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Internet Research Task Force                             F. Templin, Ed.
(IRTF)                                      Boeing Research & Technology
Internet-Draft                                         September 1, 2010
Intended status: Experimental
Expires: March 5, 2011


              The Internet Routing Overlay Network (IRON)
                       draft-templin-iron-12.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 (IRON) that supports sustainable
   growth through Provider Independent addressing while requiring no
   changes to end systems and no changes to the existing routing system.
   IRON further addresses other important issues including routing
   scaling, mobility management, multihoming, traffic engineering and
   NAT traversal.  While business considerations are an important
   determining factor for widespread adoption, they are out of scope for
   this document.  This document is a product of the IRTF Routing
   Research Group.

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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   This Internet-Draft will expire on March 5, 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



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   Provisions Relating to IETF Documents
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   publication of this document.  Please review these documents
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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  The Internet Routing Overlay Network . . . . . . . . . . . . .  6
     3.1.  IR[CE] - IRON Customer Edge Router . . . . . . . . . . . .  8
     3.2.  IR[VE] - IRON Virtual Prefix Company Edge Router . . . . .  8
     3.3.  IR[VC] - IRON Virtual Prefix Company Core Router . . . . .  9
     3.4.  IR[VP] - IRON Virtual Prefix Company Combined Router . . . 10
   4.  IRON Organizational Principles . . . . . . . . . . . . . . . . 11
   5.  IRON Initialization  . . . . . . . . . . . . . . . . . . . . . 12
     5.1.  IR[VC] Initialization  . . . . . . . . . . . . . . . . . . 13
     5.2.  IR[VE] Initialization  . . . . . . . . . . . . . . . . . . 13
     5.3.  IR[CE] Initialization  . . . . . . . . . . . . . . . . . . 14
   6.  IRON Operation . . . . . . . . . . . . . . . . . . . . . . . . 15
     6.1.  IR[CE] Operation . . . . . . . . . . . . . . . . . . . . . 15
     6.2.  IR[VE] Operation . . . . . . . . . . . . . . . . . . . . . 16
     6.3.  IR(VC) Operation . . . . . . . . . . . . . . . . . . . . . 18
     6.4.  IRON Reference Operating Scenarios . . . . . . . . . . . . 18
       6.4.1.  Both Hosts Within IRON EUNs  . . . . . . . . . . . . . 19
       6.4.2.  Mixed IRON and Non-IRON Hosts  . . . . . . . . . . . . 21
     6.5.  Mobility, Multihoming and Traffic Engineering
           Considerations . . . . . . . . . . . . . . . . . . . . . . 24
       6.5.1.  Mobility Management  . . . . . . . . . . . . . . . . . 24
       6.5.2.  Multihoming  . . . . . . . . . . . . . . . . . . . . . 25
       6.5.3.  Inbound Traffic Engineering  . . . . . . . . . . . . . 25
       6.5.4.  Outbound Traffic Engineering . . . . . . . . . . . . . 25
     6.6.  Renumbering Considerations . . . . . . . . . . . . . . . . 25
     6.7.  NAT Traversal Considerations . . . . . . . . . . . . . . . 26
     6.8.  Nested EUN Considerations  . . . . . . . . . . . . . . . . 26
       6.8.1.  Host A Sends Packets to Host Z . . . . . . . . . . . . 27
       6.8.2.  Host Z Sends Packets to Host A . . . . . . . . . . . . 28
   7.  Additional Considerations  . . . . . . . . . . . . . . . . . . 29
   8.  Related Initiatives  . . . . . . . . . . . . . . . . . . . . . 29
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 29
   10. Security Considerations  . . . . . . . . . . . . . . . . . . . 30
   11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 30
   12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 30
     12.1. Normative References . . . . . . . . . . . . . . . . . . . 30
     12.2. Informative References . . . . . . . . . . . . . . . . . . 30
   Appendix A.  IRON VPs Over Internetworks with Different
                Address Families  . . . . . . . . . . . . . . . . . . 33
   Appendix B.  Scaling Considerations  . . . . . . . . . . . . . . . 33
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 35







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1.  Introduction

   Growth in the number of entries instantiated 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.
   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) [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
   [I-D.carpenter-softwire-sample].



