use RLOCs for operating the enterprise-interior routing
      protocol and for next-hop determination in forwarding packets
      addressed to other RLOCs.  End systems use RLOCs as addresses for
      end-to-end communications between peers within the same
      enterprise.  VET interfaces treat RLOCs as *outer* IP addresses
      during IP in IP encapsulation.

   Endpoint Interface iDentifier (EID)
      an IPv4 or IPv6 address taken from a PI/PA prefix that is routable
      within an enterprise-edge or VET overlay network scope, and may
      also appear in enterprise-interior and/or interdomain mapping
      tables.  EID prefixes are separate and distinct from any RLOC
      prefix space.

      Edge network routers use EIDs for operating the enterprise-edge or
      VET overlay network routing protocol and for next-hop
      determination in forwarding packets addressed to other EIDs.  End
      systems use EIDs as addresses for end-to-end communications
      between peers either within the same enterprise or within
      different enterprises.  VET interfaces treat EIDs as *inner* IP
      addresses during IP in IP encapsulation.

   The following additional acronyms are used throughout the document:

   CGA - Cryptographically Generated Address
   DHCP(v4, v6) - Dynamic Host Configuration Protocol
   FIB - Forwarding Information Base
   ISATAP - Intra-Site Automatic Tunnel Addressing Protocol
   NBMA - Non-Broadcast, Multiple Access
   ND - Neighbor Discovery
   PIO - Prefix Information Option
   PRL - Potential Router List
   PRLNAME - Identifying name for the PRL (default is "isatapv2")



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   RIO - Route Information Option
   RPF - Reverse Path Forwarding
   RS/RA - IPv6 ND 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 connect enterprises
   to provider networks.

   Conceptually, an ER embodies both a host function and router
   function.  The host function supports Endpoint Interface iDentifier
   (EID)-based and/or Routing LOCator (RLOC)-based communications
   according to the weak end-system model [RFC1122].  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 Figure 1).

   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.
   Finally, an enterprise may contain many internal partitions that are
   logical or physical groupings of nodes for the purpose of load
   balancing, organizational separation, etc.  In that case, each
   internal partition resembles an individual segment of a bridged LAN.

   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 an enterprise-
   interior routing service that operates as an IP layer mechanism.  In
   that case, multiple IP hops may be necessary to traverse the
   enterprise such that care must be taken to avoid multi-link subnet



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   issues [RFC4903].

   In addition to other interface types, VET nodes configure VET
   interfaces that view all other nodes on the VET link as single-hop
   neighbors.  VET nodes configure a separate VET interface for each
   distinct VET link to which they connect, and discover other EBRs on
   the link that can be used for forwarding packets to off-link
   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
   anchors.  Still other enterprises may have sufficient infrastructure
   trust basis (e.g., through proper deployment of filtering gateways at
   enterprise borders) and may not require nodes to implement such
   additional mechanisms.

   Finally, in enterprises with a centralized management structure
   (e.g., a corporate campus network), an enterprise mapping service and
   a synchronized set of EBGs can provide sufficient 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., MANETs), 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 any
   routing protocols over those interfaces.

   When an ER joins an enterprise, it first configures an IPv6 link-
   local address on each enterprise-interior interface and configures an
   IPv4 link-local address on each enterprise-interior interface that



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   requires an IPv4 link-local capability.  IPv6 link-local address
   generation mechanisms include Cryptographically Generated Addresses
   (CGAs) [RFC3972], IPv6 Privacy Addresses [RFC4941], StateLess Address
   AutoConfiguration (SLAAC) using EUI-64 interface identifiers
   [RFC4291] [RFC4862], etc.  The mechanisms specified in [RFC3927]
   provide an IPv4 link-local address generation capability.

   Next, the ER configures one or more RLOCs and engages in any routing
   protocols on its enterprise-interior interfaces.  The ER can
   configure RLOCs via explicit management, DHCP autoconfiguration,
   pseudo-random self-generation from a suitably large address pool, or
   through an alternate autoconfiguration mechanism.  The ER may
   optionally configure and assign a separate RLOC for each underlying
   interface, or it may configure only a single RLOC and assign it to a
   VET interface configured over the underlying interfaces (see Section
   4.2.1).  In the latter case, the ER can use the VET interface for
   link layer multiplexing and traffic engineering purposes as specified
   in Appendix B.

   Alternatively (or in addition), the ER can request RLOC prefix
   delegations via an automated prefix delegation exchange over an
   enterprise-interior interface and can assign the prefix(es) on
   enterprise-edge interfaces.  Note that in some cases, the same
   enterprise-edge interfaces may assign both RLOC and EID addresses if
   there is a means for source address selection.  In other cases (e.g.,
   for separation of security domains), RLOCs and EIDs must be assigned
   on separate sets of enterprise-edge interfaces.

   Self-generation of RLOCs for IPv6 can be from a large public or
   local-use IPv6 address range (e.g., IPv6 Unique Local Addresses
   [RFC4193]).  Self-generation of RLOCs for IPv4 can be from a large
   public or local-use IPv4 address range (e.g., [RFC1918]).  When self-
   generation is used alone, the ER must continuously monitor the RLOCs
   for uniqueness, e.g., by monitoring the enterprise-interior routing
   protocol.

   DHCP generation of RLOCs may require support from relays within the
   enterprise.  For DHCPv6, relays that do not already know the RLOC of
   a server within the enterprise forward requests to the
   'All_DHCP_Servers' site-scoped IPv6 multicast group [RFC3315].  For
   DHCPv4, relays that do not already know the RLOC of a server within
   the enterprise forward requests to the site-scoped IPv4 multicast
   group address 'All_DHCPv4_Servers', which should be set to
   239.255.2.1 unless an alternate multicast group for the site is
   known.  DHCPv4 servers that delegate RLOCs should therefore join the
   'All_DHCPv4_Servers' multicast group and service any DHCPv4 messages
   received for that group.




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

   In some enterprise use cases (e.g., MANETs), assignment of RLOCs on
   enterprise-interior interfaces as singleton addresses (i.e., as
   addresses with /32 prefix lengths for IPv4, or as addresses with /128
   prefix lengths for IPv6) may be necessary to avoid multi-link subnet
   issues.  In other use cases, assignment of an RLOC on a VET interface
   as specified in Appendix B can provide link layer multiplexing and
   traffic engineering over multiple underlying interfaces using only a
   single IP address.

4.2.  Enterprise Border Router (EBR) Autoconfiguration

   EBRs are ERs that configure VET interfaces over distinct sets of
   underlying interfaces belonging to the same enterprise; an EBR can
   connect to multiple enterprises, in which case it would configure
   multiple VET interfaces.  In addition to the ER autoconfiguration
   procedures specified in Section 4.1, EBRs perform the following
   autoconfiguration operations.

