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Network Working Group                                           A. Doria
Internet-Draft                                                       LTU
Intended status: Historic                                      E. Davies
Expires: July 5, 2008                                   Folly Consulting
                                                           F. Kastenholz
                                                         January 2, 2008


                 Requirements for Inter-Domain Routing
                     draft-irtf-routing-reqs-09.txt

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   Copyright (C) The IETF Trust (2008).












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Abstract

   The requirements for routing architectures described in this document
   were produced by two sub-groups under the IRTF Routing Research Group
   in 2001, with some editorial updates up to 2006.  The two sub-groups
   worked independently, and the resulting requirements represent two
   separate views of the problem and of what is required to fix the
   problem.  This document may usefully serve as part of the recommended
   reading for anyone who works on routing architecture designs for the
   Internet in the future.

   The document is published with the support of the IRTF RRG as a
   record of the work completed at that time, but with the understanding
   that it does not necessarily represent either the latest technical
   understanding or the technical consensus of the research group at the
   date of publication.



































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Table of Contents

   1.  Background . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   2.  Results from Group A . . . . . . . . . . . . . . . . . . . . .  7
     2.1.  Group A - Requirements For a Next Generation Routing
           and Addressing Architecture  . . . . . . . . . . . . . . .  7
       2.1.1.   Architecture  . . . . . . . . . . . . . . . . . . . .  7
       2.1.2.   Separable Components  . . . . . . . . . . . . . . . .  7
       2.1.3.   Scalable  . . . . . . . . . . . . . . . . . . . . . .  8
       2.1.4.   Lots of Interconnectivity . . . . . . . . . . . . . . 11
       2.1.5.   Random Structure  . . . . . . . . . . . . . . . . . . 11
       2.1.6.   Multi-homing  . . . . . . . . . . . . . . . . . . . . 12
       2.1.7.   Multi-path  . . . . . . . . . . . . . . . . . . . . . 12
       2.1.8.   Convergence . . . . . . . . . . . . . . . . . . . . . 13
       2.1.9.   Routing System Security . . . . . . . . . . . . . . . 15
       2.1.10.  End Host Security . . . . . . . . . . . . . . . . . . 17
       2.1.11.  Rich Policy . . . . . . . . . . . . . . . . . . . . . 17
       2.1.12.  Incremental Deployment  . . . . . . . . . . . . . . . 20
       2.1.13.  Mobility  . . . . . . . . . . . . . . . . . . . . . . 20
       2.1.14.  Address Portability . . . . . . . . . . . . . . . . . 21
       2.1.15.  Multi-Protocol  . . . . . . . . . . . . . . . . . . . 21
       2.1.16.  Abstraction . . . . . . . . . . . . . . . . . . . . . 21
       2.1.17.  Simplicity  . . . . . . . . . . . . . . . . . . . . . 22
       2.1.18.  Robustness  . . . . . . . . . . . . . . . . . . . . . 22
       2.1.19.  Media Independence  . . . . . . . . . . . . . . . . . 23
       2.1.20.  Stand-alone . . . . . . . . . . . . . . . . . . . . . 23
       2.1.21.  Safety of Configuration . . . . . . . . . . . . . . . 24
       2.1.22.  Renumbering . . . . . . . . . . . . . . . . . . . . . 24
       2.1.23.  Multi-prefix  . . . . . . . . . . . . . . . . . . . . 24
       2.1.24.  Cooperative Anarchy . . . . . . . . . . . . . . . . . 24
       2.1.25.  Network Layer Protocols and Forwarding Model  . . . . 24
       2.1.26.  Routing Algorithm . . . . . . . . . . . . . . . . . . 24
       2.1.27.  Positive Benefit  . . . . . . . . . . . . . . . . . . 25
       2.1.28.  Administrative Entities and the IGP/EGP Split . . . . 25
     2.2.  Non-Requirements . . . . . . . . . . . . . . . . . . . . . 26
       2.2.1.   Forwarding Table Optimization . . . . . . . . . . . . 26
       2.2.2.   Traffic Engineering . . . . . . . . . . . . . . . . . 26
       2.2.3.   Multicast . . . . . . . . . . . . . . . . . . . . . . 26
       2.2.4.   Quality of Service (QoS)  . . . . . . . . . . . . . . 26
       2.2.5.   IP Prefix Aggregation . . . . . . . . . . . . . . . . 27
       2.2.6.   Perfect Safety  . . . . . . . . . . . . . . . . . . . 27
       2.2.7.   Dynamic Load Balancing  . . . . . . . . . . . . . . . 27
       2.2.8.   Renumbering of Hosts and Routers  . . . . . . . . . . 28
       2.2.9.   Host Mobility . . . . . . . . . . . . . . . . . . . . 28
       2.2.10.  Backward Compatibility  . . . . . . . . . . . . . . . 28
   3.  Requirements from Group B  . . . . . . . . . . . . . . . . . . 29
     3.1.  Group B - Future Domain Routing Requirements . . . . . . . 29
     3.2.  Underlying Principles  . . . . . . . . . . . . . . . . . . 29



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       3.2.1.   Inter-domain and Intra-domain . . . . . . . . . . . . 30
       3.2.2.   Influences on a Changing Network  . . . . . . . . . . 30
       3.2.3.   High Level Goals  . . . . . . . . . . . . . . . . . . 32
     3.3.  High Level User Requirements . . . . . . . . . . . . . . . 36
       3.3.1.   Organisational Users  . . . . . . . . . . . . . . . . 36
       3.3.2.   Individual Users  . . . . . . . . . . . . . . . . . . 38
     3.4.  Mandated Constraints . . . . . . . . . . . . . . . . . . . 39
       3.4.1.   The Federated Environment . . . . . . . . . . . . . . 40
       3.4.2.   Working with Different Sorts of Networks  . . . . . . 40
       3.4.3.   Delivering Resilient Service  . . . . . . . . . . . . 40
       3.4.4.   When Will the New Solution Be Required? . . . . . . . 41
     3.5.  Assumptions  . . . . . . . . . . . . . . . . . . . . . . . 41
     3.6.  Functional Requirements  . . . . . . . . . . . . . . . . . 43
       3.6.1.   Topology  . . . . . . . . . . . . . . . . . . . . . . 44
       3.6.2.   Distribution  . . . . . . . . . . . . . . . . . . . . 45
       3.6.3.   Addressing  . . . . . . . . . . . . . . . . . . . . . 49
       3.6.4.   Statistics Support  . . . . . . . . . . . . . . . . . 51
       3.6.5.   Management Requirements . . . . . . . . . . . . . . . 51
       3.6.6.   Provability . . . . . . . . . . . . . . . . . . . . . 52
       3.6.7.   Traffic Engineering . . . . . . . . . . . . . . . . . 53
       3.6.8.   Support for Middleboxes . . . . . . . . . . . . . . . 55
     3.7.  Performance Requirements . . . . . . . . . . . . . . . . . 55
     3.8.  Backwards Compatibility (Cutover) and Maintainability  . . 56
     3.9.  Security Requirements  . . . . . . . . . . . . . . . . . . 56
     3.10. Debatable Issues . . . . . . . . . . . . . . . . . . . . . 58
       3.10.1.  Network Modeling  . . . . . . . . . . . . . . . . . . 58
       3.10.2.  System Modeling . . . . . . . . . . . . . . . . . . . 59
       3.10.3.  One, Two or Many Protocols  . . . . . . . . . . . . . 59
       3.10.4.  Class of Protocol . . . . . . . . . . . . . . . . . . 60
       3.10.5.  Map Abstraction . . . . . . . . . . . . . . . . . . . 60
       3.10.6.  Clear Identification for All Entities . . . . . . . . 60
       3.10.7.  Robustness and Redundancy . . . . . . . . . . . . . . 61
       3.10.8.  Hierarchy . . . . . . . . . . . . . . . . . . . . . . 61
       3.10.9.  Control Theory  . . . . . . . . . . . . . . . . . . . 61
       3.10.10. Byzantium . . . . . . . . . . . . . . . . . . . . . . 62
       3.10.11. VPN Support . . . . . . . . . . . . . . . . . . . . . 62
       3.10.12. End-to-End Reliability  . . . . . . . . . . . . . . . 62
       3.10.13. End-to-End Transparency . . . . . . . . . . . . . . . 62
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . . 64
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 65
   6.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 66
   7.  Informative References . . . . . . . . . . . . . . . . . . . . 68
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 71
   Intellectual Property and Copyright Statements . . . . . . . . . . 72







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1.  Background

   In 2001, the IRTF Routing Research Group (IRTF RRG) chairs, Abha
   Ahuja and Sean Doran, decided to establish a sub-group to look at
   requirements for inter-domain routing (IDR).  A group of well known
   routing experts was assembled to develop requirements for a new
   routing architecture.  Their mandate was to approach the problem
   starting from a blank sheet.  This group was free to take any
   approach, including a revolutionary approach, in developing
   requirements for solving the problems they saw in inter-domain
   routing.

   Simultaneously, an independent effort was started in Sweden with a
   similar goal.  A team, calling itself Babylon, with participation
   from vendors, service providers, and academia, assembled to
   understand the history of inter-domain routing, to research the
   problems seen by the service providers, and to develop a proposal of
   requirements for a follow-on to the current routing architecture.
   This group's remit required an evolutionary approach starting from
   current routing architecture and practice.  In other words the group
   limited itself to developing an evolutionary strategy.  The Babylon
   group was later folded into the IRTF RRG as Sub-Group B to
   distinguish it from the original RRG Sub-group A.

   One of the questions that arose while the groups were working in
   isolation was whether there would be many similarities between their
   sets of requirements.  That is, would the requirements that grew from
   a blank sheet of paper resemble those that started with the
   evolutionary approach?  As can be seen from reading the two sets of
   requirements, there were many areas of fundamental agreement but some
   areas of disagreement.

   There were suggestions within the RRG that the two teams should work
   together to create a single set of requirements.  Since these
   requirements are only guidelines to future work, however, some felt
   that doing so would risk losing content without gaining any
   particular advantage.  It is not as if any group, for example the
   IRTF RRG or the IETF Routing Area, was expected to use these
   requirements as written and to create an architecture that met these
   requirements.  Rather, the requirements were in practice strong
   recommendations for a way to proceed in creating a new routing
   architecture.  In the end the decision was made to include the
   results of both efforts, side by side, in one document.

   This document contains the two requirement sets produced by the
   teams.  The text has received only editorial modifications; the
   requirements themselves have been left unaltered.  Whenever the
   editors felt that conditions had changed in the few years since the



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   text was written, an editors' note has been added to the text.

   In reading this document it is important to keep in mind that all of
   these requirements are suggestions, which are laid out to assist
   those interested in developing new routing architectures.  It is also
   important to remember that, while the people working on these
   suggestions have done their best to make intelligent suggestions,
   there are no guarantees.  So a reader of this document should not
   treat what it says as absolute, nor treat every suggestion as
   necessary.  No architecture is expected to fulfill every
   'requirement.'  Hopefully, though, future architectures will consider
   what is offered in this document.

   The IRTF RRG supported publication of this document as a historical
   record of the work completed on the understanding that it does not
   necessarily represent either the latest technical understanding or
   the technical consensus of the research group at the time of
   publication.  The document has had substantial review by members of
   the two teams, other members of the IRTF RRG and additional experts
   over the years.

   Finally, this document does not make any claims that it is possible
   to have a practical solution that meets all the listed requirements.




























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2.  Results from Group A

   This section presents the results of the work done by Sub-Group A of
   the IRTF-RRG during 2001- 2002.  The work originally appeared under
   the title: "Requirements For a Next Generation Routing and Addressing
   Architecture" and was edited by Frank Kastenholz.

2.1.  Group A - Requirements For a Next Generation Routing and
      Addressing Architecture

   The requirements presented in this section are not presented in any
   particular order.

2.1.1.  Architecture

   The new routing and addressing protocols, data structures, and
   algorithms need to be developed from a clear, well thought out,
   documented, architecture.

   The new routing and addressing system must have an architectural
   specification which describes all of the routing and addressing
   elements, their interactions, what functions the system performs, and
   how it goes about performing them.  The architectural specification
   does not go into issues such as protocol and data structure design.

   The architecture should be agnostic with regard to specific
   algorithms and protocols.

   Doing architecture before doing detailed protocol design is good
   engineering practice.  This allows the architecture to be reviewed
   and commented upon, with changes made as necessary, when it is still
   easy to do so.  Also, by producing an architecture, the eventual
   users of the protocols (the operations community) will have a better
   understanding of how the designers of the protocols meant them to be
   used.

2.1.2.  Separable Components

   The architecture must place different functions into separate
   components.

   Separating functions, capabilities, and so forth, into individual
   components and making each component "stand alone" is generally
   considered by system architects to be "A Good Thing".  It allows
   individual elements of the system to be designed and tuned to do
   their jobs "very well".  It also allows for piecemeal replacement and
   upgrading of elements as new technologies and algorithms become
   available.



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   The architecture must have the ability to replace or upgrade existing
   components and to add new ones, without disrupting the remaining
   parts of the system.  Operators must be able to roll out these
   changes and additions incrementally (i.e., no "flag days").  These
   abilities are needed to allow the architecture to evolve as the
   Internet changes.

   The architecture specification shall define each of these components,
   their jobs, and their interactions.

   Some thoughts to consider along these lines are

   o  Making topology and addressing separate subsystems.  This may
      allow highly optimized topology management and discovery without
      constraining the addressing structure or physical topology in
      unacceptable ways.

   o  Separate "fault detection and healing" from basic topology.
      From Mike O'Dell:

         "Historically the same machinery is used for both.  While
         attractive for many reasons, the availability of exogenous
         topology information (i.e., the intended topology) should, it
         seems, make some tasks easier than the general case of starting
         with zero knowledge.  It certainly helps with recovery in the
         case of constraint satisfaction.  In fact, the intended
         topology is a powerful way to state certain kinds of policy."
         [ODell01]

   o  Making policy definition and application a separate subsystem,
      layered over the others.

   The architecture should also separate topology, routing, and
   addressing from the application that uses those components.  This
   implies that applications such as policy definition, forwarding, and
   circuit and tunnel management are separate subsystems layered on top
   of the basic topology, routing, and addressing systems.

