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Internet Research Task Force                             F. Templin, Ed.
(IRTF)                                      Boeing Research & Technology
Internet-Draft                                            August 6, 2010
Intended status: Informational
Expires: February 7, 2011


              The Internet Routing Overlay Network (IRON)
                       draft-templin-iron-09.txt

Abstract

   Since the Internet must continue to support escalating growth due to
   increasing demand, it is clear that current routing architectures and
   operational practices must be updated.  This document proposes an
   Internet Routing Overlay Network for supporting sustainable growth
   through Provider Independent addressing while requiring no changes to
   end systems and no changes to the existing routing system.  This
   document is a product of the IRTF Routing Research Group (RRG).

Status of this Memo

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

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

   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on February 7, 2011.

Copyright Notice

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

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



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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  The Internet Routing Overlay Network (IRON)  . . . . . . . . .  5
     3.1.  IR[CE] - IRON Customer Edge Router . . . . . . . . . . . .  7
     3.2.  IR[VE] - IRON Virtual Prefix Company Edge Router . . . . .  7
     3.3.  IR[VC] - IRON Virtual Prefix Company Core Router . . . . .  8
     3.4.  IR[VP] - IRON Virtual Prefix Company Combined Router . . .  9
   4.  IRON Organizational Principles . . . . . . . . . . . . . . . . 10
   5.  IRON Initialization  . . . . . . . . . . . . . . . . . . . . . 12
     5.1.  IR[VC] Initialization  . . . . . . . . . . . . . . . . . . 12
     5.2.  IR[VE] Initialization  . . . . . . . . . . . . . . . . . . 12
     5.3.  IR[CE] Initialization  . . . . . . . . . . . . . . . . . . 13
   6.  IRON Operation . . . . . . . . . . . . . . . . . . . . . . . . 13
     6.1.  IR[CE] Operation . . . . . . . . . . . . . . . . . . . . . 14
     6.2.  IR[VE] Operation . . . . . . . . . . . . . . . . . . . . . 16
     6.3.  IR(VC) Operation . . . . . . . . . . . . . . . . . . . . . 17
     6.4.  IRON Reference Operating Scenarios . . . . . . . . . . . . 17
       6.4.1.  Both Hosts Within IRON EUNs  . . . . . . . . . . . . . 18
       6.4.2.  Mixed IRON and Non-IRON Hosts  . . . . . . . . . . . . 24
     6.5.  Mobility, Multihoming and Traffic Engineering
           Considerations . . . . . . . . . . . . . . . . . . . . . . 27
       6.5.1.  Mobility Management  . . . . . . . . . . . . . . . . . 27
       6.5.2.  Multihoming  . . . . . . . . . . . . . . . . . . . . . 28
       6.5.3.  Inbound Traffic Engineering  . . . . . . . . . . . . . 28
       6.5.4.  Outbound Traffic Engineering . . . . . . . . . . . . . 28
     6.6.  Renumbering Considerations . . . . . . . . . . . . . . . . 28
     6.7.  NAT Traversal Considerations . . . . . . . . . . . . . . . 29
     6.8.  Nested EUN Considerations  . . . . . . . . . . . . . . . . 29
       6.8.1.  Host A Sends Packets to Host Z . . . . . . . . . . . . 30
       6.8.2.  Host Z Sends Packets to Host A . . . . . . . . . . . . 32
   7.  Additional Considerations  . . . . . . . . . . . . . . . . . . 33
   8.  Related Initiatives  . . . . . . . . . . . . . . . . . . . . . 33
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 33
   10. Security Considerations  . . . . . . . . . . . . . . . . . . . 34
   11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 34
   12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 34
     12.1. Normative References . . . . . . . . . . . . . . . . . . . 34
     12.2. Informative References . . . . . . . . . . . . . . . . . . 34
   Appendix A.  IRON VPs Over Non-Native Internetworks  . . . . . . . 36
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 38




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1.  Introduction

   Growth in the number of entries carried in the Internet routing
   system has led to concerns for unsustainable routing scaling
   [I-D.narten-radir-problem-statement].  Operational practices such as
   increased use of multihoming with IPv4 Provider-Independent (PI)
   addressing are resulting in more and more fine-grained prefixes
   injected into the routing system from more and more end user
   networks.  Furthermore, the forthcoming depletion of the public IPv4
   address space has raised concerns for both increased deaggregation
   (leading to yet further routing table entries) and an impending
   address space run-out scenario.  At the same time, the IPv6 routing
   system is beginning to see growth in IPv6 Provider-Aggregated (PA)
   prefixes [BGPMON] which must be managed in order to avoid the same
   routing scaling issues the IPv4 Internet now faces.  Since the
   Internet must continue to scale to accommodate increasing demand, it
   is clear that new routing methodologies and operational practices are
   needed.

   Several related works have investigated routing scaling issues and
   proposed solutions.  Virtual Aggregation (VA) [I-D.ietf-grow-va] and
   Aggregation in Increasing Scopes (AIS) [I-D.zhang-evolution] are
   global routing proposals that introduce routing overlays with Virtual
   Prefixes (VPs) to reduce the number of entries required in each
   router's Forwarding Information Base (FIB) and Routing Information
   Base (RIB).  Routing and Addressing in Networks with Global
   Enterprise Recursion (RANGER) [RFC5720] examines recursive
   arrangements of enterprise networks that can apply to a very broad
   set of use case scenarios [I-D.russert-rangers].  In particular,
   RANGER supports encapsulation and secure redirection by treating each
   layer in the recursive hierarchy as a virtual non-broadcast, multiple
   access (NBMA) "link".  RANGER is an architectural framework that
   includes Virtual Enterprise Traversal (VET) [I-D.templin-intarea-vet]
   and the Subnetwork Adaptation and Encapsulation Layer (SEAL)
   (including the SEAL Control Message Protocol (SCMP))
   [I-D.templin-intarea-seal] as its functional building blocks.

   This document proposes an Internet Routing Overlay Network (IRON)
   with goals of supporting sustainable growth while requiring no
   changes to the existing routing system.  IRON borrows concepts from
   VA, AIS and RANGER, and further borrows concepts from the Internet
   Vastly Improved Plumbing (Ivip) [I-D.whittle-ivip-arch] architecture
   proposal along with its associated Translating Tunnel Router (TTR)
   mobility extensions [TTRMOB].  Indeed, the TTR model to a great
   degree inspired the IRON mobility architecture design discussed in
   this document.  The Network Address Translator (NAT) traversal
   techniques adapted for IRON were inspired by the Simple Address
   Mapping for Premises Legacy Equipment (SAMPLE) proposal



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   [I-D.carpenter-softwire-sample].

   IRON specifically seeks to provide scalable PI addressing without
   changing the current BGP [RFC4271] routing system.  IRON observes the
   Internet Protocol standards [RFC0791][RFC2460].  Other network layer
   protocols that can be encapsulated within IP packets (e.g., OSI/CLNP
   [RFC1070], etc.) are also within scope.

   The IRON is a global overlay network routing system comprising
   Virtual Prefix Companies (VPCs) that own and manage Virtual Prefixes
   (VPs) from which End User Network (EUN) PI prefixes (EPs) are
   delegated to customer sites.  The IRON is motivated by a growing
   customer demand for multihoming, mobility management and traffic
   engineering while using stable PI addressing to avoid network
   renumbering [RFC4192][RFC5887].  The IRON uses the existing IPv4 and
   IPv6 global Internet routing systems as virtual links for tunneling
   inner network protocol packets within outer IPv4 or IPv6 headers
   (see: Section 3).  The IRON requires deployment of a small number of
   new routers that can often be simple commodity hardware platforms.
   No modifications to hosts, and no modifications to most routers are
   required.

   Note: This document is offered in compliance with Internet Research
   Task Force (IRTF) document stream procedures [RFC5743]; it is not an
   IETF product and is not a standard.  The views in this document were
   considered controversial by the IRTF Routing Research Group (RRG) but
   the RG reached a consensus that the document should still be
   published.  The document will undergo a period of review within the
   RRG and through selected expert reviewers prior to publication.  The
   following sections discuss details of the IRON architecture.


2.  Terminology

   This document makes use of the following terms:

   End User Network (EUN)
      an edge network that connects an organization's devices (e.g.,
      computers, routers, printers, etc.) to the Internet and possibly
      also the IRON.

   Internet Service Provider (ISP)
      a service provider which physically connects customer EUNs to the
      Internet.







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   Provider Aggregated (PA) prefix
      a network layer address prefix delegated to an EUN by a service
      provider.

   Provider Independent (PI) prefix
      a network layer address prefix delegated to an EUN by a third
      party independently of the EUN's ISP arrangements.

   Virtual Prefix (VP)
      a highly-aggregated PI prefix block (e.g., an IPv4 /16, an IPv6
      /20, an OSI NSAP prefix, etc.) that is owned and managed by a
      Virtual Prefix Company (VPC).

   Virtual Prefix Company (VPC)
      a company that owns and manages a set of VPs from which it
      delegates End User Network PI Prefixes (EPs) to EUNs

   Master Virtual Prefix database (MVPd)
      a distributed database that maintains VP-to-locator mappings for
      all VPs in the IRON.

   End User Network PI prefix (EP)
      a more-specific PI prefix derived from a VP (e.g., an IPv4 /28, an
      IPv6 /56, etc.) and delegated to an EUN by a VPC.

   EP Address (EPA)
      a network layer address taken from an EP address range and
      assigned to the interface of an end system in an EUN.

   locator
      an IP address assigned to the interface of a router or end system
      within a public or private network.  Locators taken from public IP
      address spaces are routable within the global Internet while
      locators taken from private IP address spaces are routable only
      within the network where the private IP addressing plan is
      deployed.

   Internet Routing Overlay Network (IRON)
      an overlay network configured over the global Internet.  The IRON
      supports routing through encapsulation of inner packets with EPA
      addresses within outer headers that use locator addresses.


