Routing and Addressing in Networks with Global Enterprise Recursion (RANGER)

Independent Submission                                        F. Templin
Request for Comments: 5720                          Boeing Phantom Works
Category: Informational                                    February 2010
ISSN: 2070-1721


                Routing and Addressing in Networks with
                  Global Enterprise Recursion (RANGER)

Abstract

   RANGER is an architectural framework for scalable routing and
   addressing in networks with global enterprise recursion.  The term
   "enterprise network" within this context extends to a wide variety of
   use cases and deployment scenarios, where an "enterprise" can be as
   small as a Small Office, Home Office (SOHO) network, as dynamic as a
   Mobile Ad Hoc Network, as complex as a multi-organizational
   corporation, or as large as the global Internet itself.  Such
   networks will require an architected solution for the coordination of
   routing and addressing plans with accommodations for scalability,
   provider-independence, mobility, multihoming, and security.  These
   considerations are particularly true for existing deployments, but
   the same principles apply even for clean-slate approaches.  The
   RANGER architecture addresses these requirements and provides a
   comprehensive framework for IPv6/IPv4 coexistence.

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/rfc5720.

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Table of Contents

   1. Introduction ....................................................3
   2. Terminology .....................................................4
   3. The RANGER Architecture .........................................7
      3.1. Routing and Addressing .....................................7
      3.2. The Enterprise-within-Enterprise Framework .................9
      3.3. Virtual Enterprise Traversal (VET) ........................12
           3.3.1. RANGER Organizational Principles ...................12
           3.3.2. RANGER End-to-End Addressing Example ...............14
           3.3.3. Dynamic Routing and On-Demand Mapping ..............14
           3.3.4. Support for Legacy RLOC-Based Services .............16
      3.4. Subnetwork Encapsulation and Adaptation Layer (SEAL) ......18
      3.5. Mobility Management .......................................18
      3.6. Multihoming ...............................................20
      3.7. Implications for the Internet .............................20
   4. Related Initiatives ............................................21
   5. Security Considerations ........................................22
   6. Acknowledgements ...............................................23
   7. References .....................................................23
      7.1. Normative References ......................................23
      7.2. Informative References ....................................24

1.  Introduction

   RANGER is an architectural framework for scalable routing and
   addressing in networks with global enterprise recursion.  The term
   "enterprise network" within this context extends to a wide variety of
   use cases and deployment scenarios, where an "enterprise" can be as
   small as a SOHO network, as dynamic as a Mobile Ad Hoc Network, as
   complex as a multi-organizational corporation, or as large as the
   global Internet itself.  Such networks will require an architected
   solution for the coordination of routing and addressing plans with
   accommodations for scalability, provider-independence, mobility,
   multihoming, and security.  These considerations are particularly
   true for existing deployments, but the same principles apply even for
   clean-slate approaches.  The RANGER architecture addresses these
   requirements and also provides a comprehensive framework for IPv6/
   IPv4 coexistence [COEXIST].

   RANGER provides a unifying architecture for enterprises that contain
   one or more distinct interior IP routing and addressing domains (or
   "Routing LOCator (RLOC) space"), with each distinct RLOC space
   containing one or more organizational groupings.  Each RLOC space may
   coordinate their own internal addressing plans independently of one
   another, such that limited-scope addresses (e.g., [RFC1918] private-
   use IPv4 addresses) may be reused with impunity to provide unlimited
   scaling through spatial reuse.  Each RLOC space therefore appears as
   an enterprise unto itself, where organizational partitioning of the
   enterprise into one or more "sub-enterprises" (or "sites") is also
   possible and beneficial in many scenarios.  Without an architected
   approach, routing and addressing within such a framework would be
   fragmented due to address/prefix reuse between disjoint enterprises.
   With RANGER, however, multiple enterprises can be linked together to
   provide a multi-hop transit for nodes attached to enterprise edge
   networks that use Endpoint Interface iDentifier (EID) addresses taken
   from an IP addressing range that is distinct from any RLOC space.

   RANGER is recursive in that multiple enterprises can be joined
   together in a nested "enterprise-within-enterprise" fashion, where
   each enterprise also connects edge networks with nodes that configure
   addresses taken from EID space to support edge/core separation.  In
   this way, the same RANGER principles that apply in lower levels of
   recursion can extend upwards to parent enterprises and ultimately to
   the core of the global Internet itself.  Furthermore, it is also
   worth considering whether today's global Internet represents a
   limiting condition for recursion -- in particular, whether other
   internets could be manifested as "parallel universes" and joined
   together at still higher levels of recursion.

   The RANGER architecture is manifested through composite technologies,
   including Virtual Enterprise Traversal (VET) [VET], the Subnetwork
   Encapsulation and Adaptation Layer (SEAL) [SEAL], and the Intra-Site
   Automatic Tunnel Addressing Protocol (ISATAP) [RFC5214].  Other
   mechanisms such as IPsec [RFC4301] are also in scope for use within
   certain scenarios.

   Noting that combinations with still other technologies are also
   possible, the issues addressed either in full or in part by RANGER
   include:

   o  scalable routing and addressing

   o  provider-independent addressing and its relation to provider-
      aggregated addressing

   o  site mobility and multihoming

   o  address and prefix autoconfiguration

   o  border router discovery

   o  router/host-to-router/host tunneling

   o  neighbor discovery over tunnels

   o  MTU determination for tunnels

   o  IPv6/IPv4 coexistence and transition

   Note that while this document primarily uses the illustrative example
   of IPv6 [RFC2460] as a virtual overlay over IPv4 [RFC0791] networks,
   it is important to note that the same architectural principles apply
   to any combination of IPvX virtual overlays over IPvY networks.

2.  Terminology

   Routing Locator (RLOC)
      an IPv4 or IPv6 address assigned to an interface in an enterprise-
      interior routing region.  Note that private-use IP addresses are
      local to each enterprise; hence, the same private-use addresses
      may appear within disjoint enterprises.

   Endpoint Interface iDentifier (EID)
      an IPv4 or IPv6 address assigned to an edge network interface of
      an end system.  Note that EID space must be separate and distinct
      from any RLOC space.

   commons
      an enterprise-interior routing region that provides a subnetwork
      for cooperative peering between the border routers of diverse
      organizations that may have competing interests.  A prime example
      of a commons is the Default-Free Zone (DFZ) of the global
      Internet.  The enterprise-interior routing region within the
      commons uses an addressing plan taken from RLOC space.

   enterprise
      the same as defined in [RFC4852], where the enterprise deploys a
      unified RLOC space addressing plan within the commons but may also
      contain partitions with disjoint RLOC spaces and/or organizational
      groupings that can be considered as enterprises unto themselves.
      An enterprise therefore need not be "one big happy family", but
      instead provides a commons for the cooperative interconnection of
      diverse organizations that may have competing interests (e.g.,
      such as the case within the global Internet DFZ).