2.1.3.  Scalable

   Scaling is the primary problem facing the routing and addressing
   architecture today.  This problem must be solved and it must be
   solved for the long term.

   The architecture must support a large and complex network.  Ideally,
   it will serve our needs for the next 20 years.  Unfortunately:





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   1.  we do not know how big the Internet will grow over that time, and

   2.  the architecture developed from these requirements may change the
       fundamental structure of the Internet and therefore its growth
       patterns.  This change makes it difficult to predict future
       growth patterns of the Internet.

   As a result, we can't quantify the requirement in any meaningful way.
   Using today's architectural elements as a mechanism for describing
   things, we believe that the network could grow to:

   1.  tens of thousands of AS's

          Editors' Note: As of 2005, this level had already been
          reached.

   2.  tens to hundreds of millions of prefixes, during the lifetime of
       this architecture.

   These sizes are given as a 'flavor' for how we expect the Internet to
   grow.  We fully believe that any new architecture may eliminate some
   current architectural elements and introduce new ones.

   A new routing and addressing architecture designed for a specific
   network size would be inappropriate.  First, the cost of routing
   calculations is based only in part on the number of AS's or prefixes
   in the network.  The number and locations of the links in the network
   are also significant factors.  Second, past predictions of Internet
   growth and topology patterns have proven to be wildly inaccurate so
   developing an architecture to a specific size goal would at best be
   shortsighted.

      Editors' note: At the time of these meetings, the BGP statistics
      kept at sites such as www.routeviews.org either did not exist or
      had been running for only a few months.  After 5 years of
      recording public Internet data trends in AS growth, routing table
      growth can be observed (past) with some short term prediction.  As
      each year of data collection continues the ability to observe and
      predict trends improves.  This architecture work pointed out the
      need for such statistics to improve future routing designs.

   Therefore we will not make the scaling requirement based on a
   specific network size.  Instead, the new routing and addressing
   architecture should have the ability to constrain the increase in
   load (CPU, memory space and bandwidth, and network bandwidth) on ANY
   SINGLE ROUTER to be less than these specific functions:





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   1.  The computational power and memory sizes required to execute the
       routing protocol software and to contain the tables must grow
       more slowly than hardware capabilities described by Moore's Law,
       doubling every 18 months.  Other observations indicate that
       memory sizes double every 2 years or so.

   2.  Network bandwidth and latency are some key constraints on how
       fast routing protocol updates can be disseminated (and therefore
       how fast the routing system can adapt to changes).  Raw network
       bandwidth seems to quadruple every 3 years or so.  However, it
       seems that there are some serious physics problems in going
       faster than 40Gbit/s (OC768); we should not expect raw network
       link speed to grow much beyond OC768.  On the other hand, for
       economic reasons, large swathes of the core of the Internet will
       still operate at lower speeds, possibly as slow as DS3.

          Editors' Note: Technology is running ahead of imagination and
          higher speeds are already common.

       Furthermore, in some sections of the Internet even lower speed
       links are found.  Corporate access links are often T1, or slower.
       Low-speed radio links exist.  Intra-domain links may be T1 or
       fractional-T1 (or slower).

       Therefore, the architecture must not make assumptions about the
       bandwidth available.

   3.  The speeds of high-speed RAMs (SRAMs, used for caches and the
       like) are growing, though slowly.  Because of their use in caches
       and other very specific applications, these RAMs tend to be
       small, a few megabits, and the size of these RAMs is not
       increasing very rapidly.

       On the other hand, the speed of "large" memories (DRAMs) is
       increasing even slower than that for the high speed RAMs.  This
       is because the development of these RAMs is driven by the PC
       market, where size is very important, and low speed can be made
       up for by better caches.

       Memory access rates should not be expected to increase
       significantly.

          Editors' Note: Various techniques have significantly increased
          memory bandwidth. 800MHz is now possible, compared with less
          than 100MHz in year 2000.  This does not, however, contradict
          the next paragraph, but rather just extends the timescales
          somewhat.




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   The growth in resources available to any one router will eventually
   slow down.  It may even stop.  Even so, the network will continue to
   grow.  The routing and addressing architecture must continue to scale
   in even this extreme condition.  We cannot continue to add more
   computing power to routers forever.  Other strategies must be
   available.  Some possible strategies are hierarchy, abstraction, and
   aggregation of topology information.

2.1.4.  Lots of Interconnectivity

   The new routing and addressing architecture must be able to cope with
   a high degree of interconnectivity in the Internet.  That is, there
   are large numbers of alternate paths and routes among the various
   elements.  Mechanisms are required to prevent this interconnectivity
   (and continued growth in interconnectivity) from causing tables,
   compute time, and routing protocol traffic to grow without bound.
   The "cost" to the routing system of an increase in complexity must be
   limited in scope; sections of the network that do not see, or do not
   care about, the complexity ought not pay the cost of that complexity.

   Over the past several years, the Internet has seen an increase in
   interconnectivity.  Individual end sites (companies, customers,
   etc.), ISPs, exchange points, and so on, all are connecting to more
   "other things".  Companies multi-home to multiple ISPs, ISPs peer
   with more ISPs, and so on.  These connections are made for many
   reasons, such as getting more bandwidth, increased reliability and
   availability, policy, and so on.  However, this increased
   interconnectivity has a price.  It leads to more scaling problems as
   it increases the number of AS paths in the networks.

   Any new architecture must assume that the Internet will become a
   denser mesh.  It must not assume, nor can it dictate, certain
   patterns or limits on how various elements of the network
   interconnect.

   Another facet of this requirement is that there may be multiple
   valid, loop free, paths available to a destination.  See
   Section 2.1.7 for a further discussion.

   We wryly note that one of the original design goals of IP was to
   support a large, heavily interconnected, network, which would be
   highly survivable (such as in the face of a nuclear war).

2.1.5.  Random Structure

   The routing and addressing architecture must not place any
   constraints on or make assumptions about the topology or
   connectedness of the elements comprising the Internet.  The routing



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   and addressing architecture must not presume any particular network
   structure.  The network does not have a "nice" structure.  In the
   past we used to believe that there was this nice "backbone/tier-1/
   tier-2/end-site" sort of hierarchy.  This is not so.  Therefore, any
   new architecture must not presume any such structure.

   Some have proposed that a geographic addressing scheme be used,
   requiring exchange points to be situated within each geographic
   'region'.  There are many reasons why we believe this to be a bad
   approach, but those arguments are irrelevant.  The main issue is that
   the routing architecture should not presume a specific network
   structure.

2.1.6.  Multi-homing

   The architecture must provide multi-homing for all elements of the
   Internet.  That is, multi-homing of hosts, subnetworks, end- sites,
   "low-level" ISPs, and backbones (i.e., lots of redundant
   interconnections) must be supported.  Among the reasons to multi-home
   are reliability, load sharing, and performance tuning.

   The term "multi-homing" may be interpreted in its broadest sense --
   one "place" has multiple connections or links to another "place".

   The architecture must not limit the number of alternate paths to a
   multi-homed site.

   When multi-homing is used, it must be possible to use one, some (more
   than one but less than all), or all of the available paths to the
   multi-homed site.  The multi-homed site must have the ability to
   declare which path(s) are used and under what conditions (for
   example, one path may be declared "primary" and the other "backup"
   and to be used only when the primary fails).

   A current problem in the Internet is that multi-homing leads to undue
   increases in the size of the BGP routing tables.  The new
   architecture must support multi-homing without undue routing table
   growth.

2.1.7.  Multi-path

   As a corollary to multi-homing, the architecture must allow for
   multiple paths from a source to a destination to be active at the
   same time.  These paths need not have the same attributes.  Policies
   are to be used to disseminate the attributes and to classify traffic
   for the different paths.

   There must be a rich "language" for specifying the rules for



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   classifying the traffic and assigning classes of traffic to different
   paths (or prohibiting it from certain paths).  The rules should allow
   traffic to be classified based upon at least the following:

   o  IPv6 FlowIDs,

   o  DSCP values,

   o  source and/or destination prefixes, or

   o  random selections at some probability.

   A mechanism is needed that allows operators to plan and manage the
   traffic load on the various paths.  To start, this mechanism can be
   semi-automatic or even manual.  Eventually it ought to become fully
   automatic.

   When multi-path forwarding is used, options must be available to
   preserve packet ordering where appropriate (such as for individual
   TCP connections).

   Please refer to Section 2.2.7 for a discussion of dynamic load-
   balancing and management over multiple paths.

2.1.8.  Convergence

   The speed of convergence (also called the "stabilization time") is
   the time it takes for a router's routing processes to reach a new,
   stable, "solution" (i.e., forwarding information base) after a change
   someplace in the network.  In effect, what happens is that the output
   of the routing calculations stabilizes -- the Nth iteration of the
   software produces the same results as the N-1th iteration.

   The speed of convergence is generally considered to be a function of
   the number of subnetworks in the network and the amount of
   connections between those networks.  As either number grows, the time
   it takes to converge increases.

   In addition, a change can "ripple" back and forth through the system.
   One change can go through the system, causing some other router to
   change its advertised connectivity, causing a new change to ripple
   through.  These oscillations can take a while to work their way out
   of the network.  It is also possible that these ripples never die
   out.  In this situation the routing and addressing system is
   unstable; it never converges.

   Finally, it is more than likely that the routers comprising the
   Internet never converge simply because the Internet is so large and



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   complex.  Assume it takes S seconds for the routers to stabilize on a
   solution for any one change to the network.  Also assume that changes
   occur, on average, every C seconds.  Because of the size and
   complexity of the Internet, C is now less than S. Therefore, if a
   change, C1, occurs at time T, the routing system would stabilize at
   time T+S, but a new change, C2, will occur at time T+C, which is
   before T+S. The system will start processing the new change before
   it's done with the old.

   This is not to say that all routers are constantly processing
   changes.  The effects of changes are like ripples in a pond.  They
   spread outward from where they occur.  Some routers will be
   processing just C1, others C2, others both C1 and C2, and others
   neither.

   We have two separate scopes over which we can set requirements with
   respect to convergence:

   1.  Single Change
       In this requirement a single change of any type (link addition or
       deletion, router failure or restart, etc.) is introduced into a
       stabilized system.  No additional changes are introduced.  The
       system must re-stabilize within some measure of bounded time.
       This requirement is a fairly abstract one as it would be
       impossible to test in a real network.  Definition of the time
       constraints remains an open research issue.

   2.  System-wide
       Defining a single target for maximum convergence time for the
       real Internet is absurd.  As we mentioned earlier, the Internet
       is large enough and diverse enough so that it is quite likely
       that new changes are introduced somewhere before the system fully
       digests old ones.

   So, the first requirement here is that there must be mechanisms to
   limit the scope of any one change's visibility and effects.  The
   number of routers that have to perform calculations in response to a
   change is kept small, as is the settling time.

   The second requirement is based on the following assumptions:

   -  the scope of a change's visibility and impact can be limited.
      That is, routers within that scope know of the change and
      recalculate their tables based on the change.  Routers outside of
      the scope don't see it at all.






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   -  Within any scope, S, network changes are constantly occurring and
      the average inter-change interval is Tc seconds.

   -  There are Rs routers within scope S.

   -  A subset of the destinations known to the routers in S, Ds, are
      impacted by a given change.

   -  We can state that for Z% of the changes, within Y% of Tc seconds
      after a change, C, X% of the Rs routers have their routes to Ds
      settled to a useful answer (useful meaning that packets can get to
      Ds, though perhaps not by the optimal path -- this allows some
      'hunting' for the optimal solution)

      X, Y, and Z are yet to be defined.  Their definition remains a
      research issue.

   This requirement implies that the scopes can be kept relatively small
   in order to minimize Rs and maximize Tc.

   The growth rate of the convergence time must not be related to the
   growth rate of the Internet as a whole.  This implies that the
   convergence time either

   1.  not be a function of basic network elements (such as prefixes and
       links/paths), and/or

   2.  that the Internet be continuously divisible into chunks that
       limit the scope and effect of a change, thereby limiting the
       number of routers, prefixes, links, and so on, involved in the
       new calculations.

2.1.9.  Routing System Security

   The security of the Internet's routing system is paramount.  If the
   routing system is compromised or attacked, the entire Internet can
   fail.  This is unacceptable.  Any new architecture must be secure.

   Architectures by themselves are not secure.  It is the implementation
   of an architecture; its protocols, algorithms, and data structures,
   that are secure.  These requirements apply primarily to the
   implementation.  The architecture must provide the elements that the
   implementation needs to meet these security requirements.  Also, the
   architecture must not prevent these security requirements from being
   met.

   Security means different things to different people.  In order for
   this requirement to be useful, we must define what we mean by



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   security.  We do this by identifying the attackers and threats we
   wish to protect against.  They are:

   Masquerading
       The system, including its protocols, must be secure against
       intruders adopting the identity of other known, trusted, elements
       of the routing system and then using that position of trust for
       carrying out other attacks.  Protocols must use cryptographically
       strong authentication.

   Denial of Service (DoS) Attacks
       The architecture and protocols should be secure against DoS
       attacks directed at the routers.

       The new architecture and protocols should provide as much
       information as it can to allow administrators to track down
       sources of DoS and Distributed DOS (DDoS) attacks.

   No Bad Data
       Any new architecture and protocols must provide protection
       against the introduction of bad, erroneous, or misleading, data
       by attackers.  Of particular importance, an attacker must not be
       able to redirect traffic flows, with the intent of

       o  directing legitimate traffic away from a target, causing a
          denial-of-service attack by preventing legitimate data from
          reaching its destination,

       o  directing additional traffic (going to other destinations
          which are 'innocent bystanders') to a target, causing the
          target to be overloaded, or

       o  directing traffic addressed to the target to a place where the
          attacker can copy, snoop, alter, or otherwise affect the
          traffic.

   Topology Hiding
       Any new architecture and protocols must provide mechanisms to
       allow network owners to hide the details of their internal
       topologies, while maintaining the desired levels of service
       connectivity and reachability.

   Privacy
       By "privacy" we mean privacy of the routing protocol exchanges
       between routers.

       When the routers are on point-to-point links, with routers at
       each end, there may not be any need to encrypt the routing



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       protocol traffic as the possibility of a third party intercepting
       the traffic is limited though not impossible.  We do believe,
       however, that it is important to have the ability to protect
       routing protocol traffic in two cases:

       1.  When the routers are on a shared network, it is possible that
           there are hosts on the network that have been compromised.
           These hosts could surreptitiously monitor the protocol
           traffic.