4.2.1.  VET Interface Initialization

   EBRs configure a VET interface over a set of underlying interfaces
   belonging to the same enterprise such that all other VET nodes in the
   enterprise appear as single-hop neighbors through the use of IP in IP
   encapsulation.  After the EBR configures a VET interface, it
   initializes the interface and assigns an IPv6 link-local address and
   an IPv4 link-local address if necessary.  The EBR also associates an
   RLOC obtained as specified in Section 4.1 with the VET interface to
   serve as the source address for outer IP packets.

   When IPv6 and IPv4 are used as the inner/outer protocols
   (respectively), the EBR autoconfigures an IPv6 link-local VET address
   on the VET interface to support packet forwarding and operation of
   the IPv6 neighbor discovery protocol.  The link-local VET address is
   formed exactly as specified in Sections 6.1 and 6.2 of [RFC5214].
   The link-local address need not be checked for uniqueness since the



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   IPv4 RLOC embedded in the address itself is managed for uniqueness
   (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.  However, link-local address
   configuration for other inner/outer IP protocol combinations may not
   be necessary if a non-link-local address can be configured through
   other means (e.g., administrative configuration, DHCP, etc.).

   After the EBR initializes a VET interface, it can communicate with
   other VET nodes as single-hop neighbors on the VET link from the
   viewpoint of the inner IP protocol.  The EBR can also configure the
   VET interface for link-layer multiplexing and traffic engineering
   purposes as specified in Appendix B.

4.2.2.  PRL Discovery and Enterprise Identification

   Following VET interface initialization, the EBR next discovers a
   Potential Router List (PRL) used to track the RLOC addresses of EBGs.
   The PRL can be discovered through information conveyed in the
   enterprise-interior routing protocol, through the mechanisms outlined
   in Section 8.3.2 of [RFC5214], through a DHCP option
   [I-D.templin-isatap-dhcp], etc.  In multicast-capable enterprises,
   EBRs can also listen for advertisements on the 'rasadv' [RASADV]
   multicast group address.

   Whether or not routing information is available, the EBR can discover
   the list of EBGs by resolving an identifying name 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, the DHCP Domain Name option [RFC2132], 'rasadv'
   protocol advertisements, link-layer information (e.g., an IEEE 802.11
   Service Set Identifier (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 "isatapv2" and sets the 'domainname'
   component to the enterprise-specific DNS suffix "example.com" (e.g.,
   as "isatapv2.example.com").  Note that this naming convention is
   intentionally distinct from the convention specified in [RFC5214],
   and is used by the EBR to distinguish between ISATAP and VET virtual
   interfaces.

   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



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   routing core is "isatapv2.net".  Isolated enterprise networks that do
   not connect to the outside world may have no enterprise-specific DNS
   suffix.  In that case, the 'PRLNAME' consists only of the 'hostname'
   component (e.g., "isatapv2").

   After discovering 'PRLNAME', the EBR resolves the name into a list of
   RLOC addresses through a name service lookup.  For centrally managed
   enterprises, the EBR resolves 'PRLNAME' using an enterprise-local
   name service (e.g., the DNS).  For enterprises with a distributed
   management structure, the EBR resolves 'PRLNAME' using Link-Local
   Multicast Name Resolution (LLMNR) [RFC4795] 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.

   Each distinct enterprise must have a unique identity that EBRs can
   use to uniquely discern their enterprise affiliations.  'PRLNAME' as
   well as the RLOCs of EBGs in the PRL serve as an identifier for the
   enterprise.

4.2.3.  Provider-Aggregated (PA) EID Prefix Autoconfiguration

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

   For IPv4 EIDs, the EBR acquires prefixes via an automated IPv4 prefix
   delegation exchange, explicit management, etc.

   For IPv6 EIDs, the EBR acquires prefixes via DHCPv6 Prefix Delegation
   exchanges.  In particular, the EBR (acting as a requesting router)
   can use DHCPv6 prefix delegation [RFC3633] over the VET interface to
   obtain IPv6 EID prefixes from the server (acting as a delegating
   router).

   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 an 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 also propose a specific prefix to the DHCPv6 server per
   Section 7 of [RFC3633].  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.




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   After the EBR receives PA prefix delegations, it can provision the
   prefixes on enterprise-edge interfaces as well as on other VET
   interfaces for which it is configured as an EBG.  It can also
   provision the prefixes on enterprise-interior interfaces to service
   any hosts attached to the link.

   The PA prefix delegations remain active 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,
   power failure, etc.).

4.2.4.  Provider-Independent (PI) EID Prefix Autoconfiguration

   Independent of any PA prefixes, EBRs can acquire and use Provider-
   Independent (PI) EID prefixes that are self-configured (e.g., using
   [RFC4193], etc.) and/or delegated by a registration authority (e.g.,
   through a regional Internet registry, through a different provider,
   through a centrally-assigned unique local address delegation
   authority [I-D.hain-ipv6-ulac], etc.).  When an EBR acquires a PI
   prefix, it must also obtain credentials that it can use to prove
   ownership when it registers the prefixes (see Section 5.3 and
   Section 5.3.6).

   After the EBR receives PI prefix delegations, it can provision the
   prefixes on enterprise-edge interfaces as well as on other VET
   interfaces for which it is configured as an EBG.  It can also
   provision the prefixes on enterprise-interior interfaces to service
   any hosts attached to the link.

   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 provider networks via
   provider-edge interfaces and/or via VET interfaces configured over
   parent enterprises.  EBGs autoconfigure their provider-edge
   interfaces in a manner that is specific to the provider connections,
   and they autoconfigure their VET interfaces that were configured over
   parent enterprises using the EBR autoconfiguration procedures
   specified in Section 4.2.

   For each of its VET interfaces configured over a child enterprise,
   the EBG initializes the interface the same as for an ordinary EBR
   (see Section 4.2.1).  It must then arrange to add one or more of its



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   RLOCs associated with the child enterprise to the PRL as specified in
   [RFC5214], Section 9.  In particular, for each VET interface
   configured over a child enterprise the EBG adds the RLOCs to name
   service resource records for 'PRLNAME' ("isatapv2.example.com", by
   default).

   EBGs respond to LLMNR queries for 'PRLNAME' on VET interfaces
   configured over child enterprises with a distributed management
   structure.

   EBGs configure a DHCP relay/server on VET interfaces configured over
   child enterprises that require DHCP services.

   To avoid looping, EBGs must not configure a default route on a VET
   interface configured over a child interface.