      Enterprise networks are typically associated with large
      corporations or academic campuses; however, the RANGER
      architectural principles apply to any network that has some degree
      of cooperative active management.  This definition therefore
      extends to home networks, small office networks, ISP networks, a
      wide variety of Mobile Ad Hoc Networks (MANETs), and even to the
      global Internet itself.

   site
      a logical and/or physical grouping of interfaces within an
      enterprise commons, where the topology of the site is a proper
      subset of the topology of the enterprise.  A site may contain many
      interior sites, which may themselves contain many interior sites
      in a recursive fashion.

      Throughout the remainder of this document, the term "enterprise"
      refers to either enterprise or site, i.e., the RANGER principles
      apply equally to enterprises and sites of any size or shape.  At
      the lowest level of recursive decomposition, a singleton
      Enterprise Border Router can be considered as an enterprise unto
      itself.

   Enterprise Border Router (EBR)
      a router at the edge of an enterprise that is also configured as a
      tunnel endpoint in an overlay network.  EBRs connect their
      directly attached networks to the overlay network, and connect to
      other networks via IP-in-IP tunneling across the commons to other
      EBRs.  This definition is intended as an architectural equivalent
      of the functional term "EBR" defined in [VET].

   Enterprise Border Gateway (EBG)
      an EBR that also connects the enterprise to provider networks
      and/or to the global Internet.  EBGs are typically configured as
      default routers in the overlay and provide forwarding services for
      accessing IP networks not reachable via an EBR within the commons.
      This definition is intended as an architectural equivalent of the
      functional term "EBG" defined in [VET], and is synonymous with the
      term "default mapper" used in other contexts (e.g., [JEN]).

   Ingress Tunnel Endpoint (ITE)
      a host or router interface that encapsulates inner IP packets
      within an outer IP header for transmission over an enterprise-
      interior routing region to the RLOC address of an Egress Tunnel
      Endpoint (ETE).

   Egress Tunnel Endpoint (ETE)
      a host or router interface that receives encapsulated packets sent
      to its RLOC address, decapsulates the inner IP packets, then
      delivers them to the EID address of the final destination.

   overlay network
      a virtual network manifested by routing and addressing over
      virtual links formed through automatic tunneling.  An overlay
      network may span many underlying enterprises.

   Provider-Independent (PI) prefix
      an IPv6 or IPv4 EID prefix (e.g., 2001:DB8::/48, 192.0.2/24, etc.)
      that is routable within a limited scope and may also appear in
      enterprise mapping tables.  PI prefixes that can appear in mapping
      tables are typically delegated to a Border Router (BR) by a
      registry but are not aggregated by a provider network.  Local-use
      IPv6 and IPv4 prefixes (e.g., FD00::/8, 192.168/16, etc.) are
      another example of a PI prefix, but these typically do not appear
      in mapping tables.

   Provider-Aggregated (PA) prefix
      an IPv6 or IPv4 EID prefix that is either derived from a PI prefix
      or delegated directly to a provider network by a registry.
      Although not widely discussed, it bears specific mention that a
      prefix taken from a delegating router's PI space becomes a PA
      prefix from the perspective of the requesting router.

   Additionally, RANGER provides an informative consideration of
   functional specifications and operational practices outlined in other
   documents.  These documents include:

   6over4
      Transmission of IPv6 over IPv4 Domains without Explicit Tunnels
      [RFC2529]; functional specifications and operational practices for
      automatic tunneling of unicast/multicast IPv6 packets over
      multicast-capable IPv4 enterprises.

   ISATAP
      Intra-Site Automatic Tunnel Addressing Protocol (ISATAP)
      [RFC5214]; functional specifications and operational practices for
      automatic tunneling of unicast IPv6 packets over unicast-only IPv4
      enterprises.

   VET
      Virtual Enterprise Traversal (VET) [VET]; functional
      specifications and operational practices for automatic tunneling
      of both unicast and multicast IP packets with provisions for
      address/prefix autoconfiguration, provider-independent addressing,
      mobility, multihoming, and security.  VET is descended from both
      6over4 and ISATAP and is also known as "ISATAP version 2
      (ISATAPv2)".

   SEAL
      Subnetwork Encapsulation and Adaptation Layer (SEAL) [SEAL]; an
      encapsulation sublayer that provides an extended IP Identification
      field and mechanisms for link MTU adaptation over tunnels.

3.  The RANGER Architecture

   The RANGER architecture enables scalable routing and addressing in
   networks with global enterprise recursion while sustaining support
   for legacy networks and services.  Key to this approach is a
   framework that accommodates interconnection of diverse organizations
   across a commons that have a mutual spirit of cooperation but also
   have the potential for competing interests.  The following sections
   outline the RANGER architecture within the context of anticipated use
   cases:

3.1.  Routing and Addressing

   The Internet today is facing "growing pains", with indications that
   core Routing Information Base (RIB) scaling may not be sustainable
   over the long term and that the remaining space for IPv4 address
   allocations may be depleted in the near future.  Therefore, there is
   an emerging need for scalable routing and addressing solutions.  It
   must further be noted that the same solutions selected to address
   global Internet routing and addressing scaling can apply equally for
   large enterprises -- or for any enterprise that would benefit from a
   separation of core and edge addressing domains.

   RANGER supports scalable routing through an approach that parallels
   the "New Scheme for Internet Routing and Addressing" described in
   [RFC1955].  This approach is also commonly known as "map-and-encaps".
   In this approach, an Ingress Tunnel Endpoint (ITE) that must forward
   an IP packet first consults a mapping system to discover a mapping
   for the destination Endpoint Interface iDentifier (EID) to a Routing
   LOCator (RLOC) assigned to an Egress Tunnel Endpoint (ETE).  The
   mapping system is typically maintained as a per-enterprise
   distributed database that is synchronized among a limited set of
   mapping agents.  Distributed database management alternatives include
   a routing protocol instance maintained by Enterprise Border Gateways
   (EBGs), a DNS reverse zone distributed among a restricted set of
   caching servers, etc.  Mapping entries are inserted into the mapping
   system through administrative configuration, automated prefix
   registrations, etc.

