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Network Working Group                                    F. Templin, Ed.
Internet-Draft                              Boeing Research & Technology
Intended status: Standards Track                      September 30, 2009
Expires: April 3, 2010


                   Virtual Enterprise Traversal (VET)
                    draft-templin-intarea-vet-04.txt

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on April 3, 2010.

Copyright Notice

   Copyright (c) 2009 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
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Abstract

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



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   IP addresses/prefixes and support internetworking operation in a wide
   variety of use cases including Small Office, Home Office (SOHO)
   networks, Mobile Ad hoc Networks (MANETs), ISP networks, multi-
   organizational corporate networks and the interdomain core of the
   global Internet itself.  This document specifies a Virtual Enterprise
   Traversal (VET) abstraction for autoconfiguration and operation of
   nodes in enterprise networks.  VET can also be considered as version
   2 of the Intra-Site Automatic Tunnel Addressing Protocol (i.e.,
   "ISATAPv2").










































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  6
   3.  Enterprise Characteristics . . . . . . . . . . . . . . . . . . 10
   4.  Autoconfiguration  . . . . . . . . . . . . . . . . . . . . . . 12
     4.1.  Enterprise Router (ER) Autoconfiguration . . . . . . . . . 12
     4.2.  Enterprise Border Router (EBR) Autoconfiguration . . . . . 14
       4.2.1.  VET Interface Autoconfiguration  . . . . . . . . . . . 14
       4.2.2.  Provider-Aggregated (PA) EID Prefix
               Autoconfiguration  . . . . . . . . . . . . . . . . . . 16
       4.2.3.  Provider-Independent (PI) EID Prefix
               Autoconfiguration  . . . . . . . . . . . . . . . . . . 17
     4.3.  Enterprise Border Gateway (EBG) Autoconfiguration  . . . . 17
     4.4.  VET Host Autoconfiguration . . . . . . . . . . . . . . . . 18
   5.  Internetworking Operation  . . . . . . . . . . . . . . . . . . 18
     5.1.  Routing Protocol Participation . . . . . . . . . . . . . . 18
     5.2.  RLOC-Based Communications  . . . . . . . . . . . . . . . . 19
     5.3.  EID-Based Communications . . . . . . . . . . . . . . . . . 19
     5.4.  IPv6 Router and Prefix Discovery . . . . . . . . . . . . . 19
       5.4.1.  Router and Prefix Discovery  . . . . . . . . . . . . . 19
       5.4.2.  Address Autoconfiguration on VET Interfaces  . . . . . 20
       5.4.3.  PA Prefix Registration . . . . . . . . . . . . . . . . 22
       5.4.4.  PI Prefix Registration . . . . . . . . . . . . . . . . 22
       5.4.5.  Next-Hop Discovery . . . . . . . . . . . . . . . . . . 24
     5.5.  IPv4 Router and Prefix Discovery . . . . . . . . . . . . . 26
     5.6.  Forwarding Packets on VET Interfaces . . . . . . . . . . . 26
     5.7.  VET and SEAL Encapsulation . . . . . . . . . . . . . . . . 27
     5.8.  Generating Errors  . . . . . . . . . . . . . . . . . . . . 28
     5.9.  Processing Errors  . . . . . . . . . . . . . . . . . . . . 29
     5.10. Mobility and Multihoming Considerations  . . . . . . . . . 30
     5.11. Multicast  . . . . . . . . . . . . . . . . . . . . . . . . 31
     5.12. Service Discovery  . . . . . . . . . . . . . . . . . . . . 32
     5.13. Enterprise Partitioning  . . . . . . . . . . . . . . . . . 32
     5.14. EBG Prefix State Recovery  . . . . . . . . . . . . . . . . 32
     5.15. Support for Legacy ISATAP Services . . . . . . . . . . . . 33
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 33
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 33
   8.  Related Work . . . . . . . . . . . . . . . . . . . . . . . . . 34
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 35
   10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 35
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 35
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 35
     11.2. Informative References . . . . . . . . . . . . . . . . . . 37
   Appendix A.  Duplicate Address Detection (DAD) Considerations  . . 40
   Appendix B.  Link-Layer Multiplexing and Traffic Engineering . . . 41
   Appendix C.  Change Log  . . . . . . . . . . . . . . . . . . . . . 43
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 44



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1.  Introduction

   Enterprise networks [RFC4852] connect routers over various link types
   (see [RFC4861], Section 2.2).  The term "enterprise network" in this
   context extends to a wide variety of use cases and deployment
   scenarios.  For example, an "enterprise" can be as small as a SOHO
   network, as complex as a multi-organizational corporation, or as
   large as the global Internet itself.  ISP networks are another
   example use case that fits well with the VET enterprise network
   model.  Mobile Ad hoc Networks (MANETs) [RFC2501] can also be
   considered as a challenging example of an enterprise network, in that
   their topologies may change dynamically over time and that they may
   employ little/no active management by a centralized network
   administrative authority.  These specialized characteristics for
   MANETs require careful consideration, but the same principles apply
   equally to other enterprise network scenarios.

   This document specifies a Virtual Enterprise Traversal (VET)
   abstraction for autoconfiguration and internetworking operation,
   where addresses of different scopes may be assigned on various types
   of interfaces with diverse properties.  Both IPv4 [RFC0791] and IPv6
   [RFC2460] are discussed within this context.  The use of standard
   DHCP [RFC2131] [RFC3315] and neighbor discovery [RFC0826] [RFC1256]
   [RFC4861] mechanisms is assumed unless otherwise specified.



























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

               Figure 1: Enterprise Router (ER) Architecture

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

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



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

   VET represents a functional superset of 6over4 [RFC2529] and the
   Intra-Site Automatic Tunnel Addressing Protocol (ISATAP) [RFC5214],
   where VET can be considered as version 2 of the ISATAP protocol
   (i.e., "ISATAPv2").  VET also works in conjunction with the
   Subnetwork Encapsulation and Adaptation Layer (SEAL)
   [I-D.templin-intarea-seal] and supports additional encapsulations
   such as IPsec [RFC4301].  Together, these technologies serve as
   functional building blocks for a new Internetworking architecture
   known as Routing and Addressing in Next Generation EnteRprises
   [I-D.templin-ranger] [I-D.russert-rangers].

