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RFC 5558 - Virtual Enterprise Traversal (VET)


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Independent Submission                                   F. Templin, Ed.
Request for Comments: 5558                  Boeing Research & Technology
Category: Informational                                    February 2010
ISSN: 2070-1721

                   Virtual Enterprise Traversal (VET)

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
   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), multi-organizational
   corporate networks and the interdomain core of the global Internet
   itself.  This document specifies a Virtual Enterprise Traversal (VET)
   abstraction for autoconfiguration and operation of nodes in
   enterprise networks.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This is a contribution to the RFC Series, independently of any other
   RFC stream.  The RFC Editor has chosen to publish this document at
   its discretion and makes no statement about its value for
   implementation or deployment.  Documents approved for publication by
   the RFC Editor are not a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc5558.

IESG Note

   This RFC is not a candidate for any level of Internet Standard.  The
   IETF disclaims any knowledge of the fitness of this RFC for any
   purpose and in particular notes that the decision to publish is not
   based on IETF review for such things as security, congestion control,
   or inappropriate interaction with deployed protocols.  The RFC Editor
   has chosen to publish this document at its discretion.  Readers of
   this RFC should exercise caution in evaluating its value for
   implementation and deployment.  See RFC 3932 for more information.

   Note that the IETF AUTOCONF Working Group is working on a similar
   protocol solution that may become available in the future.

Copyright Notice

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

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

Table of Contents

   1. Introduction ....................................................4
   2. Terminology .....................................................6
   3. Enterprise Characteristics .....................................10
   4. Autoconfiguration ..............................................11
      4.1. Enterprise Router (ER) Autoconfiguration ..................12
      4.2. Enterprise Border Router (EBR) Autoconfiguration ..........13
           4.2.1. VET Interface Autoconfiguration ....................13
                  4.2.1.1. Interface Initialization ..................14
                  4.2.1.2. Enterprise Border Gateway
                           Discovery and Enterprise Identification ...14
                  4.2.1.3. EID Configuration .........................15
           4.2.2. Provider-Aggregated (PA) EID Prefix
                  Autoconfiguration ..................................15
           4.2.3. Provider-Independent (PI) EID Prefix
                  Autoconfiguration ..................................16
      4.3. Enterprise Border Gateway (EBG) Autoconfiguration .........17
      4.4. VET Host Autoconfiguration ................................17
   5. Internetworking Operation ......................................18
      5.1. Routing Protocol Participation ............................18
      5.2. RLOC-Based Communications .................................18
      5.3. EID-Based Communications ..................................18
      5.4. IPv6 Router Discovery and Prefix Registration .............18
           5.4.1. IPv6 Router and Prefix Discovery ...................18
           5.4.2. IPv6 PA Prefix Registration ........................19
           5.4.3. IPv6 PI Prefix Registration ........................20
           5.4.4. IPv6 Next-Hop EBR Discovery ........................21
      5.5. IPv4 Router Discovery and Prefix Registration .............23
      5.6. VET Encapsulation .........................................24
      5.7. SEAL Encapsulation ........................................24
      5.8. Generating Errors .........................................25
      5.9. Processing Errors .........................................25
      5.10. Mobility and Multihoming Considerations ..................26
      5.11. Multicast ................................................27
      5.12. Service Discovery ........................................28
      5.13. Enterprise Partitioning ..................................29
      5.14. EBG Prefix State Recovery ................................29
   6. Security Considerations ........................................30
   7. Related Work ...................................................30
   8. Acknowledgements ...............................................31
   9. Contributors ...................................................31
   10. References ....................................................31
      10.1. Normative References .....................................31
      10.2. Informative References ...................................33
   Appendix A.  Duplicate Address Detection (DAD) Considerations .... 36

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.  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.

                         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.

   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 Intra-
   Site Automatic Tunnel Addressing Protocol (ISATAP) [RFC5214], and it
   further supports additional encapsulations such as IPsec [RFC4301],
   Subnetwork Encapsulation and Adaptation Layer (SEAL) [RFC5320], etc.
   Together, these technologies serve as functional building blocks for
   a new Internetworking architecture known as Routing and Addressing in
   Networks with Global Enterprise Recursion [RFC5720][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], the Catenet model for
   internetworking [CATENET] [IEN48] [RFC2775], etc.  [RFC1955] captures
   the high-level architectural aspects of the ROAD group deliberations
   in a "New Scheme for Internet Routing and Addressing (ENCAPS) for
   IPNG".