   RANGER allows for an ITE to either consult the mapping system itself
   (while delaying or dropping initial IP packets) or forward initial
   packets to an EBG acting as a "default mapper".  In either case, the
   ITE receives a mapping reply that it can use to populate its
   Forwarding Information Base (FIB).  The choice of mapping approaches
   must be considered with respect to the individual enterprise network
   scenario, e.g., forwarding to an EBG may be more appropriate in some
   scenarios while ITE self-discovery may be more appropriate in others.
   Use of other mapping mechanisms is also possible according to the
   specific enterprise scenario.

   After discovering the mapping, the ITE encapsulates inner IP packets
   in an outer IP header for transmission across the commons to the RLOC
   address of an ETE.  The ETE in turn decapsulates the packets and
   forwards them over the next hop toward the EID address of the final
   destination.  Therefore, the Routing Information Base (RIB) within
   the commons only needs to maintain state regarding RLOCs and not
   EIDs, while the synchronized EID-to-RLOC mapping state is maintained
   by a smaller number of nodes and is not subject to oscillations due
   to link state changes within the commons.  Finally, EIDs are routable
   only within a limited scope within edge networks (which may be as
   small as node-local scope in the limiting case).

   RANGER supports scalable addressing by selecting a suitably large EID
   addressing range that is distinct and kept separate from any
   enterprise-interior RLOC addressing ranges.  It should therefore come
   as no surprise that taking EID space from the IPv6 addressing
   architecture should lead to a viable, scalable addressing
   alternative, while taking EID space from the (already exhausted) IPv4
   addressing architecture may not.

3.2.  The Enterprise-within-Enterprise Framework

   Enterprise networks traditionally distribute routing information via
   Interior Gateway Protocols (IGPs) such as Open Shortest Path First
   (OSPF), while large enterprises may even use an Exterior Gateway
   Protocol (EGP) internally in place of an IGP.  Thus, it is becoming
   increasingly commonplace for large enterprises to use the Border
   Gateway Protocol (BGP) internally and independently from the BGP
   instance that maintains the RIB within the global Internet DFZ.

   As such, large enterprises may run an internal instance of BGP across
   many internal Autonomous Systems (ASs).  Such a large enterprise can
   therefore appear as an internet unto itself, albeit with default
   routes leading to the true global Internet.  Additionally, each
   internal AS within such an enterprise may itself run BGP internally
   in place of an IGP, and can therefore also appear as an independent,
   lower-tier enterprise unto itself.  This enterprise-within-enterprise
   framework can be extended in a recursive fashion as broadly and as
   deeply as desired to achieve scaling factors as well as
   organizational and/or functional compartmentalization, e.g., as shown
   in Figure 1.

                               ,---------------.
                            ,-'     Global      `-.  <--------+
                           (       IPv6/IPv4       )     ,----|-----.
                            `-.    Internet     ,-'     ( Enterprises)
                               `+--+..+--+ ...+--+      ( E2 thru EN )
                             _.-|R1|--|R2+----|Rn|-._    `.---------/
                      _.---''   +--+  +--+ ...+--+   -.
                 ,--''           ,---.                 `---.
              ,-'              X5     X6            .---..  `-.
            ,'  ,.X1-..       /         \        ,'       `.   `.
          ,'  ,'       `.    .'  E1.2   '.     X8    E1.m   \    `.
         /   /           \   |   ,--.    |     / _,.._       \     \
        /   /   E1.1      \  | Y3    `.  |    | /     Y7       |     \
       ;   |    ___        | |  ` W  Y4  |... | `Y6  ,'       |      :
       |   | ,-'   `.     X2 |   `--'    |    |   `''         |      |
       :   | |  V  Y2      | \    _      /    |               |      ;
        \  | `-Y1,,'       |  \ .' Y5   /      \    ,-Y8'`-   /      /
         \  \             /    \ \_'  /        X9   `.    ,'/      /
          `. \          X3      `.__,,'          `._  Y9'','     ,'
            ` `._     _,'      ___.......X7_        `---'      ,'
              `  `---'      ,-'             `-.              -'
                 `---.      `.    E1.3   Z   _'        _.--'
                      `-----. \---.......---'   _.---''
                             `----------------''

           <----------------   Enterprise E1  ---------------->

             Figure 1: Enterprise-within-Enterprise Framework

   Figure 1 depicts an enterprise 'E1' connected to the global IPv6/IPv4
   Internet via routers 'R1' through 'Rn' and additional enterprises
   'E2' through 'EN' that also connect to the global Internet.  Within
   the 'E1' commons, there may be arbitrarily many hosts, routers, and
   networks (not shown in the diagram) that use addresses taken from
   RLOC space and over which both encapsulated and unencapsulated IP
   packets can be forwarded.  There may also be many lower-tier
   enterprises, 'E1.1' through 'E1.m' (shown in the diagram), that
   interconnect within the 'E1' commons via Enterprise Border Routers
   (EBRs), depicted as 'X1' through 'X9' (where 'X1' through 'X9' see
   'R1' through 'Rn' as EBGs).  Within each 'E1.*' enterprise, there may
   also be arbitrarily many lower-tier enterprises that interconnect
   within the 'E1.*' commons via EBRs, depicted as 'Y1' through 'Y9' in
   the diagram (where 'Y1' through 'Y9' see 'X1' through 'X9' as EBGs).
   This recursive decomposition can be nested as deeply as desired and
   ultimately terminates at singleton nodes such as those depicted as
   'V', 'W', and 'Z' in the diagram.

   It is important to note that nodes such as 'V', 'W', and 'Z' may be
   simple hosts or they may be EBRs that attach arbitrarily complex edge
   networks with addresses taken from EID space.  Such edge networks
   could be as simple as a home network behind a residential gateway or
   as complex as a major corporate/academic campus, a large service
   provider network, etc.

   Again, this enterprise-within-enterprise framework can be recursively
   nested as broadly and deeply as desired.  From the highest level of
   the recursion, consider now that the global Internet itself can be
   viewed as an "enterprise" that interconnects lower-tier enterprises
   E1 through EN such that all RANGER architectural principles apply
   equally within that context.  Furthermore, the RANGER architecture
   recognizes that the global Internet need not represent a limiting
   condition for recursion, but rather allows that other internets could
   be manifested as "parallel universes" and joined together at still
   higher levels of recursion.