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

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


2.  Terminology

   The mechanisms within this document build upon the fundamental
   principles of IP in IP encapsulation.  The terms "inner" and "outer"
   are used to, respectively, refer to the innermost IP {address,
   protocol, header, packet, etc.} *before* encapsulation, and the
   outermost IP {address, protocol, header, packet, etc.} *after*
   encapsulation.  VET also uses the Subnetwork Encapsulation and
   Adaptation Layer (SEAL) [I-D.templin-intarea-seal] as a "mid-layer"
   encapsulation between the inner and outer IP headers, and also allows
   for inclusion of other mid-layer encapsulations including IPSec
   [RFC4301].

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

   subnetwork
      the same as defined in [RFC3819].






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

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

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

   enterprise/site/MANET
      throughout the remainder of this document, the term "enterprise"
      is used to collectively refer to any of {enterprise, site, MANET},
      i.e., the VET mechanisms and operational principles can be applied
      to enterprises, sites, and MANETs of any size or shape.

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

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







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

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

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

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

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

   Virtual Enterprise Traversal (VET)
      an abstraction that uses IP in IP encapsulation to create an
      overlay that spans an enterprise in a single (inner) IP hop.  VET
      can be considered as version 2 of the ISATAP protocol (i.e.,
      "ISATAPv2").

   VET interface
      an EBR's tunnel virtual interface used for Virtual Enterprise
      Traversal.  The EBR configures a VET interface over a set of
      underlying interfaces belonging to the same enterprise.  When
      there are multiple distinct enterprises (each with their own
      distinct set of underlying interfaces), the EBR configures a



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      separate VET interface over each set of underlying interfaces,
      i.e., the EBR configures multiple VET interfaces.  VET interfaces
      natively use the Subnetwork Encapsulation and Adaptation Layer
      (SEAL).

      The VET interface encapsulates each inner IP packet in any mid-
      layer headers followed by the SEAL header 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 enterprise.  The VET
      interface therefore presents an automatic tunneling abstraction
      that represents the enterprise as a single IP hop.

      VET interfaces in non-multicast environments are Non-Broadcast,
      Multiple Access (NBMA); VET interfaces in multicast environments
      are multicast capable.

   VET address
      an IPv6 address format associated with a VET interface that use
      IPv6 and IPv4 as the inner and outer IP protocols, respectively.
      VET addresses are formed exactly as specified for ISATAP addresses
      in Sections 6.1 and 6.2 of [RFC5214].

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

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

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

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

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



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      enterprises and routable only within the enterprise-interior
      routing region.

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

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

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

   The following additional acronyms are used throughout the document:

   CGA - Cryptographically Generated Address
   DHCP(v4, v6) - Dynamic Host Configuration Protocol
   FIB - Forwarding Information Base
   ISATAP - Intra-Site Automatic Tunnel Addressing Protocol
   NBMA - Non-Broadcast, Multiple Access
   ND - Neighbor Discovery
   PIO - Prefix Information Option
   PRL - Potential Router List
   PRLNAME - Identifying name for the PRL (default is "isatapv2")
   RIO - Route Information Option
   RS/RA - IPv6 ND Router Solicitation/Advertisement
   SEAL - Subnetwork Encapsulation and Adaptation Layer
   SLAAC - IPv6 StateLess Address AutoConfiguation


3.  Enterprise Characteristics

   Enterprises consist of links that are connected by Enterprise Routers
   (ERs) as depicted in Figure 1.  ERs typically participate in a
   routing protocol over enterprise-interior interfaces to discover
   routes that may include multiple Layer 2 or Layer 3 forwarding hops.



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   Enterprise Border Routers (EBRs) are ERs that connect edge networks
   to the enterprise and/or join multiple enterprises together.
   Enterprise Border Gateways (EBGs) are EBRs that either directly or
   indirectly connect enterprises to provider networks.

   Conceptually, an ER embodies both a host function and router
   function.  The host function supports Endpoint Interface iDentifier
   (EID)-based and/or Routing LOCator (RLOC)-based communications
   according to the weak end-system model [RFC1122].  The router
   function engages in the enterprise-interior routing protocol,
   connects any of the ER's edge networks to the enterprise, and may
   also connect the enterprise to provider networks (see Figure 1).

   An enterprise may be as simple as a small collection of ERs and their
   attached edge networks; an enterprise may also contain other
   enterprises and/or be a subnetwork of a larger enterprise.  An
   enterprise may further encompass a set of branch offices and/or
   nomadic hosts connected to a home office over one or several service
   providers, e.g., through Virtual Private Network (VPN) tunnels.
   Finally, an enterprise may contain many internal partitions that are
   logical groupings of nodes for the purpose of load balancing,
   organizational separation, etc.  In that case, each internal
   partition resembles an individual segment of a bridged LAN.

   Enterprises that comprise link types with sufficiently similar
   properties (e.g., Layer 2 (L2) address formats, maximum transmission
   units (MTUs), etc.) can configure a sub-IP layer routing service such
   that IP sees the enterprise as an ordinary shared link the same as
   for a (bridged) campus LAN.  In that case, a single IP hop is
   sufficient to traverse the enterprise without IP layer encapsulation.
   Enterprises that comprise link types with diverse properties and/or
   configure multiple IP subnets must also provide a routing service
   that operates as an IP layer mechanism.  In that case, multiple IP
   hops may be necessary to traverse the enterprise such that 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 VET nodes in an enterprise as single-
   hop neighbors attached to a virtual link.  VET nodes configure a
   separate VET interface for each distinct enterprise to which they
   connect, and discover other EBRs on each VET interface that can be
   used for forwarding packets to off-enterprise destinations.

   For each distinct enterprise, an enterprise trust basis must be
   established and consistently applied.  For example, in enterprises in
   which EBRs establish symmetric security associations, mechanisms such
   as IPsec [RFC4301] can be used to assure authentication and
   confidentiality.  In other enterprise network scenarios, asymmetric



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   securing mechanisms such as SEcure Neighbor Discovery (SEND)
   [RFC3971] may be necessary to authenticate exchanges based on trust
   anchors.  Still other enterprises may have sufficient infrastructure
   trust basis (e.g., through proper deployment of filtering gateways at
   enterprise borders) and may not require nodes to implement such
   additional mechanisms.

