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Network Working Group                                    F. Templin, Ed.
Internet-Draft                              Boeing Research & Technology
Intended status: Informational                         December 19, 2011
Expires: June 21, 2012

                   Virtual Enterprise Traversal (VET)


   Enterprise networks connect hosts and routers over various link
   types, and often also connect to provider networks and/or the global
   Internet.  Enterprise network nodes require a means to automatically
   provision 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.

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on June 21, 2012.

Copyright Notice

   Copyright (c) 2011 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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   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  6
   3.  Enterprise Network Characteristics . . . . . . . . . . . . . . 11
   4.  Autoconfiguration  . . . . . . . . . . . . . . . . . . . . . . 13
     4.1.  Enterprise Router (ER) Autoconfiguration . . . . . . . . . 13
     4.2.  VET Border Router (VBR) Autoconfiguration  . . . . . . . . 15
       4.2.1.  VET Interface Initialization . . . . . . . . . . . . . 15
       4.2.2.  Potential Router List (PRL) Discovery  . . . . . . . . 16
       4.2.3.  Provider-Aggregated (PA) EID Prefix
               Autoconfiguration  . . . . . . . . . . . . . . . . . . 16
       4.2.4.  ISP-Independent EID Prefix Autoconfiguration . . . . . 18
     4.3.  VET Border Gateway (VBG) Autoconfiguration . . . . . . . . 19
     4.4.  VET Host Autoconfiguration . . . . . . . . . . . . . . . . 19
   5.  Internetworking Operation  . . . . . . . . . . . . . . . . . . 20
     5.1.  Routing Protocol Participation . . . . . . . . . . . . . . 20
       5.1.1.  PI Prefix Routing Considerations . . . . . . . . . . . 21
       5.1.2.  Client Prefix (CP) Routing Considerations  . . . . . . 21
     5.2.  Default Route Configuration and Selection  . . . . . . . . 21
     5.3.  Address Selection  . . . . . . . . . . . . . . . . . . . . 22
     5.4.  Next Hop Determination . . . . . . . . . . . . . . . . . . 22
     5.5.  VET Interface Encapsulation/Decapsulation  . . . . . . . . 23
       5.5.1.  Inner Network Layer Protocol . . . . . . . . . . . . . 24
       5.5.2.  SEAL Encapsulation . . . . . . . . . . . . . . . . . . 24
       5.5.3.  Outer Transport-Layer Header Encapsulation . . . . . . 24
       5.5.4.  Outer IP Header Encapsulation  . . . . . . . . . . . . 25
       5.5.5.  Decapsulation and Re-Encapsulation . . . . . . . . . . 26
     5.6.  Neighbor Coordination on VET Interfaces that use SEAL  . . 26
       5.6.1.  Router Discovery . . . . . . . . . . . . . . . . . . . 27
       5.6.2.  Neighbor Unreachability Detection  . . . . . . . . . . 28
       5.6.3.  Redirection  . . . . . . . . . . . . . . . . . . . . . 28
       5.6.4.  Bidirectional Neighbor Synchronization . . . . . . . . 30
     5.7.  Neighbor Coordination on VET Interfaces using IPsec  . . . 31
     5.8.  Mobility and Multihoming Considerations  . . . . . . . . . 31
     5.9.  Multicast  . . . . . . . . . . . . . . . . . . . . . . . . 32
       5.9.1.  Multicast over (Non)Multicast Enterprise Networks  . . 32
       5.9.2.  Multicast Over Multicast-Capable Enterprise
               Networks . . . . . . . . . . . . . . . . . . . . . . . 32
     5.10. Service Discovery  . . . . . . . . . . . . . . . . . . . . 33
     5.11. VET Link Partitioning  . . . . . . . . . . . . . . . . . . 33

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     5.12. VBG Prefix State Recovery  . . . . . . . . . . . . . . . . 34
     5.13. Legacy ISATAP Services . . . . . . . . . . . . . . . . . . 34
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 34
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 34
   8.  Related Work . . . . . . . . . . . . . . . . . . . . . . . . . 35
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 35
   10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 36
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 36
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 36
     11.2. Informative References . . . . . . . . . . . . . . . . . . 38
   Appendix A.  Duplicate Address Detection (DAD) Considerations  . . 43
   Appendix B.  Anycast Services  . . . . . . . . . . . . . . . . . . 43
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 44

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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 Small Office, Home Office (SOHO) network, as complex as a multi-
   organizational corporation, or as large as the global Internet
   itself.  Internet Service Provider (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/ICMPv4
   [RFC0791][RFC0792] and IPv6/ICMPv6 [RFC2460][RFC4443] are discussed
   within this context (other network layer protocols are also
   considered).  The use of standard DHCP [RFC2131] [RFC3315] 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
   encapsulating inner network layer protocol packets for transmission
   over outer IPv4 or IPv6 networks.  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 typically correspond to the
   wireless multihop radio interfaces associated with MANETs.  Out of
   scope for this document is the autoconfiguration of provider
   interfaces, which must be coordinated in a manner specific to the
   service provider's network.

   The VET framework builds on a Non-Broadcast Multiple Access (NBMA)
   [RFC2491] virtual interface model in a manner similar to other
   automatic tunneling technologies [RFC2529][RFC5214].  VET interfaces
   support the encapsulation of inner network layer protocol packets
   over IP networks (i.e., either IPv4 or IPv6), and provide an NBMA
   interface abstraction for coordination between tunnel endpoint

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   "neighbors".  VET is also compatible with mid-layer encapsulation
   technologies including IPsec [RFC4301], and supports both stateful
   and stateless prefix delegation.

   VET and its associated technologies (including the Subnetwork
   Encapsulation and Adaptation Layer (SEAL) [I-D.templin-intarea-seal]
   and Asymmetric Extended Route Optimization (AERO) [I-D.templin-aero])
   are functional building blocks for a new Internetworking architecture
   known as the Internet Routing Overlay Network (IRON)
   [I-D.templin-ironbis] and Routing and Addressing in Networks with
   Global Enterprise Recursion (RANGER) [RFC5720][RFC6139].  Many of the
   VET principles can be traced to the deliberations of the ROAD group
   in January 1992, and also to still earlier initiatives including
   NIMROD [RFC1753] and the Catenet model for internetworking [CATENET]
   [IEN48] [RFC2775].  The high-level architectural aspects of the ROAD
   group deliberations are captured in a "New Scheme for Internet
   Routing and Addressing (ENCAPS) for IPNG" [RFC1955].

   VET is related to the present-day activities of the IETF INTAREA,
   AUTOCONF, DHC, IPv6, MANET, RENUM 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 encapsulation.  The term "inner" refers to the
   innermost {address, protocol, header, packet, etc.} *before*
   encapsulation, and the term "outer" refers to the outermost {address,
   protocol, header, packet, etc.} *after* encapsulation.  VET also
   accommodates "mid-layer" encapsulations including SEAL
   [I-D.templin-intarea-seal], IPsec [RFC4301], etc.

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

   Virtual Enterprise Traversal (VET)
      an abstraction that uses encapsulation to create virtual overlays
      for transporting inner network layer packets over outer IPv4 and
      IPv6 enterprise networks.

   enterprise network
      the same as defined in [RFC4852].  An enterprise network is
      further understood to refer to a cooperative networked collective
      of devices within a structured IP routing and addressing plan 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

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      of connectivity itself.

      the same as defined in [RFC3819].

      a logical and/or physical grouping of interfaces that connect a
      topological area less than or equal to an enterprise network in
      scope.  From a network organizational standpoint, a site within an
      enterprise network can be considered as an enterprise network unto

   Mobile Ad hoc Network (MANET)
      a connected topology of mobile or fixed routers that maintain a
      routing structure among themselves over links that often have
      dynamic connectivity properties.  The characteristics of MANETs
      are described in [RFC2501], Section 3, and a wide variety of
      MANETs share common properties with enterprise networks.

      throughout the remainder of this document, the term "enterprise
      network" 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

   VET link
      a virtual link that uses automatic tunneling to create an overlay
      network that spans an enterprise network routing region.  VET
      links can be segmented (e.g., by 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 links can further be partitioned into multiple logical
      areas, where each area is identified by a distinct set of border

      VET links configured over non-multicast enterprise networks
      support only Non-Broadcast, Multiple Access (NBMA) services; VET
      links configured over enterprise networks that support multicast
      can support both NBMA and native multicast services.  All nodes
      connected to the same VET link appear as neighbors from the
      standpoint of the inner network layer.