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   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 routing system comprising virtual overlay
   networks managed by 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 BGP core routers and supporting servers, as well
   as IRON-aware routers/servers in customer EUNs.  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.  In other words, an ISP is responsible for providing IP
      connectivity to a customer owning an EUN.

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





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

   Virtual Prefix (VP)
      a 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).

   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 belonging to an EP 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
      prefixes are routable on a global basis, while locators taken from
      private IP prefixes are made public via Network Address
      Translation (NAT).

   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

   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

   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
   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:







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                                         +-------------------------+
                                         |    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
   the SEAL Control Message Protocol (SCMP) to deterministically
   exchange and authenticate control messages such as route
   redirections, indications of Path Maximum Transmission Unit (PMTU)
   limitations, destination unreachables, etc.

   The IRON is manifested through a business model in which Virtual
   Prefix Companies (VPCs) own and manage virtual overlay networks
   comprising 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 Internet connectivity.  Therefore,
   unless the ISP also acts as a VPC the customer must have two business
   relationships - one with the ISP and a second with the VPC.  In that
   case, the VPC can open for business and begin serving its customers
   immediately without the need to coordinate its activities with ISPs
   or with other VPCs.  Further details on business considerations are
   out of scope for this document.

   The IRON requires no changes to end systems and no changes to most



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   routers in the Internet.  Instead, the IRON comprises IRs that are
   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 as shown in Figure 2.  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 standalone server 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).
                           .-.
                        ,-(  _)-.
        +--------+   .-(_    (_  )-.
        | 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

   Each IR[VE] serves as a customer-facing tunnel endpoint router that
   IR[CE]s form bidirectional tunnels with over the IRON.  Each IR[VE]
   also associates with an Internet-facing IR[VC] 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.  It
   therefore also serves as an Autonomous System Border Router (ASBR)
   that is owned and managed by the VPC.

   Each VPC configures one or more IR[VC]s which advertise the company's
   VPs into the IPv4 and IPv6 global Internet BGP routing systems.  Each
   IR[VC] associates with all of the VPC's overlay network IR[VE]
   routers, e.g., via tunnels over the IRON, via a direct interconnect
   such as an Ethernet cable, etc.  The IR[VC] role (as well as its
   relationship with overlay network IR[VE]s) is depicted in Figure 4:












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                   ,-(  _)-.
                .-(_    (_  )-.
               (_   Internet   )
                  `-(______)-'   |  +--------+
                        |        |--| IR[VE] |
                   +----+---+    |  +--------+
                   | IR[VC] |----|  +--------+
                   +--------+    |--| IR[VE] |
                       _||       |  +--------+
                      (:::)-.  (Ethernet)
                  .-(::::::::)
   +--------+  .-(::::::::::::)-.  +--------+
   | IR[VE] |=(:::: The IRON ::::)=| IR[VE] |
   +--------+  `-(::::::::::::)-'  +--------+
                  `-(::::::)-'
                       ||      (Tunnels)
                   +--------+
                   | 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].  While not in itself a
   fundamental building block of the architecture, it is mentioned here
   to clarify an implementation option available to VPCs.

   In the IR[VP] model, 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] platform 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 coordinates its activities independently of all others (with
   the exception that the IR[VE]s of each patch must be aware of all
   VP's in the IRON).

   Each VPC overlay network in the IRON maintains a set of IR[VC]s that
   connect the overlay network directly to the public IPv4 and IPv6
   Internets.  Each IR[VC] advertises the VPC overlay network's IPv4 VPs
   into the IPv4 BGP routing system and advertises the overlay network'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 and direct them toward EPA-addressed end systems
   connected to the VPC overlay network.