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 initialization and border gateway discovery
   procedures as specified for EBRs in Section 4.2.1, but they configure
   their VET interfaces as host interfaces (and not router interfaces).
   Note also that a node may be configured as a host on some VET
   interfaces and as an EBR/EBG on other VET interfaces.

   VET hosts perform address autoconfiguration on VET interfaces
   according to [RFC4862].  When a VET host generates a VET address, it
   first creates an interface identifier that embeds its IPv4 RLOC
   address as specified in Section 6.1 of [RFC5214].  The host then
   configures IPv6 unicast VET addresses from advertised on-link
   prefixes received in RA messages and assigns them to the VET
   interface, i.e., it does not perform Duplicate Address Detection
   (DAD) on the addresses since the embedded IPv4 RLOC address already
   provides uniqueness.


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.







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5.1.  Routing Protocol Participation

   ERs engage in any intra-enterpise routing protocols over enterprise-
   interior interfaces to discover routing information for forwarding IP
   packets with RLOC addresses.  EBRs can additionally engage in any
   inter-enterprise routing protocols over VET, enterprise-edge and
   provider-edge interfaces to discover routing information for
   forwarding IP packets with EID addresses.  Note that the EID-based
   inter-enterprise IP routing domains are separate and distinct from
   any RLOC-based enterprise interior IP routing domains.

   EBRs use the list of EBGs in the PRL (see: Section 4.2.2) as an
   initial list of neighbors for inter-enterprise routing protocol
   participation.  Routing protocol participation on non-multicast VET
   interfaces uses the NBMA model, e.g., in the same manner as for OSPF
   over NBMA interfaces [RFC5340].

5.2.  Address Selection

   When permitted by policy and supported by enterprise interior
   routing, end systems can avoid VET interface encapsulation through
   communications that directly invoke the outer IP protocol using RLOC
   addresses instead of EID addresses for end-to-end communications.
   For example, an enterprise that provides native IPv4 internal network
   services can provide continued support for native IPv4 communications
   even when encapsulated IPv6 services are available for inter-
   enterprise communications.  In other enterprise scenarios, the use of
   EID-based communications (i.e., instead of RLOC-based communications)
   may be necessary and/or beneficial to support address scaling, NAT
   avoidance, security domain separation, site multihoming, traffic
   engineering, etc. .

   End systems can use source address selection rules to determine
   whether to use EID-based or RLOC-based addressing based on, e.g.,
   name service information.  The remainder of this section discusses
   internetworking operation for EID-based communications using the VET
   interface abstraction.

5.3.  VET interface Neighbor Discovery

   The following sections discuss IPv6 Neighbor Discovery (ND)
   considerations for VET interfaces for the case of IPv6 as the inner
   IP protocol and IPv4 as the outer IP protocol (ND considerations for
   other protocol combinations are out of scope).  Depending on the
   enterprise network trust basis, VET nodes may be required to use
   mechanisms such as SEND to secure their ND exchanges.





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5.3.1.  Router and Prefix Discovery

5.3.1.1.  EBR Specification

   EBRs discover the PRL for each VET interface as specified in
   Section 4.2.2, and participate in a dynamic routing protocol over the
   VET interface using the EBG addresses in the PRL as addresses of
   potential neighboring routers.  When a dynamic routing protocol
   cannot be used, EBRs instead send RS messages to receive solicited
   RAs from each EBG in the PRL.  (Note that this will cause the EBG to
   set the 'IsRouter' flag in the neighbor cache entry for this EBR to
   FALSE - see: [RFC4861], Appendix D.)  When the EBR receives a
   solicited RA from an EBG (see Section 5.3.1.2), it authenticates the
   message then processes any autoconfiguration information.  (Note
   however that the EBR should not configure prefixes received in Prefix
   Information Options (PIOs) on its VET interfaces if it will have EID
   addresses and prefixes configured on any of its other interfaces.
   This prevents the EBR from sending packets directly to VET hosts
   without first going through a default router, since VET hosts will
   only accept routed packets that come through a PRL router.)

   Next, the EBR creates RA messages to send to each EBG in the PRL.
   The EBR includes Route Information Options (RIOs) [RFC4191] that
   contain its EID prefixes in each RA, but it MUST NOT include any
   other autoconfiguration parameters (e.g., non-zero Router Lifetime,
   Prefix Information Options (PIOs), etc.)  The EBR also
   unconditionally sets the 'M' bit to 0 and the 'O' bit to 1 in order
   to avoid conflicting with the information included in RA messages
   from EBGs (see: Section 5.3.1.2).  The EBR also includes an RLOC for
   the EBG as the outer IP destination address and includes the IPv6
   link-local "All Routers Multicast" address as the inner IP
   destination address [RFC4291] of the RA.

   The EBR next creates a CGA or IPv6 privacy link-local address and
   includes it as the inner IP source address of the RA.  When CGAs are
   used, the EBR additionally includes SEND credentials plus any router
   certificates needed to prove its ownership of the prefixes in its
   Route Information Options (RIOs).  Note that the CGA/privacy link-
   local address is used only as the inner source address of unsolicited
   RA messages, and therefore need not be checked for uniqueness on the
   link.  The EBR finally includes the RLOC assigned to an underlying
   interface as the outer source address of the RA.

   If the EBR has multiple RLOC addresses assigned to underlying
   interfaces, it can either send multiple RA messages to each EBG (each
   with a different RLOC) or send a single RA message that includes
   multiple Source Link Layer Address Options (SLLAOs) formatted using a
   modified version of the form specified in Section 5 of [RFC2529] as



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   shown in Figure 2:

   +-------+-------+-------+-------+-------+-------+-------+-------+
   | Type  |Length |    Reserved   |       IPv4 RLOC Address       |
   +-------+-------+-------+-------+-------+-------+-------+-------+

              Figure 2: VET Link-Layer Address Option Format

   Each SLLAO contains the IPv4 RLOC of an underlying interface.  The
   SLLAOs are arranged in order from lowest to highest priority (i.e.,
   the first SLLAO contains the lowest priority RLOC and the final SLLAO
   option contains the highest priority).

   The EBR then sends the RA message(s) to the EBG and must thereafter
   periodically send new RA messages to refresh prefix lifetimes, where
   an RA interval of 120 seconds is recommended.  Each EBG that receives
   an EBR's RA will in turn relay a proxied version of the RA to EBGs on
   their parent enterprises.  This procedure has a direct analogy in the
   Teredo method of maintaining state in network middleboxes through the
   periodic transmission of "bubbles" [RFC4380].

