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Network Working Group                                    F. Templin, Ed.
Internet-Draft                              Boeing Research & Technology
Intended status: Standards Track                        December 1, 2010
Expires: June 4, 2011


                   Virtual Enterprise Traversal (VET)
                    draft-templin-intarea-vet-17.txt

Abstract

   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 4, 2011.

Copyright Notice

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

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents



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   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  . . . . . . . . . . . . . . . . . . . . . . 12
     4.1.  Enterprise Router (ER) Autoconfiguration . . . . . . . . . 13
     4.2.  Enterprise Border Router (EBR) Autoconfiguration . . . . . 14
       4.2.1.  VET Interface Initialization . . . . . . . . . . . . . 15
       4.2.2.  Provider-Aggregated (PA) EID Prefix
               Autoconfiguration  . . . . . . . . . . . . . . . . . . 16
       4.2.3.  Provider-(In)dependent (PI) EID Prefix
               Autoconfiguration  . . . . . . . . . . . . . . . . . . 17
     4.3.  Enterprise Border Gateway (EBG) Autoconfiguration  . . . . 18
     4.4.  VET Host Autoconfiguration . . . . . . . . . . . . . . . . 19
   5.  Internetworking Operation  . . . . . . . . . . . . . . . . . . 19
     5.1.  Routing Protocol Participation . . . . . . . . . . . . . . 19
       5.1.1.  PI Prefix Routing Considerations . . . . . . . . . . . 20
     5.2.  Default Route Configuration and Selection  . . . . . . . . 20
     5.3.  Address Selection  . . . . . . . . . . . . . . . . . . . . 21
     5.4.  Next Hop Determination . . . . . . . . . . . . . . . . . . 21
     5.5.  VET Interface Encapsulation/Decapsulation  . . . . . . . . 22
       5.5.1.  Inner Network Layer Protocol . . . . . . . . . . . . . 22
       5.5.2.  Mid-Layer Encapsulation  . . . . . . . . . . . . . . . 23
       5.5.3.  SEAL Encapsulation . . . . . . . . . . . . . . . . . . 23
       5.5.4.  Outer UDP Header Encapsulation . . . . . . . . . . . . 23
       5.5.5.  Outer IP Header Encapsulation  . . . . . . . . . . . . 24
       5.5.6.  Decapsulation  . . . . . . . . . . . . . . . . . . . . 24
     5.6.  Mobility and Multihoming Considerations  . . . . . . . . . 25
     5.7.  Neighbor Coordination on VET Interfaces using SEAL . . . . 25
       5.7.1.  Router Discovery . . . . . . . . . . . . . . . . . . . 25
       5.7.2.  Neighbor Unreachability Detection  . . . . . . . . . . 26
       5.7.3.  Redirect Function  . . . . . . . . . . . . . . . . . . 26
       5.7.4.  Mobility . . . . . . . . . . . . . . . . . . . . . . . 29
     5.8.  Neighbor Coordination on VET Interfaces using IPsec  . . . 29
     5.9.  Multicast  . . . . . . . . . . . . . . . . . . . . . . . . 30
     5.10. Service Discovery  . . . . . . . . . . . . . . . . . . . . 31
     5.11. Enterprise Network Partitioning  . . . . . . . . . . . . . 31
     5.12. EBG Prefix State Recovery  . . . . . . . . . . . . . . . . 31
     5.13. Support for Legacy ISATAP Services . . . . . . . . . . . . 31
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 32



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   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 32
   8.  Related Work . . . . . . . . . . . . . . . . . . . . . . . . . 32
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 33
   10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 33
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 34
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 34
     11.2. Informative References . . . . . . . . . . . . . . . . . . 35
   Appendix A.  Duplicate Address Detection (DAD) Considerations  . . 40
   Appendix B.  Link-Layer Multiplexing and Traffic Engineering . . . 40
   Appendix C.  Anycast Services  . . . . . . . . . . . . . . . . . . 42
   Appendix D.  Change Log  . . . . . . . . . . . . . . . . . . . . . 43
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 46







































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1.  Introduction

   Enterprise networks [RFC4852] connect hosts and routers over various
   link types (see [RFC4861], Section 2.2).  The term "enterprise
   network" in this context extends to a wide variety of use cases and
   deployment scenarios.  For example, an "enterprise" can be as small
   as a SOHO network, as complex as a multi-organizational corporation,
   or as large as the global Internet itself.  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 correspond to the wireless
   multihop radio interfaces typically associated with MANETs.  Out of
   scope for this document is the autoconfiguration of provider
   interfaces, which must be coordinated in a manner specific to the
   service provider's network.

   Enterprise networks require a means for supporting both Provider-
   (In)dependent (PI) and Provider-Aggregated (PA) addressing.  This is
   especially true for enterprise network scenarios that involve
   mobility and multihoming.  The VET specification provides adaptable
   mechanisms that address these and other issues in a wide variety of
   enterprise network use cases.