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


4.  Autoconfiguration

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

4.1.  Enterprise Router (ER) Autoconfiguration

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

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



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   VET interface configured over the underlying interfaces (see Section
   4.2.1).  In the latter case, the ER can use the VET interface for
   link layer multiplexing and traffic engineering purposes as specified
   in Appendix B.

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

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

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

   A combined approach using both DHCP and self-generation is also
   possible when the ER configures both a DHCP client and relay that are
   connected, e.g., via a pair of back-to-back connected Ethernet
   interfaces, a tun/tap interface, a loopback interface, inter-process
   communication, etc.  The ER first self-generates a temporary RLOC
   used only for the purpose of procuring an actual RLOC taken from a
   disjoint addressing range.  The ER then engages in the 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 routing protocol using an RLOC
   taken from the delegation.

   In some enterprise use cases (e.g., MANETs), assignment of RLOCs on
   enterprise-interior interfaces as singleton addresses (i.e., as



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

4.2.  Enterprise Border Router (EBR) Autoconfiguration

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

4.2.1.  VET Interface Autoconfiguration

   VET interface autoconfiguration entails: 1) interface initialization,
   2) EBG discovery and enterprise identification, and 3) EID
   configuration.  These functions are specified in the following
   sections.

4.2.1.1.  Interface Initialization

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

   When IPv6 and IPv4 are used as the inner/outer protocols
   (respectively), the EBR autoconfigures an IPv6 link-local VET address
   on the VET interface to support packet forwarding and operation of
   the IPv6 neighbor discovery protocol.  The link-local VET address is
   formed exactly as specified in Sections 6.1 and 6.2 of [RFC5214].
   The link-local address need not be checked for uniqueness since the
   IPv4 RLOC embedded in the address itself is managed for uniqueness
   (see Section 4.1).

   Link-local address configuration for other inner/outer IP protocol
   combinations is through administrative configuration or through an
   unspecified alternate method.  Link-local address configuration for
   other inner/outer IP protocol combinations may not be necessary if an



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   EID can be configured through other means (see Section 4.2.1.3).

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

4.2.1.2.  Enterprise Border Gateway Discovery and Enterprise
          Identification

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

   In particular, whether or not routing information is available, the
   EBR can discover the list of EBGs by resolving an identifying name
   for the PRL ('PRLNAME') formed as 'hostname.domainname', where
   'hostname' is an enterprise-specific name string and 'domainname' is
   an enterprise-specific DNS suffix.  The EBR discovers 'PRLNAME'
   through manual configuration, the DHCP Domain Name option [RFC2132],
   'rasadv' protocol advertisements, link-layer information (e.g., an
   IEEE 802.11 Service Set Identifier (SSID)), or through some other
   means specific to the enterprise.

   In the absence of other information, the EBR sets the 'hostname'
   component of 'PRLNAME' to "isatapv2" and sets the 'domainname'
   component to the enterprise-specific DNS suffix "example.com" (e.g.,
   as "isatapv2.example.com").  Note that this naming convention is
   intentionally distinct from the convention specified in [RFC5214],
   and is used by the EBR to distinguish between ISATAP and VET virtual
   interfaces.

   The global Internet interdomain routing core represents a specific
   example of an enterprise network scenario, albeit on an enormous
   scale.  The 'PRLNAME' assigned to the global Internet interdomain
   routing core for the purpose of VET is "isatapv2.net".

   After discovering 'PRLNAME', the EBR can discover the list of EBGs by
   resolving 'PRLNAME' to a list of RLOC addresses through a name
   service lookup.  For centrally managed enterprises, the EBR resolves
   'PRLNAME' using an enterprise-local name service (e.g., the
   enterprise-local DNS).  For enterprises with a distributed management
   structure, the EBR resolves 'PRLNAME' using Link-Local Multicast Name
   Resolution (LLMNR) [RFC4795] over the VET interface.  In that case,



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   all EBGs in the PRL respond to the LLMNR query, and the EBR accepts
   the union of all responses.

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

4.2.1.3.  EID Configuration

   After EBG discovery, the EBR configures EIDs on its VET interfaces.
   When IPv6 and IPv4 are used as the inner/outer protocols
   (respectively), the EBR autoconfigures EIDs as specified in
   Section 5.4.  In particular, the EBR acts as a host on its VET
   interfaces for router and prefix discovery purposes but acts as a
   router on its VET interfaces for routing protocol operation and
   packet forwarding purposes.

   EID configuration for other inner/outer IP protocol combinations is
   through administrative configuration or through an unspecified
   alternate method; in some cases, such EID configuration can be
   performed independently of EBG discovery.

4.2.2.  Provider-Aggregated (PA) EID Prefix Autoconfiguration

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

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

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

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

   The EBR can propose a specific prefix to the DHCPv6 server per



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   Section 7 of [RFC3633], e.g., if a prefix delegation hint is
   available.  The server will check the proposed prefix for consistency
   and uniqueness, then return it in the reply to the EBR if it was able
   to perform the delegation.

   After the EBR receives PA prefix delegations, it can provision the
   prefixes on enterprise-edge interfaces as well as on other VET
   interfaces for which it is configured as an EBG.  It can also
   provision the prefixes on enterprise-interior interfaces as long as
   other nodes on those interfaces unambiguously associate the prefixes
   with the EBR.

4.2.3.  Provider-Independent (PI) EID Prefix Autoconfiguration

   Independent of any PA prefixes, EBRs can acquire and use Provider-
   Independent (PI) EID prefixes that are self-configured (e.g., using
   [RFC4193], etc.) and/or delegated by a registration authority (e.g.,
   through a regional Internet registry, through a centrally-assigned
   unique local address delegation authority [I-D.hain-ipv6-ulac],
   etc.).  When an EBR acquires a PI prefix, it must also obtain
   credentials that it can use to prove prefix ownership when it
   registers the prefixes with EBGs within an enterprise (see
   Section 5.4 and Section 5.5).