   Each VPC overlay network also manages a set of IR[VE]s that connect
   customer EUNs to the IRON and to the IPv6 and IPv4 Internets via
   their associations with IR[VC]s.  IR[VE]s therefore need not be BGP
   routers themselves and can be simple commodity hardware platforms.



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   Moreover, 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 IR[VC]s in the VPC overlay network via a dynamic routing
   protocol (e.g., an overlay network internal BGP instance that carries
   only the EP-to-IR[VE] mappings and does not interact with the
   external BGP routing system).  Each IR[VE] therefore only needs to
   track 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 both the VPC
   overlay network and to the rest of the IRON.  Each EUN can connect to
   the IRON 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 anycast discovery process (described
   below).  It then selects one of these nearby IR[VE]s as its server
   and forms a bidirectional tunnel with the IR[VE] through an initial
   exchange followed by periodic keepalives.

   After the IR[CE] selects a serving IR[VE], it forwards initial
   outbound packets from its EUNs by tunneling them to its own serving
   IR[VE] which in turn forwards them to the nearest IR[VC] within the
   IRON that serves the final destination.  The IR[CE] will subsequently
   receive redirect messages informing it of a more direct route through
   the IR[VE] that serves the final destination.

   The IRON can also be used to support VPs of network layer address
   families that cannot be routed natively in the underlying
   Internetwork (e.g., OSI/CLNP over the public Internet, IPv6 over
   IPv4-only Internetworks, IPv4 over IPv6-only Internetworks, etc.).
   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.




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5.1.  IR[VC] Initialization

   Before its first operational use, each IR[VC] in a VPC overlay
   network is 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 external BGP
   interconnections the same as for any BGP router.

   Upon startup, the IR[VC] engages in BGP routing exchanges with its
   peers in the IPv4 and IPv6 Internets the same as for any BGP router.
   It then connects to all of the IR[VE]s in the overlay network (e.g.,
   via a TCP connection over a bidirectional tunnel, via an iBGP route
   reflector, etc.) for the purpose of discovering EP->IR[VE] mappings.
   After the IR[VC] has fully populated its EP->IR[VE] mapping
   information database, it is said to be "synchronized" wrt its VPs.

   After this initial synchronization procedure, the IR[VC] then
   advertises the overlay network's VPs externally.  In particular, the
   IR[VC] advertises the IPv6 VPs into the IPv6 BGP routing system and
   advertises the IPv4 VPs into the IPv4 BGP routing system.  The IR[VC]
   additionally advertises an IPv4 /24 companion prefix (e.g.,
   192.0.2.0/24) into the IPv4 routing system and an IPv6 ::/64
   companion prefix (e.g., 2001:DB8::/64) into the IPv6 routing system
   (note that these may also be sub-prefixes taken from a VP).  The
   IR[VC] then configures the host number '1' in the IPv4 companion
   prefix (e.g., as 192.0.2.1) and the interface identifier '0' in the
   IPv6 companion prefix (e.g., as 2001:DB8::0) and assigns the
   resulting addresses as subnet router anycast addresses
   [RFC3068][RFC2526] for the VPC overlay network.  (See Appendix A for
   more information on the discovery and use of companion prefixes.)
   The IR[VC] then 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 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 provisioned with the list of all VPs in the
   IRON (i.e., and not just the VPs of its own overlay network) so that
   it can discern EPA and non-EPA addresses.  (The IR[VE] could
   therefore be greatly simplified if the list of VPs could be covered
   within a small number of very short prefixes, e.g., one or a few IPv6
   ::/20's) The IR[VE] must also discover the VP companion prefix
   relationships discussed in Section 5.1, e.g., via a global database
   such as discussed in Appendix A.