5.3.1.2.  EBG Specification

   EBGs follow the router and prefix discovery procedures specified in
   Section 8.2 of [RFC5214].  When an EBG receives an RS message, it
   first authenticates the message.  If the VET interface maintains a
   neighbor cache, the EBG next creates or updates a neighbor cache
   entry for the VET link-local source address corresponding to the
   outer IP source address of the solicitation according to Section
   6.2.6 of [RFC4861].  If the neighbor cache entry cannot be created or
   updated (e.g., due to insufficient resources), the EBG silently
   discards the solicitation and does not send an RA.  Otherwise, the
   EBG creates/updates the neighbor cache entry, sets a "Time To Live
   (TTL)" on the entry that is no shorter than any of its advertised
   router or prefix lifetimes, and sends an RA response to the
   solicitation.  If the neighbor cache entry TTL subsequently expires
   before a new solicitation arrives, the EBG deletes the neighbor cache
   entry.  Note that if the VET interface does not maintain a neighbor
   cache, the EBG simply omits these neighbor cache manipulations.

   The EBG then prepares the RA response to the solicitation that
   includes Router Lifetimes, PIOs, and any other options/parameters
   that the EBG is configured to include.  The EBG unconditionally sets
   the 'M' bit to 0 and the 'O' bit to 1.  Next, the EBG includes SEND
   parameters if necessary and sets the inner and outer IP source and
   destination addresses.  The EBG sets the inner IP source address to
   either a CGA address (i.e., if SEND is used) or a VET link-local
   source address that embeds one of the EBG's RLOC addresses, then sets



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   the outer IP source address to one of its RLOC address.  The EBG next
   sets the inner IP source address to a VET link-local address that
   embeds the EBR's RLOC addresses, then sets the outer IP destination
   address to the EBR's RLOC address.  Finally, the EBG sends the
   solicited RA to the VET node that sent the solicitation.

   In addition to RS messages, the EBG will receive RA messages sent by
   EBRs as specified in Section 5.3.1.1.  When an EBG receives the RA,
   it first authenticates the message; if the authentication fails, the
   EBG discards the RA.  Otherwise, the EBG uses any EID prefixes in
   PIOs with their respective lifetimes to updates its Forwarding
   Information Base (FIB).  The EBG also caches each RLOC received in
   SLLAO options in the RA message as equivalent neighbors associated
   with the FIB entries, i.e., each FIB entry may include multiple
   potential next-hops.  Finally, the EBG caches the RA message as
   ancillary data attached to the FIB entries so that the message can be
   replayed in the future to support router-to-router redirects (see:
   Section 5.3.3).

   After the EBG authenticates the RA and updates its FIB, 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 recurses in this fashion and ends when an EBR
   attached to an interdomain routing core is reached.

5.3.1.3.  VET Host Specification

   VET hosts follow the router and prefix discovery procedures specified
   in [RFC5214], Section 8.3.  They discover the addresses of EBGs for
   each VET interface as specified in Section 4.2.2, and send an RS
   message to each EBG in order to receive RAs with autoconfiguration
   information.

   When the VET host receives a solicited RA from an EBG, it
   authenticates the message then performs autoconfiguration the same as
   for any link (see also: Section 4.4).  When the VET host receives an
   unsolicited RA from an EBR, it authenticates the message then
   processes any RIOs in order to update its FIB.

5.3.2.  Next Hop Determination

   VET nodes perform next-hop determination via longest prefix match the
   same as for any IPv6 interface and sends packets according to the



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   most-specific matching entry in the FIB, i.e., even if the most
   specific FIB entry is "default".  When there is no matching entry in
   the FIB (i.e., not even "default"), VET nodes can discover next-hop
   EBRs within the enterprise by querying the name service for the /56
   IPv6 EID prefix taken from a packet's destination address (or, by
   some other inner-IP to outer-IP address mapping mechanism).  For
   example, for the IPv6 destination address '2001:DB8:1:2::1' and
   'PRLNAME' "isatapv2.example.com" the VET node can lookup the domain
   name:
   '0.0.1.0.0.0.8.b.d.0.1.0.0.2.ip6.isatapv2.example.com'.

   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
   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.

   If the name-service lookup succeeds, it will return RLOC addresses
   (e.g., in DNS A records) that correspond to next-hop EBRs to which
   the VET node can forward packets.

5.3.3.  Redirect Function

   In enterprises with a stable and highly-available set of EBGs, the
   VET node can simply forward initial packets via a default route to an
   EBG.  The EBG will forward the packet and return an ICMPv6 Redirect
   as specified in Section 8 of [RFC4861] if the next-hop corresponds to
   a node on the same VET interface.  If the source address of the
   packet causing the redirect is on-link on the VET interface, the EBG
   returns an ordinary "router-to-host" redirect with the source address
   of the packet as its destination.  When a VET host receives the
   redirect, it processes the message exactly as specified in Section 8
   of [RFC4861].

   If the source address of the packet causing the redirect is not on-
   link, the EBG instead prepares a "router-to-router" redirect with the
   link-local VET address of the EBR that sent the packet as its
   destination and with the destination address of the original packet
   as the redirected destination.  If the destination address is on-
   link, the EBG sets the address of the VET host as the redirected
   target, includes the header of the redirected packet, and returns the
   redirect to the EBR that sent the packet.



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   If the destination is not on link, however, the EBG sets the link-
   local address of the next-hop toward the destination as the
   redirected target.  The EBG then includes in the redirect a Route
   Information Option (RIO) (i.e., the same as described for RA messages
   in [RFC4191]) that includes the routing information from the EBG's
   forwarding tables corresponding to the prefix that covers the
   packet's destination address.  The EBG may also include in the
   redirect one or more IPv6 Target Link Layer Address Options (TLLAOs)
   formatted using the form shown in Figure 2.  Each TLLAO contains the
   IPv4 RLOC of a potential next-hop EBR interface that can provide
   forwarding services toward the redirected destination.  The TLLAOs
   are arranged in order from lowest to highest priority (i.e., the
   first TLLAO contains the lowest priority RLOC and the final TLLAO
   option contains the highest priority).  Finally, the EBG includes the
   header of the redirected packet and returns the redirect to the EBR
   that sent the packet.

   When the EBR receives the "router-to-router" redirect, it caches the
   addresses included in the redirected target and TLLAO options in its
   neighbor cache for use as RLOCs associated with the redirected
   destination.  The EBR then creates a FIB entry using the prefix
   information in the RIO option.  The EBR then "replays" the cached RA
   message associated with the FIB entry corresponding to the packet's
   source address by proxying the message with the RLOC address from the
   redirected target as its outer IP destination address.  This proxying
   process is otherwise the same as specified in Section 5.3.1.2.  When
   a next-hop VET node receives the replayed RA, it authenticates the
   message (e.g., using SEND credentials) then installs any prefixes in
   RIOs in its FIB.