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   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).  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])
   are functional building blocks for a new Internetworking architecture
   based on the Internet Routing Overlay Network (IRON)
   [I-D.templin-iron] and Routing and Addressing in Networks with Global
   Enterprise Recursion (RANGER) [RFC5720] [I-D.russert-rangers].  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].  [RFC1955] captures the high-level
   architectural aspects of the ROAD group deliberations in a "New
   Scheme for Internet Routing and Addressing (ENCAPS) for IPNG".

   VET is related to the present-day activities of the IETF INTAREA,
   AUTOCONF, DHC, IPv6, MANET, and V6OPS working groups, as well as the
   IRTF RRG working group.


2.  Terminology

   The mechanisms within this document build upon the fundamental
   principles of IP 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 the Subnetwork
   Encapsulation and Adaptation Layer (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 IP encapsulation to create overlays for
      traversing 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



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      with a commonality of business, social, political, etc.,
      interests.  Minimally, the only commonality of interest in some
      enterprise network scenarios may be the cooperative provisioning
      of connectivity itself.

   subnetwork
      the same as defined in [RFC3819].

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

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

   enterprise/site/MANET
      throughout the remainder of this document, the term "enterprise
      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
      shape.

   Enterprise Router (ER)
      As depicted in Figure 1, an Enterprise Router (ER) is a fixed or
      mobile router that comprises a router function, a host function,
      one or more enterprise-interior interfaces, and zero or more
      internal virtual, enterprise-edge, provider-edge, and VET
      interfaces.  At a minimum, an ER forwards outer IP packets over
      one or more sets of enterprise-interior interfaces, where each set
      connects to a distinct enterprise network.

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






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

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

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

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

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

   provider-edge interface
      an EBR's attachment to the Internet or to a provider network 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 an EBR and does not in itself
      directly attach to a tangible physical link (e.g., an Ethernet
      cable, a WiFi radio, etc.).  Examples include a loopback
      interface, a virtual private network interface, or some form of
      tunnel interface.






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

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

   VET interface
      a VET node's attachment to a VET link.  VET nodes configure each
      VET interface over a set of underlying 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 separate VET interfaces 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 link as a
      single IP hop.

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

   Provider-Independent (PI) address/prefix
      a network layer protocol prefix that is delegated to an EBR by an
      independent prefix registration authority.

   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.)
      are self-generated by individual enterprise networks and routable



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      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 an
      enterprise-edge or VET overlay network.  EID prefixes are separate
      and distinct from any RLOC prefix space, but are mapped to RLOC
      addresses to support routing over VET interfaces.

      EBRs use EIDs for operating the enterprise-edge or VET overlay
      network routing protocol and for next-hop determination in
      forwarding packets addressed to other EIDs.  End systems 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
   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
   NS/NA - Neighbor Solicitation/Advertisement
   PIO - Prefix Information Option
   PRL - Potential Router List
   PRLNAME - Identifying name for the PRL
   RIB - Routing Information Base
   RIO - Route Information Option
   RPF - Reverse Path Forwarding
   RS/RA - Router Solicitation/Advertisement
   SCMP - SEAL Control Message Protocol
   SEAL - Subnetwork Encapsulation and Adaptation Layer



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   SLAAC - IPv6 StateLess Address AutoConfiguration

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   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.
   Enterprise Border Routers (EBRs) are ERs that connect edge networks
   to the enterprise network and/or join multiple enterprise networks
   together.  Enterprise Border Gateways (EBGs) are EBRs that connect
   enterprise networks 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, connects any of the ER's edge
   networks to the enterprise networks, and may also connect the
   enterprise network 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 edge networks; 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.

   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 sub-IP layer routing
   service such that IP sees the network as an ordinary shared link the
   same as for a (bridged) campus LAN.  In that case, a single IP hop is



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   sufficient to traverse the network without need for encapsulation.
   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 IP hops may be necessary to traverse the network
   such that care must be taken to avoid multi-link subnet issues
   [RFC4903].

   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 other
   EBRs on the link that can be used for forwarding packets to off-link
   destinations.

   For each distinct enterprise network, a trust basis must be
   established and consistently applied.  For example, in enterprise
   networks in which EBRs establish symmetric security associations,
   mechanisms such as IPsec [RFC4301] can be used to assure
   authentication and confidentiality.  In other enterprise network
   scenarios, asymmetric securing mechanisms such as SEcure Neighbor
   Discovery (SEND) [RFC3971] may be necessary.  Still other enterprise
   networks may find it sufficient to employ additional encapsulations
   (e.g., SEAL [I-D.templin-intarea-seal]) that include a nonce to
   detect off-path attacks.

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


4.  Autoconfiguration

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






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

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

   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
   intended as unicast.)




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

   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 from a
   temporary addressing range used only for the bootstrapping purpose of
   procuring an actual RLOC taken from a preferred addressing range.
   The ER then engages in the enterprise-interior routing protocol and
   performs a DHCP client/relay exchange using the temporary RLOC as the
   address of the relay.  When the DHCP server delegates an actual RLOC
   address/prefix, the ER abandons the temporary RLOC and re-engages in
   the enterprise-interior routing protocol using an RLOC taken from the
   delegation.