3.  The Internet Routing Overlay Network (IRON)

   The Internet Routing Overlay Network (IRON) consists of IRON Routers
   (IRs) that automatically tunnel the packets of end-to-end
   communication sessions within encapsulating headers used for



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   Internetwork routing.  IRs use Virtual Enterprise Traversal (VET)
   [I-D.templin-intarea-vet] in conjunction with the Subnetwork
   Encapsulation and Adaptation Layer (SEAL) [I-D.templin-intarea-seal]
   to encapsulate inner network layer packets within outer headers as
   shown in Figure 1:

                                         +-------------------------+
                                         |    Outer headers with   |
                                         ~     locator addresses   ~
                                         |     (IPv4 or IPv6)      |
                                         +-------------------------+
                                         |       SEAL Header       |
       +-------------------------+       +-------------------------+
       |   Inner Packet Header   |  -->  |   Inner Packet Header   |
       ~    with EP addresses    ~  -->  ~    with EP addresses    ~
       | (IPv4, IPv6, OSI, etc.) |  -->  | (IPv4, IPv6, OSI, etc.) |
       +-------------------------+       +-------------------------+
       |                         |  -->  |                         |
       ~    Inner Packet Body    ~  -->  ~    Inner Packet Body    ~
       |                         |  -->  |                         |
       +-------------------------+       +-------------------------+

          Inner packet before                Outer packet after
          before encapsulation               after encapsulation

     Figure 1: Encapsulation of Inner Packets Within Outer IP Headers

   VET specifies the automatic tunneling mechanisms used for
   encapsulation, while SEAL specifies the format and usage of the SEAL
   header as well as a set of control messages.  Most notably, IRs use
   SEAL to deterministically exchange and authenticate control messages
   such as indications of Path Maximum Transmission Unit (PMTU)
   limitations.

   The IRON is manifested through a business model in which Virtual
   Prefix Companies (VPCs) own and manage a set of IRs that are
   distributed throughout the Internet and serve highly-aggregated
   Virtual Prefixes (VPs).  VPCs delegate sub-prefixes from their VPs
   which they lease to customers as End User Network PI prefixes (EPs).
   The customers in turn assign the EPs to their customer edge IRs which
   connect their End User Networks (EUNs) to the IRON.  VPCs may have no
   affiliation with the ISP networks from which customers obtain their
   basic connectivity.  Therefore, VPCs can open for business and begin
   serving their customers immediately without the need to coordinate
   their activities with ISPs or with other VPCs.

   The IRON requires no changes to end systems and no changes to most
   routers in the Internet.  Instead, the IRON comprises IRs that are



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   deployed either as new platforms or as modifications to existing
   platforms.  IRs may be deployed incrementally without disturbing the
   existing Internet routing system, and act as waypoints (or "cairns")
   for navigating the IRON.  The functional roles for IRs are described
   in the following sections.

3.1.  IR[CE] - IRON Customer Edge Router

   An "IR[CE]" is a Customer Edge router (or host with embedded gateway
   function) that logically connects the customer's EUNs and their
   associated EPs to the IRON via tunnels.  IR[CE]s obtain EPs from VPCs
   and use them to number subnets and interfaces within their EUNs.  An
   IR[CE] can be deployed on the same physical platform that also
   connects the customer's EUNs to its ISPs, but it may also be a
   separate router or even a singleton end system located within the
   EUN.  (This model applies even if the EUN connects to the ISP via a
   Network Address Translator (NAT) - see Section 6.7).  An IR[CE]
   connects its EUNs to the IRON via tunnels as shown in Figure 2:
                           .-.
                        ,-(  _)-.
        +--------+   .-(_    (_  )-.
        | IR[CE] |--(_     ISP      )
        +---+----+     `-(______)-'
            |   <= T         \     .-.
           .-.       u        \ ,-(  _)-.
        ,-(  _)-.       n     .-(_    (-  )-.
     .-(_    (_  )-.      n  (_   Internet   )
    (_     EUN      )       e   `-(______)-
       `-(______)-'           l          ___
            |                   s =>    (:::)-.
       +----+---+                   .-(::::::::)
       |  Host  |                .-(::::::::::::)-.
       +--------+               (:::: The IRON ::::)
                                 `-(::::::::::::)-'
                                    `-(::::::)-'

                Figure 2: IR[CE] Connecting EUN to the IRON

3.2.  IR[VE] - IRON Virtual Prefix Company Edge Router

   An "IR[VE]" is a VPC's overlay network edge router that provides
   forwarding and mapping services for the EPs owned by customer
   IR[CE]s.  In typical deployments, a VPC will deploy many IR[VE]s
   around the IRON in a globally-distributed fashion (e.g., as depicted
   in Figure 3) so that IR[CE] clients can discover those that are
   nearby.





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             +--------+    +--------+
             | IR[VE] |    | IR[VE] |
             | Boston |    | Tokyo  |
             +--+-----+    ++-------+
     +--------+  \         /
     | IR[VE] |   \   ___ /
     | Seattle|    \ (:::)-.       +--------+
     +------+-+  .-(::::::::)------+ IR[VE] |
             \.-(::::::::::::)-.   | Paris  |
             (:::: The IRON ::::)  +--------+
              `-(::::::::::::)-'
   +--------+ /  `-(::::::)-'  \     +--------+
   | IR[VE] +          |        \--- + IR[VE] |
   | Moscow |     +----+---+         | Sydney |
   +--------+     | IR[VE] |         +--------+
                  | Cairo  |
                  +--------+

               Figure 3: IR[VE] Global Distribution Example

   An IR[VE] is a customer-facing tunnel endpoint router that IR[CE]s
   form bidirectional tunnels with over the IRON.  Each IR[VE]
   associates with the VPC's Internet-facing IR[VC]s that can forward
   packets from the IRON out to the native public Internet and vice-
   versa as discussed in the next section.

3.3.  IR[VC] - IRON Virtual Prefix Company Core Router

   An "IR[VC]" is a VPC's overlay network core router that acts as a
   gateway between the IRON and the native public Internet.  Each VPC
   configures one or more IR[VC]s which advertise the company's VPs into
   the IPv4 and/or IPv6 global Internet BGP routing systems.  Each
   IR[VC] associates with all of the VPC's overlay network edge routers,
   either via tunnels over the IRON or via a direct interconnect (e.g.,
   via an Ethernet cable, etc. ).  The IR[VC] role is depicted in
   Figure 4:















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                   ,-(  _)-.
                .-(_    (_  )-.
               (_   Internet   )
                  `-(______)-'
                        |
                   +----+---+
                   | IR[VC] |
                   +----+---+
                       _|_
                      (:::)-.
                  .-(::::::::)
   +--------+  .-(::::::::::::)-.  +--------+
   | IR[VE] | (:::: The IRON ::::) | IR[VE] |
   +--------+  `-(::::::::::::)-'  +--------+
                  `-(::::::)-'

                   +--------+
                   | IR[VE] |
                   +--------+

            Figure 4: IR[VC] Connecting IRON to Native Internet

3.4.  IR[VP] - IRON Virtual Prefix Company Combined Router

   An "IR[VP]" is a VPC's overlay network router that combines the
   functions of both the IR[VE] and IR[VC].  In that case, the IR[VE]
   and IR[VC] functions can be thought of as "half-gateway" functions
   that together comprise a unified IR[VP].  The IR[VE] and IR[VC]
   functions can therefore be discussed separately even when both
   functions reside within the same physical IR[VP] router as shown in
   Figure 5:




















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                   ,-(  _)-.
                .-(_    (_  )-.
               (_   Internet   )
                  `-(______)-'
                        |
             +----------+----------+
             | IR[VC] half-gateway |
             +---------------------+
             | IR[VE] half-gateway |
             +----------+----------+
          <- IR[VP] Unified Gateway ->
                       _|_
                      (:::)-.
                  .-(::::::::)
               .-(::::::::::::)-.
              (:::: The IRON ::::)
               `-(::::::::::::)-'
                  `-(::::::)-'

          Figure 5: IR[VP] Combining IR[VE] and IR[VC] Functions


4.  IRON Organizational Principles

   The IRON consists of the union of all VPC overlay networks worldwide.
   Each such overlay network represents a distinct "patch" on the
   Internet "quilt", where the patches are stitched together by tunnels
   over the links, routers, bridges, etc that connect the public
   Internet.  When a new VPC overlay network is deployed, it becomes yet
   another patch on the quilt.  The IRON is therefore a composite
   overlay network consisting of multiple individual patches, where each
   patch can be discussed independently of all others.  In particular,
   each patch (i.e., each VP overlay network) can operate independently
   of the other patches.  (NB: each patch needs to be aware of the VPs
   assigned to all other patches.)

   Each VPC in the IRON maintains a set of IR[VC]s that connect its
   overlay network directly to the public IPv4 and/or IPv6 Internets.
   In particular, if the VPC serves IPv4 VPs the IR[VC]s must configure
   locator addresses on the public IPv4 Internet, and if the VPC serves
   IPv6 VPs the IR[VC]s must configure locator addresses on the public
   IPv6 Internet.  Each IR[VC] advertises the VPC's IPv4 VPs into the
   IPv4 BGP routing system and advertises the VPC's IPv6 VPs into the
   IPv6 BGP routing system.  IR[VC]s will therefore receive packets with
   EPA destination addresses sent by end systems in the Internet then
   (re)encapsulate and forward them to the correct EPA-addressed end
   systems connected to the VPC overlay network.