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   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 network.

   VET Border Router (VBR)
      an ER that connects end user networks (EUNs) to VET links and/or
      connects multiple VET links together.  A VBR is a tunnel endpoint
      router, and it configures a separate VET interface for each
      distinct VET link.  All VBRs are also ERs.

   VET Border Gateway (VBG)
      a VBR that connects VET links to provider networks.  A VBG may
      alternately act as a "half-gateway", and forward the packets it
      receives from neighbors on the VET link to another VBG on the same
      VET link.  All VBGs are also VBRs.

   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

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

   enterprise-interior interface
      an ER's attachment to a link within an enterprise network.
      Packets sent over enterprise-interior interfaces may be forwarded
      over multiple additional enterprise-interior interfaces before
      they reach either their final destination or a border router/
      gateway.  Enterprise-interior interfaces connect laterally within
      the IP network hierarchy.

   enterprise-edge interface
      a VBR's attachment to a link (e.g., an Ethernet, a wireless
      personal area network, etc.) on an arbitrarily complex EUN that
      the VBR connects to a VET link and/or a provider network.
      Enterprise-edge interfaces connect to lower levels within the IP
      network hierarchy.

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   provider-edge interface
      a VBR's attachment to the Internet or to a provider network via
      which the Internet can be reached.  Provider-edge interfaces
      connect to higher levels within the IP network hierarchy.

   internal-virtual interface
      an interface that is internal to a VET node and does not in itself
      directly attach to a tangible link, e.g., a loopback interface.

   VET interface
      a VET node's attachment to a VET link.  VET nodes configure each
      VET interface over a set of underlying enterprise-interior
      interfaces that connect to a 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 a separate VET interface for each link.

      The VET interface encapsulates each inner 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 VET link as a
      single hop to the inner network layer.

   Provider Aggregated (PA) prefix
      a network layer protocol prefix that is delegated to a VET node by
      a provider network.

   Provider Independent (PI) prefix
      a network layer protocol prefix that is delegated to a VET node by
      an independent registration authority.  The VET node then becomes
      solely responsible for representing the PI prefix into the global
      Internet routing system on its own behalf.

   Client Prefix (CP)
      a network layer protocol prefix that is delegated to a VET node by
      a Virtual Service Provider (VSP) that may operate independently of
      the node's provider networks.  The term "Client Prefix (CP)" is
      the same as used in IRON [I-D.templin-ironbis].

   Routing Locator (RLOC)
      a public-scope or enterprise-local-scope IP address that can
      appear in enterprise-interior and/or interdomain routing tables.
      Public-scope RLOCs are delegated to specific enterprise networks
      and routable within both the enterprise-interior and interdomain
      routing regions.  Enterprise-local-scope RLOCs (e.g., IPv6 Unique
      Local Addresses [RFC4193], IPv4 privacy addresses [RFC1918], etc.)

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      are self-generated by individual enterprise networks 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 can use RLOCs as addresses
      for end-to-end communications between peers within the same
      enterprise network.  VET interfaces treat RLOCs as *outer* IP
      addresses during encapsulation.

   Endpoint Interface iDentifier (EID)
      a public-scope network layer address that is routable within
      enterprise-edge and/or VET overlay networks.  In a pure mapping
      system, EID prefixes are not routable within the interdomain
      routing system.  In a hybrid routing/mapping system, EID prefixes
      may be represented within the same interdomain routing instances
      that distribute RLOC prefixes.  In either case, EID prefixes are
      separate and distinct from any RLOC prefix space, but they are
      mapped to RLOC addresses to support packet forwarding over VET

      VBRs participate in any EID-based routing instances and use EID
      addresses for next-hop determination.  End systems can use EIDs as
      addresses for end-to-end communications between peers either
      within the same enterprise network or within different enterprise
      networks.  VET interfaces treat EIDs as *inner* network layer
      addresses during encapsulation.

      Note that an EID can also be used as an *outer* network layer
      address if there are nested encapsulations.  In that case, the EID
      would appear as an RLOC to the innermost encapsulation.

   The following additional acronyms are used throughout the document:

   CGA - Cryptographically Generated Address
   DHCP(v4, v6) - Dynamic Host Configuration Protocol
   ECMP - Equal Cost Multi Path
   EUN - End User Network
   FIB - Forwarding Information Base
   ICMP - either ICMPv4 or ICMPv6
   IP - either IPv4 or IPv6
   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
   RIB - Routing Information Base

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   RIO - Route Information Option
   SCMP - SEAL Control Message Protocol
   SEAL - Subnetwork Encapsulation and Adaptation Layer
   SLAAC - IPv6 StateLess Address AutoConfiguration
   SNS/SNA - SCMP Neighbor Solicitation/Advertisement
   SRD - SCMP Redirect
   SRS/SRA - SCMP Router Solicitation/Advertisement

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].  When used
   in lower case (e.g., must, must not, etc.), these words MUST NOT be
   interpreted as described in [RFC2119], but are rather interpreted as
   they would be in common English.

3.  Enterprise Network Characteristics

   Enterprise networks 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.
   VET Border Routers (VBRs) are ERs that connect End User Networks
   (EUNs) to VET links that span enterprise networks.  VET Border
   Gateways (VBGs) are VBRs that connect VET links to provider networks.

   Conceptually, an ER embodies both a host function and router
   function, and supports communications according to the weak end-
   system model [RFC1122].  The router function engages in the
   enterprise-interior routing protocol on its enterprise-interior
   interfaces, connects any of the ER's EUNs to its VET links, and may
   also connect the VET links to provider networks (see Figure 1).  The
   host function typically supports network management applications, but
   may also support diverse applications typically associated with
   general-purpose computing platforms.

   An enterprise network may be as simple as a small collection of ERs
   and their attached EUNs; an enterprise network may also contain other
   enterprise networks and/or be a subnetwork of a larger enterprise
   network.  An enterprise network 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 network 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.

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   Enterprise networks that comprise link types with sufficiently
   similar properties (e.g., Layer 2 (L2) address formats, maximum
   transmission units (MTUs), etc.) can configure a subnetwork routing
   service such that the network layer sees the underlying network as an
   ordinary shared link the same as for a (bridged) campus LAN (this is
   often the case with large cellular operator networks).  In that case,
   a single network layer hop is sufficient to traverse the underlying
   network.  Enterprise networks 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 network layer hops may be
   necessary to traverse the underlying network.

   In addition to other interface types, VET nodes configure VET
   interfaces that view all other nodes on the VET link as neighbors on
   a virtual NBMA link.  VET nodes configure a separate VET interface
   for each distinct VET link to which they connect, and discover
   neighbors on the link that can be used for forwarding packets to off-
   link destinations.  VET interface neighbor relationships may be
   either unidirectional or bidirectional.

   A unidirectional neighbor relationship is typically established and
   maintained as a result of network layer control protocol messaging in
   a manner that parallels IPv6 neighbor discovery [RFC4861].  A
   bidirectional neighbor relationship is typically established and
   maintained as result of a short transaction between the neighbors
   (see: Section 5.6.4).