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

4.2.  Enterprise Border Router (EBR) Autoconfiguration

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







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4.2.1.  VET Interface Initialization

   EBRs configure a VET interface over a set of underlying interfaces
   belonging to the same enterprise network such that all other nodes on
   the VET link appear as single-hop neighbors from the standpoint of
   the inner network layer protocol through the use of encapsulation.
   If there are multiple inner network layer protocols (e.g., IPv4,
   IPv6, OSI, etc.) the EBR configures a separate VET interface for each
   protocol.

   After the EBR configures a VET interface, it associates one or more
   RLOCs with the interface to serve as the source addresses for outer
   IP packets to be sent over underlying interfaces.  The EBR then
   assigns link-local addresses to the interface if necessary.  When
   IPv6 and IPv4 are used as the inner/outer protocols (respectively),
   the EBR autoconfigures an IPv6 link-local address on the VET
   interface using a modified EUI-64 interface identifier based on an
   IPv4 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.
   However, link-local address configuration for other inner/outer
   protocol combinations may not be necessary if a non-link-local
   address can be configured through other means (e.g., administrative
   configuration, DHCP, etc.).

   The EBR next discovers a Potential Router List (PRL) that includes
   the RLOC addresses of EBGs.  The PRL names the VET interface, and is
   specific to the address family of the inner network layer protocol
   (e.g., IPv4, IPv6, OSI, etc.).  If there are multiple address
   families, then there will be multiple VET interfaces; each with its
   own PRL.

   The PRL can be discovered through information conveyed in the
   enterprise-interior routing protocol, through a DHCP option
   [I-D.templin-isatap-dhcp], an unspecified anycast EBG discovery
   message exchange, etc.  In multicast-capable enterprise networks,
   EBRs can also listen for advertisements on the 'rasadv' [RASADV]
   multicast group address.

   Whether or not other information is available, the EBR 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 EBR discovers 'PRLNAME' through
   manual configuration, the DHCP Domain Name option [RFC2132], 'rasadv'
   protocol advertisements, link-layer information (e.g., an IEEE 802.11
   Service Set Identifier (SSID)), or through some other means specific



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   to the enterprise network.  The EBR can also obtain 'PRLNAME' as part
   of an arrangement with a private-sector PI prefix vendor (see:
   Section 4.2.3).

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

4.2.2.  Provider-Aggregated (PA) EID Prefix Autoconfiguration

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

4.2.2.1.  Stateful Prefix Delegation

   For IPv4, EBRs acquire IPv4 PA EID prefixes via an automated IPv4
   prefix delegation exchange, explicit management, etc.

   For IPv6, EBRs acquire IPv6 PA EID prefixes via DHCPv6 Prefix
   Delegation exchanges with an EBG acting as a DHCP relay/server.  In
   particular, the EBR (acting as a requesting router) can use DHCPv6
   prefix delegation [RFC3633] over the VET interface to obtain prefixes
   from the server (acting as a delegating router).  The EBR obtains
   prefixes using either a 2-message or 4-message DHCPv6 exchange
   [RFC3315].  For example, to perform the 2-message exchange, the EBR's
   DHCPv6 client forwards a Solicit message with an IA_PD option to its
   DHCPv6 relay, i.e., the EBR acts as a combined client/relay (see
   Section 4.1).  The relay then forwards the message over the VET
   interface using VET encapsulation (see: Section 5.4) to an EBG which
   either services the request or relays it further.  The forwarded
   Solicit message will elicit a reply from the server containing prefix
   delegations.  The EBR can also propose a specific prefix to the



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   DHCPv6 server per Section 7 of [RFC3633].  The server will check the
   proposed prefix for consistency and uniqueness, then return it in the
   reply to the EBR if it was able to perform the delegation.

   After the EBR 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 an EBG.  The EBR can also provision the prefixes on
   enterprise-interior interfaces to service any hosts attached to the
   link.

   The prefix delegations remain active as long as the EBR continues to
   renew them via the delegating EBG before lease lifetimes expire.  The
   lease lifetime also keeps the delegation state active even if
   communications between the EBR and delegating EBG are disrupted for a
   period of time (e.g., due to an enterprise network partition, power
   failure, etc.).  Note however that if the EBR 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.

4.2.2.2.  Stateless Prefix Delegation

   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 [RFC5569][RFC5969].  EBRs
   can use these mechanisms to statelessly configure IPv6 PA prefixes
   that embed one of the EBR's IPv4 RLOCs.

   Using this stateless prefix delegation, if the IPv4 RLOC changes the
   IPv6 prefix also changes and the EBR 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
   used.

   Stateless prefix delegation for other protocol combinations is out of
   scope.

4.2.3.  Provider-(In)dependent (PI) EID Prefix Autoconfiguration

   EBRs can acquire Provider (In)dependent (PI) prefixes to facilitate
   multihoming, mobility and traffic engineering without requiring site-
   wide renumbering events.  These PI prefixes are made available to



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   EBRs through a prefix registration authority that may or may not be
   associated with a specific ISP.