   VET nodes retain the FIB entries created as a result of receipt of an
   ICMP redirect until the route lifetimes expire, or until no hints of
   forward progress through any of the FIB entry's associated RLOCs are
   received.  In this way, RLOC liveness detection exactly parallels
   IPv6 Neighbor Unreachability Detection ([RFC4861], Section 7).

5.3.4.  Neighbor Unreachability Detection

   VET nodes use their neighbor cache for Neighbor Unreachability
   Detection (NUD) the same as for any IPv6 link as described in Section
   7 of [RFC4861].  When a neighbor fails (or appears to be failing),
   FIB entries are updated to select a different next-hop when there are
   multiple next-hops available.

   The NUD mechanism uses hints of forward progress (i.e., evidence that
   the tunnel neighbor is receiving packets) coupled with the Neighbor
   Solicitation/Advertisement (NS/NA) process.  When hints of forward
   progress are available, NS/NA messaging is suppressed; when no hints



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   are available, NS/NA messages are used in the normal fashion the same
   as for any IPv6 link.  The SEAL mechanism includes an explicit data
   packet acknowledgement mechanism that can provide hints of forward
   progress.

   Responsiveness to routing changes is directly related to the
   "REACHABLE_TIME" constant used for NUD as specified in [RFC4861].  In
   order to provide responsiveness comparable to dynamic routing
   protocols, a reasonably short "REACHABLE_TIME" value (e.g., 5sec)
   should be used.

5.3.5.  Reverse Path Forwarding Checks

   VET nodes determine whether a packet received on a VET interface can
   be accepted based on an ingress filtering check [RFC3704].  The VET
   node determines the previous hop router for a received packet by
   constructing a VET link-local address that embeds the outer IPv4
   source address.  It then examines its FIB to determine whether there
   is an entry that matches the inner IPv6 source address and that has
   the VET link-local address as the next hop.  If such a FIB entry
   exists, the VET host accepts the packet; otherwise, it discards the
   packet.

5.3.6.  IPv4 Neighbor Discovery

   When IPv4 is used as the inner IP protocol, router discovery and
   prefix registration exactly parallel the mechanisms specified for
   IPv6 in Section 5.3.  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 'ip4.isatapv2.example.com' domain.  For
   example, the IPv4 prefix 192.0.2/24 would be represented as:
   '2.0.0.0.0.c.ip4.isatapv2.example.com'

5.4.  Generating Errors

   When an EBR receives an IPv6 packet over a VET interface and there is
   no matching ingress filter entry, it drops the packet and returns an
   ICMPv6 [RFC4443] "Destination Unreachable; Reject route to
   destination" message to the previous-hop EBR subject to rate
   limiting.

   When an EBR receives an IPv6 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.



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   When an EBR receives an IPv6 packet over a VET interface and the
   longest-prefix-match FIB entry for the destination is via a next-hop
   configured over the same VET interface the packet arrived on, the EBR
   forwards the packet.  If the FIB prefix is longer than ::/0, the EBR
   then sends a router-to-router ICMPv6 Redirect message (using SEND, if
   necessary) to the previous-hop EBR as specified in Section 5.3.3.

   Generation of other ICMP messages [RFC0792] [RFC4443] is the same as
   for any IP interface.

5.5.  Processing Errors

   When a VET node receives an ICMPv6 "Destination Unreachable; Reject
   route to destination" message, and there is a longest-prefix-match
   FIB entry for the original packet's destination that is more specific
   than ::/0, the node discards the message and marks the FIB entry for
   the destination as "forwarding suspended" for the RLOC taken from the
   source address of the ICMPv6 message.  The node should then allow
   subsequent packets to flow through different RLOCs associated with
   the FIB entry.  If the node receives excessive ICMPv6 reject route to
   destination messages through multiple RLOCs 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, it forwards the ICMPv6 message to the source
   of the original packet as normal.  If the node has a longest-prefix-
   match FIB entry for the original packet's destination that is more
   specific than ::/0, the node also deletes the FIB entry.

   When a VET node receives an authentic ICMPv6 Redirect, it processes
   the packet as specified in Section 5.3.3.

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





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5.6.  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 mobility 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 (preferably) withdraw the prefixes from old EBGs prior to
   departure.  Prefix registration with new EBGs is coordinated exactly
   as specified in Section 4.2.4; prefix withdrawal 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
   additional RAs to refresh lifetimes before they expire.  (EBRs should
   place conservative limits on the RAs they send to reduce congestion,
   however.)

   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" 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.

   The EBGs of a multihomed 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).






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5.7.  Multicast

   In multicast-capable deployments, ERs provide an enterprise-wide
   multicasting service (e.g., Simplified Multicast Forwarding (SMF)
   [I-D.ietf-manet-smf], Protocol Independent Multicast (PIM) routing,
   Distance Vector Multicast Routing Protocol (DVMRP) routing, etc.)
   over their enterprise-interior interfaces such that outer IP
   multicast messages of site-scope 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 multicast address space.  In that case, operation of
   link-scoped (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 flooding.

   VET nodes encapsulate inner IP multicast messages sent over the VET
   interface in any mid-layer headers (e.g., SEAL, IPsec, etc.) followed
   by 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 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 mapping,
   the VET interface acts as a virtual outer IP multicast host connected
   to its underlying interfaces.  When the VET interface detects that an
   inner IP multicast group joins or leaves, it forwards corresponding
   outer IP multicast group membership reports on an underlying
   interface over which the VET interface is configured.  If the VET
   node is configured as an outer IP multicast router on the underlying
   interfaces, the VET interface forwards locally looped-back group
   membership reports to the outer IP multicast routing process.  If the
   VET node is configured as a simple outer IP multicast host, the VET
   interface instead forwards actual group membership reports (e.g.,
   IGMP messages) directly over an underlying interface.

   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 underlying interfaces for one
   VET interface do not "leak out" to the underlying interfaces of
   another VET interface.  This is accommodated through normal site-



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   scoped outer IP multicast group filtering at enterprise boundaries.

5.8.  Service Discovery

   VET nodes can perform enterprise-wide service discovery using a
   suitable name-to-address resolution service.  Examples of flooding-
   based services include the use of LLMNR [RFC4795] over the VET
   interface or multicast DNS (mDNS) [I-D.cheshire-dnsext-multicastdns]
   over an underlying interface.  More scalable and efficient service
   discovery mechanisms are for further study.