   After the EBR receives PI prefix delegations, it can provision the
   prefixes on enterprise-edge interfaces as well as on other VET
   interfaces for which it is configured as an EBG.  It can also
   provision the prefixes on enterprise-interior interfaces as long as
   other nodes on those interfaces can unambiguously associate the
   prefixes with the EBR.

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

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

4.3.  Enterprise Border Gateway (EBG) Autoconfiguration

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

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



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

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

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

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

4.4.  VET Host Autoconfiguration

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

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


5.  Internetworking Operation

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

5.1.  Routing Protocol Participation

   Following autoconfiguration, ERs engage in any RLOC-based IP routing
   protocols and forward IP packets with RLOC addresses.  EBRs can
   additionally engage in any EID-based IP routing protocols and forward
   IP packets with EID addresses.  Note that the EID-based IP routing
   domains are separate and distinct from any RLOC-based IP routing
   domains.





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5.2.  RLOC-Based Communications

   When permitted by policy and supported by routing, end systems can
   avoid VET interface encapsulation through communications that
   directly invoke the outer IP protocol using RLOC addresses instead of
   EID addresses.  End systems can use source address selection rules to
   determine whether to use EID or RLOC addresses based on, e.g., name
   service information.

5.3.  EID-Based Communications

   In many enterprise scenarios, the use of EID-based communications
   (i.e., instead of RLOC-based communications) may be necessary and/or
   beneficial to support address scaling, NAT avoidance, security domain
   separation, site multihoming, traffic engineering, etc.  The
   remainder of this section discusses internetworking operation for
   EID-based communications using the VET interface abstraction.

5.4.  IPv6 Router and Prefix Discovery

   The following sections discuss router and prefix discovery
   considerations for the case of IPv6 as the inner IP protocol and IPv4
   as the outer protocol.  Router discovery and prefix discovery for
   other IP protocol combinations are out of scope.

5.4.1.  Router and Prefix Discovery

   VET nodes follow the router and prefix discovery procedures specified
   in [RFC5214], Section 8.3.  They discover EBGs within the enterprise
   as specified in Section 4.2.1.2, then perform RS/RA exchanges with
   the EBGs to establish and maintain routes and prefixes.  Depending on
   the enterprise network trust basis, VET nodes may be required to use
   SEND to secure the RS/RA exchanges.

   EBGs follow the router and prefix discovery procedures specified in
   [RFC5214], Section 8.2.  They send solicited RAs over VET interfaces
   for which they are configured as gateways where the RAs include
   Router Lifetimes, Prefix Information Options (PIOs) that contain PA
   prefixes for SLAAC, and with other required options/parameters.  The
   RAs can also include PIOs with the 'L' bit set to 0 and with a prefix
   such as '2001:DB8::/48' as a hint of an aggregated prefix from which
   the EBG is willing to delegate longer PA prefixes.  When PIOs that
   contain PA prefixes for SLAAC are included, the 'M' flag in the RA
   should also be set to 0.

   When an EBG receives an RS on a VET interface, it authenticates the
   message then proceeds according to whether/not the VET interface
   maintains a neighbor cache.  If the VET interface maintains a



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   neighbor cache, the EBG first creates or updates a neighbor cache
   entry for the VET link-local source address in the RS according to
   Section 6.2.6 of [RFC4861].  If the neighbor cache entry cannot be
   created/updated (e.g., due to insufficient resources), the EBG
   silently discards the RS message and does not send an RA.  Otherwise,
   the EBG creates/updates the neighbor cache entry, sets a "Time To
   Live (TTL)" on the entry that is no shorter than the its advertised
   Router Lifetime, and sends the RA response to the RS.  If the
   neighbor cache entry TTL subsequently expires before a new RS
   arrives, the EBG deletes the neighbor cache entry.  Note that if the
   VET interface does not maintain a neighbor cache, the EBG simply
   omits these neighbor cache manipulations and sends the RA response to
   the RS.

   When the VET node receives an RA on a VET interface, it authenticates
   the message then configures a default route based on the Router
   Lifetime.  Thereafter, the VET node accepts packets that are
   forwarded by EBGs for which it has current default routing
   information (i.e., ingress filtering is based on the default router
   trust relationship rather than a prefix-specific ingress filter
   entry).  If the RA also contains Prefix Information Options (PIOs)
   with the 'A' and 'L' bits set to 1, the VET node autoconfigures IPv6
   VET addresses from the advertised prefixes and assigns them to the
   VET interface as specified in Section 5.4.2.

5.4.2.  Address Autoconfiguration on VET Interfaces

   VET nodes perform address autoconfiguration to generate both VET
   addresses and other types of IPv6 addresses (e.g.,CGA addresses
   [RFC3972], IPv6 Privacy addresses [RFC4941], etc.).

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

   When the node self-generates a non-VET IPv6 address from one of the
   EBG's advertised on-link prefixes, it first verifies that the
   interface identifier does not begin with the reserved tokens "00-00-
   5E-FE" or "02-00-5E-FE"; otherwise, it repeats the self-generation
   process until it obtains an interface identifier that does not
   collide.  The VET node next marks each self-generated non-VET address
   as tentative and uses the address as the target address in an IPv6
   Neighbor Solicitation (NS) message [RFC4861] used for DAD [RFC4862].



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   If the self-generated address is a CGA, the node also includes SEND
   credentials to prove address ownership.  The VET node sets the IPv6
   source address of the NS to 0 and sets the IPv6 destination address
   to the VET link-local unicast address of the EBG that advertised the
   prefix, but does not include a Source Link-Layer Address Option
   (SLLAO) in the NS message.