   EBRs that connect major enterprise networks (e.g., large
   corporations, academic campuses, ISP networks, etc.) to a parent
   enterprise network and/or the global Internet can acquire highly-
   aggregated PI prefixes (e.g., an IPv6 ::/20, an IPv4 /16, etc.)
   through a registration authority such as the Internet Assigned
   Numbers Authority (IANA) or a major regional Internet registry.  EBRs
   that connect small enterprise networks (e.g., SOHO networks, MANETs,
   etc.) to a parent enterprise network can acquire de-aggregated PI
   prefixes through arrangements with a PI prefix commercial vendor
   organization.

   After an EBR receives PI prefixes, it can sub-delegate portions of
   the prefixes on enterprise-edge interfaces, on other VET interfaces
   for which it is configured as an EBG and on enterprise-interior
   interfaces to service any hosts attached to the link.  The EBR can
   also sub-delegate portions of its PI prefixes to requesting routers
   within child enterprise networks.  These requesting routers consider
   their sub-delegated portions of the PI prefix as PA, and consider the
   delegating routers as their points of connection to a provider
   network.

4.3.  Enterprise Border Gateway (EBG) Autoconfiguration

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

   For each of its VET interfaces configured over a child enterprise
   network, the EBG initializes the interface the same as for an
   ordinary EBR (see Section 4.2.1).  It then arranges to add one or
   more of its RLOCs associated with the child enterprise network to the
   PRL.  In particular, for each VET interface configured over a child
   enterprise network the EBG adds the RLOCs to name service resource
   records for 'PRLNAME'.

   EBGs respond to LLMNR queries for 'PRLNAME' on VET interfaces
   configured over child enterprise networks with a distributed
   management structure.  EBGs may also engage in an unspecified anycast
   EBG discovery message exchange if they are configured to do so.

   EBGs configure a DHCP relay/server on VET interfaces configured over



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   child enterprise networks that require DHCP services.

   To avoid looping, EBGs MUST NOT configure a default route on a VET
   interface configured over a child enterprise network interface.

4.4.  VET Host Autoconfiguration

   Nodes that cannot be attached via an EBR's enterprise-edge interface
   (e.g., nomadic laptops that connect to a home office via a Virtual
   Private Network (VPN)) can instead be configured for operation as a
   simple host with a VET interface.  Such VET hosts perform the same
   VET interface initialization and EBG discovery procedures as
   specified for EBRs in Section 4.2.1, but they configure their VET
   interfaces as host interfaces (and not router interfaces).  Note also
   that a node may be configured as a host on some VET interfaces and as
   an EBR/EBG on other VET interfaces.

   A VET host may receive non-link-local addresses and/or prefixes to
   assign to the VET interface via DHCP exchanges and/or through
   information conveyed in Router Advertisements (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 prefixes
   that are appropriate according to these specific cases (i.e., shared
   prefixes vs. individual prefixes), and depend on the EBGs within the
   enterprise keeping track of which prefixes were assigned to which
   hosts.


5.  Internetworking Operation

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

5.1.  Routing Protocol Participation

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

   Routing protocol participation on non-multicast VET interfaces uses



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   the NBMA interface model, e.g., in the same manner as for OSPF over
   NBMA interfaces [RFC5340], while routing protocol participation on
   multicast-capable VET interfaces uses the standard multicast
   interface model.  EBRs use the list of EBGs in the PRL (see:
   Section 4.2.1) as an initial list of neighbors for inter-enterprise
   routing protocol participation.

5.1.1.  PI Prefix Routing Considerations

   EBRs 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] the same as
   for a major service provider network.  EBRs that connect large
   enterprise networks to provider networks can instead advertise their
   EID PI prefixes into the providers' routing system(s) if the provider
   networks are configured to accept them.

   EBRs that connect small enterprise networks to provider networks
   obtain one or more public IP address(es) (i.e., either EID or RLOC IP
   address) then dynamically register the mapping of their PI prefixes
   to the public IP address.  The registrations are through secured end-
   to-end exchanges between the EBR and a server in the PI prefix
   vendor's network (e.g., through a vendor-specific short http(s)
   transaction).  The PI prefix vendor network then acts as a virtual
   "home" enterprise network that connects its customer small enterprise
   networks to the Internet routing system.  The customer small
   enterprise networks in turn appear as mobile components of the PI
   prefix vendor's network, i.e., the customer networks are always "away
   from home".

   Further details on routing for PI prefixes is discussed in "The
   Internet Routing Overlay Network (IRON)" [I-D.templin-iron] and "Fib
   Suppression with Virtual Aggregation" [I-D.ietf-grow-va].

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



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   interface then more-specific routes could be configured on underlying
   interfaces to avoid looping.  In a preferred method, however,
   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 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, NAT traversal avoidance, 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
   EBR 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



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   underlying interface.

   As a last resort when there is no matching entry in the FIB (i.e.,
   not even default), VET nodes can discover next-hop addresses within
   the enterprise network through on-demand name service queries for the
   EID prefix taken from a packet's destination address (or, by some
   other inner address to outer address mapping mechanism).  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:
   '0.0.1.0.0.0.8.b.d.0.1.0.0.2.ip6.isatapv2.example.com'.