   As a specific case in point, the future global Aeronautical
   Telecommunications Network (ATN), under consideration within the
   civil aviation industry [BAUER], will take the form of a large
   enterprise network that appears as an internet unto itself, i.e.,
   exactly as depicted for 'E1' in Figure 1.  Within the ATN, there will
   be many Air Communications Service Provider (ACSP) and Air Navigation
   Service Provider (ANSP) networks organized as autonomous systems
   internal to the ATN, i.e., exactly as depicted for 'E1.*' in the
   diagram.  The ACSP/ANSP network EBGs will participate in a BGP
   instance internal to the ATN, and may themselves run independent BGP
   instances internally that are further sub-divided into lower-tier
   enterprises organized as regional, organizational, functional, etc.
   compartments.  It is important to note that, while ACSPs/ANSPs within
   the ATN will share a common objective of safety-of-flight for civil
   aviation services, there may be competing business/social/political
   interests between them, such that the ATN is not necessarily "one big
   happy family".  Therefore, the model parallels that of the global
   Internet itself.

   Such an operational framework may indeed be the case for many next-
   generation enterprises.  In particular, although the routing and
   addressing arrangements of all enterprises will require a mutual
   level of cooperative active management at a certain level, free
   market forces, business objectives, political alliances, etc. may
   drive internal competition.

3.3.  Virtual Enterprise Traversal (VET)

   Within the enterprise-within-enterprise framework outlined in Section
   3.2, the RANGER architecture is based on overlay networks manifested
   through Virtual Enterprise Traversal (VET) ([VET], [RFC5214]).  The
   VET approach uses automatic IP-in-IP tunneling in which ITEs
   encapsulate EID-based inner IP packets within RLOC-based, outer IP
   headers for transmission across the commons to ETEs.

   For each enterprise they connect to, EBRs that use VET configure a
   Non-Broadcast, Multiple Access (NBMA) interface known as a "VET
   interface" that sees all other EBRs within the enterprise as
   potential single-hop neighbors from the perspective of the inner IP
   protocol.  This means that, for many enterprise scenarios, standard
   neighbor discovery mechanisms (e.g., router advertisements,
   redirects, etc.) can be used between EBR pairs.  This gives rise to a
   data-driven model in which neighbor relationships are formed based on
   traffic demand in the data plane, which in many cases can relax the
   requirement for dynamic routing exchanges across the overlay in the
   control plane.

   When multiple VET interfaces are linked together, end-to-end
   traversal is seen as multiple VET hops from the perspective of the
   inner IP protocol.  In that case, transition between VET interfaces
   entails a "re-encapsulation" approach in which a packet that exits
   VET interface 'i' is decapsulated then re-encapsulated before it is
   forwarded into VET interface 'i+1'.  For example, if an end-to-end
   path between two EID-based peers crosses N distinct VET interfaces, a
   traceroute would show N inner IP forwarding hops corresponding to the
   portions of the path that traverse the VET interfaces.

   VET and its related works specify necessary mechanisms and
   operational practices to manifest the RANGER architecture.  The use
   of VET in conjunction with SEAL (see Section 3.4) is essential in
   certain deployments to avoid issues related to source address
   spoofing and black holing due to path Maximum Transmission Unit (MTU)
   limitations.  (The use of VET in conjunction with IPsec [RFC4301] may
   also be necessary in some enterprise network scenarios.)  The
   following sections discuss operational considerations and use cases
   within the VET approach.

3.3.1.  RANGER Organizational Principles

   Figure 2 below depicts a vertical slice (albeit represented
   horizontally) from the enterprise-within-enterprise framework shown
   in Figure 1:

                                                            +------+
                                                            | IPv6 |
       " " " " " " " "" " " " " " " " " " " " " " " "       |Server|
     "         <----------------- 2001:DB8::/40 (PA) "      |  S1  |
   "    2001:DB8:10::/56 (PI)  ---------------->      "     +--+---+
   "     . . . . . . .       . . . .      . . . .     "        |
   "   .               .    .       .    .       .    "        |
   "   .  +----+   v    +--- +   v  +----+   v   +----+  +-----+-------+
   "   .  | V  +=  e   =+ Y1 +=  e =+ X2 +=  e  =+ R2 +==+   Internet  |
   "   .  +-+--+   t    +----+   t  +----+   t   +----+  +-----+-------+
   "   .    |      1   .    .    2  .    .   3   .    "        |
   "    .   H         .     .       .    .       .    "        |
   "      . . . . . .        . . . .      . . . .     "     +--+---+
    "       <E1.1.1>         <E1.1>        <E1>       "     | IPv4 |
      "      10/8             10/8         10/8      "      |Server|
        " " " " " " " " " " " " " " "" " " " " " " "        |  S2  |
                     <-- Enterprise E1 -->                  +------+

            Figure 2: Virtual Enterprise Traversal

   Within this vertical slice, each enterprise within the 'E1' recursive
   hierarchy is spanned by VET interfaces, represented as 'vet1' through
   'vet3'.  Each VET interface within this framework is a Non-Broadcast,
   Multiple Access (NBMA) interface that connects all EBRs within the
   same enterprise.  Each enterprise within the 'E1' hierarchy may
   comprise a smaller topological region within a larger RLOC space, or
   they may configure an independent RLOC space from a common (but
   spatially reused) limited-scope prefix, e.g., depicted as multiple
   disjoint instances of '10/8' in the diagram.

   In the RANGER approach, EBRs within lower-tier enterprises coordinate
   their EID prefixes with EBGs that connect to an upper-tier
   enterprise.  EID prefixes could be either provider-independent (PI)
   prefixes owned by the EBR or provider-aggregated (PA) prefixes
   delegated by the EBG.  In either case, EID prefixes must be
   coordinated with the enterprise routing/mapping systems.

   When PA EID prefixes are used, the EBR for each 'E1*' enterprise
   receives an EID prefix delegation from a delegating EBG in a parent
   enterprise.  In this example, when 'R2' is a delegating router for
   the prefix '2001:DB8::/40', it may delegate '2001:DB8::/48' to 'X2',
   which in turn delegates '2001:DB8::/52' to 'Y1', which in turn
   delegates '2001:DB8::/56' to 'V'.  The preferred mechanism for this
   recursive PA prefix sub-delegation is DHCP Prefix Delegation
   [RFC3633], which also arranges for publication of the prefixes in the
   enterprise routing system.