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   Each VPC also manages a set of IR[VE]s that connect its overlay
   network directly to the public IPv4 and/or IPv6 Internets the same as
   for IR[VC]s, except that IR[VE]s need not be BGP routers and can
   often be simple commodity hardware platforms.  As such, the IR[VE]
   and IR[VC] functions can be deployed together on the same physical
   platform as an IR[VP], or they may be deployed on separate platforms
   (e.g., for load balancing purposes).  Each IR[VE] maintains a working
   set of IR[CE]s for which it caches EP-to-IR[CE] mappings in its
   Forwarding Information Base (FIB).  Each IR[VE] also in turn
   propagates the list of EPs in its working set to each of the VPC's
   IR[VC]s, e.g., via a dynamic routing protocol.  Each IR[VE] will
   therefore commonly track only the EPs for its current working set of
   IR[CE]s, while each IR[VC] will maintain a full EP-to-IR[VE] mapping
   table that represents reachability information for all EPs in the VPC
   overlay network.

   Customers establish IR[CE]s to connect their EUNs to the VPC overlay
   network.  Each EUN can connect to the overlay network via one or
   multiple IR[CE]s as long as the multiple IR[CE]s coordinate with one
   another, e.g., to mitigate EUN partitions.  Unlike IR[VC]s and
   IR[VE]s, IR[CE]s may use private addresses behind one or several
   layers of NATs.  The IR[CE] initially discovers a list of nearby
   IR[VE]s through an exchange with its VPC, then forms tunnels with one
   or more of the IR[VE]s through initial exchanges followed by periodic
   keepalives.  The IR[CE] then adds each such IR[VE] to its default
   router list.

   The IR[CE] forwards outbound packets from its EUNs by tunneling them
   to an IR[VC]/IR[VE] that can forward them further toward their final
   destination.  When the IR[CE] configures a locator with the same
   protocol version of its EPs, it tunnels packets with EPA destination
   addresses to an IR[VC]/IR[VE] within the VPC overlay network that
   manages the EUN of the final destination without involving one of the
   IR[VE]s in its default router list.  When the IR[CE] configures a
   locator of a different protocol version than its EPs, or when it
   forwards packets with non-EPA destination addresses, it instead
   tunnels the packets to one of the IR[VE]s in its default router list.

   If a flow of packets uses an EPA destination address, the IR[CE]/
   IR[VE] tunnels the initial packets of the flow by encapsulating them
   within an outer header that also uses the EPA as a destination
   address.  It then forwards the encapsulated packets into the public
   Internet where they will be routed to an IR[VC] that owns a VP that
   covers destination.  Thereafter, the IR[VE]/IR[CE] may receive
   redirects from the IR[VC] informing it of a more direct route via an
   IR[VE] that manages the EUN.  If a flow of packets uses a non-EPA
   address, however, the IR[CE] tunnels them to a IR[VE] in its default
   router list which will then forward them into the public Internet.



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   These arrangements are necessary to avoid ingress filtering issues
   and to allow for generally shortest path routes.

   The IRON can also be used to support VPs of network layer protocols
   that cannot be routed natively in the underlying Internetwork (e.g.,
   OSI/CLNP within the public Internet, IPv6 within in IPv4-only
   Internetworks, IPv4 within IPv6-only Internetworks, etc.).  In that
   case, however, the native routing capabilities of the Internetwork
   cannot be leveraged such that a more rigid structure that depends on
   a globally-distributed mapping database is required.  Further details
   for support of IRON VPs over non-native Internetworks are discussed
   in Appendix A.


5.  IRON Initialization

   IRON initialization entails the startup actions of IRs within the VPC
   overlay network and customer EUNs.  The following sections discuss
   these startups procedures.

5.1.  IR[VC] Initialization

   Before its first operational use, each IR[VC] in a VPC overlay
   network is pre-provisioned with the list of VPs that it will serve as
   well as the locators for all IR[VE]s that belong to the same overlay
   network.  The IR[VC] is also provisioned with BGP peerings the same
   as for any BGP router.

   Upon startup, the IR[VC] engages in BGP routing exchanges with its
   peers in the IPv4 and/or IPv6 Internets the same as for any BGP
   router.  It then connects to all of the IR[VE]s that service its VPs
   (e.g., via a TCP connection over a two-way tunnel, via a route
   reflector, etc.) for the purpose of discovering EP->IR[VE] mappings.
   After the IR[VC] has thus fully populated its EP->IR[VE] mapping
   information database, it is said to be "synchronized" wrt its VPs.
   The IR[VC] then advertises its VPs into the IPv4 and/or IPv6 Internet
   BGP routing systems and engages in ordinary packet forwarding
   operations.

5.2.  IR[VE] Initialization

   Before its first operational use, each IR[VE] in a VPC overlay
   network is pre-provisioned with the locators for all IR[VC]s that
   serve the overlay network's VPs.  In order to support route
   optimization, the IR[VE] must also be pre-provisioned with the list
   of all VPs in the IRON (i.e., and not just the VPs of it own overlay
   network) so that it can discern EPA and non-EPA addresses.




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   Upon startup, the IR[VE] connects to all of the IR[VC]s in the
   overlay network for the purpose of reporting its EP->IR[VE] mappings.
   The IR[VE] then actively listens for IR[CE] customers which will
   create a two-way tunnel while registering its EP prefixes.  When a
   new IR[CE] registers its EP prefixes, the IR[VE] informs all IR[VC]s
   of the new EP additions; when an existing IR[CE] unregisters its EP
   prefixes, the IR[VE] informs all IR[VC]s of the deletions.

5.3.  IR[CE] Initialization

   Before its first operational use, each IR[CE] must obtain one or more
   EPs from a VPC along with a certificate and a public/private key pair
   from the VPC that it can later use to prove ownership of its EPs.
   This implies that each VPC must run its own key infrastructure to be
   used only for the purpose of verifying a customer's claimed right to
   use an EP.  Hence, the VPC need not coordinate its key infrastructure
   with any other organizations.  In order to support route
   optimization, the IR[CE] must also be pre-provisioned with the list
   of all VPs in the IRON (i.e., and not just the VPs of this VPC) so
   that it can discern EPA and non-EPA addresses.

   Upon startup, the IR[CE] sends a router discovery message using an
   implicit anycast procedure (see Section 6.1) to discover the nearest
   IR[VC].  The IR[VC] will in turn return a list of locators of the
   company's nearby IR[VE]s.  (This list is analogous to the ISATAP
   Potential Router List (PRL) [RFC5214].)  The IR[CE] then selects a
   subset of IR[VE]s from this list and tests them to determine those
   that offer the best performance (see: Section 6.1).  The IR[CE] then
   registers its EP prefixes with one or more IR[VE]s and adds them to
   its default router list.


6.  IRON Operation

   Following this IRON initialization, IRs engage in the steady-state
   process of receiving and forwarding packets.  All IRs forward
   encapsulated packets over the IRON using the mechanisms of VET
   [I-D.templin-intarea-vet] and SEAL [I-D.templin-intarea-seal], while
   IR[VC]s and IR[VE]s additionally forward packets to and from the
   native IPv6 and IPv4 Internets.  IRs also use the SEAL Control
   Message Protocol (SCMP) to coordinate with other IRs, including the
   process of sending and receiving redirect messages for route
   optimization.  Each IR operates as specified in the following sub-
   sections.







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6.1.  IR[CE] Operation

   During its initialization phase, the IR[CE] first sends a SEAL
   Control Message Protocol (SCMP) Router Solicitation (SRS) message
   using an implicit anycast addressing scheme to determine the closest
   IR[VC] in its VPC overlay network.  In this procedure, the IR[CE]
   sets the "Router Alert" bit in the SEAL header to alert the nearest
   IR[VC] that this SRS message must be processed locally and not
   forwarded.  The IR[CE] then sets the source address of the SRS
   message to one of its locator addresses and sets the destination
   address of the message to one of its own EPA addresses.  (If the EPA
   address is of a different protocol version than the underlying
   Internetwork routing system, however, the IR[CE] sets the destination
   address to any EPA address of the Internetwork protocol version that
   is covered by a VP owned by the VPC overlay network.)  Normal
   Internet routing will then convey the SRS message to the nearest
   IR[VC] that advertises a VP that covers the EPA.  When the IR[VC]
   receives the SRS message, it notices that the Router Alert bit is set
   and sends back an SCMP Router Advertisement (SRA) message that lists
   the locator addresses of one or more nearby IR[VE] routers.

   After the IR[CE] receives an SRS message from the nearby IR[VC]
   listing the locator addresses of nearby IR[VE]s, it sends SRS test
   messages to one or more of the locator addresses to elicit SRA
   messages.  The IR[VE] that configures the locator will include the
   header of the soliciting SRS message in its SRA message so that the
   IR[CE] can determine the number of hops along the forward path.  The
   IR[VE] also includes a metric in its SRA messages indicating its
   current load average so that the IR[CE] can avoid selecting IR[VE]s
   that are overloaded.  The IR[VE] also includes a challenge/response
   puzzle that the IR[CE] must answer if it wishes to enlist this
   IR[VE]'s services.

   When the IR[CE] receives these SRA messages, it can measure the round
   trip time between sending the SRS and receiving the SRA as an
   indication of round-trip delay.  If the IR[CE] wishes the enlist the
   services of a specific IR[VE] (e.g., based on the measured
   performance), it then calculates the answer to the puzzle using its
   keying information and sends the answer back to the IR[VE] in a new
   SRS message that also contains all of the IR[CE]'s EP prefixes for
   which it claims ownership.  If the IR[CE] answered the puzzle
   correctly, the IR[VE] will send back a new SRA message that includes
   a non-zero default router lifetime and that signifies the
   establishment of a two-way tunnel.  (A zero default router lifetime
   on the other hand signifies that the IR[VE] is currently unable to
   establish a two-way tunnel, e.g., due to heavy load, due to
   challenge/response failure, etc.)




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   Note that in the above procedure it is essential that the IR[CE]
   select one and only one IR[VE].  This is to allow the VPC overlay
   network mapping system to have one and only one active EP-to-IR[VE]
   mapping at any point in time which shares fate with the IR[VE]
   itself.  If this IR[VE] fails, the IR[CE] will quickly select a new
   one which will automatically update the VPC overlay network mapping
   system with a new EP-to-IR[VE] mapping.