5.9.  Enterprise Partitioning

   An enterprise can be partitioned into multiple distinct logical
   groupings.  In that case, each partition must configure its own
   distinct 'PRLNAME' (e.g., 'isatapv2.zone1.example.com',
   'isatapv2.zone2.example.com', etc.).

   EBGs can further create multiple IP subnets within a partition by
   sending RAs with PIOs containing different IPv6 prefixes to different
   groups of nodes.  EBGs can identify subnets, e.g., by examining RLOC
   prefixes, observing the enterprise interior interfaces over which RSs
   are received, etc.

5.10.  EBG Prefix State Recovery

   EBGs must retain explicit state that tracks the inner IP PA prefixes
   delegated to EBRs within the enterprise, e.g., so that packets are
   delivered to the correct EBRs.  When an EBG loses some or all of its
   state (e.g., due to a power failure), it must recover the state so
   that packets can be forwarded over correct routes.

5.11.  Support for Legacy ISATAP Services

   EBGs support legacy ISATAP services according to the specifications
   in [RFC5214].  In particular, EBGs can configure legacy ISATAP
   interfaces and VET interfaces over the same sets of underlying
   interface as long as the PRLs and IPv6 prefixes associated with the
   ISATAP/VET interfaces are distinct.

5.12.  SEAL Encapsulation

   When SEAL is used, the VET interface encapsulates the inner IP packet
   in any mid-layer headers (e.g., IPsec [RFC4301]) followed a SEAL
   header [I-D.templin-intarea-seal] followed by an outer IP header; it
   next submits the encapsulated packet to the outer IP forwarding
   engine for transmission on an underlying interface.




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   VET interfaces can use SEAL encapsulation to accommodate path MTU
   diversity, to defeat source address spoofing, and to enable sub-IP
   layer hints of forward progress that can be piggybacked on ordinary
   data messages.  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 receives
   an authentic neighbor discovery message from another VET node, it can
   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 or a
   SEAL error message, it can confirm that the packet-in-error within
   the 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
   window.  (Note that for IPv6 in IPv4 encapsulation packets with a
   link-local IPv6 destination address are excluded from this check to
   support operation of the neighbor discovery protocol.)

   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.  (Note that this is a mid-layer
   reachability confirmation, and not an L2 reachability indication.)
   Setting the "Acknowledgement Requested" bit is also used as the
   method for maintaining the window of outstanding SEAL_IDs.


6.  IANA Considerations

   There are no IANA considerations for this document.


7.  Security Considerations

   Security considerations for MANETs are found in [RFC2501].

   The security considerations found in [RFC2529] [RFC5214]
   [I-D.nakibly-v6ops-tunnel-loops] also apply to VET.  In particular:

   o  VET nodes must ensure that a VET interface does not span multiple
      sites as specified in Section 6.2 of [RFC5214].

   o  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; for the case of IPv6 in IPv4 encapsulation, this is
      accommodated using the procedures specified in Section 7.3 of



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      [RFC5214].

   o  EBRs must implement both inner and outer IP ingress filtering in a
      manner that is consistent with [RFC2827] as well as ip-proto-41
      filtering.  When the node at the physical boundary of the
      enterprise is an ordinary ER (i.e., and not an EBR), the ER itself
      should implement filtering.

   Additionally, VET interfaces that use IPv6 in IPv4 encapsulation and
   that maintain a coherent neighbor cache drop all outbound packet for
   which the IPv6 next hop is not a neighbor and the IPv6 source address
   is not link-local; they also drop all incoming packets for which the
   IPv6 previous hop is not a neighbor and the IPv6 destination address
   is not link-local.  (Here, the previous hop is determined by
   examining the IPv4 source address.)

   Finally, VET interfaces that use IPv6 in IPv4 encapsulation drop all
   outbound packets for which the IPv6 source address is "foreign-
   prefix::0200:5efe:V4ADDR" and drop all incoming packets for which the
   IPv6 destination address is "foreign-prefix::0200:5efe:V4ADDR" .
   (Here, "foreign-prefix" is an IPv6 prefix that is not assigned to the
   VET interface, and "V4ADDR" is a public IPv4 address over which the
   VET interface is configured.)  Note that these checks are only
   required for VET interfaces that cannot maintain a coherent neighbor
   cache.

   SEND [RFC3971] and/or IPsec [RFC4301] can be used in environments
   where attacks on the neighbor discovery protocol are possible.  SEAL
   [I-D.templin-intarea-seal] provides a per-packet identification that
   can be used to detect source address spoofing.

   Rogue neighbor discovery messages with spoofed RLOC source addresses
   can consume network resources and cause VET nodes to perform extra
   work.  Nonetheless, VET nodes should not "blacklist" such RLOCs, as
   that may result in a denial of service to the RLOCs' 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



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   CECOM MOSAIC program.

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

   Security concerns pertaining to tunneling mechanisms are discussed in
   [I-D.ietf-v6ops-tunnel-security-concerns].

   Default router and prefix information options for DHCPv6 are
   discussed in [I-D.droms-dhc-dhcpv6-default-router].

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

   RLOC prefix delegation for enterprise-edge interfaces is discussed in
   [I-D.clausen-manet-autoconf-recommendations].

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

   Various proposals within the IETF have suggested similar mechanisms.


9.  Acknowledgements

   The following individuals gave direct and/or indirect input that was
   essential to the work: Jari Arkko, Teco Boot, Emmanuel Bacelli, James
   Bound, Scott Brim, Brian Carpenter, Thomas Clausen, Claudiu Danilov,
   Chris Dearlove, Gert Doering, Ralph Droms, Washam Fan, Dino
   Farinacci, Vince Fuller, Thomas Goff, David Green, Joel Halpern, Bob
   Hinden, Sascha Hlusiak, Sapumal Jayatissa, Dan Jen, Darrel Lewis,
   Tony Li, Joe Macker, David Meyer, Gabi Nakibly, Thomas Narten, Pekka
   Nikander, Dave Oran, Alexandru Petrescu, Mark Smith, John Spence,
   Jinmei Tatuya, Dave Thaler, Ole Troan, Michaela Vanderveen, James
   Woodyatt, 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 (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



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   of the document.

   Jim Bound's foundational work on enterprise networks provided
   significant guidance for this effort.  We mourn his loss and honor
   his contributions.


11.  References

11.1.  Normative References

   [I-D.templin-intarea-seal]
              Templin, F., "The Subnetwork Encapsulation and Adaptation
              Layer (SEAL)", draft-templin-intarea-seal-08 (work in
              progress), January 2010.

   [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.