   When PI EID prefixes are used, individual EBRs (e.g., 'V') register
   their PI prefixes (e.g., '2001:DB1:10::/56') by sending Router
   Advertisement (RA) messages to EBGs within the enterprise to assert
   prefix ownership.  When stronger authentication is necessary, the
   EBRs can digitally sign the messages using the mechanisms specified
   for SEcure Neighbor Discovery (SEND) [RFC3971].  EBGs that receive
   the RAs (e.g., 'Y1') first verify the sender's credentials, then
   register the prefixes in the enterprise mapping system.  Next, they
   forward a proxied version of the RA to EBGs within their parent
   enterprises (e.g., 'X2').  This proxying process continues up the
   recursive hierarchy until a default-free commons is reached.  (In
   this case, the proxying process ends at 'R2').  After the initial
   registration, the EBR that owns the PI prefixes must periodically
   send additional RAs to update prefix expiration timers.

3.3.2.  RANGER End-to-End Addressing Example

   In Figure 2, an IPv6 host 'H' that is deeply nested within Enterprise
   'E1' connects to IPv6 server 'S1', located somewhere on the IPv6
   Internet.  'H' is attached to a shared link with IPv6/IPv4 dual-stack
   router 'V', which advertises the IPv6 prefixes '2001:DB8:0:0::/64'
   and '2001:DB8:10:0::/64'.  'H' uses standard IPv6 neighbor discovery
   mechanisms to discover 'V' as a default IPv6 router that can forward
   its packets off the local link, and configures addresses from both of
   the advertised prefixes.  'V' in turn sees node 'Y1' as an EBG that
   is reachable via VET interface 'vet1' and that can forward packets
   toward IPv6 server 'S1'.  Similarly, node 'Y1' is an EBR on the
   enterprise spanned by 'vet2' that sees 'X2' as an EBG, and node 'X2'
   is an EBR on 'vet3' that sees 'R2' as an EBG.  Ultimately, 'R2' is an
   EBR that connects 'E1' to the global Internet.

3.3.3.  Dynamic Routing and On-Demand Mapping

   In the example shown in Figure 2, 'V', 'Y1', 'X2', and 'R2' configure
   separate VET interfaces for each enterprise they connect to in order
   to discover routes through a dynamic routing protocol and/or mapping
   database lookups.  After tunnels 'vet1' through 'vet3' are
   established, the EBRs connected to a VET interface can run a dynamic
   routing protocol such as OSPVFv3 [RFC5340] and exchange topology
   information over the VET interface using the NBMA interface model.
   In this way, each EBR can discover other EBRs on the link via routing
   protocol control message exchanges.

   In a second example, Figure 3 depicts an instance of on-demand
   discovery of more specific routes in which an IPv6 end system 'H'
   connects to a peer end system 'J', located in a different
   organizational entity within 'E1':

                                                            +------+
                                                            | IPv6 |
       " " " " " " " "" " " " " " " " " " " " " " " "       |Server|
     "         <----------------- 2001:DB8::/40 (PA) "      |  S1  |
   "    2001:DB8:10::/56 (PI)  ---------------->      "     +--+---+
   "     . . . . . . .       . . . .      . . . .     "        |
   "   .               .    .       .    .       .    "        |
   "   .  +----+   v   +----+   v   +----+       +----+  +-----+-------+
   "   .  | V  +=  e  =+ Y1 +=  e  =+ X2 +=     =+ R2 +==+   Internet  |
   "   .  +-+--+   t   +----+   t   +----+       +----+  +-----+-------+
   "   .    |      1   .    .   2   .    .       .    "        |
   "    .   H         .     .       .    .   v   .    "        |
   "      . . . . . .        . . . .     .   e   .    "     +--+---+
   "                                     .   t   .    "     | IPv4 |
   "                  . . . . . . ,      .   3   .    "     |Server|
   "                .  +----+   v   +----+       .    "     |  S2  |
   "                .  | Z  +=  e  =+ X7 +=      .    "     +------+
   "                .  +-+--+   t   +----+       .    "
   "                .    |      4   .    .       .    "
   "                .    J         .      . . . .     "
    "                 . . . . . . .                   "
      "           2001:DB8:20::/56 (PI) -------->    "
        " " " " " " " " " " " " " " "" " " " " " " "
                     <-- Enterprise E1 -->

                Figure 3: On-Demand Discovery

   In this example, tunnel interfaces 'vet1' through 'vet4' as well as
   IPv6 PI prefix registrations have been established through VET
   enterprise autoconfiguration procedures.  When IPv6 end system 'H'
   with IPv6 address '2001:DB8:10::1' sends packets to a peer end system
   'J' with IPv6 address '2001:DB8:20::1', the packets will be conveyed
   through 'V', 'Y1', and finally to 'X2' via default routes.  Then,
   unless 'X2' has an IPv6 FIB entry matching 'J', it must discover that
   'J' can be reached using a more direct route via 'X7' as the next-hop
   across the 'E1' commons.

   In particular, when 'X2' receives a packet on the 'vet2' interface
   with inner destination address 'J', it can perform an on-demand
   mapping lookup by consulting the enterprise mapping service, e.g., by
   consulting the DNS reverse zone.  Alternatively, 'X2' can send the
   packet to a default router (e.g., 'R2'), which in turn can forward
   the packet to 'X7' and return an ICMPv6 redirect message.  When 'X2'
   receives the redirect, it can send an RA message to 'X7' to prove
   that it is authorized to produce packets with a prefix that matches
   source address 'J'.  'X2' can then forward subsequent packets
   directly to 'X7' without involving 'R2'.

   In some enterprise scenarios, dynamic routing and on-demand mapping
   can be combined as complementary functions.  In other scenarios, it
   may be preferable to use either dynamic routing only or on-demand
   mapping only.

3.3.4.  Support for Legacy RLOC-Based Services

   Legacy hosts, routers, and networks that were already present in pre-
   RANGER deployments and have already numbered their interfaces with
   RLOC addresses must see continued support for RLOC-based services for
   the long term, even as EID-based services are rolled out in new
   deployments.  For example, a legacy IPv4-only node behind an IPv4
   Network Address Translator (NAT) must still be able to reach legacy
   IPv4-only Internet services (e.g., "http://example.com") long after
   the RANGER architecture and EID-based services are widely deployed.