   VET is related to the present-day activities of the IETF AUTOCONF,
   DHC, IPv6, MANET, and v6OPS working groups, as well as the IRTF RRG
   working group.

2.  Terminology

   The mechanisms within this document build upon the fundamental
   principles of IP-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 allows for inclusion of "mid-layer"
   encapsulations between the inner and outer layers, including IPsec
   [RFC4301], the Subnetwork Encapsulation and Adaptation Layer (SEAL)
   [RFC5320], etc.

   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].

   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.

   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 LAN
      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 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
      separate VET interface over each set of underlying interfaces,
      i.e., the EBR configures multiple VET interfaces.

      The VET interface encapsulates each inner IP packet in any mid-
      layer headers plus an outer IP header, then it forwards it 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 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 are routable within both the enterprise-interior
      and interdomain routing regions.  Enterprise-local-scope RLOC
      prefixes (e.g., IPv6 Unique Local Addresses [RFC4193], IPv4
      privacy addresses [RFC1918], etc.) are self-generated by
      individual enterprises and routable only within the enterprise-
      interior routing region.

      ERs use RLOCs for operating the enterprise-interior routing
      protocol and for next-hop determination in forwarding packets
      addressed to other RLOCs.  End systems use RLOCs as addresses for
      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 "isatap")
   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.
   Enterprise Border Routers (EBRs) are ERs that connect edge networks
   to the enterprise and/or join multiple enterprises together.
   Enterprise Border Gateways (EBGs) are EBRs that either directly or
   indirectly connect enterprises to provider networks.

   An enterprise may be as simple as a small collection of ERs and their
   attached edge networks; an enterprise may also contain other
   enterprises and/or be a subnetwork of a larger enterprise.  An
   enterprise may further encompass a set of branch offices and/or
   nomadic hosts connected to a home office over one or several service
   providers, e.g., through Virtual Private Network (VPN) tunnels.

   Enterprises that comprise link types with sufficiently similar
   properties (e.g., Layer 2 (L2) address formats, maximum transmission
   units (MTUs), etc.) can configure a sub-IP layer routing service such
   that IP sees the enterprise as an ordinary shared link the same as
   for a (bridged) campus LAN.  In that case, a single IP hop is
   sufficient to traverse the enterprise without IP layer encapsulation.

   Enterprises that comprise link types with diverse properties and/or
   configure multiple IP subnets must also provide a routing service
   that operates as an IP layer mechanism.  In that case, multiple IP
   hops may be necessary to traverse the enterprise such that care must
   be taken to avoid multi-link subnet issues [RFC4903].

   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).

   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
   securing mechanisms such as SEcure Neighbor Discovery (SEND)
   [RFC3971] may be necessary to authenticate exchanges based on trust
   anchors.

   Finally, in enterprises with a centralized management structure
   (e.g., a corporate campus network), the enterprise name service and a
   synchronized set of EBGs can provide infrastructure support for
   virtual enterprise traversal.  In that case, the EBGs can provide a
   "default mapper" [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 a unique 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 that provide sufficient
   uniqueness 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 an RLOC on each of its enterprise-interior
   interfaces and engages in any routing protocols on those interfaces.
   The ER can configure an RLOC via explicit management, DHCP
   autoconfiguration, pseudo-random self-generation from a suitably
   large address pool, or through an alternate autoconfiguration
   mechanism.

   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.  In that case, the ER can use an RLOC
   assigned to an enterprise-edge interface for enterprise-interior
   routing protocol operation and next-hop determination purposes.  Note
   that in some cases, the same enterprise-edge interfaces may assign
   both RLOC and an 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 IPv6 local-use
   address range, e.g., IPv6 Unique Local Addresses [RFC4193].  Self-
   generation of RLOCs for IPv4 can be from a large IPv4 private address
   range (e.g., [RFC1918]).  When self-generation is used alone, the ER
   must continuously monitor the 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
   addresses with /32 prefix lengths for IPv4, and as addresses with
   /128 prefix lengths for IPv6) may be necessary to avoid multi-link
   subnet issues.

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.