   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 LLMNR over the VET
   interface.  When LLMNR is used, the EBR that performs the lookup
   sends an LLMNR query (with the prefix taken from the IP destination
   address encoded in dotted-nibble format as shown above) and accepts
   the union of all replies it receives from other EBRs on the VET
   interface.  When an EBR receives an LLMNR query, it responds to the
   query IFF it aggregates an IP prefix that covers the prefix in the
   query.  If the name-service lookup succeeds, it will return RLOC
   addresses (e.g., in DNS A records) that correspond to next-hop EBRs
   to which the VET node can forward packets.

5.5.  VET Interface Encapsulation/Decapsulation

   VET interfaces encapsulate inner network layer packets in any
   necessary mid-layer headers and trailers (e.g., IPsec [RFC4301],
   etc.) followed by a SEAL header (if necessary) followed by an outer
   UDP header (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
   encapsulation:

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 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].




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5.5.2.  Mid-Layer Encapsulation

   VET interfaces that use mid-layer encapsulations encapsulate each
   inner network layer packet in any mid-layer headers and trailers as
   the first step in a potentially multi-layer encapsulation.

5.5.3.  SEAL Encapsulation

   Following any mid-layer encapsulations, VET interfaces that use SEAL
   add a SEAL header as specified in [I-D.templin-intarea-seal].
   Inclusion of a SEAL header MUST be applied uniformly between all
   nodes on the VET link.  Note that when a VET interface sends a SEAL-
   encapsulated packet to a VET node that does not use SEAL
   encapsulation, it may receive an ICMP "port unreachable" or "protocol
   unreachable" depending on whether/not an outer UDP header is
   included.

   SEAL encapsulation is used on VET links that require path MTU
   mitigations due to encapsulation overhead and/or mechanisms for VET
   interface neighbor coordination.  When SEAL encapsulation is used,
   the VET interface sets the 'Next Header' value in the SEAL header to
   the IP protocol number associated with either the mid-layer
   encapsulation or the IP protocol number of the inner network layer
   (if no mid-layer encapsulation is used).  The VET interface sets the
   other fields in the SEAL header as specified in
   [I-D.templin-intarea-seal].

5.5.4.  Outer UDP Header Encapsulation

   Following any mid-layer and/or SEAL encapsulations, VET interfaces
   that use UDP encapsulation add an outer UDP header.  Inclusion of an
   outer UDP header must be applied uniformly between all nodes on the
   VET link.  Note that when a VET interface sends a UDP-encapsulated
   packet to a node 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
   Network Address Translators (NATs) and/or legacy networking gear that
   only recognizes certain network layer protocols, e.g., Equal Cost
   MultiPath (ECMP) routers, Link Aggregation Gateways (LAGs), etc.
   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 [I-D.templin-intarea-seal]
   is used as the outermost mid-layer protocol, the VET interface sets
   the UDP source port number to a hash calculated over the inner
   network layer {destination, source} values or (optionally) over the
   inner network layer {dest addr, source addr, protocol, dest port,



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   source port} values.  The VET interface uses a hash function of its
   own choosing, but it MUST be consistent in the manner in which the
   hash is applied..

   For VET links configured over IPv4 enterprise networks, the VET
   interface 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].

5.5.5.  Outer IP Header Encapsulation

   Following any mid-layer, SEAL 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., [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
   [I-D.carpenter-flow-ecmp].

5.5.6.  Decapsulation

   When a VET interface receives an encapsulated packet, it retains the
   outer headers and processes the SEAL header as specified in
   [I-D.templin-intarea-seal].

   Next, if the packet will be forwarded from the receiving VET
   interface into a forwarding VET interface, the VET node copies the
   "TTL/Hop Limit", "Type of Service/Traffic Class" and "Congestion
   Experienced" values in the outer IP header received on the receiving
   VET interface into the corresponding fields in the outer IP header to
   be sent over the forwarding VET interface (i.e., the values are
   transferred between outer headers and *not* copied from the inner
   network layer header).  This is true even if the packet is forwarded
   out the same VET interface that it arrived on, and necessary to
   support diagnostic functions (e.g., traceroute) and avoid looping.

   During decapsulation, when the next-hop is via a non-VET interface,
   the "Congestion Experienced" value in the outer IP header is copied
   into the corresponding field in the inner network layer header.







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5.6.  Mobility and Multihoming Considerations

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

   EBRs can retain their PI prefixes as they travel between distinct
   enterprise networks as long as they update their PI prefix to public
   IP address mappings with their PI prefix vendors.  This is
   accomplished by performing the same PI prefix vendor-specific short
   transactions as specified in Section 5.1.1.  In this way, EBRs can
   update their PI prefix to RLOC mappings in real time as their RLOCs
   change.

   The EBGs of a multihomed enterprise network participate in a private
   inner network layer routing protocol instance (possibly over an
   alternate topology) to accommodate network partitions/merges as well
   as intra-enterprise mobility events.