       2.  When two routers are exchanging information "at a distance"
           (over intervening routers and, possibly, across
           administrative domain boundaries).  In this case, the
           security of the intervening routers, links, and so on, cannot
           be assured.  Thus, the ability to encrypt this traffic is
           important.

       Therefore, we believe that the option to encrypt routing protocol
       traffic is required.

   Data Consistency
       A router should be able to detect and recover from any data that
       is received from other routers which is inconsistent.  That is,
       it must not be possible for data from multiple routers, none of
       which is malicious, to "break" another router.

   Where security mechanisms are provided, they must use methods that
   are considered to be cryptographically secure (e.g., using
   cryptographically strong encryption and signatures -- no clear text
   passwords!).

   Use of security features should not be optional (except as required
   above).  This may be "social engineering" on our part, but we believe
   it to be necessary.  If a security feature is optional, the
   implementation of the feature must default to the "secure" setting.

2.1.10.  End Host Security

   The architecture must not prevent individual host-to-host
   communications sessions from being secured (i.e., it cannot interfere
   with things like IPsec).

2.1.11.  Rich Policy

   Before setting out Policy requirements, we need to define the term.
   Like "security", "policy" means many things to many people.  For our
   purposes, policy is the set of administrative influences that alter
   the path determination and next-hop selection procedures of the



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   routing software.

   The main motivators for influencing path and next-hop selection seem
   to be transit rules, business decisions, and load management.

   The new architecture must support rich policy mechanisms.
   Furthermore, the policy definition and dissemination mechanisms
   should be separated from the network topology and connectivity
   dissemination mechanisms.  Policy provides input to and controls the
   generation of the forwarding table and the abstraction, filtering,
   aggregation, and dissemination of topology information.

   Note that if the architecture is properly divided into subsystems
   then at a later time, new policy subsystems that include new features
   and capabilities could be developed and installed as needed.

   We divide the general area of policy into two sub-categories, routing
   information and traffic control.  Routing Information Policies
   control what routing information is disseminated or accepted, how it
   is disseminated, and how routers determine paths and next-hops from
   the received information.  Traffic Control Policies determine how
   traffic is classified and assigned to routes.

2.1.11.1.  Routing Information Policies

   There must be mechanisms to allow network administrators, operators,
   and designers to control receipt and dissemination of routing
   information.  These controls include, but are not limited to:

   -  Selecting to which other routers routing information will be
      transmitted.

   -  Specifying the "granularity" and type of transmitted information.
      The length of IPv4 prefixes is an example of "granularity".

   -  Selection and filtering of topology and service information that
      is transmitted.  This gives different 'views' of internal
      structure and topology to different peers.

   -  Selecting the level of security and authenticity for transmitted
      information.

   -  Being able to cause the level of detail that is visible for some
      portion of the network to reduce the farther you get from that
      part of the network.






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   -  Selecting from whom routing information will be accepted.  This
      control should be "provisional" in the sense of "accept routes
      from "foo" only if there are no others available".

   -  Accepting or rejecting routing information based on the path the
      information traveled (using the current system as an example, this
      would be filtering routes based on an AS appearing anywhere in the
      AS path).  This control should be "use only if there are no other
      paths available".

   -  Selecting the desired level of "granularity" for received routing
      information (this would include, but is not limited to, things
      similar in nature to the prefix-length filters widely used in the
      current routing and addressing system).

   -  Selecting the level of security and authenticity of received
      information in order for that information to be accepted.

   -  Determining the treatment of received routing information based on
      attributes supplied with the information.

   -  Applying attributes to routing information that is to be
      transmitted and then determining treatment of information (e.g.,
      sending it "here" but not "there") based on those tags.

   -  Selection and filtering of topology and service information that
      is received.

2.1.11.2.  Traffic Control Policies

   The architecture should provide mechanisms that allow network
   operators to manage and control the flow of traffic.  The traffic
   controls should include, but are not limited to:

   - The ability to detect and eliminate congestion points in the
   network (by re-directing traffic around those points)

   - The ability to develop multiple paths through the network with
   different attributes and then assign traffic to those paths based on
   some discriminators within the packets (discriminators include, but
   are not limited to, IP Addresses or prefixes, IPv6 flow ID, DSCP
   values, and MPLS labels)

   - The ability to find and use multiple, equivalent, paths through the
   network (i.e., they would have the "same" attributes) and allocate
   traffic across the paths.

   - The ability to accept or refuse traffic based on some traffic



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   classification (providing, in effect, transit policies).

   Traffic classification must at least include the source and
   destination IP addresses (prefixes) and the DSCP value.  Other fields
   may be supported, such as

   o  Protocol and port based functions,

   o  DSCP/QoS tuple (such as ports)

   o  Per-host operations (i.e., /32s for IPv4 and /128s for IPv6),

   o  Traffic matrices (e.g., traffic from prefix X and to prefix Y).

2.1.12.  Incremental Deployment

   The reality of the Internet is that there can be no Internet wide cut
   over from one architecture and protocol to another.  This means that
   any new architecture and protocol must be incrementally deployable;
   ISPs must be able to set up small sections of the new architecture,
   check it out, and then slowly grow the sections.  Eventually, these
   sections will "touch" and "squeeze out" the old architecture.

   The protocols that implement the architecture must be able to
   interoperate at "production levels" with currently existing routing
   protocols.  Furthermore, the protocol specifications must define how
   the interoperability is done.

   We also believe that sections of the Internet will never convert over
   to the new architecture.  Thus, it is important that the new
   architecture and its protocols be able to interoperate with "old
   architecture" regions of the network indefinitely.

   The architecture's addressing system must not force existing address
   allocations to be redone: no renumbering!

2.1.13.  Mobility

   There are two kinds of mobility; host mobility and network mobility.
   Host mobility is when an individual host moves from where it was to
   where it is.  Network mobility is when an entire network (or
   subnetwork) moves.

   The architecture must support network level mobility.  Please refer
   to Section 2.2.9 for a discussion of Host Mobility.






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      Editor's Note: Since the time of this work, the NEMO extensions to
      Mobile IP [RFC3963] to accommodate mobile networks have been
      developed.

2.1.14.  Address Portability

   One of the big "hot items" in the current Internet political climate
   is portability of IP addresses (both v4 and v6).  The short
   explanation is that people do not like to renumber when changing
   connection point or provider and do not trust automated renumbering
   tools.

   The architecture must provide complete address portability.

2.1.15.  Multi-Protocol

   The Internet is expected to be "multi-protocol" for at least the next
   several years.  IPv4 and IPv6 will co-exist in many different ways
   during a transition period.  The architecture must be able to handle
   both IPv4 and IPv6 addresses.  Furthermore, protocols that supplant
   IPv4 and IPv6 may be developed and deployed during the lifetime of
   the architecture.  The architecture must be flexible and extensible
   enough to handle new protocols as they arise.

   Furthermore, the architecture must not assume any given relationships
   between a topological element's IPv4 address and its IPv6 address.
   The architecture must not assume that all topological elements have
   IPv4 addresses/prefixes, nor can it assume that they have IPv6
   addresses/prefixes.

   The architecture should allow different paths to the same destination
   to be used for different protocols, even if all paths can carry all
   protocols.

   In addition to the addressing technology, the architecture need not
   be restricted to only packet based multiplexing/demultiplexing
   technology (such as IP); support for other multiplexing/
   demultiplexing technologies may be added.

2.1.16.  Abstraction

   The architecture must provide mechanisms for network designers and
   operators to:

   o  Group elements together for administrative control purposes,






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   o  Hide the internal structure and topology of those groupings for
      administrative and security reasons,

   o  Limit the amount of topology information that is exported from the
      groupings in order to control the load placed on external routers,

   o  Define rules for traffic transiting or terminating in the
      grouping.

   The architecture must allow the current Autonomous System structure
   to be mapped into any new abstraction schemes.

   Mapping mechanisms, algorithms, and techniques must be specified.

2.1.17.  Simplicity

   The architecture must be simple enough so that someone who is
   extremely knowledgeable in routing and who is skilled at creating
   straightforward and simple explanations can explain all the important
   concepts in less than an hour.

   This criterion has been chosen since developing an objective measure
   of complexity for an architecture can be very difficult and is out of
   scope for this document.

   The requirement is that the routing architecture be kept as simple as
   possible.  This requires careful evaluation of possible features and
   functions with a merciless weeding out of those that "might be nice"
   but are not necessary.

   By keeping the architecture simple, the protocols and software used
   to implement the architecture are simpler.  This simplicity in turn
   leads to:

   1.  Faster implementation of the protocols.  If there are fewer bells
       and whistles, then there are fewer things that need to be
       implemented.

   2.  More reliable implementations.  With fewer components, there is
       less code, reducing bug counts, and fewer interactions between
       components that could lead to unforeseen and incorrect behavior.

2.1.18.  Robustness

   The architecture, and the protocols implementing it, should be
   robust.  Robustness comes in many different flavors.  Some
   considerations with regard to robustness include (but are not limited
   to):



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   o  Continued correct operation in the face of:

      *  Defective (even malicious) trusted routers.

      *  Network failures.  Whenever possible, valid alternate paths are
         to be found and used.

   o  Failures must be localized.  That is, the architecture must limit
      the "spread" of any adverse effects of a misconfiguration or
      failure.  Badness must not spread.

   Of course, the general robustness principle of being liberal in
   what's accepted and conservative in what's sent must also be applied.

   Original Editor's note:
                    Some of the contributors to this section have argued
                    that robustness is an aspect of Security.  I have
                    exercised editor's discretion by making it a
                    separate section.  The reason for this is that to
                    too many people "security" means "protection from
                    break-ins" and "authenticating and encrypting data".
                    This requirement goes beyond those views.

2.1.19.  Media Independence

   While it is an article of faith that IP operates over a wide variety
   of media (such as Ethernet, X.25, ATM, and so on), IP routing must
   take an agnostic view toward any "routing" or "topology" services
   that are offered by the medium over which IP is operating.  That is,
   the new architecture must not be designed to integrate with any
   media-specific topology management or routing scheme.

   The routing architecture must assume, and must work over, the
   simplest possible media.

   The routing and addressing architecture can certainly make use of
   lower-layer information and services, when and where available, and
   to the extent that IP routing wishes.

2.1.20.  Stand-alone

   The routing architecture and protocols must not rely on other
   components of the Internet (such as DNS) for their correct operation.
   Routing is the fundamental process by which data "finds its way
   around the Internet" and most, if not all, of those other components
   rely on routing to properly forward their data.  Thus, Routing cannot
   rely on any Internet systems, services or capabilities that in turn
   rely on Routing.  If it did, a dependency loop would result.



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2.1.21.  Safety of Configuration

   The architecture, protocols, and standard implementation defaults
   must be such that a router installed "out of the box" with no
   configuration, etc., by the operators will not cause "bad things" to
   happen to the rest of the routing system (e.g., no dial-up customers
   advertising routes to 18/8!)

2.1.22.  Renumbering

   The routing system must allow topological entities to be renumbered.

2.1.23.  Multi-prefix

   The architecture must allow topological entities to have multiple
   prefixes (or the equivalent under the new architecture).

2.1.24.  Cooperative Anarchy

   As RFC1726[RFC1726] said:
      "A major contributor to the Internet's success is the fact that
      there is no single, centralized, point of control or promulgator
      of policy for the entire network.  This allows individual
      constituents of the network to tailor their own networks,
      environments, and policies to suit their own needs.  The
      individual constituents must cooperate only to the degree
      necessary to ensure that they interoperate."

   This decentralization, called "cooperative anarchy", is still a key
   feature of the Internet today.  The new routing architecture must
   retain this feature.  There can be no centralized point of control or
   promulgator of policy for the entire Internet.

2.1.25.  Network Layer Protocols and Forwarding Model

   For the purposes of backward compatibility, any new routing and
   addressing architecture and protocols must work with IPv4 and IPv6
   using the traditional "hop by hop" forwarding and packet-based
   multiplex/demultiplex models.  However, the architecture need not be
   restricted to these models.  Additional forwarding and multiplex/
   demultiplex models may be added.

2.1.26.  Routing Algorithm

   The architecture should not require a particular routing algorithm
   family.  That is to say, the architecture should be agnostic about
   link-state, distance-vector, or path-vector routing algorithms.




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2.1.27.  Positive Benefit

   Finally, the architecture must show benefits in terms of increased
   stability, decreased operational costs, and increased functionality
   and lifetime, over the current schemes.  This benefit must remain
   even after the inevitable costs of developing and debugging the new
   protocols, enduring the inevitable instabilities as things get shaken
   out, and so on.

2.1.28.  Administrative Entities and the IGP/EGP Split

   We explicitly recognize that the Internet consists of resources under
   control of multiple administrative entities.  Each entity must be
   able to manage its own portion of the Internet as it sees fit.
   Moreover, the constraints that can be imposed on routing and
   addressing on the portion of the Internet under the control of one
   administration may not be feasibly extended to cover multiple
   administrations.  Therefore, we recognize a natural and inevitable
   split between routing and addressing that is under a single
   administrative control and routing and addressing that involves
   multiple administrative entities.  Moreover, while there may be
   multiple administrative authorities, the administrative authority
   boundaries may be complex and overlapping, rather than being a strict
   hierarchy.

   Furthermore, there may be multiple levels of administration, each
   with its own level of policy and control.  For example, a large
   network might have "continental-level" administrations covering its
   European and Asian operations, respectively.  There would also be
   that network's "inter-continental" administration covering the
   Europe-to-Asia links.  Finally, there would be the "Internet" level
   in the administrative structure (analogous to the "exterior" concept
   in the current routing architecture).

   Thus, we believe that the administrative structure of the Internet
   must be extensible to many levels (more than the two provided by the
   current IGP/EGP split).  The interior/exterior property is not
   absolute.  The interior/exterior property of any point in the network
   is relative; a point on the network is interior with respect to some
   points on the network and exterior with respect to others.

   Administrative entities may not trust each other; some may be almost
   actively hostile toward each other.  The architecture must
   accommodate these models.  Furthermore, the architecture must not
   require any particular level of trust among administrative entities.