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

   [RFC2827]  Ferguson, P. and D. Senie, "Network Ingress Filtering:
              Defeating Denial of Service Attacks which employ IP Source
              Address Spoofing", BCP 38, RFC 2827, May 2000.

   [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,



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              "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.

11.2.  Informative References

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

   [I-D.cheshire-dnsext-multicastdns]
              Cheshire, S. and M. Krochmal, "Multicast DNS",
              draft-cheshire-dnsext-multicastdns-08 (work in progress),
              September 2009.

   [I-D.clausen-manet-autoconf-recommendations]
              Clausen, T. and U. Herberg, "MANET Router Configuration
              Recommendations",
              draft-clausen-manet-autoconf-recommendations-00 (work in



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              progress), February 2009.

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

   [I-D.droms-dhc-dhcpv6-default-router]
              Droms, R. and T. Narten, "Default Router and Prefix
              Advertisement Options for DHCPv6",
              draft-droms-dhc-dhcpv6-default-router-00 (work in
              progress), March 2009.

   [I-D.hain-ipv6-ulac]
              Hain, T., Hinden, R., and G. Huston, "Centrally Assigned
              IPv6 Unicast Unique Local Address Prefixes",
              draft-hain-ipv6-ulac-01 (work in progress), October 2009.

   [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-csi-proxy-send]
              Krishnan, S., Laganier, J., and M. Bonola, "Secure Proxy
              ND Support for SEND", draft-ietf-csi-proxy-send-01 (work
              in progress), July 2009.

   [I-D.ietf-dhc-dhcpv6-agentopt-delegate]
              Droms, R., Volz, B., and O. Troan, "DHCPv6 Relay Agent
              Assignment Notification (RAAN) Option",
              draft-ietf-dhc-dhcpv6-agentopt-delegate-04 (work in
              progress), July 2009.

   [I-D.ietf-dhc-subnet-alloc]
              Johnson, R., Kumarasamy, J., Kinnear, K., and M. Stapp,
              "Subnet Allocation Option", draft-ietf-dhc-subnet-alloc-10
              (work in progress), November 2009.

   [I-D.ietf-manet-smf]
              Macker, J. and S. Team, "Simplified Multicast Forwarding",
              draft-ietf-manet-smf-09 (work in progress), July 2009.

   [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.



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   [I-D.jen-apt]
              Jen, D., Meisel, M., Massey, D., Wang, L., Zhang, B., and
              L. Zhang, "APT: A Practical Transit Mapping Service",
              draft-jen-apt-01 (work in progress), November 2007.

   [I-D.nakibly-v6ops-tunnel-loops]
              Nakibly, G., "Routing Loops using ISATAP and 6to4: Problem
              Statement and Proposed Solutions",
              draft-nakibly-v6ops-tunnel-loops-00 (work in progress),
              October 2009.

   [I-D.russert-rangers]
              Russert, S., Fleischman, E., and F. Templin, "RANGER
              Scenarios", draft-russert-rangers-01 (work in progress),
              September 2009.

   [I-D.templin-isatap-dhcp]
              Templin, F., "Dynamic Host Configuration Protocol (DHCPv4)
              Option for the Intra-Site Automatic Tunnel Addressing
              Protocol (ISATAP)", draft-templin-isatap-dhcp-06 (work in
              progress), December 2009.

   [I-D.templin-ranger]
              Templin, F., "Routing and Addressing in Next-Generation
              EnteRprises (RANGER)", draft-templin-ranger-09 (work in
              progress), October 2009.

   [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



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              Addressing (ENCAPS) for IPNG", RFC 1955, June 1996.

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

   [RFC2491]  Armitage, G., Schulter, P., Jork, M., and G. Harter, "IPv6
              over Non-Broadcast Multiple Access (NBMA) networks",
              RFC 2491, January 1999.

   [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",
              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



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              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.

   [RFC4795]  Aboba, B., Thaler, D., and L. Esibov, "Link-local
              Multicast Name Resolution (LLMNR)", RFC 4795,
              January 2007.

   [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.

   [RFC5340]  Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
              for IPv6", RFC 5340, July 2008.


Appendix A.  Duplicate Address Detection (DAD) Considerations

   A priori uniqueness determination (also known as "pre-service DAD")
   for an RLOC assigned on an enterprise-interior interface would
   require 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 RLOCs 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 RLOCs can be generated with mechanisms such as
   CGAs, IPv6 privacy addresses, etc. with very small probability of
   collision.  Pseudo-random IPv4 RLOCs 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
   RLOCs assigned on an ER's enterprise-interior interfaces.  Still, an



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   RLOC delegation authority should be used when available, while a
   passive in-service DAD mechanism should be used to detect RLOC
   duplications when there is no RLOC delegation authority.


Appendix B.  Link-Layer Multiplexing and Traffic Engineering

   For each distinct enterprise that it connects to, an EBR configures a
   VET interface over possibly multiple underlying interfaces that all
   connect to the same enterprise.  The VET interface therefore
   represents the EBR's logical point of attachment to the enterprise,
   and provides a logical interface for link-layer multiplexing over its
   underlying interfaces as described in Section 3.3.4.1 of [RFC1122]:

      "Finally, we note another possibility that is NOT multihoming: one
      logical interface may be bound to multiple physical interfaces, in
      order to increase the reliability or throughput between directly
      connected machines by providing alternative physical paths between
      them.  For instance, two systems might be connected by multiple
      point-to-point links.  We call this "link-layer multiplexing".
      With link-layer multiplexing, the protocols above the link layer
      are unaware that multiple physical interfaces are present; the
      link-layer device driver is responsible for multiplexing and
      routing packets across the physical interfaces."

   EBRs can support such a link-layer multiplexing capability across the
   enterprise in accordance with the Weak End System Model (see Section
   3.3.4.2 of [RFC1122]).  In particular, when an EBR autoconfigures an
   RLOC address (see Section 4.1), it can associate it with the VET
   interface only instead of assigning it to an underlying interface.
   The EBR therefore only needs to obtain a single RLOC address even if
   there are multiple underlying interfaces, i.e., it does not need to
   obtain one for each underlying interface.  The EBR can then leave the
   underlying interfaces unnumbered, or it can configure a randomly
   chosen IP link-local address (e.g., from the prefix 169.254/16
   [RFC3927] for IPv4) on underlying interfaces that require a
   configuration.  The EBR need not check these link-local addresses for
   uniqueness within the enterprise, as they will not normally be used
   as the source address for packets.