5.7.  Neighbor Coordination on VET Interfaces using SEAL

   VET interfaces that use SEAL use the SEAL Control Message Protocol
   (SCMP) as specified in Section 4.5 of [I-D.templin-intarea-seal] to
   coordinate reachability, routing information, and mappings between
   the inner and outer network layer protocols.  SCMP directly parallels
   the IPv6 Neighbor Discovery (ND) [RFC4191][RFC4861] and ICMPv6
   [RFC4443] protocols, but operates from within the tunnel and supports
   operation for any combinations of inner and outer network layer
   protocols.

   The following subsections discuss VET interface neighbor coordination
   using SCMP:

5.7.1.  Router Discovery

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

   When an EBG 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
   EBG is configured to include.  If necessary, the EBG also includes



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   Route Information Options (RIOs) formatted as specified in Section
   5.7.3, i.e., the RIO may contain both IPv6 and non-IPv6 prefixes in
   RIOs as identified by an Address Family designator.

5.7.2.  Neighbor Unreachability Detection

   VET nodes perform Neighbor Unreachability Detection (NUD) on VET
   interface neighbors by monitoring hints of forward progress as
   evidence that a neighbor is reachable.  SEAL includes an explicit
   acknowledgement mechanism that can provide hints of forward progress.
   When data packets are flowing, the VET node can periodically set the
   A bit in data packets to elicit SCMP responses from the neighbor.
   When no data packets are flowing, the VET node can send periodic
   probes such as SCMP Neighbor Solicitation (SNS) messages for the same
   purpose.

   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 VET neighbor may be failing.  The 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.

5.7.3.  Redirect Function

   A VET node (i.e., the redirectee) may receive a redirect message when
   it forwards packets over a VET interface to a neighboring VET node
   (i.e., the redirector).  The redirector will forward the packet and
   return an SCMP Redirect message if necessary to inform the redirectee
   of a better next hop.

   The SCMP Redirect message is formatted the same as for ordinary
   ICMPv6 redirect messages (see Section 4.5 of [RFC4861]), except that
   the Destination and Target Address fields are unnecessary and
   therefore omitted.  The format of the SCMP Redirect message is shown
   in Figure 2








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    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 = 137  |    Code = 0   |          Checksum             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Reserved                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Options ...
   +-+-+-+-+-+-+-+-+-+-+-+-

                  Figure 2: SCMP Redirect Message Format

   The redirector then adds any necessary Options to the Redirect
   message.  It first includes one or more Target Link-Layer Address
   Options (TLLAOs) (see: Section 4.6.1 of [RFC4861]) that include RLOCs
   corresponding to better next hops.  The TLLAO formats for IPv4 and
   IPv6 RLOCs are shown in Figure 3 and Figure 4:

    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 3: SCMP 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 4: SCMP TLLAO Option for IPv6 RLOCs

   The redirector next includes a Route Information Option (RIO) (see:
   [RFC4191]) that contains a prefix from its FIB that covers the



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   destination address of the original packet.  SCMP uses a modified
   version of the RIO option formatted as shown in Figure 5:

    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 = 24   |    Length     | Prefix Length |  AF |Prf|E|RSV|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Route Lifetime                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Prefix (Variable Length)                    |
   .                                                               .
   .                                                               .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

              Figure 5: SCMP Route Information Option Format

   In this modified format, the redirector prepares the Route Lifetime
   and Prefix fields in the RIO option the same as specified in
   [RFC4191].  It then sets the fields in the header as follows:

   o  the 'Type', 'Length' and 'Prf' fields are set the same as
      specified in [RFC4191].

   o  the 'RSV' field is set to 0.

   o  he 'Length' field is set to 1, 2, or 3 as specified in [RFC4191],
      or set to 4 if the 'Prefix Length' is greater than 128 in order to
      accommodate prefixes of non-IP protocols of up to 192 bits in
      length.

   o  the 'Prefix Length' field ranges from 0 to 192.  The 'Prefix'
      field is 0, 8, 16 or 24 octets depending on the length, and the
      embedded prefix MAY be up to 192 bits in length.

   o  bits 24 - 26 are used to contain an 'Address Family (AF)' value
      that indicates the embedded prefix protocol type.  This document
      defines the following values for AF:

      *  000 - IPv4

      *  001 - IPv6

      *  010 - OSI/CLNP NSAP

   o  the 'E' bit is set to 1 if this prefix is assigned to an End User
      Network, and set to 0 otherwise.




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   Following the RIO option, the redirector includes any other necessary
   options (e.g., SEND options) followed by a Redirected Header
   containing the leading portion of the packet that triggered the
   redirect as the final option in the message.  The redirector then
   encapsulates the Redirect message the same as for any other SCMP
   message and sends it to the redirectee.

   When the redirectee receives the Redirect, it first authenticates the
   message (i.e., by checking the SEAL_ID in the Redirected Header, by
   examining SEND options, etc.) then uses the EID prefix in the RIO
   with its respective lifetime to update its FIB.  The redirectee also
   caches the IPv4 or IPv6 addresses in TLLAOs as the layer 2 addresses
   of potential next-hops.