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2.2.  Non-Requirements

   The following are not required or are non-goals.  This should not be
   taken to mean that these issues must not be addressed by a new
   architecture.  Rather, addressing these issues or not is purely an
   optional matter for the architects.

2.2.1.  Forwarding Table Optimization

   We believe that it is not necessary for the architecture to minimize
   the size of the forwarding tables (FIBs).  Current memory sizes,
   speeds, and prices, along with processor and ASIC capabilities allow
   forwarding tables to be very large, O(E6), and allow fast (100M
   lookups/second) tables to be built with little difficulty.

2.2.2.  Traffic Engineering

   Traffic Engineering is one of those terms that has become terribly
   overloaded.  If one asks N people what traffic engineering is, one
   would get something like N! disjoint answers.  Therefore, we elect
   not to require "traffic engineering", per se.  Instead, we have
   endeavored to determine what the ultimate intent is when operators
   "traffic engineer" their networks and then make those capabilities an
   inherent part of the system.

2.2.3.  Multicast

   The new architecture is not designed explicitly to be an inter-domain
   multicast routing architecture.  However, given the notable lack of a
   viable, robust, and widely deployed inter-domain multicast routing
   architecture, the architecture should not hinder the development and
   deployment of inter-domain multicast routing without adverse effect
   on meeting the other requirements.

   We do note however that one respected network sage [Clark91] has said
   (roughly)

      "When you see a bunch of engineers standing around congratulating
      themselves for solving some particularly ugly problem in
      networking, go up to them, whisper "multicast", jump back, and
      watch the fun begin..."

2.2.4.  Quality of Service (QoS)

   The architecture concerns itself primarily with disseminating network
   topology information so that routers may select paths to destinations
   and build appropriate forwarding tables.  Quality of Service (QoS) is
   not a part of this function and we make no requirements with respect



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   to QoS.

   However, QoS is an area of great and evolving interest.  It is
   reasonable to expect that in the not too distant future,
   sophisticated QoS facilities will be deployed in the Internet.  Any
   new architecture and protocols should be developed with an eye toward
   these future evolutions.  Extensibility mechanisms, allowing future
   QoS routing and signaling protocols to "piggy-back" on top of the
   basic routing system are desired.

   We do require the ability to assign attributes to entities and then
   do path generation and selection based on those attributes.  Some may
   call this QoS.

2.2.5.  IP Prefix Aggregation

   There is no specific requirement that CIDR-style IP Prefix
   aggregation be done by the new architecture.  Address allocation
   policies, societal pressure, and the random growth and structure of
   the Internet have all conspired to make prefix aggregation
   extraordinarily difficult, if not impossible.  This means that large
   numbers of prefixes will be sloshing about in the routing system and
   that forwarding tables will grow quite big.  This is a cost that we
   believe must be borne.

   Nothing in this non-requirement should be interpreted as saying that
   prefix aggregation is explicitly prohibited.  CIDR-style IP Prefix
   aggregation might be used as a mechanism to meet other requirements,
   such as scaling.

2.2.6.  Perfect Safety

   Making the system impossible to mis-configure is, we believe, not
   required.  The checking, constraints, and controls necessary to
   achieve this could, we believe, prevent operators from performing
   necessary tasks in the face of unforeseen circumstances.

   However, safety is always a "good thing", and any results from
   research in this area should certainly be taken into consideration
   and, where practical, incorporated into the new routing architecture.

2.2.7.  Dynamic Load Balancing

   Past history has shown that using the routing system to perform
   highly dynamic load balancing among multiple more-or-less-equal paths
   usually ends up causing all kinds of instability, etc., in the
   network.  Thus, we do not require such a capability.




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   However, this is an area that is ripe for additional research, and
   some believe that the capability will be necessary in the future.
   Thus, the architecture and protocols should be "malleable" enough to
   allow development and deployment of dynamic load balancing
   capabilities, should we ever figure out how to do it.

2.2.8.  Renumbering of Hosts and Routers

   We believe that the routing system is not required to "do
   renumbering" of hosts and routers.  That's an IP issue.

   Of course, the routing and addressing architecture must be able to
   deal with renumbering when it happens.

2.2.9.  Host Mobility

   In the Internet architecture, host-mobility is handled on a per-host
   basis by a dedicated, Mobile-IP protocol [RFC3344].  Traffic destined
   for a mobile-host is explicitly forwarded by dedicated relay agents.
   Mobile-IP [RFC3344] adequately solves the host-mobility problem and
   we do not see a need for any additional requirements in this area.
   Of course, the new architecture must not impede or conflict with
   Mobile-IP.

2.2.10.  Backward Compatibility

   For the purposes of development of the architecture, we assume that
   there is a 'clean slate'.  Unless specified in Section 2.1, there are
   no explicit requirements that elements, concepts, or mechanisms of
   the current routing architecture be carried forward into the new one.





















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3.  Requirements from Group B

   The following is the result of the work done by Sub-Group B of the
   IRTF-RRG in 2001-2002.  It was originally released under the title:
   "Future Domain Routing Requirements" and was edited by Avri Doria and
   Elwyn Davies.

3.1.  Group B - Future Domain Routing Requirements

   It is generally accepted that there are major shortcomings in the
   inter-domain routing of the Internet today and that these may result
   in meltdown within an unspecified period of time.  Remedying these
   shortcomings will require extensive research to tie down the exact
   failure modes that lead to these shortcomings and identify the best
   techniques to remedy the situation.

   Changes in the nature and quality of the services that users want
   from the Internet are difficult to provide within the current
   framework, as they impose requirements never foreseen by the original
   architects of the Internet routing system.

   The kind of radical changes that have to be accommodated are
   epitomized by the advent of IPv6 and the application of IP mechanisms
   to private commercial networks that offer specific service guarantees
   beyond the best-effort services of the public Internet.  Major
   changes to the inter-domain routing system are inevitable to provide
   an efficient underpinning for the radically changed and increasingly
   commercially-based networks that rely on the IP protocol suite.

3.2.  Underlying Principles

   Although inter-domain routing is seen as the major source of
   problems, the interactions with intra-domain routing, and the
   constraints that confining changes to the inter-domain arena would
   impose, mean that we should consider the whole area of routing as an
   integrated system.  This is done for two reasons:

   -  Requirements should not presuppose the solution.  A continued
      commitment to the current definitions and split between inter-
      domain and intra-domain routing would constitute such a
      presupposition.  Therefore this part of the document uses the name
      Future Domain Routing (FDR).

   -  It is necessary to understand the degree to which inter-domain and
      intra-domain routing are related within today's routing
      architecture.

   We are aware that using the term "domain routing" is already fraught



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   with danger because of possible misinterpretation due to prior usage.
   The meaning of "domain routing" will be developed implicitly
   throughout the document, but a little advance explicit definition of
   the word 'domain' is required, as well as some explanation on the
   scope of 'routing'.

   This document uses "domain" in a very broad sense, to mean any
   collection of systems or domains that come under a common authority
   that determines the attributes defining, and the policies
   controlling, that collection.  The use of domain in this manner is
   very similar to the concept of region that was put forth by John
   Wroclawski in his Metanet model [Wroclawski95].  The idea includes
   the notion that certain attributes will characterize the behavior of
   the systems within a domain and that there will be borders between
   domains.  The idea of domain presented here does not presuppose that
   two domains will have the same behavior.  Nor does it presuppose
   anything about the hierarchical nature of domains.  Finally, it does
   not place restrictions on the nature of the attributes that might be
   used to determine membership in a domain.  Since today's routing
   domains are an example of the concept of domains in this document,
   there has been no attempt to create a new term.

   Current practice in routing system design stresses the need to
   separate the concerns of the control plane and the forwarding plane
   in a router.  This document will follow this practice, but we still
   use the term "routing" as a global portmanteau to cover all aspects
   of the system.  Specifically, however, routing will be used to mean
   the process of discovering, interpreting, and distributing
   information about the logical and topological structure of the
   network.

3.2.1.  Inter-domain and Intra-domain

   Throughout this section the terms intra-domain and inter-domain will
   be used.  These should be understood as relative terms.  In all cases
   of domains, there will be a set of network systems that are within
   that domain; routing between these systems will be termed intra-
   domain.  In some cases there will be routing between domains, which
   will be termed inter-domain.  It is possible that the routing
   exchange between two network systems can be viewed as intra-domain
   from one perspective and as inter-domain from another perspective.

3.2.2.  Influences on a Changing Network

   The development of the Internet is likely to be driven by a number of
   changes that will affect the organization and the usage of the
   network, including:




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   -  Ongoing evolution of the commercial relationships between
      (connectivity) service providers, leading to changes in the way in
      which peering between providers is organized and the way in which
      transit traffic is routed.

   -  Requirements for traffic engineering within and between domains
      including coping with multiple paths between domains.

   -  Addition of a second IP addressing technique, in the form of IPv6.

   -  The use of VPNs and private address space with IPv4 and IPv6.

   -  Evolution of the end-to-end principle to deal with the expanded
      role of the Internet, as discussed in [Blumenthal01]: This paper
      discusses the possibility that the range of new requirements,
      especially the social and techno-political ones that are being
      placed on the future, may compromise the Internet's original
      design principles.  This might cause the Internet to lose some of
      its key features, in particular its ability to support new and
      unanticipated applications.  This discussion is linked to the rise
      of new stakeholders in the Internet, especially ISPs; new
      government interests; the changing motivations of the ever growing
      user base; and the tension between the demand for trustworthy
      overall operation and the inability to trust the behaviour of
      individual users.

   -  Incorporation of alternative forwarding techniques such as the
      explicit routing (pipes) supplied by the MPLS [RFC3031] and GMPLS
      [RFC3471] environments.

   -  Integration of additional constraints into route determination
      from interactions with other layers (e.g., Shared Risk Link Groups
      [I-D.many-inference-srlg]).  This includes the concern that
      redundant routes should not fate-share, e.g., because they
      physically run in the same trench.

   -  Support for alternative and multiple routing techniques that are
      better suited to delivering types of content organised in ways
      other than into IP addressed packets.

   Philosophically, the Internet has the mission of transferring
   information from one place to another.  Conceptually, this
   information is rarely organised into conveniently sized, IP-addressed
   packets, and the FDR needs to consider how the information (content)
   to be carried is identified, named and addressed.  Routing techniques
   can then be adapted to handle the expected types of content.





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3.2.3.  High Level Goals

   This section attempts to answer two questions:

   -  What are we trying to achieve in a new architecture?

   -  Why should the Internet community care?

   There is a third question that needs to be answered as well, but that
   has seldom been explicitly discussed:

   -  How will we know when we have succeeded?

3.2.3.1.  Providing a Routing System Matched to Domain Organization

   Many of today's routing problems are caused by a routing system that
   is not well matched to the organization and policies that it is
   trying to support.  Our goal is to develop a routing architecture
   where even a domain organization that is not envisioned today can be
   served by a routing architecture that matches its requirements.  We
   will know when this goal is achieved when the desired policies,
   rules, and organization can be mapped into the routing system in a
   natural, consistent, and simply understood way.

3.2.3.2.  Supporting a Range of Different Communication Services

   Today's routing protocols only support a single data forwarding
   service that is typically used to deliver a best-effort service in
   the public Internet.  On the other hand, DiffServ for example, can
   construct a number of different bit transport services within the
   network.  Using some of the per-domain behaviors (PDB)s that have
   been discussed in the IETF, it is possible to construct services such
   as Virtual Wire [I-D.ietf-diffserv-pdb-vw] and Assured Rate
   [I-D.ietf-diffserv-pdb-ar].

   Providers today offer rudimentary promises about traffic handling in
   the network, for example delay and long-term packet loss guarantees.
   As time goes on, this becomes even more relevant.  Communicating the
   service characteristics of paths in routing protocols will be
   necessary in the near future, and it will be necessary to be able to
   route packets according to their service requirements.

   Thus, a goal of this architecture is to allow adequate information
   about path service characteristics to be passed between domains and
   consequently, to allow the delivery of bit transport services other
   than the best-effort datagram connectivity service that is the
   current common denominator.




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3.2.3.3.  Scalable Well Beyond Current Predictable Needs

   Any proposed FDR system should scale beyond the size and performance
   we can foresee for the next ten years.  The previous IDR proposal as
   implemented by BGP, has, with some massaging, held up for over ten
   years.  In that time the Internet has grown far beyond the
   predictions that were implied by the original requirements.

   Unfortunately, we will only know if we have succeeded in this goal if
   the FDR system survives beyond its design lifetime without serious
   massaging.  Failure will be much easier to spot!

3.2.3.4.  Alternative Forwarding Mechanisms

   With the advent of circuit-based technologies (e.g., MPLS [RFC3031]
   and GMPLS [RFC3471]) managed by IP routers there are forwarding
   mechanisms other than the datagram service that need to be supported
   by the routing architecture.

   An explicit goal of this architecture is to add support for
   forwarding mechanisms other then the current hop-by-hop datagram
   forwarding service driven by globally unique IP addresses.

3.2.3.5.  Separation of Topology Map from Connectivity Service

   It is envisioned that an organization can support multiple services
   within a single network.  These services can, for example, be of
   different quality, of different connectivity type, or of different
   protocols (e.g., IPv4 and IPv6).  For all these services there may be
   common domain topology, even though the policies controlling the
   routing of information might differ from service to service.  Thus, a
   goal with this architecture is to support separation between creation
   of a domain (or organization) topology map and service creation.

3.2.3.6.  Separation Between Routing and Forwarding

   The architecture of a router is composed of two main separable parts,
   control and forwarding.  These components, while inter-dependent,
   perform functions that are largely independent of each other.
   Control (routing, signaling, and management) is typically done in
   software while forwarding typically is done with specialized ASICs or
   network processors.

   The nature of an IP-based network today is that control and data
   protocols share the same network and forwarding regime.  This may not
   always be the case in future networks, and we should be careful to
   avoid building in this sharing as an assumption in the FDR.




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   A goal of this architecture is to support full separation of control
   and forwarding, and to consider what additional concerns might be
   properly considered separately (e.g., adjacency management).