   For each distinct VET link , a trust basis must be established and
   consistently applied.  For example, for VET links configured over
   enterprise networks in which VBRs establish symmetric security
   associations, mechanisms such as IPsec [RFC4301] can be used to
   assure authentication and confidentiality.  In other enterprise
   network scenarios, VET links may require asymmetric securing
   mechanisms such as SEcure Neighbor Discovery (SEND) [RFC3971].  VET
   links configured over still other enterprise networks may find it
   sufficient to employ ancillary encapsulations (e.g., SEAL
   [I-D.templin-intarea-seal]) that can be configured to provide
   services such as anti-replay, packet header integrity, and data
   origin authentication necessary for source address validation

   Finally, for VET links configured over enterprise networks with a
   centralized management structure (e.g., a corporate campus network,
   an ISP network, etc.), a hybrid routing/mapping service can be
   deployed using a synchronized set of VBGs.  In that case, the VBGs
   can provide a "default mapper" [I-D.jen-apt] service used for short-
   term packet forwarding until route-optimized paths can be

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   established.  For VET links configured over enterprise networks with
   a distributed management structure (e.g., disconnected MANETs), peer-
   to-peer coordination between the VET nodes themselves without the
   assistance of VBGs may be required.  Recognizing that various use
   cases may entail a continuum between a fully centralized and fully
   distributed approach, the following sections present the mechanisms
   of Virtual Enterprise Traversal as they apply to a wide variety of

4.  Autoconfiguration

   ERs, VBRs, VBGs, 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 network, it first configures an IPv6
   link-local address on each enterprise-interior interface that
   requires an IPv6 link-local capability and configures an IPv4 link-
   local address on each enterprise-interior interface that 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 administrative configuration, pseudo-random self-
   generation from a suitably large address pool, SLAAC, DHCP
   autoconfiguration, or through an alternate autoconfiguration

   Pseudo-random self-generation of IPv6 RLOCs can be from a large
   public or local-use IPv6 address range (e.g., IPv6 Unique Local
   Addresses [RFC4193]).  Pseudo-random self-generation of IPv4 RLOCs
   can be from a large public or local-use IPv4 address range (e.g.,
   [RFC1918]).  When self-generation is used alone, the ER continuously
   monitors the RLOCs for uniqueness, e.g., by monitoring the
   enterprise-interior routing protocol.  (Note however that anycast
   RLOCs may be assigned to multiple enterprise-interior interfaces;
   hence, monitoring for uniqueness applies only to RLOCs that are
   provisioned as unicast.)

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   SLAAC autoconfiguration of RLOCs can be through the receipt of IPv6
   Router Advertisements (RAs) followed by the stateless configuration
   of addresses based on any included Prefix Information Options (PIOs)

   DHCP autoconfiguration of RLOCs uses standard DHCP procedures,
   however ERs acting as DHCP clients SHOULD also use DHCP
   Authentication [RFC3118] [RFC3315] as discussed further below.  In
   typical enterprise network scenarios (i.e., those with stable links),
   it may be sufficient to configure one or a few DHCP relays on each
   link that does not include a DHCP server.  In more extreme scenarios
   (e.g., MANETs that include links with dynamic connectivity
   properties), DHCP operation may require any ERs that have already
   configured RLOCs to act as DHCP relays to ensure that client DHCP
   requests eventually reach a DHCP server.  This may result in
   considerable DHCP message relaying until a server is located, but the
   DHCP Authentication Replay Detection vector provides relays with a
   means for avoiding message duplication.

   In all enterprise network scenarios, the amount of DHCP relaying
   required can be significantly reduced if each relay has a way of
   contacting a DHCP server directly.  In particular, if the relay can
   discover the unicast addresses for one or more servers (e.g., by
   discovering the unicast RLOC addresses of VBGs as described in
   Section 4.2.2) it can forward DHCP requests directly to the unicast
   address(es) of the server(s).  If the relay does not know the unicast
   address of a server, it can forward DHCP requests to a site-scoped
   DHCP server multicast address if the enterprise network supports
   site-scoped multicast services.  For DHCPv6, relays can forward
   requests to the site-scoped IPv6 multicast group address
   'All_DHCP_Servers' [RFC3315].  For DHCPv4, relays can forward
   requests to the site-scoped IPv4 multicast group address
   'All_DHCPv4_Servers', which SHOULD be set to unless an
   alternate multicast group for the enterprise network 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.

   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 an RLOC taken from a
   temporary addressing range used only for the bootstrapping purpose of
   procuring an actual RLOC taken from a delegated addressing range.
   The ER then engages in the enterprise-interior routing protocol and
   performs a DHCP exchange as above using the temporary RLOC as the
   address of its relay function.  When the DHCP server delegates an

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   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.

   Alternatively (or in addition to the above), 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 are assigned on
   separate sets of enterprise-edge interfaces.

   In some enterprise network scenarios (e.g., MANETs that include links
   with dynamic connectivity properties), 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 [RFC4903].

4.2.  VET Border Router (VBR) Autoconfiguration

   VBRs are ERs that configure and use one or more VET interfaces.  In
   addition to the ER autoconfiguration procedures specified in
   Section 4.1, VBRs perform the following autoconfiguration operations.

4.2.1.  VET Interface Initialization

   VBRs configure a separate VET interface for each VET link, where each
   VET link spans a distinct sets of underlying links belonging to the
   same enterprise network.  All nodes on the VET link appear as single-
   hop neighbors from the standpoint of the inner network layer protocol
   through the use of encapsulation.

   The VBR binds each VET interface to one or more underlying
   interfaces, and uses the underlying interface addresses as RLOCs to
   serve as the outer source addresses for encapsulated packets.  The
   VBR then assigns a link-local address to each VET interface if
   necessary.  When IPv6 and IPv4 are used as the inner/outer protocols
   (respectively), the VBR can autoconfigure an IPv6 link-local address
   on the VET interface using a modified EUI-64 interface identifier
   based on an IPv4 RLOC address (see Section 2.2.1 of [RFC5342]).
   Link-local address configuration for other inner/outer protocol
   combinations is through administrative configuration, random self-
   generation (e.g., [RFC4941], etc.) or through an unspecified
   alternate method.

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4.2.2.  Potential Router List (PRL) Discovery

   After initializing the VET interface, the VBR next discovers a
   Potential Router List (PRL) for the VET link that includes the RLOC
   addresses of VBGs.  The PRL can be discovered through administrative
   configuration, information conveyed in the enterprise-interior
   routing protocol, an anycast VBG discovery message exchange, a DHCP
   option, etc.  In multicast-capable enterprise networks, VBRs can also
   listen for advertisements on the 'rasadv' [RASADV] multicast group

   When no other information is available, the VBR can resolve 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 Domain Name
   System (DNS) suffix [RFC1035].  The VBR discovers 'PRLNAME' through
   administrative 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 network.  The VBR can also obtain
   'PRLNAME' as part of an arrangement with a private-sector Virtual
   Service Provider (VSP) (see: Section 4.2.4).

   In the absence of other information, the VBR sets the 'hostname'
   component of 'PRLNAME' to "isatapv2" and sets the 'domainname'
   component to an enterprise-specific DNS suffix (e.g., "example.com").
   Isolated enterprise networks that do not connect to the outside world
   may have no enterprise-specific DNS suffix, in which case the
   'PRLNAME' consists only of the 'hostname' component.  (Note that the
   default hostname "isatapv2" is intentionally distinct from the
   convention specified in [RFC5214].)

   After discovering 'PRLNAME', the VBR resolves the name into a list of
   RLOC addresses through a name service lookup.  For centrally managed
   enterprise networks, the VBR resolves 'PRLNAME' using an enterprise-
   local name service (e.g., the DNS).  For enterprises with no
   centralized management structure, the VBR resolves 'PRLNAME' using a
   distributed name service query such as Link-Local Multicast Name
   Resolution (LLMNR) [RFC4795] over the VET interface.  In that case,
   all VBGs in the PRL respond to the query, and the VBR accepts the
   union of all responses.

4.2.3.  Provider-Aggregated (PA) EID Prefix Autoconfiguration

   VBRs that connect their enterprise networks to a provider network can
   obtain Provider-Aggregated (PA) EID prefixes through stateful and/or
   stateless autoconfiguration mechanisms.  The stateful and stateless
   approaches are discussed in the following subsections.

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   For IPv4, VBRs acquire IPv4 PA EID prefixes through administrative
   configuration, an automated IPv4 prefix delegation exchange, etc.

   For IPv6, VBRs acquire IPv6 PA EID prefixes through administrative
   configuration or through DHCPv6 Prefix Delegation exchanges with a
   VBG acting as a DHCP relay/server.  In particular, the VBR (acting as
   a requesting router) can use DHCPv6 prefix delegation [RFC3633] over
   the VET interface to obtain prefixes from the VBG (acting as a
   delegating router).  The VBR obtains prefixes using either a
   2-message or 4-message DHCPv6 exchange [RFC3315].  When the VBR acts
   as a DHCPv6 client, it maps the IPv6
   "All_DHCP_Relay_Agents_and_Servers" link- scoped multicast address to
   the VBG's outer RLOC address.

   To perform the 2-message exchange, the VBR's DHCPv6 client function
   can send a Solicit message with an IA_PD option either directly or
   via the VBR's own DHCPv6 relay function (see Section 4.1).  The VBR's
   VET interface then forwards the message using VET encapsulation (see:
   Section 5.4) to a VBG which either services the request or relays it
   further.  The forwarded Solicit message will elicit a Reply message
   from the server containing prefix delegations.  The VBR 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 message if it was able to
   perform the delegation.