   After selecting its serving IR[VE], the IR[CE] should register each
   of its ISP connections with the IR[VE] in order to establish multiple
   two-way tunnels for multihoming purposes.  To do so, it sends
   periodic SRS messages via each of its ISPs to establish additional
   two-way tunnels and to keep each two-way tunnel alive.  These
   messages need not include challenge/response mechanisms since prefix
   proof of ownership was already established in the initial exchange
   and the SEAL ID in the SEAL header can be used to confirm that the
   SRS message was sent by the correct IR[CE].  This implies that a
   single SEAL_ID is used to represent the set of all two-way tunnels
   between the IR[CE] and the IR[VE].  Therefore, there are multiple
   two-way tunnels and the SEAL_ID names this "bundle" of tunnels.

   If the IR[CE] ceases to receive SRA messages from its serving IR[VE]
   via a specific ISP connection, it marks the IR[VE] as unreachable
   from that address and therefore over that ISP connection.  (The
   IR[CE] must also inform its serving IR[VE] of this outage via one of
   its working ISP connections.)  If the IR[CE] ceases to receive SRA
   messages from its serving IR[VE] via multiple ISP connections, it
   marks the IR[VE] as unusable and quickly attempts to establish a
   connection with a new IR[VE].  The act of establishing the connection
   with a new serving IR[VE] will automatically purge the stale mapping
   state associated with the old serving IR[VE].

   When an end system in an EUN has a packet to send, the packet is
   forwarded through the EUN via normal routing until it reaches the
   IR[CE], which then tunnels the packet either to its serving IR[VE]s
   or to an IR[VC]/IR[VE] associated with the packet's destination.  In
   particular, if the IR[CE] does not configure a locator of the same
   protocol version as the packet's destination or if the destination
   address is a non-EPA address, the IR[CE] encapsulates the packet in
   an outer header with its locator as the source address and the
   locator of its serving IR[VE]s as the destination address.
   Otherwise, the IR[CE] encapsulates the packet in an outer header with
   its locator as the source address and the destination address of the
   inner packet copied into the destination address of the outer packet.
   The IR[CE] then forwards the encapsulated packet via one of its ISP
   connections, where normal Internet routing will convey it to the
   correct tunnel far end.




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   The IR[CE] uses the mechanisms specified in VET and SEAL to
   encapsulate each forwarded packet.  The IR[CE] further uses the SCMP
   protocol to coordinate with other IRs, including accepting redirect
   messages that indicate a better next hop.  When the IR[CE] receives
   an SCMP redirect, it checks the identification field of the
   encapsulated message to verify that the redirect corresponds to a
   packet that it had previously sent and accepts the redirect if there
   is a match.  Thereafter, subsequent packets forwarded by the source
   IR[CE] will follow a route-optimized path.

6.2.  IR[VE] Operation

   After an IR[VE] is initialized, it responds to SRSs from IR[CE]s by
   sending SRAs as described in Section 6.1.  When the IR[VE] receives
   an SRS message from a potential IR[CE], it sends back an SRA message
   with a challenge/response puzzle.  The IR[CE] in turn sends an SRS
   message with an answer to the puzzle.  If this authentication fails,
   the IR[VE] discards the message.  Otherwise, it creates tunnel state
   for this new IR[CE], records the EPs in its FIB, and records the
   locator address from the SCMP message as the link-layer address of
   the next hop.  The IR[VE] next sends an SRA message back to the
   IR[CE] to complete the tunnel establishment.

   When the IR[VE] receives an encapsulated packet from one of its
   IR[CE] tunnel endpoints, it decapsulates the packet and examines the
   inner destination address.  If the inner destination address is an
   EPA, the IR[VE] re-encapsulates the packet, sets the outer source
   address of the packet to one of its own locator address, sets the
   outer destination address of the packet to the inner destination
   address then forwards the encapsulated packet into the Internet via a
   default or more-specific route.  If the inner destination address is
   not an EPA, however, the IR[VE] either forwards it unencapsulated
   into the Internet if it is able to do so without loss due to ingress
   filtering or tunnels the packet over the IRON to an IR[VC] within its
   VPC overlay network which will then decapsulate the packet and
   forward it into the Internet.

   When the IR[VE] receives an encapsulated packet from the Internet, if
   the inner destination address matches an EP in its FIB the IR[VE] 'A'
   re-encapsulates the packet using VET/SEAL and forwards it to its
   client IR[CE] 'B' which in turn decapsulates the packet and forwards
   it to the correct end system in the EUN.  If 'B' has left notice with
   'A' that it has moved to a new IR[VE] 'C', however, 'A' will instead
   forward the re-encapsulated packet to 'C' and also send an SCMP
   redirect message back to the source of the packet.  In this way,
   IR[CE]s can change between IR[VE]s (e.g., due to mobility events)
   without exposing packets to loss.




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6.3.  IR(VC) Operation

   After an IR[VC] has synchronized its VPs (see: Section 5.1) it
   advertises the full set of the company's VP's into the IPv4 and/or
   IPv6 Internet BGP routing systems.  The VPs will be represented as
   ordinary routing information in the BGP, and any packets originating
   from the IPv4 or IPv6 Internet destined to an EPA covered by one of
   the VPs will be forwarded into the VPC's overlay network by an
   IR[VC].

   When an IR[VC] receives a packet from the Internet destined to an EPA
   covered by one of its VPs, it looks in its FIB for a matching EP to
   discover the locator of the serving IR[VE], then examines the packet
   format.

   If the packet is not a SEAL-encapsulated packet, the IR[VC] simply
   encapsulates the packet with its own locator as the outer source
   address and the locator of the IR[VE] as the outer destination
   address and forwards the packet to the IR[VE].

   If the packet is a SEAL-encapsulated packet, however, the IR[VC]
   examines the "Router Alert" flag in the SEAL header.  If the Router
   Alert flag is set, and the packet encodes an SRS message, the IR[VC]
   sends an SRA message back to the source listing the locator addresses
   of nearby IR[VE] routers.  In all cases when the Route Alert flag is
   set, the IR[VC] next discards the packet.

   For all other SEAL-encapsulated packets, the IR[VC] sends an SCMP
   redirect message back to the source of the packet with the locator of
   the serving IR[VE] as the redirected target.  The source and
   destination addresses of the SCMP redirect message use the outer
   destination and source addresses of the original packet,
   respectively.  This arrangement is necessary to allow the redirect
   messages to flow through any NATs on the path.

   After sending a redirect message, the IR[VC] then rewrites the outer
   source address of the packet to one of its own locators, rewrites the
   outer destination address of the packet to the locator of the IR[VE]
   and forwards the (re)encapsulated packet to the IR[VE].  In this way,
   the IR[VC] "bends" the initial encapsulated packets of a flow in
   flight to deflect them toward a correct IR[VE], while subsequent
   packets in the flow will be sent directly to the IR[VE] after the
   source receives a redirect.

6.4.  IRON Reference Operating Scenarios

   The IRON is used to support communications when one or both hosts are
   located within EP-addressed EUNs regardless of whether the EPs are



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   provisioned by the same VPC or by different VPCs .  When both hosts
   are within IRON EUNs, route optimizations that eliminate unnecessary
   IR[VC]s from the path are possible.  When only one host is within an
   IRON EUN, however, route optimization cannot be used.

   The following sections discuss the two scenarios.  Note that it is
   sufficient to discuss the scenarios in a unidirectional fashion,
   i.e., by tracing packet flows only in the forward direction from the
   source host to destination host.  The reverse direction can be
   considered separately, and incurs the same considerations as for the
   forward direction.

6.4.1.  Both Hosts Within IRON EUNs

   When both hosts are within EP-addressed EUNs, the initial packets of
   the flow may need to involve an IR[VC] of the destination host but
   route optimization can eliminate the IR[VC] from the path for
   subsequent packets.  The two sub-scenarios that exist occur based on
   whether or not the IR[CE] of the source host configures a locator of
   the same version as the packet.  The sub-cases are discussed in the
   following sections.

6.4.1.1.  IR[CE] of Source Host Configures a Locator of the Same
          Protocol Version as the EPA

   Figure 6 shows the flow of initial packets from host A to host B
   within two EP-addressed EUNs when the IR[CE] of the source host A
   configures a locator of the same protocol version as the inner
   packet:






















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                 ________________________________________
              .-(                 .-.                    )-.
           .-(                 ,-(  _)-.                    )-.
        .-( +=================+       _ +========+             )-.
      .(   //              (_|| Internet|| _)   ||                ).
    .(    //                 ||-(______)||      vv                  ).
  .(     //                  ||         ||    +------------+          ).
  (     //                   vv         ||    |  IR[VE](B) |====+      )
  (    //                    +------------+   +------------+    \\     )
  (   //  .-.                |  IR[VC](B) |                  .-. \\    )
  (  //,-(  _)-.             +------------+               ,-(  _)-\\   )
  ( .||_    (_  )-.           /                        .-(_    (_  ||. )
  ( _||  ISP A    .)        /  (redirect)             (__   ISP B  ||_))
  (  ||-(______)-'        /                              `-(______)||  )
  (  ||    |            /                                     |    vv  )
   ( +-----+-----+  <=/                                 +-----+-----+ )
     | IR[CE](A) |                                      | IR[CE](B) |
     +-----+-----+              The IRON                +-----+-----+
           |    (   (Overlaid on the native Internet)     )   |
          .-.     .-(                                .-)     .-.
       ,-(  _)-.      .-(________________________)-.      ,-(  _)-.
    .-(_    (_  )-.                                    .-(_    (_  )-.
   (_  IRON EUN A  )                                  (_  IRON EUN B  )
      `-(______)-'                                       `-(______)-'
           |                                                  |
       +---+----+                                         +---+----+
       | Host A |                                         | Host B |
       +--------+                                         +--------+

         Figure 6: EPA/Locator Matching Scenario Before Redirects

   In this scenario, host A sends its packets with destination address B
   on its network interface connected to EUN A. (This interface could be
   a physical interface such as an Ethernet NIC, an ISATAP tunnel
   virtual interface with IR[CE](A) as a PRL router, etc.)  Routing with
   EUN A will direct the packets to IR[CE](A) as a default router for
   the EUN which then uses VET and SEAL to encapsulate them in outer
   headers with its locator address as the outer source address and B as
   the outer destination address (i.e., the inner and outer destination
   address will be the same).  IR[CE](A) then simply releases the
   encapsulated packets into its ISP network connection that provided
   its locator.  The ISP will release the packet into the Internet
   without filtering since the (outer) source address is topologically
   correct.  Once the packets have been released into the Internet,
   routing will direct them to the nearest IR[VC] that advertises
   reachability to a VP that covers destination address B (namely,
   IR[VC](B)).