3.2.3.7.  Different Routing Paradigms in Different Areas of the Same
          Network

   A number of routing paradigms have been used or researched, in
   addition to the conventional shortest path by hop count paradigm that
   is the current mainstay of the Internet.  In particular, differences
   in underlying transport networks may mean that other kinds of routing
   are more relevant, and the perceived need for traffic engineering
   will certainly alter the routing chosen in various domains.

   Explicitly, one of these routing paradigms should be the current
   routing paradigm, so that the new paradigms will inter-operate in a
   backward-compatible way with today's system.  This will facilitate a
   migration strategy that avoids flag days.

3.2.3.8.  Protection Against Denial of Service and Other Security
          Attacks

   Currently, existence of a route to a destination effectively implies
   that anybody who can get a packet onto the network is entitled to use
   that route.  Whilst there are limitations to this generalization,
   this is a clear invitation to denial of service attacks.  A goal of
   the FDR system should be to allow traffic to be specifically linked
   to whole or partial routes so that a destination or link resources
   can be protected from unauthorized use.

      Editors' note: When sections like this one and the previous ones
      on quality differentiation were written, the idea of separating
      traffic for security or quality was considered an unqualified
      advantage.  Today, however, in the midst of active discussions on
      Network Neutrality, it is clear that such issues have a crucial
      policy component that also needs to be understood.  These, and
      other similar issues are open to further research.

3.2.3.9.  Provable Convergence with Verifiable Policy Interaction

   It has been shown both analytically by Griffin et al (see
   [Griffin99]) and practically (see [RFC3345]) that BGP will not
   converge stably or is only meta-stable (i.e., will not re-converge in
   the face of a single failure) when certain types of policy constraint
   are applied to categories of network topology.  The addition of
   policy to the basic distance vector algorithm invalidates the proofs
   of convergence that could be applied to a policy free implementation.




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   It has also been argued that global convergence may no longer be a
   necessary goal and that local convergence may be all that is
   required.

   A goal of the FDR should be to achieve provable convergence of the
   protocols used which may involve constraining the topologies and
   domains subject to convergence.  This will also require vetting the
   policies imposed to ensure that they are compatible across domain
   boundaries and result in a consistent policy set.

      Editors' note: This requirement is very optimistic in that it
      implies that it is possible to get operators to cooperate even it
      is seen by them to be against their business practices.  Though
      perhaps Utopian, this is a good goal.

3.2.3.10.  Robustness Despite Errors and Failures

   From time to time in the history of the Internet there have been
   occurrences where mis-configured routers have destroyed global
   connectivity.

   A goal of the FDR is to be more robust to configuration errors and
   failures.  This should probably involve ensuring that the effects of
   misconfiguration and failure can be confined to some suitable
   locality of the failure or misconfiguration.

3.2.3.11.  Simplicity in Management

   The policy work ([rap-charter02], [snmpconf-charter02] and
   [policy-charter02] ) that has been done at IETF provides an
   architecture that standardizes and simplifies management of QoS.
   This kind of simplicity is needed in a Future Domain Routing
   architecture and its protocols.

   A goal of this architecture is to make configuration and management
   of inter-domain routing as simple as possible.

      Editors' Note: Snmpconf and rap are the hopes of the past.  Today
      configuration and policy hope is focused on netconf
      [netconf-charter].

3.2.3.12.  The Legacy of RFC1126

   RFC1126 outlined a set of requirements that were used to guide the
   development of BGP.  While the network has changed in the years since
   1989, many of the same requirements remain.  A future domain routing
   solution has to support, as its base requirement, the level of
   function that is available today.  A detailed discussion of RFC1126



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   and its requirements can be found in [I-D.irtf-routing-history].
   Those requirements, while specifically spelled out in that document,
   are subsumed by the requirements in this document.

3.3.  High Level User Requirements

   This section considers the requirements imposed by the target
   audience of the FDR both in terms of organizations that might own
   networks that would use FDR, and the human users who will have to
   interact with the FDR.

3.3.1.  Organisational Users

   The organizations that own networks connected to the Internet have
   become much more diverse since RFC1126 [RFC1126] was published.  In
   particular, major parts of the network are now owned by commercial
   service provider organizations in the business of making profits from
   carrying data traffic.

3.3.1.1.  Commercial Service providers

   The routing system must take into account the commercial service
   provider's need for secrecy and security, as well as allowing them to
   organize their business as flexibly as possible.

   Service providers will often wish to conceal the details of the
   network from other connected networks.  So far as is possible, the
   routing system should not require the service providers to expose
   more details of the topology and capability of their networks than is
   strictly necessary.

   Many service providers will offer contracts to their customers in the
   form of Service Level Agreements (SLAs).  The routing system must
   allow the providers to support these SLAs through traffic engineering
   and load balancing as well as multi-homing, providing the degree of
   resilience and robustness that is needed.

   Service providers can be categorized as:

   -  Global Service Providers (GSPs) whose networks have a global
      reach.  GSPs may, and usually will, wish to constrain traffic
      between their customers to run entirely on their networks.  GSPs
      will interchange traffic at multiple peering points with other
      GSPs, and they will need extensive policy-based controls to
      control the interchange of traffic.  Peering may be through the
      use of dedicated private lines between the partners or,
      increasingly, through Internet Exchange Points.




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   -  National, or regional, Service Providers (NSPs) that are similar
      to GSPs but typically cover one country.  NSPs may operate as a
      federation that provides similar reach to a GSP and may wish to be
      able to steer traffic preferentially to other federation members
      to achieve global reach.

   -  Local Internet Service Providers (ISPs) operate regionally.  They
      will typically purchase transit capacity from NSPs or GSPs to
      provide global connectivity, but they may also peer with
      neighbouring, and sometimes distant, ISPs.

   The routing system should be sufficiently flexible to accommodate the
   continually changing business relationships of the providers and the
   various levels of trustworthiness that they apply to customers and
   partners.

   Service providers will need to be involved in accounting for Internet
   usage and monitoring the traffic.  They may be involved in government
   action to tax the usage of the Internet, enforce social mores and
   intellectual property rules, or apply surveillance to the traffic to
   detect or prevent crime.

3.3.1.2.  Enterprises

   The leaves of the network domain graph are in many cases networks
   supporting a single enterprise.  Such networks cover an enormous
   range of complexity.  Some multi-national companies own networks that
   rival the complexity and reach of a GSP, whereas many fall into the
   Small Office-Home Office (SOHO) category.  The routing system should
   allow simple and robust configuration and operation for the SOHO
   category, while effectively supporting the larger enterprise.

   Enterprises are particularly likely to lack the capability to
   configure and manage a complex routing system, and every effort
   should be made to provide simple configuration and operation for such
   networks.

   Enterprises will also need to be able to change their service
   provider with ease.  While this is predominantly a naming and
   addressing issue, the routing system must be able to support seamless
   changeover, for example, if the changeover requires a change of
   address prefix, the routing system must be able to cope with a period
   when both sets of addresses are in use.

   Enterprises will wish to be able to multi-home to one or more
   providers as one possible means of enhancing the resilience of their
   network.




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   Enterprises will also frequently need to control the trust that they
   place both in workers and external connections through firewalls and
   similar mid-boxes placed at their external connections.

3.3.1.3.  Domestic Networks

   Increasingly domestic, i.e., non-business home, networks are likely
   to be 'always on' and will resemble SOHO enterprises networks with no
   special requirements on the routing system.

   The routing system must also continue to support dial-up users.

3.3.1.4.  Internet Exchange Points

   Peering of service providers, academic networks, and larger
   enterprises is increasingly happening at specific Internet Exchange
   Points where many networks are linked together in a relatively small
   physical area.  The resources of the exchange may be owned by a
   trusted third party or owned jointly by the connecting networks.  The
   routing systems should support such exchange points without requiring
   the exchange point to either operate as a superior entity with every
   connected network logically inferior to it or by requiring the
   exchange point to be a member of one (or all) connected networks.
   The connecting networks have to delegate a certain amount of trust to
   the exchange point operator.

3.3.1.5.  Content Providers

   Content providers are at one level a special class of enterprise, but
   the desire to deliver content efficiently means that a content
   provider may provide multiple replicated origin servers or caches
   across a network.  These may also be provided by a separate content
   delivery service.  The routing system should facilitate delivering
   content from the most efficient location.

3.3.2.  Individual Users

   This section covers the most important human users of the FDR and
   their expected interactions with the system.

3.3.2.1.  All End Users

   The routing system must continue to deliver the current global
   connectivity service (i.e., any unique address to any other unique
   address, subject to policy constraints) that has always been the
   basic aim of the Internet.

   End user applications should be able to request, or have requested on



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   their behalf by agents and policy mechanisms, end-to-end
   communication services with QoS characteristics different from the
   best-effort service that is the foundation of today's Internet.  It
   should be possible to request both a single service channel and a
   bundle of service channels delivered as a single entity.

3.3.2.2.  Network Planners

   The routing system should allow network planners to plan and
   implement a network that can be proved to be stable and will meet
   their traffic engineering requirements.

3.3.2.3.  Network Operators

   The routing system should, so far as is possible, be simple to
   configure, operate and troubleshoot, behave in a predictable and
   stable fashion, and deliver appropriate statistics and events to
   allow the network to be managed and upgraded in an efficient and
   timely fashion.

3.3.2.4.  Mobile End Users

   The routing system must support mobile end users.  It is clear that
   mobility is becoming a predominant mode for network access.

3.4.  Mandated Constraints

   While many of the requirements to which the protocol must respond are
   technical, some aren't.  These mandated constraints are those that
   are determined by conditions of the world around us.  Understanding
   these requirements requires an analysis of the world in which these
   systems will be deployed.  The constraints include those that are
   determined by:

   -  environmental factors,

   -  geography,

   -  political boundaries and considerations, and

   -  technological factors such as the prevalence of different levels
      of technology in the developed world compared to those in the
      developing or undeveloped world.








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3.4.1.  The Federated Environment

   The graph of the Internet network, with routers and other control
   boxes as the nodes and communication links as the edges, is today
   partitioned administratively into a large number of disjoint domains.

   A common administration may have responsibility for one or more
   domains that may or may not be adjacent in the graph.

   Commercial and policy constraints affecting the routing system will
   typically be exercised at the boundaries of these domains where
   traffic is exchanged between the domains.

   The perceived need for commercial confidentiality will seek to
   minimise the control information transferred across these boundaries,
   leading to requirements for aggregated information, abstracted maps
   of connectivity exported from domains, and mistrust of supplied
   information.

   The perceived desire for anonymity may require the use of zero-
   knowledge security protocols to allow users to access resources
   without exposing their identity.

   The requirements should provide the ability for groups of peering
   domains to be treated as a complex domain.  These complex domains
   could have a common administrative policy.

3.4.2.  Working with Different Sorts of Networks

   The diverse Layer 2 networks over which the layer 3 routing system is
   implemented have typically been operated totally independently from
   the layer 3 network and often with their own routing mechanisms.
   Consideration needs to be given to the desirable degree and nature of
   interchange of information between the layers.  In particular, the
   need for guaranteed robustness through diverse routing layers implies
   knowledge of the underlying networks.

   Mobile access networks may also impose extra requirements on Layer 3
   routing.

3.4.3.  Delivering Resilient Service

   The routing system operates at Layer 3 in the network.  To achieve
   robustness and resilience at this layer requires that, where multiple
   diverse routes are employed as part of delivering the resilience, the
   routing system at Layer 3 needs to be assured that the Layer 2 and
   lower routes are really diverse.  The 'diamond problem' is the
   simplest form of this problem - a layer 3 provider attempting to



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   provide diversity buys layer 2 services from two separate providers
   who in turn buy layer 1 services from the same provider:

                             Layer 3 service
                              /           \
                             /             \
                         Layer 2         Layer 2
                       Provider A      Provider B
                             \             /
                              \           /
                             Layer 1 Provider

   Now when the backhoe cuts the trench, the Layer 3 provider has no
   resilience unless he had taken special steps to verify that the
   trench wasn't common.  The routing system should facilitate avoidance
   of this kind of trap.

   Some work is going on to understand the sort of problems that stem
   from this requirement, such as the work on Shared Risk Link Groups
   [I-D.many-inference-srlg].  Unfortunately, the full generality of the
   problem requires diversity be maintained over time between an
   arbitrarily large set of mutually distrustful providers.  For some
   cases, it may be sufficient for diversity to be checked at
   provisioning or route instantiation time, but this remains a hard
   problem requiring research work.

3.4.4.   When Will the New Solution Be Required?

   There is a full range of opinion on this subject.  An informal survey
   indicates that the range varies from 2 years to 6 years.  And while
   there are those, possibly outliers, who think there is no need for a
   new routing architecture as well as those who think a new
   architecture was needed years ago, the median seems to lie at around
   4 years.  As in all projections of the future, this is not provable
   at this time.

      Editors' note: The paragraph above was written in 2002, yet could
      be written without change in 2006.  As with many technical
      predictions and schedules, the horizon has remained fixed through
      this interval.

3.5.  Assumptions

   In projecting the requirements for the Future Domain Routing a number
   of assumptions have been made.  The requirements set out should be
   consistent with these assumptions, but there are doubtless a number
   of other assumptions that are not explicitly articulated here:




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   1.   The number of hosts today is somewhere in the area of 100
        million.  With dial-in, NATs and the universal deployment of
        IPv6, this is likely to become up to 500 million users (see
        [CIDR]).  In a number of years, with wireless accesses and
        different appliances attaching to the Internet, we are likely to
        see a couple of billion (10^9) 'users' on the Internet.  The
        number of globally addressable hosts is very much dependent on
        how common NATs will be in the future.

   2.   NATs, firewalls, and other middle-boxes exist, and we cannot
        assume that they will cease being a presence in the networks.

   3.   The number of operators in the Internet will probably not grow
        very much, as there is a likelihood that operators will tend to
        merge.  However, as Internet-connectivity expands to new
        countries, new operators will emerge and then merge again.

   4.   At the beginning of 2002, there are around 12000 registered
        AS's.  With current use of AS's (for e.g., multi-homing) the
        number of AS's could be expected to grow to 25000 in about 10
        years.[Broido02] This is down from a previously reported growth
        rate of 51% per year.[RFC3221].  Future growth rates are
        difficult to predict.