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

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, a DHCP option, '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 "isatap" and sets the
   'domainname' component only if an enterprise-specific DNS suffix
   "example.com" is known (e.g., as "isatap.example.com").

   The global Internet interdomain routing core represents a specific
   example of an enterprise network scenario, albeit on an enormous
   scale.  The 'PRLNAME' assigned to the global Internet interdomain
   routing core is "isatap.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,
   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
   5.4.1.  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
   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.,
   using [CENTRL-ULA], 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
   Sections 5.4 and 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 and configures an EID the same as
   for an ordinary EBR (see Section 4.2.1).  It must then arrange to add
   one or more of its 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'.

   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.

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 records.

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 Discovery and Prefix Registration

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

5.4.1.  IPv6 Router and Prefix Discovery

   EBGs follow the router and prefix discovery procedures specified in
   [RFC5214], Section 8.2.  They send solicited RAs over VET interfaces
   for which they are configured as gateways with default router
   lifetimes, with PIOs that contain PA prefixes for SLAAC, and with any
   other required options/parameters.  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.

   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 default routes.  In particular,
   the VET node sends unicast RS messages to EBGs over its VET
   interface(s) to receive RAs.  Depending on the enterprise network
   trust basis, VET nodes may be required to use SEND to secure the
   RS/RA exchanges.

   When the VET node receives an RA, it authenticates the message, then
   configures a default route based on the Router Lifetime.  If the RA
   contains Prefix Information Options (PIOs) with the 'A' and 'L' bits
   set to 1, the VET node also autoconfigures IPv6 addresses from the
   advertised prefixes using SLAAC and assigns them to the VET
   interface.  Thereafter, the VET node accepts packets that are
   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).

   In enterprises in which DHCPv6 is preferred, DHCPv6 exchanges between
   EBRs and EBGs may be sufficient to convey default router and prefix
   information.  In that case, RS/RA exchanges may not be necessary.

5.4.2.  IPv6 PA Prefix Registration

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

5.4.3.  IPv6 PI Prefix Registration

   After an EBR discovers default routes, it must register its PI
   prefixes by sending RAs to a set of one or more EBGs with Route
   Information Options (RIOs) [RFC4191] that contain the EBR's PI
   prefixes.  Each RA must include the 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
   forward packets received on other interfaces with a destination
   address taken from the PI prefixes to the EBR that registered the
   prefixes on the VET interface.

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

   In particular, the EBG publishes each /56 prefix taken from the PI
   prefixes as a 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
   "isatap.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.isatap.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
   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) [SEND-PROXY].)  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].

5.4.4.  IPv6 Next-Hop EBR Discovery

   VET nodes discover destination-specific next-hop EBRs within the
   enterprise by querying the name service for the /56 IPv6 PI prefix
   taken from a packet's destination address, by forwarding packets via
   a default route to an EBG, or by some other inner-IP-to-outer-IP
   address mapping mechanism.  For example, for the IPv6 destination
   address '2001:DB8:1:2::1' and 'PRLNAME' "isatap.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.isatap.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-
   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
   ISATAP address of the previous-hop EBR as its destination.  When IPv4
   is used as the outer IP protocol, the EBG also includes in the
   redirect one or more IPv6 Link-Layer Address Options (LLAOs) that
   contain the IPv4 RLOCs of potential next-hop EBRs arranged in order
   from lowest to highest priority (i.e., the first LLAO contains the
   lowest priority RLOC and the final LLAO option contains the highest
   priority).  These LLAOs are formatted using a modified version of the
   form specified in Section 5 of [RFC2529], as shown in Figure 2 (the
   LLAO format for IPv6 as the outer IP protocol is out of scope).

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

              Figure 2: VET Link-Layer Address Option Format

   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 one or more
   of the potential next-hop EBRs with an RLOC as the outer IP
   destination address.  The RAs must include a Route Information Option
   (RIO) [RFC4191] that contains the /56 PI prefix of the original
   packet's source address.  After sending the RAs, the EBR can either
   enable the new FIB entry for forwarding immediately or delay until it
   receives an explicit acknowledgement that a next-hop EBR received the
   RA (e.g., using the SEAL explicit acknowledgement mechanism -- see
   Section 5.7).