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   IR[VC](B) will receive the encapsulated packets from IR[CE](A) then
   check its FIB to discover an entry that covers destination address B
   with IR[VE](B) as the next hop.  IR[VC](B) will then issue SCMP
   redirect messages to inform IR[CE](A) that IR[VE](B) is a better next
   hop (*).  IR[VC](B) then rewrites the outer source address of the
   encapsulated packets to its own locator address and rewrites the
   destination address of the encapsulated packets to the locator
   address of IR[VE](B).  IR[VC](B) then releases these (re)encapsulated
   packets into the native Internet, where routing will direct them to
   IR[VE](B).

   IR[VE](B) will receive the encapsulated packets from IR[VC](B) then
   check its FIB to discover an entry that covers destination address B
   with IR[CE](B) as the next hop.  IR[VE](B) then rewrites the outer
   source address of the packets to its own locator address and rewrites
   the outer destination address to the locator address of IR[CE](B).
   (If IR[CE](B) is located behind a NAT, IR[VE](B) also rewrites the
   UDP destination port number in the encapsulating header in order to
   support NAT traversal.)  IR[VE](B) then tunnels these
   (re)encapsulated packets to IR[CE](B), which will in turn decapsulate
   the packets and forward the inner packets to host B via EUN B.

   (*) Note that after the initial flow of packets, IR[CE](A) will have
   received one or more SCMP redirect messages from IR[VC](B) informing
   it of IR[VE](B) as a better next hop.  Thereafter, IR[CE](A) will
   forward its encapsulated packets directly to the locator address of
   IR[VE](B) without involving IR[VC](B) as shown in Figure 7:
























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                 ________________________________________
              .-(                 .-.                    )-.
           .-(                 ,-(  _)-.                    )-.
        .-( +=============> .-(_    (_  )-.======+             )-.
      .(   //              (__ Internet   _)    ||                ).
    .(    //                  `-(______)-'      vv                  ).
  .(     //                                   +------------+          ).
  (     //                                    |  IR[VE](B) |====+      )
  (    //                                     +------------+    \\     )
  (   //  .-.                                                .-. \\    )
  (  //,-(  _)-.                                          ,-(  _)-\\   )
  ( .||_    (_  )-.                                    .-(_    (_  ||. )
  ( _||  ISP A    .)                                  (__   ISP B  ||_))
  (  ||-(______)-'                                       `-(______)||  )
  (  ||    |                                                  |    vv  )
   ( +-----+-----+              The IRON                +-----+-----+ )
     | IR[CE](A) |  (Overlaid on the native Internet)   | IR[CE](B) |
     +-----+-----+                                      +-----+-----+
           |    (                                         )   |
          .-.     .-(                                .-)     .-.
       ,-(  _)-.      .-(________________________)-.      ,-(  _)-.
    .-(_    (_  )-.                                    .-(_    (_  )-.
   (_  IRON EUN A  )                                  (_  IRON EUN B  )
      `-(______)-'                                       `-(______)-'
           |                                                  |
       +---+----+                                         +---+----+
       | Host A |                                         | Host B |
       +--------+                                         +--------+

          Figure 7: EPA/Locator Matching Scenario After Redirects

6.4.1.2.  IR[CE] of Source Host Configures a Locator of a Different
          Protocol Version than the EPA

   Figure 8 shows the flow of initial packets from host A to host B
   within two EP-addressed EUNs when the IR[CE] of source host A cannot
   configure a locator of the same protocol version as the inner network
   layer protocol.  For example, if the IR[CE] configures only an IPv4
   locator, but EUN A uses IPv6 natively, IR[CE] is obliged to forward
   its packets through its serving IR[VE].











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                 ________________________________________
              .-(                 .-.                    )-.
           .-(                 ,-(  _)-.                    )-.
        .-(          +========+(_    (_  +=====+               )-.
      .(             ||    (_|| Internet ||_) ||                  ).
    .(               ||      ||-(______)-||   vv                    ).
  .(        +--------++--+   ||          ||   +------------+          ).
  (     +==>|  IR[VE](A) |   vv          ||   |  IR[VE](B) |====+      )
  (    //   +------------+   +--++----++--+   +------------+    \\     )
  (   //  .-.                |  IR[VC](B) |                  .-. \\    )
  (  //,-(  _)-.             +------------+               ,-(  _)-\\   )
  ( .||_    (_  )-.           /                        .-(_    (_  ||. )
  ( _||  ISP A    .)        /  (redirect)             (__   ISP B  ||_))
  (  ||-(______)-'        /                              `-(______)||  )
  (  ||    |            /                                     |    vv  )
   ( +-----+-----+  <=/                                 +-----+-----+ )
     | IR[CE](A) |                                      | IR[CE](B) |
     +-----+-----+              The IRON                +-----+-----+
           |    (   (Overlaid on the native Internet)     )   |
          .-.     .-(                                .-)     .-.
       ,-(  _)-.      .-(________________________)-.      ,-(  _)-.
    .-(_    (_  )-.                                    .-(_    (_  )-.
   (_  IRON EUN A  )                                  (_  IRON EUN B  )
      `-(______)-'                                       `-(______)-'
           |                                                  |
       +---+----+                                         +---+----+
       | Host A |                                         | Host B |
       +--------+                                         +--------+

       Figure 8: EPA/Locator Mis-matching Scenario Before Redirects

   In this scenario, host A sends its packets with destination address B
   on its network interface connected to EUN A. (This interface could be
   a physical interface such as an Ethernet NIC, an ISATAP tunnel
   virtual interface with IR[CE](A) as a PRL router, etc.)  Routing with
   EUN A will direct the packets to IR[CE](A) as a default router for
   the EUN which then uses VET and SEAL to encapsulate them in outer
   headers with its locator address as the outer source address and the
   locator address of its serving IR[VE](A) as the outer destination
   address.  IR[CE](A) then simply releases the encapsulated packets
   into its ISP network connection that provided its locator.  The ISP
   will release the packets into the Internet without filtering since
   the (outer) source address is topologically correct.  Once the
   packets have been released into the Internet, routing will direct
   them to IR[VE](A).

   IR[VE](A) receives the encapsulated packets from IR[CE](A) then
   rewrites the outer source address to its own locator address and



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   rewrites the outer destination address to B (i.e., the inner and
   outer destination address will be the same).  IR[VE](A) then releases
   the (re)encapsulated packets into the Internet where routing will
   direct them to IR[VC](B) which advertises the VP that covers B.

   IR[VC](B) will receive the encapsulated packets from IR[VE](A) then
   check its FIB to discover an entry that covers destination address B
   with IR[VE](B) as the next hop.  IR[VC](B) will then issue SCMP
   redirect messages to inform IR[VE](A) that IR[VE](B) is a better next
   hop (*).  IR[VC](B) then rewrites the outer source address of the
   encapsulated packets to its own locator address and rewrites the
   outer destination address to the locator address of IR[VE](B).
   IR[VC](B) then releases these (re)encapsulated packets into the
   Internet, where routing will direct them to IR[VE](B).

   IR[VE](B) will receive the encapsulated packets from IR[VC](B) then
   check its FIB to discover an entry that covers destination address B
   with IR[CE](B) as the next hop.  IR[VE](B) then rewrites the outer
   source address of the packets to its own locator address and rewrites
   the outer destination address to the locator address of IR[CE](B).
   (If IR[CE](B) is located behind a NAT, then IR[VE](B) also rewrites
   the UDP destination port number in the encapsulating header in order
   to support NAT traversal.)  IR[VE](B) then releases these
   (re)encapsulated packets into the Internet, where routing will direct
   them to IR[CE](B).  IR[CE](B) will in turn decapsulate the packets
   and forward the inner packets to host B via EUN B.