   Upon startup, each IR[VE] must connect to all of the IR[VC]s within
   its overlay network (e.g., via a TCP connection over a bidirectional



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   tunnel, via an iBGP route reflector, etc.) for the purpose of
   reporting its EP->IR[VE] mappings.  The IR[VE] then actively listens
   for IR[CE] customers which register their EP prefixes as part of
   establishing a bidirectional tunnel.  When a new IR[CE] registers its
   EP prefixes, the IR[VE] announces the new EP additions to all
   IR[VC]s; when an existing IR[CE] unregisters its EP prefixes, the
   IR[VE] withdraws its announcements.

5.3.  IR[CE] Initialization

   Before its first operational use, each IR[CE] must obtain one or more
   EPs from its VPC as well as the companion prefixes associated with
   the VPC overlay network (see Section 5.1).  The IR[CE] must also
   obtain 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
   organization.

   Upon startup, the IR[CE] sends an SCMP Router Solicitation (SRS)
   message to the VPC overlay network subnet router anycast address to
   discover the nearest IR[VC].  The IR[VC] will return an SCMP Router
   Advertisement message that lists the locator addresses of one or more
   nearby IR[VE]s.  (This list is analogous to the ISATAP Potential
   Router List (PRL) [RFC5214].)

   After the IR[CE] receives an SRA 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
   service availability 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 to 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



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   a non-zero default router lifetime and that signifies the
   establishment of a bidirectional tunnel.  (A zero default router
   lifetime on the other hand signifies that the IR[VE] is currently
   unable to establish a bidirectional tunnel, e.g., due to heavy load,
   due to challenge/response failure, etc.)

   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.


6.  IRON Operation

   Following the IRON initialization detailed in Section 5, 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 in some cases IR[VE]s) additionally forward
   packets to and from the native IPv6 and IPv4 Internets.  IRs also use
   SCMP to coordinate with other IRs, including the process of sending
   and receiving redirect messages, error messages, etc.  (Note however
   that an IR must not send an SCMP message in response to an SCMP error
   message.)  Each IR operates as specified in the following sub-
   sections.

6.1.  IR[CE] Operation

   After selecting its serving IR[VE] as specified in Section 5.3, the
   IR[CE] should register each of its ISP connections with the IR[VE] in
   order to establish multiple bidirectional tunnels for multihoming
   purposes.  To do so, it sends periodic SRS messages to its serving
   IR[VE] via each of its ISPs to establish additional bidirectional
   tunnels and to keep each tunnel alive.  These messages need not
   include challenge/response mechanisms since prefix proof of ownership
   was already established in the initial exchange and a nonce 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 nonce is used to
   represent the set of all bidirectional tunnels between the IR[CE] and
   the IR[VE].  Therefore, there are multiple bidirectional tunnels, and
   the nonce names this "bundle" of tunnels.  (The IR[CE] and IR[VE] may
   conceptually represent this "bundle" as a single tunnel with multiple
   locator addresses, however each such locator address must be tested
   independently in case there are NATs on the path.)




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   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] should 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
   bidirectional tunnel with a new IR[VE].  The act of establishing the
   tunnel 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 sends a flow of packets to a
   correspondent, the packets are forwarded through the EUN via normal
   routing until they reach the IR[CE], which then tunnels the initial
   packets to its serving IR[VE] as the next hop.  In particular, the
   IR[CE] encapsulates each packet in an outer header with its locator
   as the source address and the locator of its serving IR[VE] as the
   destination address.  Note that after sending the initial packets of
   a flow, the IR[CE] may receive important SCMP messages such as
   indications of PMTU limitations, redirects that point to a better
   next hop, etc.  It is therefore essential that the IR[CE] send the
   initial packets through its serving IR[VE] to avoid loss of SCMP
   messages that cannot traverse a NAT in the reverse direction.

   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 redirects
   and other SCMP messages.  When the IR[CE] receives an SCMP message,
   it checks the nonce field of the encapsulated packet-in-error to
   verify that the message corresponds to the tunnel to its serving
   IR[VE] and accepts the message if the nonce matches.  (Note however
   that the outer source and destination addresses of the packet-in-
   error may be different than those in the original packet due to
   possible IR[VE] and/or IR[VC] address rewritings.)