   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 Discovery and Prefix Registration

   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.isatap.example.com' domain.  For
   example, the IPv4 prefix 192.0.2/24 would be represented as:

   '2.0.0.0.0.c.ip4.isatap.example.com'

5.6.  VET Encapsulation

   VET nodes forward packets by consulting the FIB to determine a
   specific EBR/EBG as the next-hop router on a VET interface.  When
   multiple next-hop routers are available, VET nodes can use default
   router preferences, routing protocol information, traffic engineering
   configurations, etc. to select the best exit router.  When there is
   no FIB information other than "default" available, VET nodes can
   discover the next-hop EBR/EBG through the mechanisms specified in
   Section 5.4 and Section 5.5.

   VET interfaces encapsulate inner IP packets in any mid-layer headers
   followed by an outer IP header according to the specific
   encapsulation type (e.g., [RFC4301], [RFC5214], [RFC5320], etc.);
   they next submit the encapsulated packet to the outer IP forwarding
   engine for transmission on an underlying interface.

   For forwarding to next-hop addresses over VET interfaces that use
   IPv6-in-IPv4 encapsulation, VET nodes determine the outer destination
   address (i.e., the IPv4 RLOC of the next-hop EBR) through static
   extraction of the IPv4 address embedded in the next-hop ISATAP
   address.  For other IP-in-IP encapsulations, determination of the
   outer destination address is through administrative configuration or
   through an unspecified alternate method.  When there are multiple
   candidate destination RLOCs available, the VET node should only
   select an RLOC for which there is current forwarding information in
   the outer IP protocol FIB.

5.7.  SEAL Encapsulation

   VET nodes should use SEAL encapsulation [RFC5320] over VET interfaces
   to accommodate path MTU diversity, to defeat source address spoofing,
   and to monitor next-hop EBR reachability.  SEAL encapsulation
   maintains a unidirectional and monotonically incrementing per-packet
   identification value known as the 'SEAL_ID'.  When a VET node that
   uses SEAL encapsulation sends a SEND-protected Router Advertisement
   (RA) or Router Solicitation (RS) message to another VET node, both
   nodes cache the new SEAL_ID as per-tunnel state used for maintaining
   a window of unacknowledged SEAL_IDs.

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

   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.  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, then (if the FIB prefix is longer than ::/0)
   sends a router-to-router ICMPv6 Redirect message (using SEND, if
   necessary) to the previous-hop EBR as specified in Section 5.4.4.

   Generation of other ICMP messages [RFC0792] [RFC4443] is the same as
   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 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 5.4.4.

   When an EBG receives new mapping information for a specific
   destination prefix, it can propagate the update to other EBRs/EBGs by
   sending an ICMPv6 redirect message to the 'All Routers' link-local
   multicast address with 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.

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 5.4.3; 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.  Downstream-
   dependent nodes that travel with a mobile provider EBR can continue
   to use addresses configured from PA prefixes; downstream-dependent
   nodes that move away from their provider EBR must perform address/
   prefix renumbering when they associate with a new provider.

   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).

5.11.  Multicast

   In multicast-capable deployments, ERs provide an enterprise-wide
   multicasting service (e.g., Simplified Multicast Forwarding (SMF)
   [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, SEAL, etc.) plus an
   outer IP header with a site-scoped outer IP multicast address as the
   destination.  For the case of IPv6 and IPv4 as the inner/outer
   protocols (respectively), [RFC2529] provides mappings from the IPv6
   multicast address space to a site-scoped IPv4 multicast address space
   (for other IP-in-IP encapsulations, mappings are established through
   administrative configuration or through an unspecified alternate
   static mapping).

   Multicast mapping for inner IP multicast groups over outer IP
   multicast groups can be accommodated, e.g., through VET interface
   snooping of inner multicast group membership and routing protocol
   control messages.  To support inner-to-outer IP multicast 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-
   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] 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.,
   'isatap.zone1.example.com', 'isatap.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 due to IP packet forwarding.  If the EBG serves
   as an anchor for PI prefixes, however, care must be taken to avoid
   looping while state is recovered through prefix registration RAs from
   EBRs.  In that case, when the EBG that is recovering state forwards
   an IP packet for which it has no explicit route other than ::/0, it
   must first perform an on-demand name-service lookup to refresh state.

6.  Security Considerations

   Security considerations for MANETs are found in [RFC2501].