   Returning to the example diagrams, while virtual enterprise traversal
   across 'E1' provides a fully connected routing and addressing
   capability for EID-based services, legacy nodes will still require
   access to RLOC-based services within connected or disjoint RLOC
   spaces for an extended (and possibly indefinite) period.  For
   example, Figure 4 below depicts the applicable RLOC-based IPv4
   service-access scenarios for the RANGER architecture when VET
   interfaces are used to link recursively nested enterprises together:

                                                            +------+
                                                            | IPv6 |
       " " " " " " " "" " " " " " " " " " " " " " " "       |Server|
     "         <----------------- 2001:DB8::/40 (PA) "      |  S1  |
   "    2001:DB8:10::/56 (PI)  ----------------->     "     +--+---+
   "     . . . . . . .       . . . .      . . . .     "        |
   "   .               .    .       .    .       .    "        |
   "   .  +----+   v   +--- +   v   +----+   v   +----+  +-----+-------+
   "   .  | V  +=  e  =+ Y1 +=  e  =+ X2 +=  e  =+ R2 +==+   Internet  |
   "   .  +-+--+   t   +----+   t   +----+   t   +----+  +-----+-------+
   "   .    |      1   .    .   2   .    .   3   .    "        |
   "    .   K   L     .     .       .    . M     .    "        |
   "      . . . . . .        . . . .      . . . .     "     +--+---+
    "       <E1.1.1>         <E1.1>        <E1>       "     | IPv4 |
      "                                              "      |Server|
        " " " " " " " " " " " " " " "" " " " " " " "        |  S2  |
                     <-- Enterprise E1 -->                  +------+

        Figure 4: Support for Legacy RLOC-Based Services

   In a first instance, a legacy RLOC-based IPv4 client 'K' within
   enterprise 'E1.1.1' can access RLOC-based IPv4 service 'L' within the
   same enterprise as normal and without the need for any encapsulation.

   Instead, 'K' discovers a "mapping" for 'L' through a simple lookup
   within the 'E1.1.1' enterprise-local name service, and conveys
   packets to 'L' through unencapsulated RLOC-based IPv4 routing and
   addressing within the 'E1.1.1' commons.  In many instances, this may
   indeed be the preferred service-access model, even when EID-based
   IPv6 services are widely deployed due to factors such as inability to
   replace legacy IPv4 applications, IPv6 header overhead avoidance,
   etc.

   In a second instance, RLOC-based IPv4 client 'K' can access RLOC-
   based IPv4 server 'S2' on the legacy global IPv4 Internet in a number
   of ways, based on the way the recursively nested 'E1.*' enterprises
   are provisioned:

   o  if all of the recursively nested 'E1.*' enterprises are configured
      within the same IPv4 RLOC space, normal IPv4 forwarding will
      convey unencapsulated IPv4 packets from 'K' toward 'R2', which
      then acts as an IPv4 Network Address Translator (NAT) and/or an
      ordinary IPv4 Enterprise Border Router.

   o  if the recursively nested 'E1.*' enterprises are configured within
      disjoint RLOC spaces, all EBGs 'Y1', 'X2', and 'R2' can be
      configured to provide an IPv4 NAT capability (i.e., a recursive
      nesting of NATs within NATs).  However, this approach places
      multiple instances of stateful NAT devices on the path, which can
      lead to an overall degree of brittleness and intolerance to
      routing changes.  Instead, 'R2' can act as a "Carrier-Grade NAT
      (CGN)", and 'V' can convey packets from 'K' to the CGN using
      IPv4-in-IPv6-in-IPv4 tunneling.  The CGN can then decapsulate the
      inner, RLOC-based IPv4 packets and translate the IPv4 source
      addresses into global IPv4 source addresses before sending the
      packets on to 'S2'.

   o  'K' could be configured as an EID-based, IPv6-capable node and use
      standard IPv6 routing to reach an IPv6/IPv4 translator located at
      an EBR for the enterprise in which 'S2' resides.  The translator
      would then use IPv6-to-IPv4 translation before sending packets
      onwards toward 'S2'.  These and other alternatives are discussed
      in [WING].

   In a final instance, RLOC-based IPv4 client 'K' can access an RLOC-
   based IPv4 server 'M' in a different enterprise within E1 as long as
   both enterprises are configured over the same IPv4 RLOC space.  If
   the enterprises are configured over disjoint IPv4 RLOC spaces,
   however, 'K' would still be able to access 'M' by using EID-based
   IPv6 services, by using EID-based IPv4 services if an EID-based IPv4
   overlay were deployed, or by using some form of RLOC-based IPv4 NAT
   traversal.  'K' could also access server 'M' if both 'V' and 'X2'
   implemented an IPv6/IPv4 protocol translation capability.  Finally,
   'K' and/or 'M' could implement a bump-in-the-wire or bump-in-the-api
   IPv6/IPv4 protocol translation capability.

3.4.  Subnetwork Encapsulation and Adaptation Layer (SEAL)

   Tunnel endpoints that depend on ICMP feedback from routers within the
   enterprise commons may be susceptible to undetected black holes due
   to ICMP filtering gateways and/or off-path ICMP spoofing attacks from
   a node pretending to be a router.  Furthermore, rogue nodes within
   enterprises that do not correctly implement ingress filtering can
   send spoofed packets of any kind, e.g., for the purpose of mounting
   denial-of-service and/or traffic amplification attacks targeting
   underprivileged links.

   The Subnetwork Encapsulation and Adaptation Layer (SEAL) provisions
   each encapsulated packet with a monotonically incrementing, extended
   Identification field (i.e., the 32-bit SEAL_ID) that tunnel endpoints
   can use as a nonce to detect off-path spoofing.  Moreover, tunnel
   endpoints that use SEAL can continue to operate correctly even if
   some/many ICMPs are lost.  Finally, tunnel endpoints that use SEAL
   can adapt to subnetworks containing links with diverse MTUs
   properties.

3.5.  Mobility Management

   Enterprise mobility use cases must be considered along several
   different vectors:

   o  nomadic enterprises and end systems may be satisfied to incur
      address renumbering events as they move between new enterprise
      network attachment points.

   o  mobile enterprises with PI prefixes may be satisfied by dynamic
      updates to the mapping system as long as they do not impart
      unacceptable churn.

   o  mobile enterprises and end systems with PA addresses/prefixes may
      require additional supporting mechanisms that can accommodate
      address/prefix renumbering.

   Nomadic enterprise mobility is already satisfied by currently
   deployed technologies.  For example, transporting a laptop computer
   from a wireless-access hot spot to a home network LAN would allow the
   nomadic device to re-establish connectivity at the expense of address
   renumbering.  Such renumbering may be acceptable, especially for
   devices that do not require session persistence across mobility
   events and do not configure servers with addresses published in the
   global DNS.