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 new 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 IR[CE]'s EPs (see Section 5.3) 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.




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   When the IR[VE] receives a SEAL-encapsulated packet from one of its
   IR[CE] tunnel endpoints, it examines the inner destination address.
   If the inner destination address is not an EPA, the IR[VE]
   decapsulates the packet and forwards it unencapsulated into the
   Internet if it is able to do so without loss due to ingress
   filtering.  Otherwise, the IR[VE] re-encapsulates the packet (i.e.,
   it removes the outer header and replaces it with a new outer header
   of the same address family) and sets the outer destination address to
   the locator address of an IR[VC] within its VPC overlay network.  It
   then forwards the re-encapsulated packet to the IR[VC], which will in
   turn decapsulate it and forward it into the Internet.

   If the inner destination address is an EPA, however, the IR[VE]
   rewrites the outer source address to one of its own locator addresses
   and rewrites the outer destination address to the subnet router
   anycast address taken from the companion prefix associated with the
   inner destination address (where the companion prefix of the same
   address family as the outer IP protocol is used).  The IR[VE] then
   forwards the revised packet into the Internet via a default or more-
   specific route, where it will be directed to the closest IR[VC]
   within the destination VPC overlay network.  After sending the
   packet, the IR[VE] may then receive an SCMP error or redirect message
   from an IR[VC]/IR[VE] within the destination VPC overlay network.  In
   that case, the IR[VE] verifies that the nonce in the message matches
   the tunnel corresponding to the IR[CE] that sent the original inner
   packet and discards the message if the nonce does not match.
   Otherwise, the IR[VE] re-encapsulates the SCMP message in a new outer
   header that uses the source address, destination address and nonce
   parameters associated with the tunnel to the IR[CE]; it then forwards
   the message to the IR[CE].  This arrangement is necessary to allow
   SCMP messages to flow through any NATs on the path.

   When an IR[VE] ('A') receives a SEAL-encapsulated packet from an
   IR[VC] or from the Internet, if the inner destination address matches
   an EP in its FIB 'A' re-encapsulates the packet in a new outer header
   that uses the source address, destination address and nonce
   parameters associated with the tunnel 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 packet to 'C' and also send an SCMP redirect message back
   to the source of the packet.  In this way, 'B' can leave behind
   forwarding information when changing between IR[VE]s 'A' and 'C'
   (e.g., due to mobility events) without exposing packets to loss.







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6.3.  IR(VC) Operation

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

   When an IR[VC] receives a packet from the Internet destined to an EPA
   covered by one of its VPs, it behaves as an ordinary IP router.  In
   particular, the IR[VC] looks in its FIB to discover a locator of the
   IR[VE] that serves the EP that covers the destination address.  The
   IR[VC] then 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].

   When an IR[VC] receives a packet from the Internet destined to one of
   its subnet router anycast addresses, it discards the packet if it is
   not SEAL-encapsulated.  If the packet is an SCMP SRS message, the
   IR[VC] instead sends an SRA message back to the source listing the
   locator addresses of nearby IR[VE] routers then discards the message.
   The IR[VC] otherwise discards all other SCMP messages.

   If the packet is an ordinary SEAL packet (i.e., one that encapsulates
   an inner packet) the IR[VC] sends an SCMP redirect message of the
   same address family back to the source 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.  After sending
   the redirect message, the IR[VC] then rewrites the outer destination
   address of the SEAL-encapsulated packet to the locator of the IR[VE]
   and forwards the revised packet to the IR[VE].  Note that in this
   arrangement any errors that occur on the path between the IR[VC] and
   the IR[VE] will be delivered to the original source but with a
   different destination address due to this IR[VC] address rewriting.

6.4.  IRON Reference Operating Scenarios

   The IRON supports communications when one or both hosts are located
   within EP-addressed EUNs regardless of whether the EPs are
   provisioned by the same VPC or by different VPCs.  When both hosts
   are within IRON EUNs, route redirections that eliminate unnecessary
   IR[VE]s and 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.