   After the VBR receives IPv4 and/or IPv6 prefix delegations, it can
   provision the prefixes on enterprise-edge interfaces as well as on
   other VET interfaces configured over child enterprise networks for
   which it acts as a VBG.  The VBR can also provision the prefixes on
   enterprise-interior interfaces to service directly-attached hosts on
   the enterprise-interior link.

   The prefix delegations remain active as long as the VBR continues to
   renew them via the delegating VBG before lease lifetimes expire.  The
   lease lifetime also keeps the delegation state active even if
   communications between the VBR and delegating VBG are disrupted for a
   period of time (e.g., due to an enterprise network partition, power
   failure, etc.).  Note however that if the VBR abandons or otherwise
   loses continuity with the prefixes, it may be obliged to perform
   network-wide renumbering if it subsequently receives a new and
   different set of prefixes.

   Stateful prefix delegation for non-IP protocols is out of scope.

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   When IPv6 and IPv4 are used as the inner and outer protocols,
   respectively, a stateless IPv6 PA prefix delegation capability is
   available using the mechanisms specified in
   [RFC5214][RFC5569][RFC5969].  VBRs can use these mechanisms to
   statelessly configure IPv6 PA prefixes that embed one of the VBR's
   IPv4 RLOCs.

   Using this stateless prefix delegation, if the IPv4 RLOC changes the
   IPv6 prefix also changes and the VBR is obliged to renumber any
   interfaces on which sub-prefixes from the delegated prefix are
   assigned.  This method may therefore be most suitable for enterprise
   networks in which IPv4 RLOC assignments rarely change, or in
   enterprise networks in which only services that do not depend on a
   long-term stable IPv6 prefix (e.g., client-side web browsing) are

   Stateless prefix delegation for other protocol combinations is out of

4.2.4.  ISP-Independent EID Prefix Autoconfiguration

   VBRs can acquire ISP-independent prefixes to facilitate multihoming,
   mobility and traffic engineering without requiring site-wide
   renumbering events due to a change in ISP connections.

   VBRs that connect major enterprise networks (e.g., large
   corporations, academic campuses, ISP networks, etc.) to the global
   Internet can acquire short Provider-Independent (PI) prefixes (e.g.,
   an IPv6 ::/32, an IPv4 /16, etc.) through a registration authority
   such as the Internet Assigned Numbers Authority (IANA) or a major
   regional Internet registry.  The VBR then advertises the PI prefixes
   into the global Internet on the behalf of its enterprise network
   without the assistance of an ISP.

   VBRs that connect enterprise networks to a provider network can
   acquire longer Client Prefixes (CPs) (e.g., an IPv6 ::/56, an IPv4
   /24, etc.) through arrangements with a Virtual Service Provider (VSP)
   that may or may not be associated with a specific ISP.  The VBR then
   coordinates its CPs with a VSP independently of any of its directly
   attached ISPs.  (In many cases, the "VSP" may in fact be a major
   enterprise network that delegates CPs from its PI prefixes.)

   After a VBR receives prefix delegations, it can sub-delegate portions
   of the prefixes on enterprise-edge interfaces, on child VET
   interfaces for which it is configured as a VBG and on enterprise-
   interior interfaces to service directly-attached hosts on the

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   enterprise-interior link.  The VBR can also sub-delegate portions of
   its prefixes to requesting routers connected to child enterprise
   networks.  These requesting routers consider their sub-delegated
   prefixes as PA, and consider the delegating routers as their points
   of connection to a provider network.

4.3.  VET Border Gateway (VBG) Autoconfiguration

   VBGs are VBRs that connect VET links configured over child enterprise
   networks to provider networks via provider-edge interfaces and/or via
   VET links configured over parent enterprise networks.  A VBG may also
   act as a "half-gateway", in that it may need to forward the packets
   it receives from neighbors on the VET link via another VBG associated
   with the same VET link.  This arrangement is seen in the IRON
   [I-D.templin-ironbis] Client/Server/Relay architecture, in which a
   Server "half-gateway" is a VBG that forwards packets with enterprise-
   external destinations via a Relay "half-gateway" that connects the
   VET link to the provider network.

   VBGs 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 VET links using the
   VBR autoconfiguration procedures specified in Section 4.2.  For each
   of its VET interfaces connected to child VET links, the VBG
   initializes the interface the same as for an ordinary VBR (see
   Section 4.2.1).  It then arranges to add one or more of its RLOCs
   associated with the child VET link to the PRL.

   VBGs configure a DHCP relay/server on VET interfaces connected to
   child VET links that require DHCP services.  VBGs may also engage in
   an unspecified anycast VBG discovery message exchange if they are
   configured to do so.  Finally, VBGs respond to distributed name
   service queries for 'PRLNAME' on VET interfaces connected to VET
   links that span child enterprise networks with a distributed
   management structure.

4.4.  VET Host Autoconfiguration

   Nodes that cannot be attached via a VBR'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 on the VET link.  Each VET host performs the same
   enterprise interior interface RLOC configuration procedures as
   specified for ERs in Section 4.1.  The VET host next performs the
   same VET interface initialization and PRL discovery procedures as
   specified for VBRs in Section 4.2, except that it configures its 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

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   a VBR/VBG on other VET interfaces.

   A VET host may receive non-link-local addresses and/or prefixes to
   assign to the VET interface via DHCP exchanges and/or through SLAAC
   information conveyed in RAs.  If prefixes are provided, however,
   there must be assurance that either 1) the VET link will not
   partition, or 2) that each VET host interface connected to the VET
   link will configure a unique set of prefixes.  VET hosts therefore
   depend on DHCP and/or RA exchanges to provide only addresses/prefixes
   that are appropriate for assignment to the VET interface according to
   these specific cases, and depend on the VBGs within the enterprise
   keeping track of which addresses/prefixes were assigned to which

   When the VET host solicits a DHCP-assigned EID address/prefix over a
   (non-multicast) VET interface, it maps the DHCP relay/server
   multicast inner destination address to the outer RLOC address of a
   VBG that it has selected as a default router.  The VET host then
   assigns any resulting DHCP-delegated addresses/prefixes to the VET
   interface for use as the source address of inner packets.  The host
   will subsequently send all packets destined to EID correspondents via
   a default router on the VET link, and may discover more-specific
   routes based on any redirect messages it receives.

5.  Internetworking Operation

   Following the autoconfiguration procedures specified in Section 4,
   ERs, VBRs, VBGs, and VET hosts engage in normal internetworking
   operations as discussed in the following sections.

5.1.  Routing Protocol Participation

   ERs engage in any RLOC-based routing protocols over enterprise-
   interior interfaces to exchange routing information for forwarding IP
   packets with RLOC addresses.  VBRs and VBGs can additionally engage
   in any EID-based routing protocols over VET, enterprise-edge and
   provider-edge interfaces to exchange routing information for
   forwarding inner network layer packets with EID addresses.  Note that
   any EID-based routing instances are separate and distinct from any
   RLOC-based routing instances.

   VBR/VBG routing protocol participation on non-multicast VET
   interfaces uses the NBMA interface model, e.g., in the same manner as
   for OSPF over NBMA interfaces [RFC5340].  (VBR/VBG routing protocol
   participation on multicast-capable VET interfaces can alternatively
   use the standard multicast interface model, but this may result in
   excessive multicast control message overhead.)

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   VBRs can use the list of VBGs in the PRL (see: Section 4.2.1) as an
   initial list of neighbors for EID-based routing protocol
   participation.  VBRs can alternatively use the list of VBGs as
   potential default routers instead of engaging in an EID-based routing
   protocol instance.  In that case, when the VBR forwards a packet via
   a VBG it may receive a redirect message indicating a different VET
   node as a better next hop.

5.1.1.  PI Prefix Routing Considerations

   VBRs that connect large enterprise networks to the global Internet
   advertise their EID PI prefixes directly into the Internet default-
   free RIB via the Border Gateway Protocol (BGP) [RFC4271] on their own
   behalf the same as for a major service provider network.  VBRs that
   connect large enterprise networks to provider networks can instead
   advertise their EID PI prefixes into their providers' routing
   system(s) if the provider networks are configured to accept them.