   When the EBG receives the NS, it checks for the VET link-local
   address of the sender in its neighbor cache.  If the EBG does not
   have the address in the cache (i.e., the EBG has not received a
   recent RS from this VET node), it silently discards the NS.
   Otherwise, it checks for the target address in the NS mesage in its
   neighbor cache.  If the target address is not already in the cache,
   the EBG first verifies the NS SEND credentials (if present) then
   creates a new neighbor cache entry for the target address in the
   STALE state and records the IPv4 RLOC source address of the
   requesting node as the link layer address.  It the target address is
   already in the cache and its link-layer address matches the IPv4 RLOC
   source address of the NS, the EBG updates the neighbor cache entry
   TTL.  If the target address is already in the neighbor cache and its
   link-layer address does not match the IPv4 source address of the NS,
   the VET node's tentative address is a duplicate and the NS does not
   update the cache.

   The EBG then prepares a Neighbor Advertisement (NA) message with the
   IPv6 source address set to the EBG's VET link-local address, the IPv6
   destination address set to the VET node's VET link-local address, the
   target address set to the VET node's proposed self-generated address,
   and with a Target Link-Layer Address Option (TLLAO) formatted using a
   modified version of the form specified in Section 5 of [RFC2529],
   i.e., as shown in Figure 2:

   +-------+-------+-------+-------+-------+-------+-------+-------+
   | Type  |Length |      TTL      |        IPv4 Address           |
   +-------+-------+-------+-------+-------+-------+-------+-------+

              Figure 2: VET Link-Layer Address Option Format

   The EBG sets "IPv4 address" in the TLLAO option to the IPv4 RLOC
   address of the VET node if the address was not a duplicate, sets
   "IPv4 address" to the EBG's own IPv4 RLOC address if the address was
   a duplicate, or sets "IPv4 address" to 0 if the address could not
   otherwise be assigned (e.g., due to incorrect SEND credentails,
   insufficient resources, etc.).  The EBG also sets "TTL" to the
   maximum time in seconds that the VET node is permitted to use the
   address, where the value '0' means that the address was either a
   duplicate or cannot otherwise be used.  The EBG then sends the NA
   message to the VET node.



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   When the VET node receives the NA message, it does not update its
   neighbor cache but rather checks the NA to verify that it is
   authorized to use the non-VET address.  In particular, if the TLLAO
   contains a non-zero TTL and IPv4 address set to the VET node's IPv4
   RLOC address, the VET node assigns the address to the VET interface
   and can subsequently use it as the IPv6 source address for on- and
   off-link communications.  If the VET node wishes to subsequently
   extend the lifetime of the non-VET address beyond TTL seconds, it
   must send additional NS(DAD) messages as above to update the EBG's
   neighbor cache.

   This implies that EBGs that maintain a neighbor cache can provide an
   address registration service for VET nodes that will autoconfigure
   non-VET IPv6 addresses, and that the EBG sets the frequency with
   which non-VET IPv6 addresses may be updated or deprecated (i.e. by
   setting the TTL).  The EBG must therefore maintain neighbor cache
   entries indexed by the node's IPv4 RLOC address (i.e., as the link-
   layer address) for each non-VET IPv6 address that the VET node
   autoconfigures in addition to maintaining a neighbor cache entry for
   the node's VET link-local address.  EBG neighbor cache entries for
   non-VET addresses are therefore purged under two possible
   circumstances: 1) that the non-VET address expires due to no NS(DAD)
   message being received within the TTL timeout period, or 2) that the
   VET link-local address of the VET node expires due to no RS message
   being received within the prefix lifetime timeout period.

5.4.3.  PA Prefix Registration

   After an EBR discovers default routes, it can use DHCP prefix
   delegation to obtain PA prefixes via an EBG as specified in
   Section 4.2.2.  The DHCP server ensures that the delegations are
   unique and that the EBG's router function will forward IP packets
   over the VET interface to the correct EBR.  In particular, the EBG
   must register and track the PA prefixes that are delegated to each
   EBR.

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

5.4.4.  PI Prefix Registration

   After an EBR discovers default routes, it must register its PI
   prefixes by sending RAs to a set of one or more EBGs with Route



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   Information Options (RIOs) [RFC4191] that contain the EBR's PI
   prefixes.  Each RA must include the RLOC of an EBG as the outer IP
   destination address and a link-local address assigned to the VET
   interface as the inner IP destination address.  For enterprises that
   use SEND, the RAs also include a CGA link-local inner source address,
   SEND credentials, plus any certificates needed to prove ownership of
   the PI prefixes.  The EBR additionally tracks the set of EBGs to
   which it sends RAs so that it can send subsequent RAs to the same
   set.

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

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

   In particular, the EBG publishes each /56 prefix taken from the PI
   prefixes as a separate Fully Qualified Domain Name (FQDN) that
   consists of a sequence of 14 nibbles in reverse order (i.e., the same
   as in [RFC3596], Section 2.5) followed by the string 'ip6' followed
   by the string 'PRLNAME'.  For example, when 'PRLNAME' is
   "isatapv2.example.com", the EBG publishes the prefix '2001:DB8::/56'
   as:
   '0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.isatapv2.example.com'.

   The EBG includes the outer RLOC source address of the RA (e.g., in a
   DNS A resource record) in each prefix publication.  For enterprises
   that use SEND, the EBG also includes the inner IPv6 CGA source
   address (e.g., in a DNS AAAA record) in each prefix publication.  If
   the prefix was already installed in the distributed database, the EBG
   instead adds the outer RLOC source address (e.g., in an additional
   DNS A record) to the preexisting publication to support PI prefixes
   that are multihomed.  For enterprises that use SEND, this latter
   provision requires all EBRs of a multihomed site that advertise the



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   same PI prefixes in RAs to use the same CGA and the same SEND
   credentials.

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

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

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

5.4.5.  Next-Hop Discovery

   VET nodes discover destination-specific next-hop EBRs within the
   enterprise by querying the name service for the /56 IPv6 PI prefix
   taken from a packet's destination address, by forwarding packets via
   a default route to an EBG, or by some other inner-IP to outer-IP
   address mapping mechanism.  For example, for the IPv6 destination
   address '2001:DB8:1:2::1' and 'PRLNAME' "isatapv2.example.com" the
   VET node can lookup the domain name:
   '0.0.1.0.0.0.8.b.d.0.1.0.0.2.ip6.isatapv2.example.com'.

   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.  (In enterprises that use SEND, it
   will also return an IPv6 CGA address, e.g., in a DNS AAAA record.)