   (*) Note that after the initial flow of packets, IR[VE](A) will have
   received one or more SCMP redirect messages from IR[VC](B) informing
   it of IR[VE](B) as a better next hop.  Thereafter, IR[VE](A) will
   forward its encapsulated packets directly to the locator address of
   IR[VE](B) without involving IR[VC](B) as shown in Figure 9:



















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                 ________________________________________
              .-(                 .-.                    )-.
           .-(                 ,-(  _)-.                    )-.
        .-(          +====> .-(_    (_  )-.======+             )-.
      .(             ||    (__ Internet   _)    ||                ).
    .(               ||       `-(______)-'      vv                  ).
  .(        +--------++--+                    +------------+          ).
  (     +==>|  IR[VE](A) |                    |  IR[VE](B) |====+      )
  (    //   +------------+                    +------------+    \\     )
  (   //  .-.                                                .-. \\    )
  (  //,-(  _)-.                                          ,-(  _)-\\   )
  ( .||_    (_  )-.                                    .-(_    (_  ||. )
  ( _||  ISP A    .)                                  (__   ISP B  ||_))
  (  ||-(______)-'                                       `-(______)||  )
  (  ||    |                                                  |    vv  )
   ( +-----+-----+              The IRON                +-----+-----+ )
     | IR[CE](A) |  (Overlaid on the native Internet)   | IR[CE](B) |
     +-----+-----+                                      +-----+-----+
           |    (                                         )   |
          .-.     .-(                                .-)     .-.
       ,-(  _)-.      .-(________________________)-.      ,-(  _)-.
    .-(_    (_  )-.                                    .-(_    (_  )-.
   (_  IRON EUN A  )                                  (_  IRON EUN B  )
      `-(______)-'                                       `-(______)-'
           |                                                  |
       +---+----+                                         +---+----+
       | Host A |                                         | Host B |
       +--------+                                         +--------+

        Figure 9: EPA/Locator Mis-matching Scenario After Redirects

6.4.2.  Mixed IRON and Non-IRON Hosts

   When one host is within an IRON EUN and the other is in a non-IRON
   EUN (i.e., one that connects to the native Internet instead of the
   IRON), the IR elements involved depend on the packet flow directions.
   The cases are described in the following sections:

6.4.2.1.  From IRON Host A to Non-IRON Host B

   Figure 10 depicts the IRON reference operating scenario for packets
   flowing from Host A in an IRON EUN to Host B in a non-IRON EUN:









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                  _________________________________________
               .-(         )-.                             )-.
            .-(      +-------)----+                           )-.
         .-(         |  IR[VC](A) |--------------+               )-.
       .(            +------------+               \                ).
     .(     +=======>|  IR[VE](A) |                \                ).
   .(     //         +--------)---+                 \                 ).
   (     //                   )                      \                 )
   (    //      The IRON      )                       \                )
   (   //  .-.                )                        \     .-.       )
   (  //,-(  _)-.             )                         \ ,-(  _)-.    )
   ( .||_    (_  )-.          ) The Native Internet    .-|_    (_  )-. )
   ( _||  ISP A     )         )                       (_ |  ISP B     ))
   (  ||-(______)-'           )                          |-(______)-'  )
   (  ||    |             )-.                            v    |        )
    ( +-----+ ----+    )-.                               +-----+-----+ )
      | IR[CE](A) |)-.                                   |  Router B |
      +-----+-----+                                      +-----+-----+
            |  (                                            )  |
           .-.   .-(____________________________________)-.   .-.
        ,-(  _)-.                                          ,-(  _)-.
     .-(_    (_  )-.                                    .-(_    (_  )-.
    (_  IRON EUN A  )                                  (_ non-IRON EUN )
       `-(______)-'                                       `-(___B___)-'
            |                                                  |
        +---+----+                                         +---+----+
        | Host A |                                         | Host B |
        +--------+                                         +--------+

              Figure 10: From IRON Host A to Non-IRON Host B

   In this scenario, host A sends its packets with destination address B
   on its network interface connected to IRON EUN A. (This interface
   could be a physical interface such as an Ethernet NIC, an ISATAP
   tunnel virtual interface with IR[CE](A) as a PRL router, etc.)
   Routing with EUN A will direct the packets to IR[CE](A) as a default
   router for the EUN which then uses VET and SEAL to encapsulate them
   in outer headers with its locator address as the outer source address
   and the locator address of a serving IR[VE] (i.e., IR[VE](A) as the
   outer destination address.  The ISP will pass the packets without
   filtering since the (outer) source address is topologically correct.
   Once the packets have been released into the native Internet, routing
   will direct them to IR[VE](A).

   IR[VE](A) receives the encapsulated packets from IR[CE](A) then
   forwards them to IR[VC](A) which simply decapsulates them and
   releases the unencapsulated packets into the Internet.  Once the
   packets are released into the Internet, routing will direct them to



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   the final destination B. (Note that in this diagram IR[VE](A) and
   IR[VC](A) are depicted as two halves of a unified IR[VP](A).  In that
   case, the "forwarding" between IR[VE](A) and IR[VC](A) is a zero-
   instruction imaginary operation.)

   Note that this scenario always involves an IR[VC](A) owned by the VPC
   that provides service to IRON EUN A. This scenario therefore imparts
   a cost that would need to be borne by either the VPC or its
   customers.

6.4.2.2.  From Non-IRON Host B to IRON Host A

   Figure 10 depicts the IRON reference operating scenario for packets
   flowing from Host B in an Non-IRON EUN to Host A in an IRON EUN:

                  _______________________________________
               .-(         )-.                             )-.
            .-(      +-------)----+                           )-.
         .-(         |  IR[VC](A) |<-------------+              )-.
       .(            +------------+               \                ).
     .(     +========|  IR[VE](A) |                \                ).
   .(     //         +--------)---+                 \                 ).
   (     //                   )                      \                 )
   (    //      The IRON      )                       \                )
   (   //  .-.                )                        \     .-.       )
   (  //,-(  _)-.             )                         \ ,-(  _)-.    )
   ( .||_    (_  )-.          ) The Native Internet    .-|_    (_  )-. )
   ( _||  ISP A     )         )                       (_ |  ISP B     ))
   (  ||-(______)-'           )                          |-(______)-'  )
   (  vv    |             )-.                            |    |        )
    ( +-----+ ----+    )-.                               +-----+-----+ )
      | IR[CE](A) |)-.                                   |  Router B |
      +-----+-----+                                      +-----+-----+
            |  (                                            )  |
           .-.   .-(____________________________________)-.   .-.
        ,-(  _)-.                                          ,-(  _)-.
     .-(_    (_  )-.                                    .-(_    (_  )-.
    (_  IRON EUN A  )                                  (_ non-IRON EUN )
       `-(______)-'                                       `-(___B___)-'
            |                                                  |
        +---+----+                                         +---+----+
        | Host A |                                         | Host B |
        +--------+                                         +--------+

              Figure 11: From Non-IRON Host B to IRON Host A

   In this scenario, host B sends its unencapsulated packets with
   destination address A on its network interface connected to non-IRON



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   EUN B. Routing will direct the packets to IR[VC](A) which then
   forwards them to IR[VE](A) using encapsulation if necessary.  (Note
   that in this diagram IR[VE](A) and IR[VC](A) are depicted as two
   halves of a unified IR[VP](A).  In that case, the "forwarding"
   between IR[VE](A) and IR[VC](A) is a zero-instruction imaginary
   operation.)

   IR[VE](A) will then check its FIB to discover an entry that covers
   destination address A with IR[CE](A) as the next hop.  IR[VE](A) then
   encapsulates the packets using its own locator address as the outer
   source address and the locator address of IR[CE](A) as the outer
   destination address.  IR[VE](A) then releases these (re)encapsulated
   packets into the Internet, where routing will direct them to
   IR[CE](A).  IR[CE](A) will in turn decapsulate the packets and
   forward the inner packets to host A via its network interface
   connected to IRON EUN A. (This interface could be a physical
   interface such as an Ethernet NIC, an ISATAP tunnel virtual interface
   with Host A as the next-hop neighbor, etc.).

   Note that this scenario always involves an IR[VC](A) owned by the VPC
   that provides service to IRON EUN A. This scenario therefore imparts
   a cost that would need to be borne by either the VPC or its
   customers.

6.5.  Mobility, Multihoming and Traffic Engineering Considerations

   While IR[VE]s and IR[VC]s can be considered as fixed infrastructure,
   IR[CE]s may need to move between different network points of
   attachment, connect to multiple ISPs, or explicitly manage their
   traffic flows.  The following sections discuss mobility, multi-homing
   and traffic engineering considerations for IR[CE]s.

6.5.1.  Mobility Management

   When an IR[CE] changes its network point of attachment (e.g., due to
   a mobility event), it configures one or more new locators.  If the
   IR[CE] has not moved far away from its previous network point of
   attachment, it simply informs its serving IR[VE] of any locator
   additions or deletions.  This operation is performance-sensitive, and
   should be conducted immediately to avoid packet loss.

   If the IR[CE] has moved far away from its previous network point of
   attachment, however, it re-issues the implicit anycast discovery
   procedure described in Section 6.1 to discover whether its candidate
   set of serving IR[VE]s has changed.  If the IR[CE]'s current serving
   IR[VE] is also included in the new list received from the VPC, this
   serves as indication that the IR[CE] has not moved far enough to
   warrant changing to a new serving IR[VE].  Otherwise, the IR[CE] may



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   wish to move to a new serving IR[VE] in order to maintain optimal
   routing.  This operation is not performance-critical, and therefore
   can be conducted over a matter of seconds/minutes instead of
   milliseconds/microseconds.

   To move to a new IR[VE], the IR[CE] first engages in the EP
   registration process with the new IR[VE] and maintains the
   registrations through periodic SRS/SRA exchanges the same as
   described in Section 6.1.  The IR[CE] then informs its former IR[VE]
   that it has moved by providing it with the locator address of the new
   IR[VE].  The IR[CE] then discontinues the SRS/SRA keepalive process
   with the former IR[VE], which will garbage-collect the stale FIB
   entries when their lifetime expires.  This will allow the former
   IR[VE] to redirect existing correspondents to the new IR[VE] so that
   no packets are lost.

6.5.2.  Multihoming

   An IR[CE] may register multiple locators with its serving IR[VE].  It
   can assign metrics with its registrations to inform its IR[VE] of
   preferred locators, and can select outgoing locators according to its
   local preferences.  Multihoming is therefore naturally supported.

6.5.3.  Inbound Traffic Engineering

   An IR[CE] can dynamically adjust the priorities of its prefix
   registrations with its serving IR[VE] in order to influence inbound
   traffic flows.  It can also change between serving IR[VE]s when
   multiple IR[VE]s are available, but should strive for stability in
   its IR[VE] selection in order to limit routing churn.

6.5.4.  Outbound Traffic Engineering

   An IR[CE] can select outgoing locators, e.g., based on current QoS
   considerations.

6.6.  Renumbering Considerations

   As better link layer technologies and service plans emerge, customers
   will be motivated to select their service providers through healthy
   competition between ISPs.  If a customer's EUN addresses are tied to
   a specific ISP, however, the customer may be forced to undergo a
   painstaking EUN renumbering process if it wishes to changes to a
   different ISP [RFC4192][RFC5887].