           Editors' Note: In the routing report table of August 2006,
           the total number of AS's present in the Internet Routing
           Table was 23000.  In 4 years this is substantial progress on
           the prediction of 25000 AS's.  Also, there are significantly
           more AS's registered then are visibly active, i.e., in excess
           of 42000 in mid-2006.  It is possible, however, that many are
           being used internally.

   5.   In contrast to the number of operators, the number of domains is
        likely to grow significantly.  Today, each operator has
        different domains within an AS, but this also shows in SLAs and
        policies internal to the operator.  Making this globally visible
        would create a number of domains 10-100 times the number of
        AS's, i.e., between 100,000 and 1,000,000.

   6.   With more and more capacity at the edge of the network the IP
        network will expand.  Today there are operators with several
        thousands of routers, but this is likely to be increased.  Some
        domains will probably contain tens of thousands of routers.

   7.   The speed of connections in the (fixed) access will technically
        be (almost) unconstrained.  However, the cost for the links will
        not be negligible so that the apparent speed will be effectively
        bounded.  Within a number of years some will have multi-gigabit



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        speed in the access.

   8.   At the same time, the bandwidth of wireless access still has a
        strict upper-bound.  Within the foreseeable future each user
        will have only a tiny amount of resources available compared to
        fixed accesses (10kbps to 2Mbps for UMTS with only a few
        achieving the higher figure as the bandwidth is shared between
        the active users in a cell and only small cells can actually
        reach this speed, but 11Mbps or more for wireless LAN
        connections).  There may also be requirements for effective use
        of bandwidth as low as 2.4 Kbps or lower, in some applications.

   9.   Assumptions 7 and 8 taken together suggest a minimum span of
        bandwidth between 2.4 kbps to 10 Gbps.

   10.  The speed in the backbone has grown rapidly, and there is no
        evidence that the growth will stop in the coming years.
        Terabit-speed is likely to be the minimum backbone speed in a
        couple of years.  The range of bandwidths that need to be
        represented will require consideration on how to represent the
        values in the protocols.

   11.  There have been discussions as to whether Moore's law will
        continue to hold for processor speed.  If Moore's law does not
        hold, then communication circuits might play a more important
        role in the future.  Also, optical routing is based on circuit
        technology, which is the main reason for taking 'circuits' into
        account when designing an FDR.

   12.  However, the datagram model still remains the fundamental model
        for the Internet.

   13.  The number of peering points in the network is likely to grow,
        as multi-homing becomes important.  Also traffic will become
        more locally distributed, which will drive the demand for local
        peering.

           Editors' note: On the other hand peer to peer networking may
           shift the balance in demand for local peering.

   14.  The FDR will achieve the same degree of ubiquity as the current
        Internet and IP routing.

3.6.  Functional Requirements

   This section includes a detailed discussion of new requirements for a
   Future Domain Routing architecture.  The nth requirement carries the
   label "R(n)".  As discussed in section 3.2.3.12 a new architecture



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   must build upon the requirements of the past routing framework and
   must not reduce the functionality of the network.  A discussion and
   analysis of the RFC1126 requirements can be found in
   [I-D.irtf-routing-history].

3.6.1.  Topology

3.6.1.1.  Routers Should Be Able To Learn and To Exploit the Domain
          Topology

   R(1)  Routers must be able to acquire and hold sufficient information
         on the underlying topology of the domain to allow the
         establishment of routes on that topology.

   R(2)  Routers must have the ability to control the establishment of
         routes on the underlying topology.

   R(3)  Routers must be able, where appropriate, to control Sub-IP
         mechanisms to support the establishment of routes.

   The OSI Inter-Domain Routing Protocol (IDRP)[ISO10747] allowed a
   collection of topologically related domains to be replaced by an
   aggregate domain object, in a similar way to the Nimrod[Chiappa02]
   domain hierarchies.  This allowed a route to be more compactly
   represented by a single collection instead of a sequence of
   individual domains.

   R(4)  Routers must, where appropriate, be able to construct
         abstractions of the topology that represent an aggregation of
         the topological features of some area of the topology.

3.6.1.2.  The Same Topology Information Should Support Different Path
          Selection Ideas

   The same topology information needs to provide the more flexible
   spectrum of path selection methods that we might expect to find in a
   future Internet, including distributed techniques such as hop-by-hop,
   shortest path, local optimization constraint-based, class of service,
   source address routing, and destination address routing, as well as
   the centralized, global optimization constraint-based 'traffic
   engineering' type.  Allowing different path selection techniques will
   produce a much more predictable and comprehensible result than the
   'clever tricks' that are currently needed to achieve the same
   results.  Traffic engineering functions need to be combined.







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   R(5)  Routers must be capable of supporting a small number of
         different path selection algorithms

3.6.1.3.  Separation of the Routing Information Topology from the Data
          transport topology.

   R(6)  The controlling network may be logically separate from the
         controlled network.

   The two functional 'planes' may physically reside in the same nodes
   and share the same links, but this is not the only possibility, and
   other options may sometimes be necessary.  An example is a pure
   circuit switch (that cannot see individual IP packets) combined with
   an external controller.  Another example may be multiple links
   between two routers, where all the links are used for data forwarding
   but only one is used for carrying the routing session.

3.6.2.  Distribution

3.6.2.1.  Distribution Mechanisms

   R(7)  Relevant changes in the state of the network, including
         modifications to the topology and changes in the values of
         dynamic capabilities, must be distributed to every entity in
         the network that needs them, in a reliable and trusted way, at
         the earliest appropriate time after the changes have occurred.

   R(8)  Information must not be distributed outside areas where it is
         needed, or believed to be needed, for the operation of the
         routing system.

   R(9)  Information must be distributed in such a way that it minimizes
         the load on the network, consistent with the required response
         time of the network to changes.

3.6.2.2.  Path Advertisement

   R(10)  The router must be able to acquire and store additional static
          and dynamic information that relates to the capabilities of
          the topology and its component nodes and links and that can
          subsequently be used by path selection methods.

   The inter-domain routing system must be able to advertise more kinds
   of information than just connectivity and domain paths.







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   R(11)  The Routing System must support service specifications, e.g.,
          the Service Level Specifications (SLSs) developed by the
          Differentiated Services working group [RFC3260].

   Careful attention should be paid to ensuring that the distribution of
   additional information with path advertisements remains scalable as
   domains and the Internet get larger, more numerous, and more
   diversified.

   R(12)  The distribution mechanism used for distributing network state
          information must be scalable with respect to the expected size
          of domains and the volume and rate of change of dynamic state
          that can be expected.

   The combination of R(9) and R(12) may result in a compromise between
   the responsiveness of the network to change and the overhead of
   distributing change notifications.  Attempts to respond to very rapid
   changes may damage the stability of the routing system.

   Possible examples of additional capability information that might be
   carried include:

   -  QoS information

      To allow an ISP to sell predictable end-to-end QoS service to any
      destination, the routing system should have information about the
      end-to-end QoS.  This means that:

   R(13)  The routing system must be able to support different paths for
          different services.

   R(14)  The routing system must be able to forward traffic on the path
          appropriate for the service selected for the traffic, either
          according to an explicit marking in each packet (e.g., MPLS
          labels, DiffServ PHB's or DSCP values) or implicitly (e.g.,
          the physical or logical port on which the traffic arrives).

   R(15)  The routing system should also be able to carry information
          about the expected (or actually, promised) characteristics of
          the entire path and the price for the service.

        (If such information is exchanged at all between network
      operators today, it is through bilateral management interfaces,
      and not through the routing protocols.)
      This would allow for the operator to optimise the choice of path
      based on a price/performance trade-off.
      In addition to providing dynamic QoS information the system should
      be able to use static class-of-service information.



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   -    Security information

      Security characteristics of other domains referred to by
      advertisements can allow the routing entity to make routing
      decisions based on political concerns.  The information itself is
      assumed to be secure so that it can be trusted.

   -    Usage and cost information

      Usage and cost information can be used for billing and traffic
      engineering.  In order to support cost-based routing policies for
      customers (i.e., peer ISPs), information such as "traffic on this
      link or path costs XXX per Gigabyte" needs to be advertised, so
      that the customer can choose a more or a less expensive route.

   -    Monitored performance

      Performance information such as delay and drop frequency can be
      carried.  (This may only be suitable inside a domain because of
      trust considerations).  This should support at least the kind of
      delay bound contractual terms that are currently being offered by
      service providers.  Note that these values refer to the outcome of
      carrying bits on the path, whereas the QoS information refers to
      the proposed behaviour that results in this outcome.

   -  Multicast information


   R(16)  The routing system must provide information needed to create
          multicast distribution trees.  This information must be
          provided for one-to-many distribution trees and should be
          provided for many-to-many distribution trees.

        The actual construction of distribution trees is not necessarily
      done by the routing system.

3.6.2.3.  Stability of Routing Information

   R(17)  The new network architecture must be stable without needing
          global convergence, i.e., convergence is a local property.

   The degree to which this is possible and the definition of "local"
   remain research topics.  Restricting the requirement for convergence
   to localities will have an effect on all of the other requirements in
   this section.






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   R(18)  The distribution and the rate of distribution of changes must
          not affect the stability of the routing information.  For
          example, commencing redistribution of a change before the
          previous one has settled must not cause instability.

3.6.2.3.1.  Avoiding Routing Oscillations

   R(19)  The routing system must minimize oscillations in route
          advertisements.

3.6.2.3.2.  Providing Loop-free Routing and Forwarding

   In line with the separation of routing and forwarding concerns:

   R(20)  The distribution of routing information must be, so far as is
          possible, loop-free.

   R(21)  The forwarding information created from this routing
          information must seek to minimize persistent loops in the data
          forwarding paths.

   It is accepted that transient loops may occur during convergence of
   the protocol and that there are trade-offs between loop avoidance and
   global scalability.

3.6.2.3.3.  Detection, Notification and Repair of Failures

   R(22)  The routing system must provide means for detecting failures
          of node equipment or communication links.

   R(23)  The routing system should be able to coordinate failure
          indications from layer 3 mechanisms, from nodal mechanisms
          built into the routing system, and from lower-layer mechanisms
          that propagate up to Layer 3 in order to determine the root
          cause of the failure.  This will allow the routing system to
          react correctly to the failure by activating appropriate
          mitigation and repair mechanisms if required, whilst ensuring
          that it does not react if lower layer repair mechanisms are
          able to repair or mitigate the fault.

   Most layer 3 routing protocols have utilized keepalives or 'hello'
   protocols as a means of detecting failures at Layer 3.  The keepalive
   mechanisms are often complemented by analog mechanisms (e.g., laser
   light detection) and hardware mechanisms (e.g., hardware/software
   watchdogs) that are built into routing nodes and communication links.
   Great care must be taken to make best possible use of the various
   failure repair methods available whilst ensuring that only one repair
   mechanism at a time is allowed to repair any given fault.



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   Interactions between, for example, fast reroute mechanisms at layer 3
   and SONET/SDH repair at Layer 1 are highly undesirable and are likely
   to cause problems in the network.

   R(24)  Where a network topology and routing system contains multiple
          fault repair mechanisms, the responses of these systems to a
          detected failure should be coordinated so that the fault is
          repaired by the most appropriate means, and no extra repairs
          are initiated.

   R(25)  Where specialized packet exchange mechanisms (e.g., layer 3
          keepalive or 'hello' protocol mechanisms) are used to detect
          failures, the routing system must allow the configuration of
          the rate of transmission of these keepalives.  This must
          include the capability to turn them off altogether for links
          that are deliberately broken when no real user or control
          traffic is present (e.g., ISDN links).

   This will allow the operator to compromise between the speed of
   failure detection and the proportion of link bandwidth dedicated to
   failure detection.

3.6.3.  Addressing

3.6.3.1.  Support Mix of IPv4, IPv6 and Other Types of Addresses

   R(26)  The routing system must support a mix of different kinds of
          addresses.

   This mix will include at least IPv4 and IPv6 addresses, and
   preferably various types of non-IP addresses too.  For instance
   networks like SDH/SONET and WDM may prefer to use non-IP addresses.
   It may also be necessary to support multiple sets of 'private' (e.g.,
   RFC1918) addresses when dealing with multiple customer VPNs.

   R(27)  The routing system should support the use of a single topology
          representation to generate routing and forwarding tables for
          multiple address families on the same network.

   This capability would minimise the protocol overhead when exchanging
   routes.

3.6.3.2.  Support for Domain Renumbering/Readdressing








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   R(28)  If a domain is subject to address reassignment that would
          cause forwarding interruption, then the routing system should
          support readdressing (e.g., when a new prefix is given to an
          old network, and the change is known in advance) by
          maintaining routing during the changeover period
          [RFC2071],[RFC2072].

3.6.3.3.  Multicast and Anycast

   R(29)  The routing system must support multicast addressing, both
          within a domain and across multiple domains.

   R(30)  The routing system should support anycast addressing within a
          domain.  The routing system may support anycast addressing
          across domains.

   An open question is whether it is possible or useful to support
   anycast addressing between cooperating domains.

3.6.3.4.  Address Scoping

   R(31)  The routing system must support scoping of unicast addresses,
          and it should support scoping of multicast and anycast address
          types.

   The unicast address scoping that is being designed for IPv6 does not
   seem to cause any special problems for routing.  IPv6 inter-domain
   routing handles only IPv6 global addresses, while intra-domain
   routing also needs to be aware of the scope of private addresses.

      Editors' note: the original reference was to site-local addresses
      but these have been deprecated by the IETF.  Link-local addresses
      are never routed at all.

   More study may be needed to identify the requirements and solutions
   for scoping in a more general sense and for scoping of multicast and
   anycast addresses.

3.6.3.5.  Mobility Support

   R(32)  The routing system must support system mobility.  The term
          "system" includes anything from an end system to an entire
          domain.

   We observe that the existing solutions based on re-numbering and/or
   tunneling are designed to work with the current routing, so they do
   not add any new requirements to future routing.  But the requirement
   is general, and future solutions may not be restricted to the ones we



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   have today.

3.6.4.  Statistics Support

   R(33)  Both the routing and forwarding parts of the routing system
          must maintain statistical information about the performance of
          their functions.

3.6.5.  Management Requirements

   While the tools of management are outside the scope of routing, the
   mechanisms to support the routing architecture and protocols are
   within scope.

   R(34)  Mechanisms to support Operational, Administrative and
          Management control of the routing architecture and protocols
          must be designed into the original fabric of the architecture.