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6.4.1.  Both Hosts Within IRON EUNs

   When both hosts are within IRON EUNs, it is sufficient to consider
   the scenario 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.

   In this scenario, the initial packets of a flow produced by a source
   host must flow through both the source's serving IR[VE] and an IR[VC]
   of the destination host, but route optimization can eliminate these
   elements from the path for subsequent packets in the flow.  Figure 6
   shows the flow of initial packets from host A to host B within two
   IRON EUNs.

                 ________________________________________
              .-(                 .-.                    )-.
           .-(                 ,-(  _)-.                    )-.
        .-(          +========+(_    (_  +=====+               )-.
      .(             ||    (_|| 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 6: Initial Packet Flow Before Redirects

   With reference to Figure 6, host A sends packets destined to host B



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   via its network interface connected to EUN A. Routing within 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 one of its own locator
   addresses, and rewrites the outer destination address to the subnet
   router anycast address of the appropriate address family associated
   with the inner destination address.  IR[VE](A) then releases the
   revised packets into the Internet where routing will direct them to
   IR[VC](B).

   IR[VC](B) will intercept the encapsulated packets from IR[VE](A) then
   check its FIB to discover an entry that covers inner destination
   address B with IR[VE](B) as the next hop.  IR[VC](B) then returns
   SCMP redirect messages to IR[VE](A) (*), rewrites the outer
   destination address of the encapsulated packets to the locator
   address of IR[VE](B), and forwards these revised packets 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 re-encapsulates the
   packets in a new outer header that uses the source address,
   destination address and nonce parameters associated with the tunnel
   to IR[CE](B).  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) listing
   IR[VE](B) as a better next hop.  IR[VE](A) will in turn forward the
   redirects to IR[CE](A), which will thereafter forward its
   encapsulated packets directly to the locator address of IR[VE](B)
   without involving either IR[VE](A) or 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: Sustained Packet Flow 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 8 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 8: From IRON Host A to Non-IRON Host B

   In this scenario, host A sends packets destined to host B via its
   network interface connected to IRON EUN A. Routing within 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 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 re-
   encapsulates and 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 the final destination B. (Note that IR[VE](A) and
   IR[VC](A) are depicted in Figure 8 as two halves of a unified
   IR[VP](A).  In that case, the "forwarding" between IR[VE](A) and



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   IR[VC](A) is a zero-instruction imaginary operation.)

   This scenario always involves an IR[VE](A) and IR[VC](A) owned by the
   VPC that provides service to IRON EUN A. It 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 9 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 9: From Non-IRON Host B to IRON Host A

   In this scenario, host B sends packets destined to host A via its
   network interface connected to non-IRON 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-



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   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
   (re-)encapsulates the packets in an outer header that uses the source
   address, destination address and nonce parameters associated with the
   tunnel to IR[CE](A).  IR[VE](A) next 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 scenario always involves an IR[VE](A) and IR[VC](A) owned by the
   VPC that provides service to IRON EUN A. It 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 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 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



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   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 VPC network routing churn.

6.5.4.  Outbound Traffic Engineering

   An IR[CE] can select outgoing locators, e.g., based on current QoS
   considerations such as minimizing one-way delay or one-way delay
   variance.

6.6.  Renumbering Considerations

   As new link layer technologies and/or service models 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 change
   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,
   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 and offering reasonable rates.






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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 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 IP address in the outer headers of SRS messages.
   When there is a NAT in the path, the UDP port number and IP 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 IP 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].  In this sense, the IR[VE]'s
   "locator" for the IR[CE] consists of the concatenation of the IP
   address and UDP port number.

   IRON does not introduce any new issues to complications raised for
   NAT traversal or for applications embedding address referrals in
   their payload.

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], and recursive
   nestings of multiple layers of encapsulations may be necessary.

   For example, in the network scenario depicted in Figure 10 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) configures 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.