   Mobile enterprises with PI prefixes that use VET and SEAL can move
   between parent enterprise attachment points as long as they withdraw
   the prefixes from the mapping systems of departed enterprises and
   inject them into the mapping systems of new enterprises.  When moving
   between the lower recursive tiers of a common parent enterprise, such
   a localized event mobility may result in no changes to the parent
   enterprise's mapping system.  Hence, the organizational structure of
   a carefully arranged enterprise-within-enterprise framework may be
   able to dampen mobility-related churn.  For enterprises that require
   in-the-network confidentiality, IKEv2 Mobility and Multihoming
   (MOBIKE) [RFC4555] may also be useful within this context.

   Mobile enterprises and end systems that move quickly between
   disparate parent enterprise attachment points should not use PI
   prefixes if withdrawing and announcing the prefixes would impart
   unacceptable mapping/routing churn and packet loss.  They should
   instead use PA addresses/prefixes that can be coordinated via a
   rendezvous service.  Mobility management mechanisms such as Mobile
   IPv6 [RFC3775] and the Host Identity Protocol (HIP) [RFC4423] can be
   used to maintain a stable identifier for fast moving devices even as
   they move quickly between visited enterprise attachment points.

   As a use case in point, consider an aircraft with a mobile router
   moving between ground station points of attachment.  If the ground
   stations are located within the same enterprise, or within lower-tier
   sites of the same parent enterprise, it should suffice for the
   aircraft to announce its PI prefixes at its new point of attachment
   and withdraw them from the old.  This would avoid excessive mapping
   system churn, since the prefixes need not be announced/withdrawn
   within the parent enterprise, i.e., the churn is isolated to lower
   layers of the recursive hierarchy.  Note also that such movement
   would not entail an aircraft-wide readdressing event.

   As a second example, consider a wireless handset moving between
   service coverage areas maintained by independent providers with
   peering arrangements.  Since the coverage range of terrestrial
   cellular wireless technologies is limited, mobility events may occur
   on a much more aggressive timescale than some other examples.  In
   this case, the handset may expect to incur a readdressing event for
   its access interface at least, and may be obliged to arrange for a
   rendezvous service linkage.

   It should specifically be noted that the contingency of mobility
   management solutions is not necessarily mutually exclusive and must
   be considered in relation to specific use cases.  The RANGER
   architecture is therefore naturally inclusive in this regard.  In
   particular, RANGER could benefit from mechanisms that could support
   rapid dynamic updates of PI prefix mappings without causing excessive
   churn.

3.6.  Multihoming

   As with mobility management, multihoming use cases must be considered
   along multiple vectors.  Within an enterprise, EBRs can discover
   multiple EBGs and use them in a fault-tolerant and load-balancing
   fashion as long as they register their PI prefixes with each such
   EBG, as described in Section 3.3.1.  These registrations are created
   through the transmission of Router Advertisement messages that
   percolate up through the recursive enterprise-within-enterprise
   hierarchy.

   As a first case in point, consider the enterprise network of a major
   corporation that obtains services from a number of ISPs.  The
   corporation should be able to register its PI prefixes with all of
   its ISPs, and use any of the ISPs for its Internet access services.

   As a second use case, consider an aircraft with a diverse set of
   wireless links (e.g., VHF, 802.16, directional, SATCOM, etc.).  The
   aircraft should be able to select and utilize the most appropriate
   link(s) based on the phase of flight and to change seamlessly between
   links as necessary.  Other examples include a nomadic laptop with
   both 802.11 and Ethernet links, a wireless handset with both CDMA
   wireless and 802.11, etc.

   As with mobility management, the contingency of solutions is not
   necessarily mutually exclusive and can combine to suit use cases
   within the scope of the RANGER architecture.

3.7.  Implications for the Internet

   Selection of mapping alternatives may have significant implications
   for applications, server selection, route determination, security,
   etc.  In particular, applications that expect all packets (including
   initial ones) to experience similar delays may be adversely affected
   by a scheme that imposes non-negligible delays when initial packets
   are queued while a look-aside mapping table is consulted.  Still
   other applications may experience significant startup delays when its
   initial packets are dropped during a mapping lookup event.  These
   factors would seem to favor a scheme that is able to forward initial
   packets along a path with sub-optimal delay while a mapping lookup is
   performed in parallel, e.g., such as when a "default mapper" is used.

   Generally speaking, proactive mapping-maintenance mechanisms may have
   scaling issues with the amount of updates they generate, while
   reactive mechanisms may involve effects to the delay of initial
   packets before the cached state is updated.  Also to be considered
   are attacks against the mapping mechanism, which may result in denial
   of service of the mapping cache.

   Encapsulation of packets in automatically created tunnels involves a
   number of issues as well.  There are obvious interactions between
   encapsulation overhead and the effective tunnel MTU, which can be
   addressed by SEAL and (when necessary) careful operational link
   arrangements.  Moreover, it is important to minimize the impact to
   the global routing table without at the same time impacting the
   ability of legacy Internet networks to connect to those employing
   RANGER.  As long as other nodes in the Internet need to connect to
   networks implementing RANGER, EID routes need to appear both in the
   mapping system and the global BGP routing tables.  This can be
   accommodated by keeping the number of prefixes aggregated by RANGER
   to the bare minimum through efficient aggregation (e.g., one or a few
   [PREF]::/4 IPv6 prefixes instead of millions of [PREF]::/32
   prefixes).

4.  Related Initiatives

   The origins of the RANGER architectural principles can be traced to
   the "Catenet model for internetworking" ([CATENET], [IEN48],
   [RFC2775]) beginning as early as the mid-1970's.  Subsequently,
   deliberations of the ROAD group [RFC1380] and related efforts such as
   NIMROD [RFC1753] provided a sustained evolution of the concepts.
   [RFC1955], "New Scheme for Internet Routing and Addressing (ENCAPS)
   for IPNG", captures the high-level architectural aspects of the ROAD
   group deliberations.

   These foundational works significantly influenced more recent
   developments, including the X-Bone initiative [XBONE], which explored
   virtual topologies manifested through tunneling.  Various tunneling
   approaches including IP-in-IP ([RFC2003], [RFC4213]), 6over4
   [RFC2529], and ISATAP [RFC5214] have evolved from the mid-1990's
   until the present day and are used in common, operational practice.
   Tunnel-mode IPsec [RFC4301] is also commonly used for separation of
   security domains within enterprises.