   When the EBR engages in the enterprise-interior routing protocol, it
   uses the RLOC address assigned to the VET interface as the source
   address for all routing protocol control messages, however it must
   also supply an interface identifier (e.g., a small integer) that
   uniquely identifies the underlying interface that the control message
   is sent over.  For example, if the underlying interfaces are known as
   "eth0", "eth1" and "eth7" the EBR can supply the token "7" when it
   sends a routing protocol control message over the "eth7" interface.



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   This is necessary to ensure that other routers can determine the
   specific interface over which the EBR's routing protocol control
   message was sent, but the token need only be unique within the EBR
   itself and need not be unique throughout the enterprise.

   When the EBR discovers an RLOC route via the enterprise interior
   routing protocol, it configures a preferred route in the IP FIB that
   points to the VET interface instead of the underlying interface.  At
   the same time, the EBR also configures an ancillary route that points
   to the underlying interface.  If the EBR discovers that the same RLOC
   route is reachable via multiple underlying interfaces, it configures
   multiple ancillary routes (i.e., one for each interface).  If the EBR
   discovers that the RLOC route is no longer reachable via any
   underlying interface, it removes the route in the IP FIB that points
   to the VET interface.

   With these arrangements, all locally-generated packets with RLOC
   destinations will flow through the VET interface (and thereby use the
   VET interface's RLOC address as the source address) instead of
   through the underlying interfaces.  In the same fashion, all
   forwarded packets with RLOC destinations will flow through the VET
   interface instead of through the underlying interfaces.

   This arrangement has several operational advantages that enable a
   number of traffic engineering capabilities.  First, the VET interface
   can insert the SEAL header so that ID-based duplicate packet
   detection is enabled within the enterprise.  Secondly, SEAL can
   dynamically adjust its packet sizing parameters so that an optimum
   Maximum Transmission Unit (MTU) can be determined.  This is true even
   if the VET interface reroutes traffic between underlying interfaces
   with different MTUs.

   Most importantly, the EBR can configure default and more-specific
   routes on the VET interface to direct traffic through a specific
   egress EBR (eEBR) that may be many outer IP hops away.  Encapsulation
   will ensure that a specific eEBR is chosen, and the best eEBR can be
   chosen when multiple are available.  Also, local applications see a
   stable IP source address even if there are multiple underlying
   interfaces.  This link-layer multiplexing can therefore provide
   continuous operation across failovers between multiple links attached
   to the same enterprise without any need for readdressing.  Finally,
   the VET interface can forward packets with RLOC-based destinations
   over an underlying interface without any encapsulation if
   encapsulation avoidance is desired.

   It must be specifically noted that the above arrangement constitutes
   a case in which the same RLOC may be used as both the inner and outer
   IP source address.  This will not present a problem as long as both



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   ends configure a VET interface in the same fashion.

   It must also be noted that EID-based communications can use the same
   VET interface arrangement, except that the EID-based next hop must be
   mapped to an RLOC-based next-hop within the VET interface.  For IPvX-
   in-SEAL-in-IPvX encapsulation, as well as for IPv4-in-SEAL-in-Pv6
   encapsulation, this requires a VET interface specific address mapping
   database.  For IPv6-in-SEAL-in-IPv4 encapsulation, the mapping is
   accomplished through simple static extraction of an IPv4 address
   embedded in a VET address.


Appendix C.  Anycast Services

   Some of the IPv4 addresses that appear in the Potential Router List
   may be anycast addresses, i.e., they may be configured on the VET
   interfaces of multiple EGBRs/EBGs.  In that case, each VET router
   interface that configures the same anycast address must provide
   equivalent packet forwarding and IPv6 Neighbor Discovery services.

   Use of an anycast address as the IP destination address of tunneled
   packets can have subtle interactions with tunnel path MTU and
   neighbor discovery.  For example, if the initial fragments of a
   fragmented tunneled packet with an anycast IP destination address are
   routed to different egress tunnel endpoints than the remaining
   fragments, the multiple endpoints will be left with incomplete
   reassembly buffers.  This issue can be mitigated by ensuring that
   each egress tunnel endpoint implements a proactive reassembly buffer
   garbage collection strategy.  Additionally, ingress tunnel endpoints
   that send packets with an anycast IP destination address must use the
   minimum path MTU for all egress tunnel endpoints that configure the
   same anycast address as the tunnel MTU.  Finally, ingress tunnel
   endpoints should treat ICMP unreachable messages from a router within
   the tunnel as at most a weak indication of neighbor unreachability,
   since the failures may only be transient and a different path to an
   alternate anycast router quickly selected through reconvergence of
   the underlying routing protocol.

   Use of an anycast address as the IP source address of tunneled
   packets can lead to more serious issues.  For example, when the IP
   source address of a tunneled packet is anycast, ICMP messages
   produced by routers within the tunnel might be delivered to different
   ingress tunnel endpoints than the ones that produced the packets.  In
   that case, functions such as path MTU discovery and neighbor
   unreachability detection may experience non-deterministic behavior
   that can lead to communications failures.  Additionally, the
   fragments of multiple tunneled packets produced by multiple ingress
   tunnel endpoints may be delivered to the same reassembly buffer at a



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   single egress tunnel endpoint.  In that case, data corruption may
   result due to fragment misassociation during reassembly.

   In view of these considerations, EBRs/EBGs that configure an anycast
   address should also configure one or more unicast addresses from the
   Potential Router List; they should further accept tunneled packets
   destined to any of their anycast or unicast addresses, but should
   send tunneled packets using a unicast address as the source address.
   In order to influence traffic to use an anycast route (and thereby
   leverage the natural fault tolerance afforded by anycast), ISATAP
   routers should set higher preferences on the default routes they
   advertise using an anycast address as the source and set lower
   preferences on the default routes they advertise using a unicast
   address as the source (see: [RFC4191]).


Appendix D.  Change Log

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

   Changed from -05 to -06:

   o  reworked VET interface ND

   o  anycast clarifications

   Changes from -03 to -04:

   o  security consideration clarifications

   Changes from -02 to -03:

   o  security consideration clarifications

   o  new PRLNAME for VET is "isatav2.example.com"

   o  VET now uses SEAL natively

   o  EBGs can support both legacy ISATAP and VET over the same
      underlying interfaces.

   Changes from -01 to -02:

   o  Defined CGA and privacy address configuration on VET interfaces

   o  Interface identifiers added to routing protocol control messages
      for link-layer multiplexing



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   Changes from -00 to -01:

   o  Section 4.1 clarifications on link-local assignment and RLOC
      autoconfiguration.

   o  Appendix B clarifications on Weak End System Model

   Changes from RFC5558 to -00:

   o  New appendix on RLOC configuration on VET interfaces.


Author's Address

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

   Email: fltemplin@acm.org






























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