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

                       Figure 10: 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

   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 once-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 IR[VE](B) as the outer destination address then
   forwards the twice-encapsulated packet into EUN(C).  Routing within



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   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 IR[VE](C)
   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 IR[VE](C).

   When IR[VE](C) receives the triple-encapsulated packet, it removes
   the outer layer of encapsulation and forwards the resulting twice-
   encapsulated packet into the Internet to IR[VE](B).  Next, IR[VE](B)
   removes the outer layer of encapsulation and forwards the resulting
   once-encapsulated packet into the Internet to IR[VE](A).  Next,
   IR[VE](A) checks the address type of the inner address 'Z'.  If Z is
   a non-EPA address, IR[VE](A) simply decapsulates the packet and
   forwards it into the Internet.  Otherwise, IR[VE](A) rewrites the
   outer source and destination addresses of the once-encapsulated
   packet and forwards it to IR[VC](Z).  IR[VC](Z) in turn rewrites the
   outer destination address of the packet to the locator for IR[VE](Z),
   then forwards the packet and sends a redirect to IR[VE](A) (which
   forwards the redirect to IR[CE](A)).  IR[VE](Z) then re-encapsulates
   the packet and forwards it to IR[CE](Z), which decapsulates it and
   forwards the inner packet to host Z. Subsequent packets from
   IR[CE](A) will then use IR[VE](Z) as the next hop toward host Z,
   which eliminates IR[VE](A) and IR[VC](Z) from the path.

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
   EPA(B) which is the locator address of IR[CE](A).  When IR[CE](A)



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   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.


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].

   [I-D.bernardos-mext-nemo-ro-cr] discussed a route optimization
   approach using a Correspondent Router (CR) model.  The IRON IR[VE]
   construct is similar to the CR concept described in this work,
   however the manner in which customer EUNs coordinates with IR[VE]s is
   different and based on the redirection model associated with NBMA
   links.

   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.  Robin Whittle and Steve Russert co-authored the TTR
   mobility architecture which strongly influenced IRON.  Eric
   Fleischman pointed out the opportunity to leverage anycast for
   discovering topologically-close servers.  Thomas Henderson
   recommended a quantitative analysis of scaling properties.

   The following individuals provided essential review input: Mohamed
   Boucadair, Wesley Eddy, Dae Young Kim and Robin Whittle.


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.bernardos-mext-nemo-ro-cr]
              Bernardos, C., Calderon, M., and I. Soto, "Correspondent
              Router based Route Optimisation for NEMO (CRON)",
              draft-bernardos-mext-nemo-ro-cr-00 (work in progress),
              July 2008.




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   [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-03 (work in progress), August 2010.

   [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), August 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



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              a subnetwork for experimentation with the OSI network
              layer", RFC 1070, February 1989.

   [RFC2526]  Johnson, D. and S. Deering, "Reserved IPv6 Subnet Anycast
              Addresses", RFC 2526, March 1999.

   [RFC3068]  Huitema, C., "An Anycast Prefix for 6to4 Relay Routers",
              RFC 3068, June 2001.

   [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
              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,



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              http://www.firstpr.com.au/ip/ivip/TTR-Mobility.pdf",
              August 2008.


Appendix A.  IRON VPs Over Internetworks with Different Address Families

   The IRON architecture leverages the routing system by providing
   generally shortest-path routing for packets with EPA addresses from
   VPs that match the address family of the underlying Internetwork.
   When the VPs are of an address family that is not routable within the
   underlying Internetwork, however, (e.g., when OSI/NSAP [RFC4548] VPs
   are used within an IPv4 Internetwork) a global mapping database is
   required to allow IR[VE]s to map VPs to companion prefixes taken from
   address families that are routable within the Internetwork.  For
   example, an IPv6 VP (e.g., 2001:DB8::/32) could be paired with a
   companion IPv4 prefix (e.g., 192.0.2.0/24) so that encapsulated IPv6
   packets can be forwarded over IPv4-only Internetworks.