   Currently, initiatives with similar properties to RANGER are under
   development within the IRTF Routing Research Group (RRG) and within
   IETF working groups such as LISP, SOFTWIRE, V6OPS, and others.
   Numerous proposals have been offered within the RRG, including the
   Locator-Identifier Split Protocol (LISP) [LISP], Six-One [VOGT], ILNP
   [ILNP], Internet vastly improved plumbing (Ivip) [WHITTLE], A
   Practical Transit-Mapping Service (APT) [JEN], and Virtual
   Aggregation [VA].  Still other similar initiatives almost certainly
   exist.

   While RANGER shares many properties with these earlier works, it
   uniquely provides a top-to-bottom articulation of how the various
   pieces fit together within a recursively nested "enterprise-within-
   enterprise" (or "network-of-networks") framework.  In this way, it
   bears striking resemblance to the network-of-networks model
   envisioned by CATENET.  RANGER further provides a detailed
   consideration of challenging issues such as autoconfiguration,
   provider-independent addressing, border router discovery, tunnel MTU,
   multihoming, etc. that many other approaches have either overlooked
   or left for future work.  A detailed analysis of RANGER applicability
   in various use case scenarios is provided in "RANGER Scenarios
   (RANGERS)" [RUSSERT].

5.  Security Considerations

   Communications between endpoints within different sites inside an
   enterprise are carried across a commons that joins organizational
   entities with a mutual spirit of cooperation, but between which there
   may be competing business/sociological/political interests.  As a
   result, mechanisms that rely on feedback from routers on the path may
   become brittle or susceptible to spoofing attacks.  This is due to
   the fact that IP packets can be lost due to congestion or packet-
   filtering gateways and that the source addresses of IP packets can be
   forged.  Moreover, IP packets in general can be generated by
   anonymous attackers, e.g., from a rogue node within a third-party
   enterprise that has malicious intent toward a victim.

   Path MTU Discovery is an example of a mechanism that relies on ICMP
   feedback from routers on the path and, as such, is susceptible to
   these issues.  For IPv4, a common workaround is to disable Path MTU
   Discovery and let fragmentation occur in the network if necessary.
   For IPv6, lack of fragmentation support in the network precludes this
   option such that the mitigation typically recommended is to discard
   ICMP messages that contain insufficient information and/or to operate
   with the minimum IPv6 path MTU.  This example extends also to other
   mechanisms that either rely on or are enhanced by feedback from
   network devices; however, attack vectors based on non-ICMP messages
   are also subject for concern.

   The RANGER architecture supports effective mitigations for attacks
   such as distributed denial-of-service, traffic amplification, etc.
   In particular, when VET and SEAL are used, EBGs can use the 32-bit
   identification encoded in the SEAL header as well as ingress
   filtering to determine if a message has come from a topologically
   correct enterprise located across the commons.  This allows
   enterprises to employ effective mitigations at their borders without
   the requirement for mutual cooperation from other enterprises.  When
   source address spoofing by on-path attackers located within the
   commons is also subject for concern, additional securing mechanisms
   such as tunnel-mode IPsec between enterprise EBGs can also be used.

   EBRs can obtain PI prefixes through arrangements with a prefix
   delegation authority.  Thereafter, the EBR can announce and/or
   withdraw the prefixes within an enterprise by sending IPv6 Router
   Advertisements (RAs).  In environments where additional
   authenticating mechanisms are necessary, the EBR can sign its RAs
   using SEcure Neighbor Discovery (SEND) [RFC3971].

   While the RANGER architecture does not in itself address security
   considerations, it proposes an architectural framework for functional
   specifications that do.  Security concerns with tunneling, along with
   recommendations that are compatible with the RANGER architecture, are
   found in [HOAGLAND].

6.  Acknowledgements

   This work was inspired through the encouragement of the Boeing DC&NT
   network technology team and through the communications of the IESG.

   Many individuals have contributed to the architectural principles
   that form the basis for RANGER over the course of many years.  The
   following individuals have given specific feedback on the RANGER
   document itself: Jari Arkko, Brian Carpenter, Eric Fleischman, Joel
   Halpern, Thomas Henderson, Steven Russert, Dallas Thomas, Robin
   Whittle.

7.  References

7.1.  Normative References

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

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

7.2.  Informative References

   [CATENET]  Pouzin, L., "A Proposal for Interconnecting Packet
              Switching Networks", Proceedings of EUROCOMP, Bronel
              University, p. 1023-1036, May 1974.

   [COEXIST]  Arkko, J. and M. Townsley, "IPv4 Run-Out and IPv4-IPv6 Co-
              Existence Scenarios", Work in Progress, July 2009.

   [BAUER]    Bauer, C. and S. Ayaz, "ATN Topology Considerations for
              Aeronautical NEMO RO", Work in Progress, September 2009.

   [LISP]     Farinacci, D., Fuller, V., Meyer, D., and D. Lewis,
              "Locator/ID Separation Protocol (LISP)", Work in Progress,
              September 2009.

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

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

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

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

   [VET]      Templin, F., Ed., "Virtual Enterprise Traversal (VET)",
              RFC 5558, February 2010.

   [WING]     Wing, D., Ward, D., and A. Durand, "A Comparison of
              Proposals to Replace NAT-PT", Work in Progress, September
              2008.

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

   [ILNP]     Atkinson, R., "ILNP Concept of Operations", Work in
              Progress, December 2008.

   [RFC1380]  Gross, P. and P. Almquist, "IESG Deliberations on Routing
              and Addressing", RFC 1380, November 1992.

   [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.

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

   [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.

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

   [RFC3775]  Johnson, D., Perkins, C., and J. Arkko, "Mobility Support
              in IPv6", RFC 3775, June 2004.

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

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

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

   [RFC4423]  Moskowitz, R. and P. Nikander, "Host Identity Protocol
              (HIP) Architecture", RFC 4423, May 2006.

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

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

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

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

   [VA]       Francis, P., Xu, X., Ballani, H., Jen, D., Raszuk, R., and
              L. Zhang, "FIB Suppression with Virtual Aggregation", Work
              in Progress, October 2009.

   [VOGT]     Vogt, C., "Six/One: A Solution for Routing and Addressing
              in IPv6", Work in Progress, October 2009.

   [WHITTLE]  Whittle, R., "Ivip (Internet Vastly Improved Plumbing)
              Architecture", Work in Progress, August 2008.

   [XBONE]    Touch, J., "The X-Bone", March 1997,
              http://www.isi.edu/touch/pubs/ngi97/x-bone-ngi97.pdf

Author's Address

   Fred L. Templin
   Boeing Phantom Works
   P.O. Box 3707 MC 7L-49
   Seattle, WA  98124
   USA

   EMail: fltemplin@acm.org