   When a customer obtains EP prefixes from a VPC, it can change between
   ISPs seamlessly and without need to renumber.  If the VPC itself
   applies unreasonable costing structures for use of the EPs, however,



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   the customer may be compelled to seek a different VPC and would again
   be required to confront a renumbering scenario.  The IRON approach to
   renumbering avoidance therefore depends on VPCs conducting ethical
   business practices with reasonable rates.

6.7.  NAT Traversal Considerations

   The Internet today consists of a global public IPv4 routing and
   addressing system with non-IRON EUNs that use either public or
   private IPv4 addressing.  The latter class of EUNs connect to the
   public IPv4 Internet via Network Address Translators (NATs).  When an
   IR[CE] is located behind a NAT, its selects IR[VE]s using the same
   procedures as for IR[CE]s with public addresses, i.e., it will send
   SRS messages to IR[VE]s in order to get SRA messages in return.  The
   only requirement is that the IR[CE] must configure its SEAL
   encapsulation to use a transport protocol that supports NAT
   traversal, namely UDP.

   Since the IR[VE] maintains state about its IR[CE] customers, it can
   discover locator information for each IR[CE] by examining the UDP
   port number and IPv4 address in the outer headers of SRS messages.
   When there is a NAT in the path, the UDP port number and IPv4 address
   in the SRS message will correspond to state in the NAT box and might
   not correspond to the actual values assigned to the IR[CE].  The
   IR[VE] can then encapsulate packets destined to hosts serviced by the
   IR[CE] within outer headers that use this IPv4 address and UDP port
   number.  The NAT box will receive the packets, translate the values
   in the outer headers to match those assigned to the IR[CE], then
   forward the packets to the IR[CE].

6.8.  Nested EUN Considerations

   Each IR[CE] configures a locator that may be taken from an ordinary
   non-EPA address assigned by an ISP or from an EPA address taken from
   an EP assigned to another IR[CE].  In that case, the IR[CE] is said
   to be "nested" within the EUN of another IR[CE].

   For example, assume a configuration in which IR[CE](A) configures a
   locator EPA(B) taken from the EP assigned to EUN(B).  IR[CE](B) in
   turn configures a locator EPA(C) taken from the EP assigned to
   EUN(C).  Finally, IR[CE](C) assigns a locator ISP(D) taken from a
   non-EPA address delegated by an ordinary ISP(D).  Using this example,
   the "nested-IRON" case must be examined in which a host A which
   configures the address EPA(A) within EUN(A) exchanges packets with
   host Z located elsewhere in the Internet.  The example configuration
   is depicted in Figure 12:





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                            .-.
                 EPA(D)  ,-(  _)-.
      +-----------+   .-(_    (_  )-.
      | IR[CE](C) |--(_    ISP(D)    )
      +-----+-----+     `-(______)-'
            |   <= T         \     .-.
           .-.       u        \ ,-(  _)-.
        ,-(  _)-.       n     .-(_    (-  )-.
     .-(_    (_  )-.      n  (_   Internet   )
    (_    EUN(C)    )       e   `-(______)-       +--------+
       `-(______)-'           l          ___      | Host Z |
            | EPA(C)           s =>    (:::)-.   +--------+
      +-----+-----+                 .-(::::::::)
      | IR[CE](B) |              .-(::::::::::::)-.
      +-----+-----+             (:::: The IRON ::::)
            |                    `-(::::::::::::)-'
           .-.                      `-(::::::)-'
        ,-(  _)-.
     .-(_    (_  )-.              +-----------------+
    (_    EUN(B)    )             | IR[VP/VC/VE]'s] |
       `-(______)-'               +-----------------+
            | EPA(B)
      +-----+-----+
      | IR[CE](A) |
      +-----------+
            |
           .-.
        ,-(  _)-.  EPA(A)
     .-(_    (_  )-.    +--------+
    (_    EUN(A)    )---| Host A |
       `-(______)-'     +--------+

                       Figure 12: Nested EUN Example

   The two cases of host A sending packets to host Z, and host Z sending
   packets to host A, must be considered separately as described below:

6.8.1.  Host A Sends Packets to Host Z

   There are two distinct cases of Host A sending packets to Host Z
   which are dependent upon whether Z is an EPA or non-EPA address.  The
   two cases are discussed below:

6.8.1.1.  Nested IRON Example When Z Configures an EPA Address

   Host A first forwards a packet with source address EPA(A) and
   destination address EPA(Z) into EUN(A).  Routing within EUN(A) will
   direct the packet to IR[CE](A), which encapsulates it in an outer



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   header with EPA(B) as the outer source address and EPA(Z) as the
   outer destination address then forwards the encapsulated packet into
   EUN(B).  Routing within EUN[B] will direct the packet to IR[CE](B),
   which encapsulates it in an outer header with EPA(C) as the outer
   source address and EPA(Z) as the outer destination address then
   forwards the encapsulated packet into EUN(C).  Routing within EUN(C)
   will direct the packet to IR[CE](C), which encapsulates it in an
   outer header with ISP(D) as the outer source address and EPA(Z) as
   the outer destination address.  IR[CE](C) then sends this "triple-
   encapsulated" packet into the ISP(D) network, where it will be routed
   into the Internet to an IR[VC](Z) that advertises a VP that covers
   destination address EPA(Z).

   When IR[VC](Z) receives the "triple-encapsulated" packet, it consults
   its FIB to determine that IR[VE](Z) is the serving router for EP(Z).
   It then (re)encapsulates the packet by changing the outer source
   address to its own locator address and the outer destination address
   to the locator address for IR[VE](Z).  It also sends a redirect
   message back to IR[CE](C) as normal.  When IR[VE](Z) receives the
   "triple-encapsulated" packet, it strips off all outer layers of
   encapsulation and (re)encapsulates the inner packet using its own
   locator address as the source address and the locator address of
   IR[CE](Z) as the destination address.  IR[VE](Z) then tunnels the
   packet to IR[CE](Z), which decapsulates the packet and forwards it to
   host Z.

   The key architectural requirement derived from this case is that each
   IR[VE] must iteratively decapsulate each layer of a multi-
   encapsulated packet when the outer destination address matches an EPA
   assigned to one of its IR[CE] customers.  When the final such layer
   of encapsulation is reached, the IR[VE] must (re)encapsulate the
   packet and forward it to the correct customer IR[CE].  This class of
   packets can be considered as "inbound" wrt the IR[VE]'s client
   customer EUNs.

6.8.1.2.  Nested IRON Example when Z Configures a non-EPA Address

   Host A first forwards a packet with source address EPA(A) and
   destination address Z into EUN(A).  Routing within EUN(A) will direct
   the packet to IR[CE](A), which encapsulates it in an outer header
   with EPA(B) as the outer source address and IR[VE](A) as the outer
   destination address then forwards the encapsulated packet into
   EUN(B).  (Note that IR[CE](A) must forward this packet via its
   serving IR[VE](A) for reasons explained in Section 6.4.2).  Routing
   within EUN[B] will direct the packet to IR[CE](B), which encapsulates
   it in an outer header with EPA(C) as the outer source address and
   IR[VE](B) as the outer destination address then forwards the
   encapsulated packet into EUN(C).  Routing within EUN(C) will direct



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   the packet to IR[CE](C), which encapsulates it in an outer header
   with ISP(D) as the outer source address and IR[VE](C) as the outer
   destination address.  IR[CE](C) then sends this "triple-encapsulated"
   packet into its ISP network, where it will be routed to IR[VE](C).

   To ease in discussion of this case, now consider that each IR[VE]
   named above is half of a unified IR[VP] that combines both the IR[VC]
   and IR[VE] functions.  With this simplification in mind, when
   IR[VP](C) receives the "triple-encapsulated" packet, it removes the
   outermost layer of encapsulation and forwards the packet into the
   Internet where Internet routing will direct it to IR[VP](B).
   IR[VP](B) in turn removes the next layer of encapsulation and
   forwards the packet into the Internet where Internet routing will
   direct it to IR[VP](A).  IR[VP](A) will finally remove the final
   layer of encapsulation and forward the packet into the Internet where
   Internet routing will direct it to host Z.

   The key architectural requirement derived from this case is that each
   IR[VP] must iteratively decapsulate each layer of a multi-
   encapsulated packet when the outer destination address is one of its
   own locator addresses.  When the final such layer of encapsulation is
   reached, the IR[VP] forwards the packet into the Internet.  This
   class of packets can be considered as "outbound" wrt the IR[VP]'s
   client customer EUNs.

6.8.2.  Host Z Sends Packets to Host A

   Whether or not host Z configures an EPA address, its packets destined
   to Host A will eventually reach IR[VE](A).  IR[VE](A) will have a
   mapping that lists IR[CE](A) as the next hop toward EPA(A).
   IR[VE](A) will then encapsulate the packet with EPA(B) as the outer
   destination address and forward the packet into the Internet.
   Internet routing will convey this once-encapsulated packet to
   IR[VE](B) which will have a mapping that lists IR[CE](B) as the next
   hop toward EPA(B).  IR[VE](B) will then encapsulate the packet with
   EPA(C) as the outer destination address and forward the packet into
   the Internet.  Internet routing will then convey this twice-
   encapsulated packet to IR[VE](C) which will have a mapping that lists
   IR[CE](C) as the next hop toward EPA(C).  IR[VE](C) will then
   encapsulate the packet with ISP(D) as the outer destination address
   and forward the packet into the Internet.  Internet routing will then
   convey this triple-encapsulated packet to IR[CE](C).