   Every VP in the IRON must therefore be represented in a globally
   distributed Master VP database (MVPd) that maintains VP-to-companion
   prefix mappings for all VPs in the IRON.  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.

   Upon startup, each IR[VE] discovers the full set of VPs for the IRON
   by reading the MVPd.  The IR[VE] reads the MVPd from a nearby server
   and periodically checks the server for deltas since the database was
   last read.  After reading the MVPd, the IR[VE] has a full list of VP
   to companion prefix mappings.

   The IR[VE] can then forward packets toward EPAs covered by a VP by
   encapsulating them in an outer header of the VP's companion prefix
   address family and using any address taken from the companion prefix
   as the outer destination address.  The companion prefix therefore
   serves as an anycast prefix.

   Possible encapsulations in this model include IPv6-in-IPv4, IPv4-in-
   IPv6, OSI/CLNP-in-IPv6, OSI/CLNP-in-IPv4, etc.


Appendix B.  Scaling Considerations

   Scaling aspects of the IRON architecture have strong implications for
   its applicability in practical deployments.  Scaling must be



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   considered along multiple vectors including Interdomain core routing
   scaling, scaling to accommodate large numbers of customer EUNs,
   traffic scaling, state requirements, etc.

   In terms of routing scaling, each VPC will advertise one or more VPs
   from which EPs are delegated to customer EUNs.  Routing scaling will
   therefore be minimized when each VP covers many EPs.  For example,
   the IPv6 prefix 2001:DB8::/32 contains 2^24 ::/56 EP prefixes for
   assignment to EUNs.  The IRON could therefore accommodate 2^32 ::/56
   EPs with only 2^8 ::/32 VPs advertised in the interdomain routing
   core.

   In terms of traffic scaling for IR[VC]s, each IR[VC] represents an
   ASBR of a "shell" enterprise network that simply directs arriving
   traffic packets with EPA destination addresses towards IR[VE]s that
   service customer EUNs.  Moreover, the IR[VC] sheds traffic destined
   to EPAs through redirection which removes it from the path for the
   vast majority of traffic packets.  On the other hand, each IR[VC]
   must handle all traffic packets forwarded between its customer EUNs
   and the non-IRON Internet.  The scaling concerns for this latter
   class of traffic are no different than for ASBR routers that connect
   large enterprise networks to the Internet.  In terms of traffic
   scaling for IR[VE]s, each IR[VE] services a set of the VPC overlay
   network's customer EUNs.  The IR[VE] services all traffic packets
   destined to its EUNs but only services the initial packets of flows
   initiated from the EUNs and destined to EPAs.  Therefore, traffic
   scaling for EPA-addressed traffic is an asymmetric consideration and
   is proportional to the number of EUNs each IR[VE] serves.

   In terms of state requirements for IR[VC]s, each IR[VC] maintains a
   list of all IR[VE]s in the VPC overlay network as well as FIB entries
   for all customer EUNs that each IR[VE] serves.  This state is
   therefore dominated by the number of EUNs in the VPC overlay network.
   Sizing the IR[VC] to accommodate state information for all EUNs is
   therefore required during VPC overlay network planning.  In terms of
   state requirements for IR[VE]s, each IR[VE] maintains tunnel state
   for each of the customer EUNs it serves but need not keep state for
   all EUNs in the VPC overlay network.  Finally, neither IR[VC]s nor
   IR[VE] need keep state for final destinations of outbound traffic.

   IR[CE]s source and sink all traffic packets originating from or
   destined to the customer EUN.  Therefore traffic scaling
   considerations for IR[CE]s are the same as for any site border
   router.  IR[CE]s also retain state for the final destinations of
   outbound traffic flows.  This can be managed as soft state, since
   stale entries purged from the cache will be refreshed when new
   traffic packets are sent.




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Internet-Draft                    IRON                    September 2010


Author's Address

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

   Email: fltemplin@acm.org










































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