5.1.2.  Client Prefix (CP) Routing Considerations

   VBRs that obtain CPs from a VSP can register them with a serving VBG
   in the VSP's network (e.g., through a vendor-specific short TCP
   transaction).  The VSP network then acts as a virtual "home"
   enterprise network that connects its customer enterprise networks to
   the Internet routing system.  The customer enterprise networks in
   turn appear as mobile components of the VSP's network, while the
   customer network uses its ISP connections solely as transits.  (In
   many cases, the "VSP" may itself be a major enterprise network that
   delegates CPs from its PI prefixes to child enterprise networks.)

5.2.  Default Route Configuration and Selection

   Configuration of default routes in the presence of VET interfaces
   must be carefully coordinated according to the inner and outer
   network protocols.  If the inner and outer protocols are different
   (e.g., IPv6 within IPv4) then default routes of the inner protocol
   version can be configured with next-hops corresponding to default
   routers on a VET interface while default routes of the outer protocol
   version can be configured with next-hops corresponding to default
   routers on an underlying interface.

   If the inner and outer protocols are the same (e.g., IPv4 within
   IPv4), care must be taken in setting the default route to avoid
   ambiguity.  For example, if default routes are configured on the VET
   interface then more-specific routes could be configured on underlying
   interfaces to avoid looping.  Alternatively, multiple default routes
   can be configured with some having next-hops corresponding to (EID-
   based) default routers on VET interfaces and others having next-hops

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   corresponding to (RLOC-based) default routers on underlying
   interfaces.  In that case, special next-hop determination rules must
   be used (see: Section 5.4).

5.3.  Address Selection

   When permitted by policy and supported by enterprise-interior
   routing, VET nodes can avoid 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 network that provides native IPv4 intra-enterprise
   services can provide continued support for native IPv4 communications
   even when encapsulated IPv6 services are available for inter-
   enterprise communications.

   In other enterprise network scenarios, the use of EID-based
   communications (i.e., instead of RLOC-based communications) may be
   necessary and/or beneficial to support address scaling, transparent
   Network Address Translator (NAT) traversal, security domain
   separation, site multihoming, traffic engineering, etc. .

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

5.4.  Next Hop Determination

   VET nodes perform normal next-hop determination via longest prefix
   match, and send packets according to the most-specific matching entry
   in the FIB.  If the FIB entry has multiple next-hop addresses, the
   VET node selects the next-hop with the best metric value.  If
   multiple next hops have the same metric value, the VET node can use
   Equal Cost Multi Path (ECMP) to forward different flows via different
   next-hop addresses, where flows are determined, e.g., by computing a
   hash of the inner packet's source address, destination address and
   flow label fields.

   If the VET node has multiple default routes of the same inner and
   outer protocol versions, with some corresponding to EID-based default
   routers and others corresponding to RLOC-based default routers, it
   must perform source address based selection of a default route.  In
   particular, if the packet's source address is taken from an EID
   prefix the VET node selects a default route configured over the VET
   interface; otherwise, it selects a default route configured over an
   underlying interface.

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   As a last resort when there is no matching entry in the FIB (i.e.,
   not even default), VET nodes can discover neighbors within the
   enterprise network through on-demand name service queries for the
   packet's destination address (or, by some other inner address to
   outer address mapping distribution system).  For example, for the
   IPv6 destination address '2001:DB8:1:2::1' and 'PRLNAME'
   "isatapv2.example.com" the VET node can perform a name service lookup
   for the domain name:

   The name service can employ wildcard matching (e.g., [RFC4592]) to
   determine the most-specific matching entry.  For example, if the
   most-specific prefix that covers the IPv6 destination address is
   '2001:DB8:1::/48' the matching entry is:


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

   Name-service lookups in enterprise networks with a centralized
   management structure use an infrastructure-based service, e.g., an
   enterprise-local DNS.  Name-service lookups in enterprise networks
   with a distributed management structure and/or that lack an
   infrastructure-based name service instead use a distributed name
   service such as LLMNR over the VET interface.  When a distributed
   name service is used, the VBR that performs the lookup sends a
   multicast query and accepts the union of all replies it receives from
   neighbors on the VET interface.  When a VET node receives the query,
   it responds IFF it aggregates an IP prefix that covers the prefix in
   the query.

5.5.  VET Interface Encapsulation/Decapsulation

   VET interfaces encapsulate inner network layer packets in any
   necessary mid-layer headers and trailers (e.g., IPsec, SEAL, etc.)
   followed by an outer transport-layer header such as UDP (if
   necessary) followed by an outer IP header.  Following all
   encapsulations, the VET interface submits the encapsulated packet to
   the outer IP forwarding engine for transmission on an underlying
   interface.  The following sections provide further details on

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5.5.1.  Inner Network Layer Protocol

   The inner network layer protocol sees the VET interface as an
   ordinary network interface, and views the outer network layer
   protocol as an ordinary L2 transport.  The inner- and outer network
   layer protocol types are mutually independent and can be used in any
   combination.  Inner network layer protocol types include IPv6
   [RFC2460] and IPv4 [RFC0791], but they may also include non-IP
   protocols such as OSI/CLNP [RFC0994][RFC1070][RFC4548].

5.5.2.  SEAL Encapsulation

   VET interfaces that use SEAL encapsulate the inner packet in a SEAL
   header/trailer as specified in [I-D.templin-intarea-seal].  SEAL
   encapsulation must be applied uniformly between all neighbors on the
   VET link.  Note that when a VET node sends a SEAL-encapsulated packet
   to a neighbor that does not use SEAL encapsulation, it may receive an
   ICMP "port unreachable" or "protocol unreachable" message.

   VET interfaces use SEAL encapsulation on VET links that require path
   MTU mitigations due to encapsulation overhead and/or mechanisms for
   VET interface neighbor coordination and error message handling.  When
   SEAL encapsulation is used, the VET interface sets the 'NEXTHDR'
   value in the SEAL header to the IP protocol number associated with
   the protocol number of the inner network layer.  The VET interface
   sets the other fields in the SEAL header as specified in

5.5.3.  Outer Transport-Layer Header Encapsulation

   Following SEAL encapsulation, VET interfaces that use a transport
   layer encapsulation such as UDP add an outer transport layer header.
   Inclusion of an outer UDP header must be applied uniformly between
   all neighbors on the VET link.  Note that when a VET node sends a
   UDP-encapsulated packet to a neighbor that does not recognize the UDP
   port number, it may receive an ICMP "port unreachable" message.

   VET interfaces use UDP encapsulation on VET links that may traverse
   NATs and/or traffic conditioning network gear (e.g., Equal Cost
   MultiPath (ECMP) routers, Link Aggregation Gateways (LAGs), etc.)
   that only recognize well-known network layer protocols.  When UDP
   encapsulation is used, the VET interface encapsulates the mid-layer
   packet in an outer UDP header then sets the UDP port numbers as
   specified for the outermost mid-layer protocol (e.g., IPsec
   [RFC3947][RFC3948], etc.).

   When SEAL encapsulation [I-D.templin-intarea-seal] is also used, the
   VET interface maintains per-neighbor local and remote UDP port

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   numbers.  For bidirectional neighbors, the VET interface sets the
   local UDP port number to the value reserved for SEAL and sets the
   remote UDP port number to the observed UDP source port number in
   packets that it receives from the neighbor.  In cases in which one of
   the bidirectional neighbors is behind a NAT, this implies that the
   one behind the NAT initiates the neighbor relationship.  If both
   neighbors have a way of knowing that there are no NATs in the path,
   then they may select and set port numbers as for unidirectional

   For unidirectional neighbors, the VET interface sets both the local
   and remote UDP port numbers to the value reserved for SEAL, and
   additionally selects a small set of dynamic port number values for
   use as additional local UDP port numbers.  The VET interface then
   selects one of this set of local port numbers for the UDP source port
   for each inner packet it sends, where the port number can be
   determined e.g., by a hash calculated over the inner network layer
   addresses and inner transport layer port numbers.  The VET interface
   uses a hash function of its own choosing when selecting a dynamic
   port number value, but it should choose a function that provides
   uniform distribution between the set of values, and it should be
   consistent in the manner in which the hash is applied.

   Finally, for VET links configured over IPv4 enterprise networks, the
   TE sets the UDP checksum field to zero.  For VET links configured
   over IPv6 enterprise networks, considerations for setting the UDP
   checksum are discussed in [I-D.ietf-6man-udpzero].  If SEAL
   encapsulation is used, the TE sets the UDP checksum field to zero
   regardless of the IP protocol version, since SEAL provides an
   integrity check vector that covers the leading 128 bytes of the
   packet beginning with the UDP header.