   Name-service lookups in enterprises with a centralized management
   structure use an infrastructure-based service, e.g., an enterprise-
   local DNS.  Name-service lookups in enterprises with a distributed
   management structure and/or that lack an infrastructure-based name-
   service instead use LLMNR over the VET interface.  When LLMNR is
   used, the EBR that performs the lookup sends an LLMNR query (with the
   /56 prefix taken from the IP destination address encoded in dotted-



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   nibble format as shown above) and accepts the union of all replies it
   receives from other EBRs on the VET interface.  When an EBR receives
   an LLMNR query, it responds to the query IFF it aggregates an IP
   prefix that covers the prefix in the query.

   Alternatively, in enterprises with a stable and highly-available set
   of EBGs, the VET node can simply forward an initial packet via a
   default route to an EBG.  The EBG will forward the packet to a next-
   hop EBR on the VET interface and return an ICMPv6 Redirect [RFC4861]
   (using SEND, if necessary).  If the packet's source address is on-
   link on the VET interface, the EBG returns an ordinary "router-to-
   host" redirect with the source address of the packet as its
   destination.  If the packet's source address is not on-link, the EBG
   instead returns a "router-to-router" redirect with the link-local VET
   address of the previous-hop EBR as its destination.

   When IPv4 is used as the outer IP protocol, the EBG includes in the
   redirect one or more IPv6 TLLAOs formatted as specified n Section
   5.4.2.  The TLLAOs contain the IPv4 RLOCs of potential next-hop EBRs
   arranged in order from lowest to highest priority (i.e., the first
   TLLAO contains the lowest priority RLOC and the final TLLAO option
   contains the highest priority).  For each such IPv6/IPv4 LLAO, the
   Type is set to 2 (for Target Link-Layer Address Option), Length is
   set to 1, and IPv4 Address is set to the IPv4 RLOC of the next-hop
   EBR.  TTL is set to the time in seconds that the recipient may cache
   the RLOC, where the value 65535 represents infinity and the value 0
   suspends forwarding through this RLOC.

   When a VET host receives an ordinary "router-to-host" redirect, it
   processes the redirect exactly as specified in [RFC4861], Section 8.
   When an EBR receives a "router-to-router" redirect, it discovers the
   RLOC addresses of potential next-hop EBRs by examining the LLAOs
   included in the redirect.  The EBR then installs a FIB entry that
   contains the /56 prefix of the destination address encoded in the
   redirect and the list of RLOCs of potential next-hop EBRs.  The EBR
   then enables the FIB entry for forwarding to next-hop EBRs but DOES
   NOT enable it for ingress filtering acceptance of packets from next-
   hop EBRs (i.e., the forwarding determination is unidirectional).

   In enterprises in which spoofing is possible, after discovering
   potential next-hop EBRs (either through name-service lookup or ICMP
   redirect) the EBR must send authenticating credentials before
   forwarding packets via the next-hops.  To do so, the EBR must send
   RAs over the VET interface (using SEND, if necessary) to the RLOCs of
   one or more of the potential next-hop EBRs.  The RAs must include a
   Route Information Option (RIO) [RFC4191] that contains the /56 PI
   prefix of the original packet's source address.  After sending the
   RAs, the EBR can either enable the new FIB entry for forwarding



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   immediately or delay until it receives an explicit acknowledgement
   that a next-hop EBR received the RA (e.g., using the SEAL explicit
   acknowledgement mechanism -- see Section 5.7).

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

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

5.5.  IPv4 Router and Prefix Discovery

   When IPv4 is used as the inner IP protocol, router discovery and
   prefix registration exactly parallel the mechanisms specified for
   IPv6 in Section 5.4.  To support this, modifications to the ICMPv4
   Router Advertisement [RFC1256] function to include SEND constructs
   and modifications to the ICMPv4 Redirect [RFC0792] function to
   support router-to-router redirects will be specified in a future
   document.  Additionally, publications for IPv4 prefixes will be in
   dotted-nibble format in the 'ip4.isatapv2.example.com' domain.  For
   example, the IPv4 prefix 192.0.2/24 would be represented as:
   '2.0.0.0.0.c.ip4.isatapv2.example.com'

5.6.  Forwarding Packets on VET Interfaces

   VET nodes forward packets by consulting the FIB to determine a route
   with a next-hop toward the destination, where the next-hop is the
   destination itself if the destination matches an interface's on-link
   prefix.  When multiple routes are available, VET nodes can use
   default router preferences, routing protocol information, traffic
   engineering configurations, etc. to select the best route.  When no
   routes other than "default" are available, VET nodes can discover the
   best next-hop through the mechanisms specified in Section 5.4 and
   Section 5.5.

   When the VET node selects a route with a next-hop configured on a VET
   interface that uses IPv6 in IPv4 encapsulation, it next performs



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   next-hop address resolution.  For VET addresses, the VET node
   performs address resolution through static extraction of the embedded
   IPv4 RLOC in the VET interface identifier.  For non-VET addresses,
   the VET node first checks for the next-hop address in its neigbhbor
   cache.  If the address is in the cache, address resolution is through
   static extraction of the IPv4 RLOC address recorded in the link-layer
   address.  Otherwise, if the node is not the EBG it sends a Neighbor
   Solicitation (NS) message to the EBG with its VET interface link-
   local address as the IPv6 source, the VET link-local address of the
   EBG as the destination, and the next-hop address as the target.

   When the EBG receives the NS message, it does not update or create a
   neighbor cache entry for the source of the solicitation, but rather
   returns an immediate Neighbor Advertisement (NA) message.  If the EBG
   has an entry for the target address in its neighbor cache, it returns
   an NA message with the next-hop address as the target, the link-local
   address of the EBG as the IPv6 source, the link-local address of the
   VET node as the IPv6 destination, and with a Target Link Layer
   Address Option (TLLAO) formatted as specified in Section 5.4.2 that
   encodes a TTL and the IPv4 RLOC address of the VET node that owns the
   next-hop address.  If the EBG does not have a neighbor cache entry
   for the target address, it returns an NA message as above except that
   the TLLAO encodes the value 0 in both the TTL and IPv4 address
   fields.