   When the triple-encapsulated packet arrives at IR[CE](C), it strips
   the outer layer of encapsulation and forwards the twice-encapsulated
   packet to EPA(C) which is the locator address of IR[CE](B).  When
   IR[CE](B) receives the twice-encapsulated packet, it strips the outer
   layer of encapsulation and forwards the once-encapsulated packet to



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   EPA(B) which is the locator address of IR[CE](A).  When IR[CE](A)
   receives the once-encapsulated packet, it strips the outer layer of
   encapsulation and forwards the unencapsulated packet to EPA(A) which
   is the host address of host A.

   The key architectural requirement derived from this case is that each
   IR[CE] must decapsulate only the outermost layer of a multi-
   encapsulated packet when the outer destination address matches an EPA
   assigned to a device in its EUN.  This class of packets can be
   considered as "inbound" wrt the IR[CE]'s EUNs.  The outbound cases
   are discussed in Section 6.8.1


7.  Additional Considerations

   Considerations for the scalability of Internet Routing due to
   multihoming, traffic engineering and provider-independent addressing
   are discussed in [I-D.narten-radir-problem-statement].  Route
   optimization considerations for mobile networks are found in
   [RFC5522].


8.  Related Initiatives

   IRON builds upon the concepts RANGER architecture [RFC5720], and
   therefore inherits the same set of related initiatives.

   Virtual Aggregation (VA) [I-D.ietf-grow-va] and Aggregation in
   Increasing Scopes (AIS) [I-D.zhang-evolution] provide the basis for
   the Virtual Prefix concepts.

   Internet vastly improved plumbing (Ivip) [I-D.whittle-ivip-arch] has
   contributed valuable insights, including the use of real-time
   mapping.  The use of IR[VE]s as mobility anchor points is directly
   influenced by Ivip's associated TTR mobility extensions [TTRMOB].

   Numerous publications have proposed NAT traversal techniques.  The
   NAT traversal techniques adapted for IRON were inspired by the Simple
   Address Mapping for Premises Legacy Equipment (SAMPLE) proposal
   [I-D.carpenter-softwire-sample].


9.  IANA Considerations

   There are no IANA considerations for this document.






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10.  Security Considerations

   Security considerations that apply to tunneling in general are
   discussed in [I-D.ietf-v6ops-tunnel-security-concerns].  Additional
   considerations that apply also to IRON are discussed in RANGER
   [RFC5720], VET [I-D.templin-intarea-vet] and SEAL
   [I-D.templin-intarea-seal].

   IR[CE]s require a means for securely registering their EP-to-locator
   bindings with their VPC.  Each VPC provides its customer IR[CE]s with
   a secure means for registering and re-registering their mappings.


11.  Acknowledgements

   This ideas behind this work have benefited greatly from discussions
   with colleagues; some of which appear on the RRG and other IRTF/IETF
   mailing lists.  Mohamed Boucadair, Wesley Eddy, Dae Young Kim and
   Robin Whittle provided review input.  Eric Fleischman pointed out the
   opportunity to leverage anycast for discovering topologically-close
   serving IR[VE]s.


12.  References

12.1.  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.

12.2.  Informative References

   [BGPMON]   net, B., "BGPmon.net - Monitoring Your Prefixes,
              http://bgpmon.net/stat.php", June 2010.

   [I-D.carpenter-softwire-sample]
              Carpenter, B. and S. Jiang, "Legacy NAT Traversal for
              IPv6: Simple Address Mapping for Premises Legacy Equipment
              (SAMPLE)", draft-carpenter-softwire-sample-00 (work in
              progress), June 2010.

   [I-D.ietf-grow-va]
              Francis, P., Xu, X., Ballani, H., Jen, D., Raszuk, R., and
              L. Zhang, "FIB Suppression with Virtual Aggregation",
              draft-ietf-grow-va-02 (work in progress), March 2010.



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   [I-D.ietf-v6ops-tunnel-security-concerns]
              Hoagland, J., Krishnan, S., and D. Thaler, "Security
              Concerns With IP Tunneling",
              draft-ietf-v6ops-tunnel-security-concerns-02 (work in
              progress), March 2010.

   [I-D.narten-radir-problem-statement]
              Narten, T., "On the Scalability of Internet Routing",
              draft-narten-radir-problem-statement-05 (work in
              progress), February 2010.

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

   [I-D.templin-intarea-seal]
              Templin, F., "The Subnetwork Encapsulation and Adaptation
              Layer (SEAL)", draft-templin-intarea-seal-16 (work in
              progress), July 2010.

   [I-D.templin-intarea-vet]
              Templin, F., "Virtual Enterprise Traversal (VET)",
              draft-templin-intarea-vet-16 (work in progress),
              July 2010.

   [I-D.whittle-ivip-arch]
              Whittle, R., "Ivip (Internet Vastly Improved Plumbing)
              Architecture", draft-whittle-ivip-arch-04 (work in
              progress), March 2010.

   [I-D.zhang-evolution]
              Zhang, B. and L. Zhang, "Evolution Towards Global Routing
              Scalability", draft-zhang-evolution-02 (work in progress),
              October 2009.

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

   [RFC3849]  Huston, G., Lord, A., and P. Smith, "IPv6 Address Prefix
              Reserved for Documentation", RFC 3849, July 2004.

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

   [RFC4271]  Rekhter, Y., Li, T., and S. Hares, "A Border Gateway



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              Protocol 4 (BGP-4)", RFC 4271, January 2006.

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

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

   [RFC5522]  Eddy, W., Ivancic, W., and T. Davis, "Network Mobility
              Route Optimization Requirements for Operational Use in
              Aeronautics and Space Exploration Mobile Networks",
              RFC 5522, October 2009.

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

   [RFC5737]  Arkko, J., Cotton, M., and L. Vegoda, "IPv4 Address Blocks
              Reserved for Documentation", RFC 5737, January 2010.

   [RFC5743]  Falk, A., "Definition of an Internet Research Task Force
              (IRTF) Document Stream", RFC 5743, December 2009.

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

   [TTRMOB]   Whittle, R. and S. Russert, "TTR Mobility Extensions for
              Core-Edge Separation Solutions to the Internet's Routing
              Scaling Problem,
              http://www.firstpr.com.au/ip/ivip/TTR-Mobility.pdf",
              August 2008.


Appendix A.  IRON VPs Over Non-Native Internetworks

   The IRON architecture leverages the native Internet routing system by
   providing generally shortest-path routing when EPAs are taken from
   VPs that are routable.  When the VPs are not routable within the
   native underlying Internetwork, however (e.g., when OSI/NSAP
   [RFC4548] VPs are used within a private IPv4 Internetwork) packets
   with EPA addresses covered by the VPs must be carried solely via
   tunnels within the IRON.  In such an environment, the IR[VC] role is
   deprecated since there is no native underlying Internetwork to
   support VP routing.  This restricted model therefore entails only
   IR[CE]s and IR[VE]s.




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   When IRON VPs are carried over a non-native Internetwork, a global
   mapping database is required to allow IR[VE]s to map VPs to locators
   which are assigned to the interfaces of other IR[VE]s.  Each such
   non-routable VP in the IRON must therefore be represented in a
   globally distributed Master VP database (MVPd).  The MVPd is
   maintained by a globally-managed assigned numbers authority in the
   same manner as the Internet Assigned Numbers Authority (IANA)
   currently maintains the master list of all top-level IPv4 and IPv6
   delegations.  The database can be replicated across multiple servers
   for load balancing much in the same way that FTP mirror sites are
   used to manage software distributions.

   Each VP in the MVPd is encoded as the tuple: "{address family,
   prefix, prefix-length, FQDN}", where:

   o  "address family" is one of IPv4, IPv6, OSI/CLNP, etc.

   o  "prefix" is the VP, e.g. - 2001:DB8::/32 (IPv6) [RFC3849],
      192.2/16 (IPv4) [RFC5737], etc.

   o  "prefix-length" is the length (in bits) of the associated VP

   o  FQDN is a DNS Fully-Qualified Domain Name

   For each VP entry in the MVPd, the VPC maintains a FQDN in the DNS to
   map the VP to a list of IR[VE]s that serve it.  Other IR[VE]s
   discover the mappings by resolving the FQDN into a list of resource
   records.  Each resource record corresponds to an individual IR[VE],
   and encodes the tuple : "{address family, locator, WGS 84
   coordinates}" where "address family" is the address family of the
   locator, "locator" is the routing locator assigned to an IR[VE]
   interface, and "WGS 84 coordinates" identify the physical location of
   the IR[VE].

   Upon startup, each IR[VE] managed by the VPC discovers the full set
   of VPs for the IRON by reading the MVPd.  Each IR[VE] reads the MVPd
   from a nearby server upon startup time, and periodically checks the
   server for deltas since the database was last read.  Upon reading the
   MVPd, each IR[VE] resolves the FQDN corresponding to each VP into a
   list of locators.  Each locator is an address that is routable within
   the underlying Internetwork and assigned to an interface of an IR[VE]
   that serves the VP.

   For each VP, each IR[VE] sorts the list of locators to determine a
   priority ranking (e.g., based on distance from the locator) and
   inserts each "VP->locator" mapping into its FIB in order of priority.
   The FIB entries must be configured such that packets with destination
   addresses covered by the VP are forwarded to the corresponding



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   locator using encapsulation of the inner network layer packet in an
   outer header of a network layer protocol that is routable within the
   Internetwork.  This is accomplished by configuring the routing table
   entry to use the locator addresses as the L2 address corresponding to
   an imaginary L3 next-hop address.

   Note that the VP and locator may be of different address families;
   hence, possible encapsulations include IPv6-in-IPv4, IPv4-in-IPv6,
   IPv6-in-IPv6, IPv4-in-IPv4, OSI/CLNP-in-IPv6, OSI/CLNP-in-IPv4, etc.
   After each IR[VE] reads in the list of VPs and sorts the information
   accordingly, it is said to be "synchronized with the IRON".  Each
   IR[VE] next installs all EPs derived from its VPs into its FIB based
   on the mapping information received from the IR[CE]s each of its EUN
   customers.


Author's Address

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

   Email: fltemplin@acm.org


























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