3.6.5.1.  Simple Policy Management

   The basic aims of this specification are:

   -  to require less manual configuration than today and

   -  to satisfy the requirements for both easy handling and maximum
      control.  That is:

      -  All the information should be available,

      -  but should not be visible except for when necessary.

      -  Policies themselves should be advertised and not only the
         result of policy, and

      -  policy conflict resolution must be provided.

   R(35)  The routing system must provide management of the system by
          means of policies.  For example, policies that can be
          expressed in terms of the business and services implemented on
          the network and reflect the operation of the network in terms
          of the services affected.

                Editors' note: This requirement is optimistic in that it
                implies that it is possible to get operators to
                cooperate even it is seen by them to be against their
                business practices.





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   R(36)  The distribution of policies must be amenable to scoping to
          protect proprietary policies that are not relevant beyond the
          local set of domains.

3.6.5.2.  Startup and Maintenance of Routers

   A major problem in today's networks is the need to perform initial
   configuration on routers from a local interface before a remote
   management system can take over.  It is not clear that this imposes
   any requirements on the routing architecture beyond what is needed
   for a ZeroConf host.

   Similarly, maintenance and upgrade of routers can cause major
   disruptions to the network routing because the routing system and
   management of routers is not organized to minimize such disruption.
   Some improvements have been made, such as graceful restart mechanisms
   in protocols, but more needs to be done.

   R(37)  The routing system and routers should provide mechanisms that
          minimize the disruption to the network caused by maintenance
          and upgrades of software and hardware.  This requirement
          recognizes that some of the capabilities needed are outside
          the scope of the routing architecture (e.g., minimum impact
          software upgrade).

3.6.6.  Provability

   R(38)  The routing system and its component protocols must be
          demonstrated to be locally convergent under the permitted
          range of parameter settings and policy options that the
          operator(s) can select.

   There are various methods for demonstration and proof that include,
   but are not limited to: mathematical proof, heuristic, and pattern
   recognition.  No requirement is made on the method used for
   demonstrating local convergence properties.

   R(39)  Routing protocols employed by the routing system and the
          overall routing system should be resistant to bad routing
          policy decisions made by operators.

   Tools are needed to check compatibility of routing policies.  While
   these tools are not part of the routing architecture, the mechanisms
   to support such tools are.

   Routing policies are compatible if their interaction does not cause
   instability.  A domain or group of domains in a system is defined as
   being convergent, either locally or globally, if and only if, after



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   an exchange of routing information, routing tables reach a stable
   state that does not change until the routing policies or the topology
   changes again.

   To achieve the above-mentioned goals:

   R(40)  The routing system must provide a mechanism to publish and
          communicate policies so that operational coordination and
          fault isolation are possible.

   Tools are required that verify the stability characteristics of the
   routing system in specified parts of the Internet.  The tools should
   be efficient (fast) and have a broad scope of operation (check large
   portions of Internet).  While these tools are not part of the
   architecture, developing them is in the interest of the architecture
   and should be defined as a Routing Research Group activity while
   research on the architecture is in progress.

   Tools analyzing routing policies can be applied statically or
   (preferably) dynamically.  Dynamic solution requires tools that can
   be used for run time checking for oscillations that arise from policy
   conflicts.  Research is needed to find an efficient solution to the
   dynamic checking of oscillations.

3.6.7.  Traffic Engineering

   The ability to do traffic engineering and to get the feedback from
   the network to enable traffic engineering should be included in the
   future domain architecture.  Though traffic engineering has many
   definitions, it is, at base, another alternative or extension for the
   path selection mechanisms of the routing system.  No fundamental
   changes to the requirements are needed, but the iterative processes
   involved in traffic engineering may require some additional
   capabilities and state in the network.

   Traffic engineering typically involves a combination of off-line
   network planning and administrative control functions in which the
   expected and measured traffic flows are examined, resulting in
   changes to static configurations and policies in the routing system.
   During operations, these configurations control the actual flow of
   traffic and affect the dynamic path selection mechanisms; the results
   are measured and fed back into further rounds of network planning.

3.6.7.1.  Support for, and Provision of, Traffic Engineering Tools

   At present there is an almost total lack of effective traffic
   engineering tools, whether in real time for network control or off-
   line for network planning.  The routing system should encourage the



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   provision of such tools.

   R(41)  The routing system must generate statistical and accounting
          information in such a way that traffic engineering and network
          planning tools can be used in both real time and off-line
          planning and management.

3.6.7.2.  Support of Multiple Parallel Paths

   R(42)  The routing system must support the controlled distribution
          over multiple links or paths of traffic toward the same
          destination.  This applies to domains with two or more
          connections to the same neighbor domain, and to domains with
          connections to more than one neighbor domain.  The paths need
          not have the same metric.

   R(43)  The routing system must support forwarding over multiple
          parallel paths when available.  This support should extend to
          cases where the offered traffic is known to exceed the
          available capacity of a single link, and to the cases where
          load is to be shared over paths for cost or resiliency
          reasons.

   R(44)  Where traffic is forwarded over multiple parallel paths, the
          routing system must, so far as is possible, avoid reordering
          of packets in individual micro-flows.

   R(45)  The routing system must have mechanisms to allow the traffic
          to be reallocated back onto a single path when multiple paths
          are not needed.

3.6.7.3.  Peering Support

   R(46)  The routing system must support peer-level connectivity as
          well as hierarchical connections between domains.

   The network is becoming increasingly complex, with private peering
   arrangements set up between providers at every level of the hierarchy
   of service providers and even by certain large enterprises, in the
   form of dedicated extranets.

   R(47)  The routing system must facilitate traffic engineering of peer
          routes so that traffic can be readily constrained to travel as
          the network operators desire, allowing optimal use of the
          available connectivity.






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3.6.8.  Support for Middleboxes

   One of our assumptions is that NATs and other middle-boxes such as
   firewalls, web proxies and address family translators (e.g., IPv4 to
   IPv6) are here to stay.

   R(48)  The routing system should work in conjunction with middle-
          boxes, e.g., NAT, to aid in bi-directional connectivity
          without compromising the additional opacity and privacy that
          the middle-boxes offer.

   This problem is closely analogous to the abstraction problem, which
   is already under discussion for the interchange of routing
   information between domains.

3.7.  Performance Requirements

   Over the past several years, the performance of the routing system
   has frequently been discussed.  The requirements that derive from
   those discussions are listed below.  The specific values for these
   performance requirements are left for further discussion.

   R(49)  The routing system must support domains of at least N systems.
          A system is taken to mean either an individual router or a
          domain.

   R(50)  Local convergence should occur within T units of time.

   R(51)  The routing system must be measurably reliable.  The measure
          of reliability remains a research question.

   R(52)  The routing system must be locally stable to a measured
          degree.  The degree of measurabilty remains a research issue.

   R(53)  The routing system must be globally stable to a measured
          degree.  The degree of measurabilty remains a research issue.

   R(54)  The routing system should scale to an indefinitely large
          number of domains.

   There has been very little data or statistical evidence for many of
   the performance claims made in the past.  In recent years, several
   efforts have been initiated to gather data and do the analyses
   required to make scientific assessments of performance issues and
   requirements.  In order to complete this section of the requirements
   analysis, the data and analyses from these studies needs to be
   gathered and collated into this document.  This work has been started
   but has yet to be completed.



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3.8.  Backwards Compatibility (Cutover) and Maintainability

   This area poses a dilemma.  On one hand it is an absolute requirement
   that:

   R(55)  The introduction of the routing system must not require any
          flag days.

   R(56)  The network currently in place must continue to run at least
          as well as it does now while the new network is being
          installed around it.

   However, at the same time, it is also an requirement that:

   R(57)  The new architecture must not be limited by the restrictions
          that plague today's network.

   It has to be admitted that R(57) is not a well defined requirement,
   because we have not fully articulated what the restrictions might be.
   Some of these restrictions can be derived by reading the discussions
   for the positive requirements above.  It would be a useful exercise
   to explicitly list all the restrictions and irritations that we wish
   to do away with.  It would be further useful to determine if these
   restrictions can currently be removed at reasonable cost or whether
   we are actually condemned to live with them.

   Those restrictions cannot be allowed to become permanent baggage on
   the new architecture.  If they do, the effort to create a new system
   will come to naught.  It may, however, be necessary to live with some
   of them temporarily for practical reasons while providing an
   architecture which will eventually allow them to be removed.  The
   last three requirements have significance not only for the transition
   strategy, but also for the architecture itself.  They imply that it
   must be possible for an internet such as today's BGP-controlled
   network, or one of its AS's, to exist as a domain within the new FDR.

3.9.  Security Requirements

   As previously discussed, one of the major changes that has overtaken
   the Internet since its inception is the erosion of trust between end
   users making use of the net, between those users and the suppliers of
   services, and between the multiplicity of providers.  Hence security,
   in all its aspects, will be much more important in the FDR.

   It must be possible to secure the routing communication.






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   R(58)  The communicating entities must be able to identify who sent
          and who received the information (authentication).

   R(59)  The communicating entities must be able to verify that the
          information has not been changed on the way (integrity).

   Security is more important in inter-domain routing where the operator
   has no control over the other domains, than in intra-domain routing
   where all the links and the nodes are under the administration of the
   operator and can be expected to share a trust relationship.  This
   property of intra-domain trust, however, should not be taken for
   granted:

   R(60)  Routing communications must be secured by default, but an
          operator must have the option to relax this requirement within
          a domain where analysis indicates that other means (such as
          physical security) provide an acceptable alternative.

   R(61)  The routing communication mechanism must be robust against
          denial-of-service attacks.

   R(62)  It should be possible to verify that the originator of the
          information was authorized to generate the information.

   Further considerations that may impose further requirements include:

   -  whether no one else but the intended recipient is able to access
      (privacy) or understand (confidentiality) the information,

   -  whether it is possible to verify that all the information has been
      received and that the two parties agree on what was sent
      (validation and non-repudiation),

   -  whether there is a need to separate security of routing from
      security of forwarding, and

   -  whether traffic flow security is needed (i.e., whether there is
      value in concealing who can connect to whom, and what volumes of
      data are exchanged).

   Securing the BGP session, as done today, only secures the exchange of
   messages from the peering domain, not the content of the information.
   In other words, we can confirm that the information we got is what
   our neighbor really sent us, but we do not know whether this
   information (that originated in some remote domain) is true or not.

   A decision has to be made on whether to rely on chains of trust (we
   trust our peers who trust their peers who..), or whether we also need



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   authentication and integrity of the information end-to-end.  This
   information includes both routes and addresses.  There has been
   interest in having digital signatures on originated routes as well as
   countersignatures by address authorities to confirm that the
   originator has authority to advertise the prefix.  Even understanding
   who can confirm the authority is non-trivial, as it might be the
   provider who delegated the prefix (with a whole chain of authority
   back to ICANN) or it may be an address registry.  Where a prefix
   delegated by a provider is being advertised through another provider
   as in multi-homing, both may have to be involved to confirm that the
   prefix may be advertised through the provider who doesn't have any
   interest in the prefix!

   R(63)  The routing system must cooperate with the security policies
          of middle-boxes whenever possible.

   This is likely to involve further requirements for abstraction of
   information.  For example, a firewall that is seeking to minimize
   interchange of information that could lead to a security breach.  The
   effect of such changes on the end-to-end principle should be
   carefully considered as discussed in [Blumenthal01].

   R(64)  The routing system must be capable of complying with local
          legal requirements for interception of communication.

3.10.  Debatable Issues

   This section covers issues that need to be considered and resolved in
   deciding on a Future Domain Routing architecture.  While they can't
   be described as requirements, they do affect the types of solution
   that are acceptable.  The discussions included below are very open-
   ended.

3.10.1.  Network Modeling

   The mathematical model that underlies today's routing system uses a
   graph representation of the network.  Hosts, routers and other
   processing boxes are represented by nodes and communications links by
   arcs.  This is a topological model in that routing does not need to
   directly model the physical length of the links or the position of
   the nodes; the model can be transformed to provide a convenient
   picture of the network by adjusting the lengths of the arcs and the
   layout of the nodes.  The connectivity is preserved and routing is
   unaffected by this transformation.

   The routing algorithms in traditional routing protocols utilize a
   small number of results from graph theory.  It is only recently that
   additional results have been employed to support constraint-based



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   routing for traffic engineering.

   The naturalness of this network model and the 'fit' of the graph
   theoretical methods may have tended to blind us to alternative
   representations and inhibited us from seeking alternative strands of
   theoretical thinking that might provide improved results.

   We should not allow this habitual behavior to stop us looking for
   alternative representations and algorithms; topological revolutions
   are possible and allowed, at least in theory.

3.10.2.  System Modeling

   The assumption that object modeling of a system is an essential first
   step to creating a new system is still novel in this context.
   Frequently the object modeling effort becomes an end in itself and
   does not lead to system creation.  But there is a balance, and a lot
   that can be discovered in an ongoing effort to model a system such as
   the Future Domain Routing system.  It is recommended that this
   process be included in the requirements.  It should not, however, be
   a gating event to all other work.

   Some of the most important realizations will occur during the process
   of determining the following:

   -  Object classification

   -  Relationships and containment

   -  Roles and Rules

3.10.3.  One, Two or Many Protocols

   There has been a lot of discussion of whether the FDR protocol
   solution should consist of one (probably new) protocol, two (intra-
   and inter-domain) protocols, or many protocols.  While it might be
   best to have one protocol that handles all situations, this seems
   improbable.  On the other hand, maintaining the 'strict' division
   evident in the network today between the IGP and EGP may be too
   restrictive an approach.  Given this, and the fact that there are
   already many routing protocols in use, the only possible answer seems
   to be that the architecture should support many protocols.  It
   remains an open issue, one for the solution, to determine if a new
   protocol needs to be designed in order to support the highest goals
   of this architecture.  The expectation is that a new protocol will be
   needed.





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3.10.4.  Class of Protocol

   If a new protocol is required to support the FDR architecture, the
   question remains open as to what kind of protocol this ought to be.
   It is our expectation that a map distribution protocol will be
   required to augment the current path-vector protocol and shortest
   path first protocols.