   When the VET node receives the NA message, it can immediately
   determine whether address resolution has succeeded or failed by
   examining the results recorded in the TLLAO.  If the address
   resolution succeeds, the VET node records the address in its neighbor
   cache and retains the neighbor cache entry for up to the duration
   recorded in the TTL.  If the address resolution fails, the VET node
   discards the packet and/or selects an alternate route (if one is
   available).

   Note that the above address resolution is peformed only for IPv6 in
   IPv4 encapsulation.  For other encapsulations, address resolutuion is
   through administrative configuration or through an unspecified
   alternate method.

5.7.  VET and SEAL Encapsulation

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

   VET interfaces use SEAL encapsulation to accommodate path MTU



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   diversity, to defeat source address spoofing, and to enable sub-IP
   layer hints of forward progress that can be piggybacked on ordinary
   data messages.  SEAL encapsulation maintains a unidirectional and
   monotonically incrementing per-packet identification value known as
   the 'SEAL_ID'.  When a VET node that uses SEAL encapsulation receives
   an authentic neighbor discovery message from another VET node, it can
   cache the new SEAL_ID as per-tunnel state used for maintaining a
   window of unacknowledged SEAL_IDs.

   In terms of security, when a VET node receives an ICMP message or a
   SEAL error message, it can confirm that the packet-in-error within
   the message corresponds to one of its recently sent packets by
   examining the SEAL_ID along with source and destination addresses,
   etc.  Additionally, a next-hop EBR can track the SEAL_ID in packets
   received from EBRs for which there is an ingress filter entry and
   discard packets that have SEAL_ID values outside of the current
   window.  (Note that for IPv6 in IPv4 encapsulation packets with a
   link-local IPv6 destination address are excluded from this check to
   support operation of the neighbor discovery protocol.)

   In terms of next-hop reachability, an EBR can set the SEAL
   "Acknowledgement Requested" bit in messages to receive confirmation
   that a next-hop EBR is reachable.  (Note that this is a mid-layer
   reachability confirmation, and not an L2 reachability indication.)
   Setting the "Acknowledgement Requested" bit is also used as the
   method for maintaining the window of outstanding SEAL_IDs.

5.8.  Generating Errors

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

   When an EBR receives an IPv6 packet over a VET interface, and there
   is no longest-prefix-match FIB entry for the destination, it returns
   an ICMPv6 "Destination Unreachable; No route to destination" message
   to the previous hop EBR subject to rate limiting.

   When an EBR receives an IPv6 packet over a VET interface and the
   longest-prefix-match FIB entry for the destination is via a next-hop
   configured over the same VET interface the packet arrived on, the EBR
   forwards the packet.  If the FIB prefix is longer than ::/0, the EBR
   then sends a router-to-router ICMPv6 Redirect message (using SEND, if
   necessary) to the previous-hop EBR as specified in Section 5.4.5.

   Generation of other ICMP messages [RFC0792] [RFC4443] is the same as



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   for any IP interface.

5.9.  Processing Errors

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

   When a VET node receives an ICMPv6 "Destination Unreachable; No route
   to destination" message from a next-hop EBR, it forwards the ICMPv6
   message to the source of the original packet as normal.  If the EBR
   has a longest-prefix-match FIB entry for the original packet's
   destination that is more specific than ::/0, the EBR also deletes the
   FIB entry.

   When an EBR receives an authentic ICMPv6 Redirect, it processes the
   packet as specified in Section 5.4.5.

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

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






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5.10.  Mobility and Multihoming Considerations

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

   EBRs can retain their PI prefixes as they travel between distinct
   enterprise networks as long as they register the prefixes with new
   EBGs and (preferably) withdraw the prefixes from old EBGs prior to
   departure.  Prefix registration with new EBGs is coordinated exactly
   as specified in Section 5.4.4; prefix withdrawal from old EBGs is
   simply through re-announcing the PI prefixes with zero lifetimes.

   Since EBRs can move about independently of one another, stale FIB
   entry state may be left in VET nodes when a neighboring EBR departs.
   Additionally, EBRs can lose state for various reasons, e.g., power
   failure, machine reboot, etc.  For this reason, EBRs are advised to
   set relatively short PI prefix lifetimes in RIO options, and to send
   additional RAs to refresh lifetimes before they expire.  (EBRs should
   place conservative limits on the RAs they send to reduce congestion,
   however.)

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

   EBRs can also act as delegating routers to sub-delegate portions of
   their PI prefixes to requesting routers on their enterprise-edge
   interfaces and on VET interfaces for which they are configured as
   EBGs.  In this sense, the sub-delegations of an EBR's PI prefixes
   become the PA prefixes for downstream-dependent nodes.

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





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5.11.  Multicast

   In multicast-capable deployments, ERs provide an enterprise-wide
   multicasting service (e.g., Simplified Multicast Forwarding (SMF)
   [I-D.ietf-manet-smf], Protocol Independent Multicast (PIM) routing,
   Distance Vector Multicast Routing Protocol (DVMRP) routing, etc.)
   over their enterprise-interior interfaces such that outer IP
   multicast messages of site-scope or greater scope will be propagated
   across the enterprise.  For such deployments, VET nodes can also
   provide an inner IP multicast/broadcast capability over their VET
   interfaces through mapping of the inner IP multicast address space to
   the outer IP multicast address space.  In that case, operation of
   link-scoped (or greater scoped) inner IP multicasting services (e.g.,
   a link-scoped neighbor discovery protocol) over the VET interface is
   available, but link-scoped services should be used sparingly to
   minimize enterprise-wide flooding.

   VET nodes encapsulate inner IP multicast messages sent over the VET
   interface in any mid-layer headers (e.g., IPsec, etc.) followed by a
   SEAL header followed by an outer IP header with a site-scoped outer
   IP multicast address as the destination.  For the case of IPv6 and
   IPv4 as the inner/outer protocols (respectively), [RFC2529] provides
   mappings from the IPv6 multicast address space to a site-scoped IPv4
   multicast address space (for other encapsulations, mappings are
   established through administrative configuration or through an
   unspecified alternate static mapping).