5.5.4.  Outer IP Header Encapsulation

   Following any mid-layer and/or UDP encapsulations, the VET interface
   adds an outer IP header.  Outer IP header construction is the same as
   specified for ordinary IP encapsulation (e.g., [RFC1070][RFC2003],
   [RFC2473], [RFC4213], etc.) except that the "TTL/Hop Limit", "Type of
   Service/Traffic Class" and "Congestion Experienced" values in the
   inner network layer header are copied into the corresponding fields
   in the outer IP header.  The VET interface also sets the IP protocol
   number to the appropriate value for the first protocol layer within
   the encapsulation (e.g., UDP, SEAL, IPsec, etc.).  When IPv6 is used
   as the outer IP protocol, the VET interface sets the flow label value
   in the outer IPv6 header the same as described in

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5.5.5.  Decapsulation and Re-Encapsulation

   When a VET node receives an encapsulated packet, it retains the outer
   headers, processes the SEAL header (if present) as specified in
   [I-D.templin-intarea-seal], then performs next hop determination on
   the packet's inner destination address.  If the inner packet will be
   forwarded out a different interface than it arrived on, the VET node
   copies the "Congestion Experienced" value in the outer IP header into
   the corresponding field in the inner network layer header.  The VET
   node then forwards the packet to the next inner network layer hop, or
   delivers the packet locally if the inner packet is addressed to

   If the inner packet will be forwarded out the same VET interface that
   it arrived on, however, the VET node copies the "TTL/Hop Limit",
   "Type of Service/Traffic Class" and "Congestion Experienced" values
   in the outer IP header of the received packet into the corresponding
   fields in the outer IP header of the packet to be forwarded (i.e.,
   the values are transferred between outer headers and *not* copied
   from the inner network layer header).  This is true even if the outer
   IP protocol version of the received packet is different than the
   outer IP protocol version of the packet to be forwarded, i.e., the
   same as for bridging dissimilar L2 media segments.  This re-
   encapsulation procedure is necessary to support diagnostic functions
   (e.g., 'traceroute'), and to ensure that the TTL/Hop Limit eventually
   decrements to 0 in case of transient routing loops.

5.6.  Neighbor Coordination on VET Interfaces that use SEAL

   VET interfaces that use SEAL use the SEAL Control Message Protocol
   (SCMP) as specified in Section 4.6 of [I-D.templin-intarea-seal] to
   coordinate reachability, routing information, and mappings between
   the inner and outer network layer protocols.  SCMP parallels the IPv6
   Neighbor Discovery (ND) [RFC4861] and ICMPv6 [RFC4443] protocols, but
   operates from within the tunnel and supports operation for any
   combinations of inner and outer network layer protocols.

   When a VET interface that uses SEAL prepares a neighbor coordination
   SCMP message, the message is formatted the same as described for the
   corresponding IPv6 ND message, except that the message is preceded by
   a SEAL header the same as for SCMP error messages.  The interface
   sets the SEAL header flags, NEXTHDR, LINK_ID, Identification, and ICV
   fields the same as for SCMP error messages, and sets PREFLEN to 0.

   The VET interface next fills out the SCMP message header fields the
   same as for SCMP error messages, calculates the SCMP message
   Checksum, encapsulates the message in the requisite outer headers,
   then calculates the SEAL header Integrity Check Vector (ICV) value if

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   it is configured to do so and places the result in the ICV field.
   The VET interface finally sends the message to the neighbor, which
   will verify the ICV and Checksum before accepting the message.

   VET and SEAL are specifically designed for encapsulation of inner
   network layer payloads over outer IPv4 and IPv6 networks as a link
   layer.  VET interfaces that use SCMP therefore require a new Source/
   Target Link-Layer Address Option (S/TLLAO) format that encapsulates
   IPv4 addresses as shown in Figure 2 and IPv6 addresses as shown in
   Figure 3:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |    Type = 2   |   Length = 1  |          Reserved             |
   |                  IPv4 address (bytes 0 thru 3)                |

               Figure 2: SCMP S/TLLAO Option for IPv4 RLOCs

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |    Type = 2   |   Length = 3  |          Reserved             |
   |                            Reserved                           |
   |               IPv6 address (bytes 0 thru 3)                   |
   |               IPv6 address (bytes 4 thru 7)                   |
   |               IPv6 address (bytes 8 thru 11)                  |
   |               IPv6 address (bytes 12 thru 15)                 |

               Figure 3: SCMP S/TLLAO Option for IPv6 RLOCs

   The following subsections discuss VET interface neighbor coordination
   using SCMP:

5.6.1.  Router Discovery

   VET hosts and VBRs can send SCMP Router Solicitation (SRS) messages
   to one or more VBGs in the PRL to receive solicited SCMP Router
   Advertisements (SRAs).

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   When a VBG receives an SRS message on a VET interface, it prepares a
   solicited SRA message.  The SRA includes Router Lifetimes, Default
   Router Preferences, PIOs and any other options/parameters that the
   VBG is configured to include.

   The VBG finally includes one or more SLLAOs formatted as specified
   above that encode the IPv6 and/or IPv4 RLOC unicast addresses of its
   own enterprise-interior interfaces or the enterprise-interior
   interfaces of other nearby VBGs.

5.6.2.  Neighbor Unreachability Detection

   VET nodes perform Neighbor Unreachability Detection (NUD) by
   monitoring hints of forward progress.  The VET node can periodically
   set the 'A' bit in the header of SEAL data packets to elicit SCMP
   responses from the neighbor.  The VET node can also send SCMP
   Neighbor Solicitation (SNS) messages to the neighbor to elicit SCMP
   Neighbor Advertisement (SNA) messages.

   Responsiveness to routing changes is directly related to the delay in
   detecting that a neighbor has gone unreachable.  In order to provide
   responsiveness comparable to dynamic routing protocols, a reasonably
   short neighbor reachable time (e.g., 5sec) SHOULD be used.

   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 neighbor may be failing.  The VET node
   SHOULD first check the packet-in-error to obtain reasonable assurance
   that the ICMP message is authentic.  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 (e.g., a default route with
   a VBG as the next hop).

5.6.3.  Redirection

   The VET node connected to the source EUN (i.e., the source VET node)
   can set R=1 in the SEAL header of a data packet to be forwarded as a
   "predirect" indication that SCMP Redirect (SRD) messages will be
   accepted from the VET node connected to the destination EUN (i.e.,
   the target VET node).  Each VBG on the VET interface chain to the
   target preserves the state of the R bit when it re-encapsulates and
   forwards the packet.

   When the target VET node receives the predirect indication, it
   returns an SRD message in the manner described in AERO
   [I-D.templin-aero].  The SRD message is formatted the same as for an
   ICMPv6 Redirect message as shown in Section 4.5 of[RFC4861].  The

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   target includes Target Link Layer Address Options (TLLAOs) formatted
   as specified above, then adds a Redirected Header Option (RHO) that
   includes the leading portion of the SEAL data packet that triggered
   the redirection event beginning immediately following the SEAL

   The target VET node then creates a 128-bit secret key value (T_Key)
   that it will use to validate the SEAL header ICV in future packets it
   will receive from the (redirected) source VET node.  The target
   encrypts T_Key with the secret key it uses to validate the ICV in
   SEAL packets received from the previous VET interface hop (P_Key(N)).
   It then writes the encrypted value in the "Target" field of the SRD
   message, i.e., instead of an IPv6 address.

   The target VET node then encapsulates the SRD message in a SEAL
   header as specified above.  The target also writes the prefix length
   associated with the inner destination address of the SEAL data packet
   that triggered the redirection event in the PREFLEN field of the SEAL
   header.  For example, if the destination address is 2001:db8::1 and
   the destination prefix is 2001:db8::/48, the target sets the PREFLEN
   field to the value 48.  The target then calculates the SEAL ICVs and
   returns the message to the previous hop VBG on the chain toward the

   When the target returns the SRD message, each intermediate VBG in the
   chain toward the source relays the message by examining the source
   address of the inner packet within the RHO to determine the previous
   hop toward the source.  Each intermediate VBG in the chain verifies
   the SRD message SEAL ICV and Checksum, and decrypts the T_Key value
   in the SRD message "Target" field using its own secret key
   (P_Key(i)).  The VBG then re-encrypts T_Key using the key
   corresponding to the next hop toward the source (P_Key(i-1)), then
   re-calculates the SEAL ICV and sends the SRD message to the previous
   hop.  This relaying process is otherwise the same as for SCMP error
   message relaying specified in Section 4.6 of

   When the source VET node receives the SRD message, it discovers both
   the PREFLEN and candidate link layer addresses for this new
   (unidirectional) target VET node.  The source node also caches the
   T_Key value, and uses it to calculate the ICVs it will include in the
   SEAL header/trailer of subsequent packets it sends to the target.