   The redirectee retains the FIB entry created as a result of receipt
   of an SCMP Redirect until the route lifetime expires, or until the
   redirected target neighbor becomes unreachable.  In this way, RLOC
   liveness detection parallels IPv6 Neighbor Unreachability Detection
   as discussed in the next section.

5.7.4.  Mobility

   When a VET node moves to a new network point of attachment resulting
   in the change of an old RLOC to a new RLOC, it leaves short-term
   forwarding information with its former network point of attachment.
   Thereafter, any existing correspondents that attempt to contact the
   mobile node via the former network point of attachment will be
   redirected to the new network point of attachment.  Any new
   correspondents will instead be directed to the new network point of
   attachment.

5.8.  Neighbor Coordination on VET Interfaces using IPsec

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

   IPsec additionally provides an extended Identification field and
   integrity check vector; these features allow IPsec to utilize outer
   IP fragmentation and reassembly with less risk of exposure to data
   corruption due to reassembly misassociations.  On the other hand,
   IPsec entails the use of symmetric security associations and hence
   may not be appropriate to all enterprise network use cases.





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5.9.  Multicast

   In multicast-capable deployments, ERs provide an enterprise-wide
   multicasting service (e.g., Simplified Multicast Forwarding (SMF)
   [I-D.ietf-manet-smf], Protocol Independent Multicast (PIM) routing,
   Distance Vector Multicast Routing Protocol (DVMRP) routing, etc.)
   over their enterprise-interior interfaces such that outer IP
   multicast messages of site-scope or greater scope will be propagated
   across the enterprise network.  For such deployments, VET nodes can
   also provide an 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-
   scoped (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
   flooding.

   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
   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-scope outer
   IP multicast messages received on the underlying interfaces for one
   VET interface do not "leak out" to the underlying interfaces of
   another VET interface.  This is accommodated through normal site-



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   scoped outer IP multicast group filtering at enterprise network
   boundaries.

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.  Enterprise Network Partitioning

   An enterprise network 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.).

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

   In the limiting case, EBGs 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.  EBG Prefix State Recovery

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

5.13.  Support for Legacy ISATAP Services

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







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6.  IANA Considerations

   There are no IANA considerations for this document.


7.  Security Considerations

   Security considerations for MANETs are found in [RFC2501].

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

   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] provides a per-packet identification
   that can be used to detect source address spoofing.

   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.

   VET EBRs and EBGs 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
   [I-D.ietf-v6ops-tunnel-security-concerns].

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




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

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

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

   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
   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.


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.





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11.  References

11.1.  Normative References

   [I-D.templin-intarea-seal]
              Templin, F., "The Subnetwork Encapsulation and Adaptation
              Layer (SEAL)", draft-templin-intarea-seal-24 (work in
              progress), November 2010.

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

   [RFC0792]  Postel, J., "Internet Control Message Protocol", STD 5,
              RFC 792, September 1981.

   [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.

   [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.

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

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




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   [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,
              September 2008.

11.2.  Informative References

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

   [I-D.carpenter-flow-ecmp]
              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.

   [I-D.cheshire-dnsext-multicastdns]
              Cheshire, S. and M. Krochmal, "Multicast DNS",
              draft-cheshire-dnsext-multicastdns-12 (work in progress),
              October 2010.

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

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

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




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   [I-D.ietf-6man-udpzero]
              Fairhurst, G. and M. Westerlund, "IPv6 UDP Checksum
              Considerations", draft-ietf-6man-udpzero-02 (work in
              progress), October 2010.

   [I-D.ietf-dhc-subnet-alloc]
              Johnson, R., Kumarasamy, J., Kinnear, K., and M. Stapp,
              "Subnet Allocation Option", draft-ietf-dhc-subnet-alloc-11
              (work in progress), May 2010.

   [I-D.ietf-grow-va]
              Francis, P., Xu, X., Ballani, H., Jen, D., Raszuk, R., and
              L. Zhang, "FIB Suppression with Virtual Aggregation",
              draft-ietf-grow-va-03 (work in progress), August 2010.

   [I-D.ietf-lisp]
              Farinacci, D., Fuller, V., Meyer, D., and D. Lewis,
              "Locator/ID Separation Protocol (LISP)",
              draft-ietf-lisp-09 (work in progress), October 2010.

   [I-D.ietf-manet-smf]
              Macker, J. and S. Team, "Simplified Multicast Forwarding",
              draft-ietf-manet-smf-10 (work in progress), March 2010.

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

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

   [I-D.nakibly-v6ops-tunnel-loops]
              Nakibly, G. and F. Templin, "Routing Loop Attack using
              IPv6 Automatic Tunnels: Problem Statement and Proposed
              Mitigations", draft-nakibly-v6ops-tunnel-loops-03 (work in
              progress), August 2010.

   [I-D.russert-rangers]
              Russert, S., Fleischman, E., and F. Templin, "RANGER
              Scenarios", draft-russert-rangers-05 (work in progress),
              July 2010.