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

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



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   scoped outer IP multicast group filtering at enterprise boundaries.

5.12.  Service Discovery

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

5.13.  Enterprise Partitioning

   EBGs can physically partition an enterprise by configuring multiple
   VET interfaces over multiple distinct sets of underlying interfaces.
   In that case, each partition (i.e., each VET interface) must
   configure its own distinct 'PRLNAME' (e.g.,
   'isatapv2.zone1.example.com', 'isatapv2.zone2.example.com', etc.).

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

5.14.  EBG Prefix State Recovery

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

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



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5.15.  Support for Legacy ISATAP Services

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


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] also apply
   to VET.  In particular:

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

   o  VET nodes must verify that the outer IP source address of a packet
      received on a VET interface is correct for the inner IP source
      address; for the case of IPv6 in IPv4 encapsulation, this is
      accomodated using the procedures specified in Section 7.3 of
      [RFC5214].

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

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

   Finally, VET interfaces that use IPv6 in IPv4 encapsulation drop all
   outbound packets for which the IPv6 source address is "foreign-
   prefix::0200:5efe:V4ADDR" and drop all incoming packets for which the
   IPv6 destination address is "foreign-prefix::0200:5efe:V4ADDR" .



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   (Here, "foreign-prefix" is an IPv6 prefix that is not assigned to the
   VET interface, and "V4ADDR" is a public IPv4 address over which the
   VET interface is configured.)  Note that these checks are only
   required for VET interfaces that cannot maintain a coherent neighbor
   cache.

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

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


8.  Related Work

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

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

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

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

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

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

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

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

   Various proposals within the IETF have suggested similar mechanisms.



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9.  Acknowledgements

   The following individuals gave direct and/or indirect input that was
   essential to the work: Jari Arkko, Teco Boot, Emmanuel Bacelli, James
   Bound, Scott Brim, Brian Carpenter, Thomas Clausen, Claudiu Danilov,
   Chris Dearlove, Ralph Droms, Dino Farinacci, Vince Fuller, Thomas
   Goff, 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, John Spence, Jinmei Tatuya, Dave Thaler, Ole Troan,
   Michaela Vanderveen, Lixia Zhang, and others in the IETF AUTOCONF and
   MANET working groups.  Many others have provided guidance over the
   course of many years.


10.  Contributors

   The following individuals have contributed to this document:

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

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

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


11.  References

11.1.  Normative References

   [I-D.templin-intarea-seal]
              Templin, F., "The Subnetwork Encapsulation and Adaptation
              Layer (SEAL)", draft-templin-intarea-seal-06 (work in
              progress), September 2009.

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

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

   [RFC0826]  Plummer, D., "Ethernet Address Resolution Protocol: Or



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              converting network protocol addresses to 48.bit Ethernet
              address for transmission on Ethernet hardware", STD 37,
              RFC 826, November 1982.

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

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

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

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

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

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

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

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

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

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

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

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

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




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   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              September 2007.

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862, September 2007.

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

11.2.  Informative References

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

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

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

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

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

   [I-D.hain-ipv6-ulac]
              Hain, T., Hinden, R., Huston, G., and T. Narten,
              "Centrally Assigned IPv6 Unicast Unique Local Address
              Prefixes", draft-hain-ipv6-ulac-00 (work in progress),
              July 2009.

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



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

   [I-D.ietf-dhc-subnet-alloc]
              Johnson, R., Kumarasamy, J., Kinnear, K., and M. Stapp,
              "Subnet Allocation Option", draft-ietf-dhc-subnet-alloc-09
              (work in progress), March 2009.

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

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

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

   [I-D.templin-ranger]
              Templin, F., "Routing and Addressing in Next-Generation
              EnteRprises (RANGER)", draft-templin-ranger-07 (work in
              progress), February 2009.

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

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

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

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

   [RFC1753]  Chiappa, J., "IPng Technical Requirements Of the Nimrod



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              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.

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

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

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

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

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

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

   [RFC3753]  Manner, J. and M. Kojo, "Mobility Related Terminology",
              RFC 3753, June 2004.

   [RFC3819]  Karn, P., Bormann, C., Fairhurst, G., Grossman, D.,
              Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L.
              Wood, "Advice for Internet Subnetwork Designers", BCP 89,
              RFC 3819, July 2004.

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

   [RFC4192]  Baker, F., Lear, E., and R. Droms, "Procedures for
              Renumbering an IPv6 Network without a Flag Day", RFC 4192,
              September 2005.

   [RFC4193]  Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
              Addresses", RFC 4193, October 2005.




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

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

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

   [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.


Appendix A.  Duplicate Address Detection (DAD) Considerations

   A priori uniqueness determination (also known as "pre-service DAD")
   for an RLOC assigned on an enterprise-interior interface would
   require either flooding the entire enterprise or somehow discovering
   a link in the enterprise on which a node that configures a duplicate
   address is attached and performing a localized DAD exchange on that
   link.  But, the control message overhead for such an enterprise-wide
   DAD would be substantial and prone to false-negatives due to packet
   loss and intermittent connectivity.  An alternative to pre-service
   DAD is to autoconfigure pseudo-random RLOCs on enterprise-interior
   interfaces and employ a passive in-service DAD (e.g., one that
   monitors routing protocol messages for duplicate assignments).

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

   Consistent operational practices can assure uniqueness for EBG-
   aggregated addresses/prefixes, while statistical properties for
   pseudo-random address self-generation can assure uniqueness for the



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

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

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

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



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   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.

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

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

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

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

   It must be specifically noted that the above arrangement constitutes
   a case in which the same RLOC may be used as both the inner and outer



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   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-
   in-SEAL-in-IPvX encapsulation, as well as for IPv4-in-SEAL-in-Pv6
   encapsulation, this requires a VET interface specific address mapping
   database.  For IPv6-in-SEAL-in-IPv4 encapsulation, the mapping is
   accomplished through simple static extraction of an IPv4 address
   embedded in a VET address.


Appendix C.  Change Log

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

   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:

   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:



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   o  New appendix on RLOC configuration on VET intefaces.


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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