   The source then applies the PREFLEN to the inner destination address
   of the packet that triggered the redirection event, then installs the
   resulting prefix in a forwarding table entry with the target as the
   next hop.

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   The source can subsequently send packets destined to an address
   covered by the destination prefix using SEAL encapsulation via the
   target as the next hop.  The target can then use the ICVs in the SEAL
   data packets for inner source address validation
   [I-D.ietf-savi-framework], but it need not also check the outer
   source addresses/port numbers of the packets.  Therefore, the outer
   addresses may change over time even if the inner source address stays
   the same.

   Following redirection, if the source is subsequently unable to reach
   the target via the route-optimized path, it deletes the destination
   prefix forwarding table entry and installs a new forwarding table
   entry for the destination prefix with a default router as the next
   hop.  The source VET node thereafter sets R=0 in the SEAL headers of
   data packets that it sends toward the destination prefix, but it may
   attempt redirection again at a later time by again setting R=1.

   Finally, the source and target VET nodes should set an expiration
   timer on the destination forwarding table entry so that stale entries
   are deleted in a timely fashion.  The source can further engage the
   target in a bidirectional neighbor synchronization exchange as
   described in Section 5.6.4 if it is configured to do so.

5.6.4.  Bidirectional Neighbor Synchronization

   The tunnel neighbor relationship between a pair of VET interface
   tunnel neighbors can be either unidirectional or bidirectional.  A
   unidirectional relationship (see: Section 5.6.3) can be established
   when the source VET node 'A' will tunnel data packets directly to a
   target VET node 'B', but 'B' will not tunnel data packets directly to
   'A'.  A bidirectional relationship is necessary, e.g., when a pair of
   VET nodes require a client/server or peer-to-peer binding.

   In order to establish a bidirectional tunnel neighbor relationship,
   the initiator (call it "A") performs a reliable exchange (e.g., a
   short TCP transaction, a DHCP client/server exchange, etc.) with the
   responder (call it "B").  The details of the transaction are out of
   scope for this document, and indeed need not be standardized as long
   as both the initiator and responder observe the same specifications.
   Note that a short transaction instead of a persistent connection is
   advised if the outer network layer protocol addresses may change,
   e.g., due to a mobility event, due to loss of state in network
   middleboxes, etc.

   During the transaction, "A" and "B" first authenticate themselves to
   each other, then exchange information regarding the inner network
   layer prefixes that will be used for conveying inner packets that
   will be forwarded over the tunnel.  In this process, the initiator

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   and responder register one or more link identifiers (LINK_IDs) with
   one another to provide "handles" for outer IP connection addresses.

   Following this bidirectional tunnel neighbor establishment, the
   neighbors monitor the soft state for liveness, e.g., using Neighbor
   Unreachability Detection hints of forward progress.  When one of the
   neighbors wishes to terminate the relationship, it performs another
   short transaction to request the termination, then both neighbors
   delete their respective tunnel soft state.

   Once a bidirectional neighbor relationship has been established, the
   initiator and responder can further engage in a dynamic routing
   protocol (e.g., OSPF[RFC5340], etc.) to exchange inner network layer
   prefix information if they are configured to do so.

5.7.  Neighbor Coordination on VET Interfaces using IPsec

   VET interfaces that use IPsec encapsulation [RFC4301] use the
   Internet Key Exchange protocol, version 2 (IKEv2) [RFC4306] to manage
   security association setup and maintenance.  IKEv2 provides a logical
   equivalent of the SCMP in terms of VET interface neighbor
   coordinations; for example, IKEv2 also provides mechanisms for
   redirection [RFC5685] and mobility [RFC4555].

   IPsec additionally provides an extended Identification field and ICV;
   these features allow IPsec to utilize outer IP fragmentation and
   reassembly with less risk of exposure to data corruption due to
   reassembly misassociations.

5.8.  Mobility and Multihoming Considerations

   VBRs that travel between distinct enterprise networks must either
   abandon their PA prefixes that are relative to the "old" network and
   obtain PA prefixes relative to the "new" network, or somehow
   coordinate with a "home" network to retain ownership of the prefixes.
   In the first instance, the VBR would be required to coordinate a
   network renumbering event on its attached networks using the new PA
   prefixes [RFC4192][RFC5887].  In the second instance, an adjunct
   mobility management mechanism is required.

   VBRs can retain their CPs as they travel between distinct network
   points of attachment as long as they continue to refresh their CP-to-
   RLOC address mappings with their serving VBG as described in
   [I-D.templin-ironbis].  (When the VBR moves far from its serving VBG,
   it can also select a new VBG in order to maintain optimal routing.)
   In this way, VBRs can update their CP-to-RLOC mappings in real time
   and without requiring an adjunct mobility management mechanism.

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   VBRs that have true PI prefixes can withdraw the prefixes from former
   Internet points of attachment and re-advertise them at new points of
   attachment as they move.  However, this method has been shown to
   produce excessive routing churn in the global internet BGP tables,
   and should be avoided for any mobility scenarios that may occur along
   short timescales.  The alternative is to employ a system in which the
   true PI prefixes are not injected into the Internet routing system,
   but rather managed through some separate global mapping database.
   This latter method is employed by the LISP proposal [I-D.ietf-lisp].

   The VBGs of a multihomed enterprise network participate in a private
   inner network layer routing protocol instance (e.g., via an interior
   BGP instance) to accommodate network partitions/merges as well as
   intra-enterprise mobility events.

5.9.  Multicast

5.9.1.  Multicast over (Non)Multicast Enterprise Networks

   Whether or not the underlying enterprise network supports a native
   multicasting service, the VET node can act as an inner network layer
   IGMP/MLD proxy [RFC4605] on behalf of its attached EUNs and convey
   its multicast group memberships over the VET interface to a VBG
   acting as a multicast router.  Its inner network layer multicast
   transmissions will therefore be encapsulated in outer headers with
   the unicast address of the VBG as the destination.

5.9.2.  Multicast Over Multicast-Capable Enterprise Networks

   In multicast-capable enterprise networks, 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 network.  For such deployments, VET nodes can
   optionally provide a native inner multicast/broadcast capability over
   their VET interfaces through mapping of the inner multicast address
   space to the outer multicast address space.  In that case, operation
   of link-or greater-scoped inner multicasting services (e.g., a link-
   scoped neighbor discovery protocol) over the VET interface is
   available, but SHOULD be used sparingly to minimize enterprise-wide

   VET nodes encapsulate inner multicast messages sent over the VET
   interface in any mid-layer headers (e.g., UDP, 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

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   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 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 multicast address 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 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 multicast groups are mapped to site-scoped outer IP
   multicast groups, the VET node MUST ensure that the site-scoped 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-
   scoped outer IP multicast group filtering at enterprise network

5.10.  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 (e.g., anycast) are for further study.

5.11.  VET Link Partitioning

   A VET link can be partitioned into multiple distinct logical
   groupings.  In that case, each partition configures its own distinct
   'PRLNAME' (e.g., 'isatapv2.zone1.example.com',
   'isatapv2.zone2.example.com', etc.).

   VBGs can further create multiple IP subnets within a partition, e.g.,
   by sending SRAs with PIOs containing different IP prefixes to

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   different groups of VET hosts.  VBGs can identify subnets, e.g., by
   examining RLOC prefixes, observing the enterprise-interior interfaces
   over which SRSs are received, etc.

   In the limiting case, VBGs can advertise a unique set of IP prefixes
   to each VET host such that each host belongs to a different subnet
   (or set of subnets) on the VET interface.