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

   SEND [RFC3971], IPsec [RFC4301], and SEAL [RFC5320] provide
   additional securing mitigations to detect source address spoofing and
   bogus RA messages sent by rogue routers.

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

7.  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
   [TUNNEL-SEC].

   Default router and prefix information options for DHCPv6 are
   discussed in [DEF-ROUTER].

   An automated IPv4 prefix delegation mechanism is proposed in
   [SUBNET].

   RLOC prefix delegation for enterprise-edge interfaces is discussed in
   [MANET-REC].

   MANET link types are discussed in [LINKTYPE].

   Various proposals within the IETF have suggested similar mechanisms.

8.  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,
   Ralph Droms, Dino Farinacci, Vince Fuller, Thomas Goff, Joel Halpern,
   Bob Hinden, Sapumal Jayatissa, Dan Jen, Darrel Lewis, Tony Li, Joe
   Macker, David Meyer, Thomas Narten, Pekka Nikander, Dave Oran,
   Alexandru Petrescu, John Spence, Jinmei Tatuya, Dave Thaler, Ole
   Troan, Michaela Vanderveen, Lixia Zhang, and others in the IETF
   AUTOCONF and MANET working groups.  Many others have provided
   guidance over the course of many years.

9.  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.

10.  References

10.1.  Normative References

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

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

   [RFC0826]    Plummer, D., "Ethernet Address Resolution Protocol: Or
                Converting Network Protocol Addresses to 48.bit Ethernet
                Address for Transmission on Ethernet Hardware", STD 37,
                RFC 826, November 1982.

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

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

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

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

   [RFC3315]    Droms, R., Ed., 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., Ed., 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, Ed., "Internet
                Control Message Protocol (ICMPv6) for the Internet
                Protocol Version 6 (IPv6) Specification", RFC 4443,
                March 2006.

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

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

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

10.2.  Informative References

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

   [mDNS]       Cheshire, S. and M. Krochmal, "Multicast DNS", Work in
                Progress, September 2009.

   [MANET-REC]  Clausen, T. and U. Herberg, "MANET Router Configuration
                Recommendations", Work in Progress, February 2009.

   [LINKTYPE]   Clausen, T., "The MANET Link Type", Work in Progress,
                October 2008.

   [DEF-ROUTER] Droms, R. and T. Narten, "Default Router and Prefix
                Advertisement Options for DHCPv6", Work in Progress,
                October 2009.

   [SEND-PROXY] Krishnan, S., Laganier, J., and M. Bonola, "Secure Proxy
                ND Support for SEND", Work in progress, July 2009.

   [SUBNET]     Johnson, R., Kumarasamy, J., Kinnear, K., and M. Stapp,
                "Subnet Allocation Option", Work in Progress, October
                2009.

   [CENTRL-ULA] Hinden, R., Huston, G., and T. Narten, "Centrally
                Assigned Unique Local IPv6 Unicast Addresses", Work in
                Progress, June 2007.

   [MANET-SMF]  Macker, J., Ed. and SMF Design Team, "Simplified
                Multicast Forwarding for MANET", Work in Progress, July
                2009.

   [TUNNEL-SEC] Hoagland, J., Krishnan, S., and D. Thaler, "Security
                Concerns With IP Tunneling", Work in Progress, October
                2008.

   [APT]        Jen, D., Meisel, M., Massey, D., Wang, L., Zhang, B.,
                and L. Zhang, "APT: A Practical Transit Mapping
                Service", Work in Progress, November 2007.

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

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

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

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

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

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

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

   [RFC2501]    Corson, S. 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.

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

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

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

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

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

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

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

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

   [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.

   [RFC5320]    Templin, F., "The Subnetwork Encapsulation and
                Adaptation Layer (SEAL)", RFC 5320, February 2010.

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

   [RANGERS]    Russert, S., Ed., Fleischman, E., Ed., and F. Templin,
                Ed., "RANGER Scenarios", Work in Progress, September
                2009.

Appendix A.  Duplicate Address Detection (DAD) Considerations

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

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

   Consistent operational practices can assure uniqueness for EBG-
   aggregated addresses/prefixes, while statistical properties for
   pseudo-random address self-generation can assure uniqueness for the
   RLOCs assigned on an ER's enterprise-interior interfaces.  Still, an
   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.

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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