   [I-D.templin-iron]
              Templin, F., "The Internet Routing Overlay Network



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              (IRON)", draft-templin-iron-13 (work in progress),
              October 2010.

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

   [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.

   [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



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              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.

   [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.



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   [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.

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

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

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

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

   [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",



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              RFC 5969, August 2010.


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
   assignments).

   Pseudo-random IPv6 RLOCs can be generated with mechanisms such as
   CGAs, IPv6 privacy addresses, etc. with very small probability of
   collision.  Pseudo-random IPv4 RLOCs can be generated through random
   assignment from a suitably large IPv4 prefix space.

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


Appendix B.  Link-Layer Multiplexing and Traffic Engineering

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

      "Finally, we note another possibility that is NOT multihoming: one
      logical interface may be bound to multiple physical interfaces, in
      order to increase the reliability or throughput between directly
      connected machines by providing alternative physical paths between
      them.  For instance, two systems might be connected by multiple
      point-to-point links.  We call this "link-layer multiplexing".



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      With link-layer multiplexing, the protocols above the link layer
      are unaware that multiple physical interfaces are present; the
      link-layer device driver is responsible for multiplexing and
      routing packets across the physical interfaces."

   EBRs can support such a link-layer multiplexing capability across the
   enterprise network in accordance with the Weak End System Model (see
   Section 3.3.4 of [RFC1122]).  In particular, when an EBR
   autoconfigures an RLOC address, it can associate it with the VET
   interface only instead of assigning it to an underlying interface.
   The EBR therefore only needs to obtain a single RLOC address even if
   there are multiple underlying interfaces, i.e., it does not need to
   obtain one for each underlying interface.  The EBR can then leave the
   underlying interfaces unnumbered, or it can configure a randomly
   chosen IP link-local address (e.g., from the prefix 169.254/16
   [RFC3927] for IPv4) on underlying interfaces that require a
   configuration.  The EBR need not check these link-local addresses for
   uniqueness within the enterprise network, as they will not normally
   be used as the source address for packets.

   When the EBR engages in the enterprise-interior routing protocol, it
   uses the RLOC address assigned to the VET interface as the source
   address for all routing protocol control messages, however it must
   also supply an interface identifier (e.g., a small integer) that
   uniquely identifies the underlying interface that the control message
   is sent over.  For example, if the underlying interfaces are known as
   "eth0", "eth1" and "eth7" the EBR can supply the token "7" when it
   sends a routing protocol control message over the "eth7" interface.
   This is necessary to ensure that other routers can determine the
   specific interface over which the EBR's routing protocol control
   message was sent, but the token need only be unique within the EBR
   itself and need not be unique throughout the enterprise network.

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

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



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   forwarded packets with RLOC destinations will flow through the VET
   interface instead of through the underlying interfaces.

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

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

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

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


Appendix C.  Anycast Services

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




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

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

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


Appendix D.  Change Log

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



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   Changes from -14 to -15:

   o  new insights into default route configuration and next-hop
      determination

   Changes from -13 to -14:

   o  fixed Idnits

   Changes from -12 to -13:

   o  Changed "VGL" *back* to "PRL"

   o  More changes for multi-protocol support

   o  Changes to Redirect function

   Changes from -11 to -12:

   o  Major section rearrangement

   o  Changed "PRL" to "VGL"

   o  Brought back text that was lost in the -10 to -11 transition

   Changes from -10 to -11:

   o  Major changes with significant simplifications

   o  Now support stateless PD using 6rd mechanisms

   o  SEAL Control Message Protocol (SCMP) used instead of ICMPv6

   o  Multi-protocol support including IPv6, IPv4, OSI/CLNP, etc.

   Changes from -09 to -10:

   o  Changed "enterprise" to "enterprise network" throughout

   o  dropped "inner IP", since inner layer may be non-IP

   o  TODO - convert "IPv6 ND" to SEAL SCMP messages so that control
      messages remain *within* the tunnel interface instead of being
      exposed to the inner network layer protocol engine.

   Changes from -08 to -09:





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   o  Expanded discussion of encapsulation/decapsulation procedures

   o  cited IRON

   Changes from -07 to -08:

   o  Specified the approach to global mapping using virtual aggregation
      and BGP

   Changes from -06 to -07:

   o  reworked redirect function

   o  created new section on VET interface encapsulation

   o  clarifications on nexthop selection

   o  fixed several bugs

   Changed from -05 to -06:

   o  reworked VET interface ND

   o  anycast clarifications

   Changes from -03 to -04:

   o  security consideration clarifications

   Changes from -02 to -03:

   o  security consideration clarifications

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

   o  VET now uses SEAL natively

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

   Changes from -01 to -02:

   o  Defined CGA and privacy address configuration on VET interfaces

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

   Changes from -00 to -01:



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

   o  Appendix B clarifications on Weak End System Model

   Changes from RFC5558 to -00:

   o  New appendix on RLOC configuration on VET interfaces.


Author's Address

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

   Email: fltemplin@acm.org
































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