5.12.  VBG Prefix State Recovery

   VBGs retain explicit state that tracks the inner network layer
   prefixes delegated to VBRs connected to the VET link, e.g., so that
   packets are delivered to the correct VBRs.  When a VBG loses some or
   all of its state (e.g., due to a power failure), client VBRs must
   refresh the VBG's state so that packets can be forwarded over correct

5.13.  Legacy ISATAP Services

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

   Legacy ISATAP hosts acquire addresses and/or prefixes in the same
   manner and using the same mechanisms as described for VET hosts in
   Section 4.4 above.

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][RFC6324] also
   apply to VET.

   SEND [RFC3971] and/or IPsec [RFC4301] can be used in environments
   where attacks on the neighbor coordination protocol are possible.
   SEAL [I-D.templin-intarea-seal] supports path MTU discovery, and
   provides per-packet authenticating information for data origin
   authentication, anti-replay and message header integrity.

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   Rogue neighbor coordination 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.

   VBRs and VBGs observe the recommendations for network ingress
   filtering [RFC2827].

8.  Related Work

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

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

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

   Security concerns pertaining to tunneling mechanisms are discussed in

   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

   RLOC prefix delegation for enterprise-edge interfaces is discussed in

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

   The LISP proposal [I-D.ietf-lisp] examines encapsulation/
   decapsulation issues and other aspects of tunneling.

   Various proposals within the IETF have suggested similar mechanisms.

9.  Acknowledgements

   The following individuals gave direct and/or indirect input that was

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   essential to the work: Jari Arkko, Teco Boot, Emmanuel Bacelli, Fred
   Baker, James Bound, Scott Brim, Brian Carpenter, Thomas Clausen,
   Claudiu Danilov, Chris Dearlove, Remi Despres, 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, Mark
   Townsley, Ole Troan, Michaela Vanderveen, Robin Whittle, 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.

   Discussions with colleagues following the publication of RFC5558 have
   provided useful insights that have resulted in significant
   improvements to this, the Second Edition of VET.

10.  Contributors

   The following individuals have contributed to this document:

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

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

   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

              Templin, F., "The Subnetwork Encapsulation and Adaptation
              Layer (SEAL)", draft-templin-intarea-seal-41 (work in
              progress), November 2011.

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

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

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              RFC 792, September 1981.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [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.

   [RFC3118]  Droms, R. and W. Arbaugh, "Authentication for DHCP
              Messages", RFC 3118, June 2001.

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

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

   [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.

   [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.

   [RFC5342]  Eastlake, D., "IANA Considerations and IETF Protocol Usage
              for IEEE 802 Parameters", BCP 141, RFC 5342,

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              September 2008.

11.2.  Informative References

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

              Carpenter, B. and S. Amante, "Using the IPv6 flow label
              for equal cost multipath routing and link aggregation in
              tunnels", draft-carpenter-flow-ecmp-03 (work in progress),
              October 2010.

              Cheshire, S. and M. Krochmal, "Multicast DNS",
              draft-cheshire-dnsext-multicastdns-15 (work in progress),
              December 2011.

              Clausen, T. and U. Herberg, "MANET Router Configuration
              draft-clausen-manet-autoconf-recommendations-00 (work in
              progress), February 2009.

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

              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.

              Fairhurst, G. and M. Westerlund, "IPv6 UDP Checksum
              Considerations", draft-ietf-6man-udpzero-04 (work in
              progress), October 2011.

              Johnson, R., Kumarasamy, J., Kinnear, K., and M. Stapp,
              "Subnet Allocation Option", draft-ietf-dhc-subnet-alloc-12
              (work in progress), June 2011.

              Francis, P., Xu, X., Ballani, H., Jen, D., Raszuk, R., and
              L. Zhang, "FIB Suppression with Virtual Aggregation",

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              draft-ietf-grow-va-05 (work in progress), June 2011.

              Farinacci, D., Fuller, V., Meyer, D., and D. Lewis,
              "Locator/ID Separation Protocol (LISP)",
              draft-ietf-lisp-18 (work in progress), December 2011.

              Macker, J., "Simplified Multicast Forwarding",
              draft-ietf-manet-smf-12 (work in progress), July 2011.

              Wu, J., Bi, J., Bagnulo, M., Baker, F., and C. Vogt,
              "Source Address Validation Improvement Framework",
              draft-ietf-savi-framework-05 (work in progress),
              July 2011.

              Krishnan, S., Thaler, D., and J. Hoagland, "Security
              Concerns With IP Tunneling",
              draft-ietf-v6ops-tunnel-security-concerns-04 (work in
              progress), October 2010.

              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.

              Templin, F., "Asymmetric Extended Route Optimization
              (AERO)", draft-templin-aero-05 (work in progress),
              December 2011.

              Templin, F., "The Internet Routing Overlay Network
              (IRON)", draft-templin-ironbis-09 (work in progress),
              November 2011.

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

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

   [RFC0994]  International Organization for Standardization (ISO) and
              American National Standards Institute (ANSI), "Final text
              of DIS 8473, Protocol for Providing the Connectionless-
              mode Network Service", RFC 994, March 1986.

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

   [RFC1070]  Hagens, R., Hall, N., and M. Rose, "Use of the Internet as
              a subnetwork for experimentation with the OSI network
              layer", RFC 1070, February 1989.

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

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

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

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

   [RFC2003]  Perkins, C., "IP Encapsulation within IP", RFC 2003,
              October 1996.

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

   [RFC2473]  Conta, A. and S. Deering, "Generic Packet Tunneling in
              IPv6 Specification", RFC 2473, December 1998.

   [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.

   [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.

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

   [RFC3947]  Kivinen, T., Swander, B., Huttunen, A., and V. Volpe,
              "Negotiation of NAT-Traversal in the IKE", RFC 3947,
              January 2005.

   [RFC3948]  Huttunen, A., Swander, B., Volpe, V., DiBurro, L., and M.
              Stenberg, "UDP Encapsulation of IPsec ESP Packets",
              RFC 3948, January 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.

   [RFC4213]  Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms
              for IPv6 Hosts and Routers", RFC 4213, October 2005.

   [RFC4271]  Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
              Protocol 4 (BGP-4)", RFC 4271, January 2006.

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

   [RFC4306]  Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
              RFC 4306, December 2005.

   [RFC4548]  Gray, E., Rutemiller, J., and G. Swallow, "Internet Code
              Point (ICP) Assignments for NSAP Addresses", RFC 4548,
              May 2006.

   [RFC4555]  Eronen, P., "IKEv2 Mobility and Multihoming Protocol
              (MOBIKE)", RFC 4555, June 2006.

   [RFC4592]  Lewis, E., "The Role of Wildcards in the Domain Name
              System", RFC 4592, July 2006.

   [RFC4605]  Fenner, B., He, H., Haberman, B., and H. Sandick,
              "Internet Group Management Protocol (IGMP) / Multicast
              Listener Discovery (MLD)-Based Multicast Forwarding
              ("IGMP/MLD Proxying")", RFC 4605, August 2006.

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

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              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.

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

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

   [RFC5569]  Despres, R., "IPv6 Rapid Deployment on IPv4
              Infrastructures (6rd)", RFC 5569, January 2010.

   [RFC5685]  Devarapalli, V. and K. Weniger, "Redirect Mechanism for
              the Internet Key Exchange Protocol Version 2 (IKEv2)",
              RFC 5685, November 2009.

   [RFC5720]  Templin, F., "Routing and Addressing in Networks with
              Global Enterprise Recursion (RANGER)", RFC 5720,
              February 2010.

   [RFC5887]  Carpenter, B., Atkinson, R., and H. Flinck, "Renumbering
              Still Needs Work", RFC 5887, May 2010.

   [RFC5969]  Townsley, W. and O. Troan, "IPv6 Rapid Deployment on IPv4
              Infrastructures (6rd) -- Protocol Specification",
              RFC 5969, August 2010.

   [RFC6139]  Russert, S., Fleischman, E., and F. Templin, "Routing and
              Addressing in Networks with Global Enterprise Recursion
              (RANGER) Scenarios", RFC 6139, February 2011.

   [RFC6324]  Nakibly, G. and F. Templin, "Routing Loop Attack Using
              IPv6 Automatic Tunnels: Problem Statement and Proposed
              Mitigations", RFC 6324, August 2011.

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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 network or somehow
   discovering a link in the network 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

   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 VBG-
   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
   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.  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 VBRs/VBGs.  In that case, each VET router
   interface that configures the same anycast address must exhibit
   equivalent outward behavior.

   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

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

   In view of these considerations, VBGs 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.

Author's Address

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

   Email: fltemplin@acm.org

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