3.10.5.  Map Abstraction

   Assuming that a map distribution protocol, as defined in [RFC1992] is
   required, what are the requirements on this protocol?  If every
   detail is advertised throughout the Internet, there will be a lot of
   information.  Scalable solutions require abstraction.

   -  If we summarise too much, some information will be lost on the
      way.

   -  If we summarise too little, then more information than required is
      available, contributing to scaling limitations.

   -  One can allow more summarisation, if there also is a mechanism to
      query for more details within policy limits.

   -  The basic requirement is not that the information shall be
      advertised, but rather that the information shall be available to
      those who need it.  We should not presuppose a solution where
      advertising is the only possible mechanism.

3.10.6.  Clear Identification for All Entities

   As in all other fields, the words used to refer to concepts and to
   describe operations about routing are important.  Rather than
   describe concepts using terms that are inaccurate or rarely used in
   the real world of networking, it is necessary to make an effort to
   use the correct words.  Many networking terms are used casually, and
   the result is a partial or incorrect understanding of the underlying
   concept.  Entities such as nodes, interfaces, sub-networks, tunnels,
   and the grouping concepts such as AS's, domains, areas, and regions,
   need to be clearly identified and defined to avoid confusion.

   There is also a need to separate identifiers (what or who) from
   locators (where) from routes (how to reach).

      Editors' Note: Work was undertaken in the shim6 working group of
      the IETF on this sort of separation.  This work needs to be taken
      into account in any new routing architecture.




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3.10.7.  Robustness and Redundancy

   The routing association between two domains should survive even if
   some individual connection between two routers goes down.

   The "session" should operate between logical "routing entities" on
   each domain side, and not necessarily be bound to individual routers
   or addresses.  Such a logical entity can be physically distributed
   over multiple network elements.  Or it can reside in a single router,
   which would default to the current situation.

3.10.8.  Hierarchy

   A more flexible hierarchy with more levels and recursive groupings in
   both upward and downward directions allows more structured routing.
   The consequence is that no single level will get too big for routers
   to handle.

   On the other hand, it appears that the real world Internet is
   becoming less hierarchical, so that it will be increasingly difficult
   to use hierarchy to control scaling.

   Note that groupings can look different depending on which aspect we
   use to define them.  A DiffServ area, an MPLS domain, a trusted
   domain, a QoS area, a multicast domain, etc., do not always coincide.
   But neither are they strict hierarchical subsets of each other.  The
   basic distinction at each level is "this grouping versus everything
   outside".

3.10.9.  Control Theory

   Is it possible to apply a control theory framework to analyze the
   stability of the control system of the whole network domain, with
   regards to e.g., convergence speed and the frequency response, and
   then use the results from that analysis to set the timers and other
   protocol parameters?

   Control theory could also play a part in QoS Routing, by modifying
   current link state protocols with link costs dependent on load and
   feedback.  Control theory is often used to increase the stability of
   dynamic systems.

   It might be possible to construct a new, totally dynamic routing
   protocol solely on a control theoretic basis, as opposed to the
   current protocols that are based in graph theory and static in
   nature.





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3.10.10.  Byzantium

   Is solving the Byzantine Generals problem a requirement?  This is the
   problem of reaching a consensus among distributed units if some of
   them give misleading answers.  The current intra-domain routing
   system is, at one level, totally intolerant of misleading
   information.  However, the effect of different sorts of misleading or
   incorrect information has vastly varying results, from total collapse
   to purely local disconnection of a single domain.  This sort of
   behavior is not very desirable.

   There are, possibly, other network robustness issues that must be
   researched and resolved.

3.10.11.  VPN Support

   Today BGP is also used for VPNs, for example as described in RFC4364
   [RFC4364].

   Internet routing and VPN routing have different purposes and most
   often exchange different information between different devices.  Most
   Internet routers do not need to know VPN-specific information.  The
   concepts should be clearly separated.

   But when it comes to the mechanisms, VPN routing can share the same
   protocol as ordinary Internet routing; it can use a separate instance
   of the same protocol or it can use a different protocol.  All
   variants are possible and have their own merits.  These requirements
   are silent on this issue.

3.10.12.  End-to-End Reliability

   The existing Internet architecture neither requires nor provides end-
   to-end reliability of control information dissemination.  There is,
   however, already a requirement for end-to-end reliability of control
   information distribution, i.e., the ends of the VPN established need
   to have an acknowledgment of the success in setting up the VPN.
   While it is not necessarily the function of a routing architecture to
   provide end-to-end reliability for this kind of purpose, we must be
   clear that end-to-end reliability becomes a requirement if the
   network has to support such reliable control signaling.  There may be
   other requirements that derive from requiring the FDR to support
   reliable control signaling.

3.10.13.  End-to-End Transparency

   The introduction of private addressing schemes, Network Address
   Translators, and firewalls has significantly reduced the end-to-end



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   transparency of the network.  In many cases the network is also no
   longer symmetric, so that communication between two addresses is
   possible if the communication session originates from one end but not
   from the other.  This impedes the deployment of new peer-to-peer
   services and some 'push' services where the server in a client-
   server arrangement originates the communication session.  Whether a
   new routing system either can or should seek to restore this
   transparency is an open issue.

   A related issue is the extent to which end user applications should
   seek to control the routing of communications to the rest of the
   network.







































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4.  Security Considerations

   We address security issues in the individual requirements.  We do
   require that the architecture and protocols developed against this
   set of requirements be "secure".  Discussion of specific security
   issues can be found in the following sections:

   o  Group A: Routing System Security - Section 2.1.9

   o  Group A: End Host Security - Section 2.1.10

   o  Group A: Routing Information Policies - Section 2.1.11.1

   o  Group A: Abstraction - Section 2.1.16

   o  Group A: Robustness - Section 2.1.18

   o  Group B: Protection against denial of service and other security
      attacks - Section 3.2.3.8

   o  Group B: Commercial service providers - Section 3.3.1.1

   o  Group B: The Federated Environment - Section 3.4.1

   o  Group B: Path advertisement - Section 3.6.2.2

   o  Group B: Security Requirements - Section 3.9
























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5.  IANA Considerations

   This document is a set of requirements from which a new routing and
   addressing architecture may be developed.  From that architecture, a
   new protocol, or set of protocols, may be developed.

   While this note poses no new tasks for IANA, the architecture and
   protocols developed from this document probably will have issues to
   be dealt with by IANA.










































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6.  Acknowledgments

   This document is the combined efforts of two groups in the IRTF.
   Group A which was formed by the IRTF Routing Research chairs and
   Group B which was self formed and later was folded into the IRTF
   Routing Research Group.  Each group has it own set of
   acknowledgments.


   Group A Acknolwedgements

      This originated in the IRTF Routing Research Group's sub-group on
      Inter-domain routing requirements.  The members of the group were:


           Abha Ahuja                      Danny McPherson
           J. Noel Chiappa                 David Meyer
           Sean Doran                      Mike O'Dell
           JJ Garcia-Luna-Aceves           Andrew Partan
           Susan Hares                     Radia Perlman
           Geoff Huston                    Yakov Rehkter
           Frank Kastenholz                John Scudder
           Dave Katz                       Curtis Villamizar
           Tony Li                         Dave Ward

      We also appreciate the comments and review received from Ran
      Atkinson, Howard Berkowitz, Randy Bush, Avri Doria, Jeffery Haas,
      Dmitri Krioukov, Russ White, and Alex Zinin.  Special thanks to
      Yakov Rehkter for contributing text and to Noel Chiappa.


   Group B Acknowledgements

      The draft is derived from work originally produced by Babylon.
      Babylon was a loose association of individuals from academia,
      service providers and vendors whose goal was to discuss issues in
      Internet routing with the intention of finding solutions for those
      problems.

      The individual members who contributed materially to this draft
      are: Anders Bergsten, Howard Berkowitz, Malin Carlzon, Lenka Carr
      Motyckova, Elwyn Davies, Avri Doria, Pierre Fransson, Yong Jiang,
      Dmitri Krioukov, Tove Madsen, Olle Pers, and Olov Schelen.

      Thanks also go to the members of Babylon and others who did
      substantial reviews of this material.  Specifically we would like
      to acknowledge the helpful comments and suggestions of the
      following individuals: Loa Andersson, Tomas Ahlstrom, Erik Aman,



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      Thomas Eriksson, Niklas Borg, Nigel Bragg, Thomas Chmara, Krister
      Edlund, Owe Grafford, Torbjorn Lundberg, Jeremy Mineweaser,
      Jasminko Mulahusic, Florian-Daniel Otel, Bernhard Stockman, Tom
      Worster, Roberto Zamparo.

      In addition, the authors are indebted to the folks who wrote all
      the references we have consulted in putting this paper together.
      This includes not only the references explicitly listed below, but
      also those who contributed to the mailing lists we have been
      participating in for years.

      Finally, it is the editors who are responsible for any lack of
      clarity, any errors, glaring omissions or misunderstandings.






































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7.  Informative References

   [Blumenthal01]
              Blumenthal, M. and D. Clark, "Rethinking the design of the
              Internet: The end to end arguments vs. the brave new
              world", May 2001,
              <http://ana-www.lcs.mit.edu/anaweb/papers.html>.

   [Broido02]
              Broido, A., Nemeth, E., Claffy, K., and C. Elves,
              "Internet Expansion, Refinement and Churn", February 2002.

   [CIDR]     Telcordia Technologies, "CIDR Report",
              <http://www.cidr-report.org/>.

   [Chiappa02]
              Chiappa, N., "A New IP Routing and Addressing
              Architecture", July 1991,
              <http://ana-3.lcs.mit.edu/~jnc/nimrod/overview.txt>.

   [Clark91]  Clark, D., "Quote reportedly from IETF Plenary
              discussion", 1991.

   [Griffin99]
              Griffin, T. and G. Wilfong, "An Analysis of BGP
              Convergence Properties", SIGCOMM , 1999.

   [I-D.ietf-diffserv-pdb-ar]
              Seddigh, N., Nandy, B., and J. Heinanen, "An Assured Rate
              Per-Domain Behaviour for Differentiated Services",
              draft-ietf-diffserv-pdb-ar-01 (work in progress),
              February 2001.

   [I-D.ietf-diffserv-pdb-vw]
              Jacobson, V., Nichols, K., and K. Poduri, "The 'Virtual
              Wire' Behavior Aggregate", draft-ietf-diffserv-pdb-vw-00
              (work in progress), July 2000.

   [I-D.irtf-routing-history]
              Davies, E., "Analysis of IDR requirements and History",
              draft-irtf-routing-history-06 (work in progress),
              August 2006.

   [I-D.many-inference-srlg]
              Papadimitriou, D. and others, "Inference of Shared Risk
              Link Groups", draft-many-inference-srlg-02 (work in
              progress), February 2002.




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   [ISO10747]
              ISO/IEC, "Protocol for Exchange of Inter-Domain Routeing
              Information among Intermediate Systems to Support
              Forwarding of ISO 8473 PDUs", International Standard
              10747 ISO/IEC JTC 1, Switzerland, 1993.

   [ODell01]  O'Dell, M., "Private Communication", 2001.

   [RFC1126]  Little, M., "Goals and functional requirements for inter-
              autonomous system routing", RFC 1126, October 1989.

   [RFC1726]  Partridge, C. and F. Kastenholz, "Technical Criteria for
              Choosing IP The Next Generation (IPng)", RFC 1726,
              Dec 1994.

   [RFC1992]  Castineyra, I., Chiappa, N., and M. Steenstrup, "The
              Nimrod Routing Architecture", RFC 1992, August 1996.

   [RFC2071]  Ferguson, P. and H. Berkowitz, "Network Renumbering
              Overview: Why would I want it and what is it anyway?",
              RFC 2071, January 1997.

   [RFC2072]  Berkowitz, H., "Router Renumbering Guide", RFC 2072,
              January 1997.

   [RFC3031]  Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
              Label Switching Architecture", RFC 3031, January 2001.

   [RFC3221]  Huston, G., "Commentary on Inter-Domain Routing in the
              Internet", RFC 3221, December 2001.

   [RFC3260]  Grossman, D., "New Terminology and Clarifications for
              Diffserv", RFC 3260, April 2002.

   [RFC3344]  Perkins, C., "IP Mobility Support.", RFC 3344,
              August 2002.

   [RFC3345]  McPherson, D., Gill, V., Walton, D., and A. Retana,
              "Border Gateway Protocol (BGP) Persistent Route
              Oscillation Condition", RFC 3345, August 2002.

   [RFC3471]  Berger, L., "Generalized Multi-Protocol Label Switching
              (GMPLS) Signaling Functional Description", RFC 3471,
              January 2003.

   [RFC3963]  Devarapalli, V., Wakikawa, R., Petrescu, A., and P.
              Thubert, "Network Mobility (NEMO) Basic Support Protocol",
              RFC 3963, January 2005.



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   [RFC4364]  Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
              Networks (VPNs)", RFC 4364, February 2006.

   [Wroclawski95]
              Wroclowski, J., "The Metanet White Paper - Workshop on
              Research Directions for the Next Generation Internet",
              1995.

   [netconf-charter]
              Internet Engineering Task Force, "IETF Network
              Configuration working group", 2005,
              <http://www.ietf.org/html.charters/netconf-charter.html>.

   [policy-charter02]
              Internet Engineering Task Force, "IETF Policy working
              group", 2002, <http://www.ietf.org/html.charters/OLD/
              policy-charter.html>.

   [rap-charter02]
              Internet Engineering Task Force, "IETF Resource Allocation
              Protocol working group", 2002,
              <http://www.ietf.org/html.charters/OLD/rap-charter.html>.

   [snmpconf-charter02]
              Internet Engineering Task Force, "IETF Configuration
              management with SNMP working group", 2002, <http://
              www.ietf.org/html.charters/OLD/snmpconf-charter.html>.
























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Authors' Addresses

   Avri Doria
   LTU
   Lulea  971 87
   Sweden

   Phone: +46 73 277 1788
   Email: avri@ltu.se


   Elwyn B. Davies
   Folly Consulting
   Soham, Cambs
   UK

   Phone: +44 7889 488 335
   Email: elwynd@dial.pipex.com


   Frank Kastenholz
   MA
   USA

   Email: frank@kastenholz.org


























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Full Copyright Statement

   Copyright (C) The IETF Trust (2008).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

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Acknowledgment

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