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Network Working Group                                           A. Doria
Internet-Draft                                                      ETRI
Expires: February 9, 2004                                      E. Davies
                                                         Nortel Networks
                                                           F. Kastenholz
                                                        Juniper Networks
                                                         August 11, 2003

                 Requirements for Inter Domain Routing

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that other
   groups may also distribute working documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time. It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at http://

   The list of Internet-Draft Shadow Directories can be accessed at

   This Internet-Draft will expire on February 9, 2004.

Copyright Notice

   Copyright (C) The Internet Society (2003). All Rights Reserved.


   These requirements for routing architectures are the product of two
   sub-groups with the IRTF Routing Research Group.  They represent two
   individual and separate views of the problem and of what is required
   to fix the problem. While speaking of requirements, the document is
   actually a recommendation to anyone who would create a routing
   architecture for the Internet in the coming years.

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Table of Contents

   1.      Background . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.      Results from Group A . . . . . . . . . . . . . . . . . . .  6
   2.1     Group A - Requirements For a Next Generation Routing
           and Addressing Architecture  . . . . . . . . . . . . . . .  6
   2.1.1   Architecture . . . . . . . . . . . . . . . . . . . . . . .  6
   2.1.2   Separable Components . . . . . . . . . . . . . . . . . . .  6
   2.1.3   Scalable . . . . . . . . . . . . . . . . . . . . . . . . .  7
   2.1.4   Lots of Interconnectivity  . . . . . . . . . . . . . . . .  9
   2.1.5   Random Structure . . . . . . . . . . . . . . . . . . . . . 10
   2.1.6   Multi-homing . . . . . . . . . . . . . . . . . . . . . . . 10
   2.1.7   Multi-path . . . . . . . . . . . . . . . . . . . . . . . . 11
   2.1.8   Convergence  . . . . . . . . . . . . . . . . . . . . . . . 12
   2.1.9   Routing System Security  . . . . . . . . . . . . . . . . . 14
   2.1.10  End Host Security  . . . . . . . . . . . . . . . . . . . . 16
   2.1.11  Rich Policy  . . . . . . . . . . . . . . . . . . . . . . . 16
   2.1.12  Incremental Deployment . . . . . . . . . . . . . . . . . . 18
   2.1.13  Mobility . . . . . . . . . . . . . . . . . . . . . . . . . 19
   2.1.14  Address Portability  . . . . . . . . . . . . . . . . . . . 19
   2.1.15  Multi-Protocol . . . . . . . . . . . . . . . . . . . . . . 19
   2.1.16  Abstraction  . . . . . . . . . . . . . . . . . . . . . . . 20
   2.1.17  Simplicity . . . . . . . . . . . . . . . . . . . . . . . . 20
   2.1.18  Robustness . . . . . . . . . . . . . . . . . . . . . . . . 21
   2.1.19  Media Independence . . . . . . . . . . . . . . . . . . . . 21
   2.1.20  Stand-alone  . . . . . . . . . . . . . . . . . . . . . . . 22
   2.1.21  Safety of Configuration  . . . . . . . . . . . . . . . . . 22
   2.1.22  Renumbering  . . . . . . . . . . . . . . . . . . . . . . . 22
   2.1.23  Multi-prefix . . . . . . . . . . . . . . . . . . . . . . . 22
   2.1.24  Cooperative Anarchy  . . . . . . . . . . . . . . . . . . . 22
   2.1.25  Network Layer Protocols and Forwarding Model . . . . . . . 22
   2.1.26  Routing Algorithm  . . . . . . . . . . . . . . . . . . . . 23
   2.1.27  Positive Benefit . . . . . . . . . . . . . . . . . . . . . 23
   2.1.28  Administrative Entities and the IGP/EGP Split  . . . . . . 23
   2.2     Non-Requirements . . . . . . . . . . . . . . . . . . . . . 24
   2.2.1   Forwarding Table Optimization  . . . . . . . . . . . . . . 24
   2.2.2   Traffic Engineering  . . . . . . . . . . . . . . . . . . . 24
   2.2.3   Multicast  . . . . . . . . . . . . . . . . . . . . . . . . 24
   2.2.4   QOS  . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
   2.2.5   IP Prefix Aggregation  . . . . . . . . . . . . . . . . . . 25
   2.2.6   Perfect Safety . . . . . . . . . . . . . . . . . . . . . . 25
   2.2.7   Dynamic Load Balancing . . . . . . . . . . . . . . . . . . 26
   2.2.8   Renumbering of hosts and routers . . . . . . . . . . . . . 26
   2.2.9   Host Mobility  . . . . . . . . . . . . . . . . . . . . . . 26
   2.2.10  Clean Slate  . . . . . . . . . . . . . . . . . . . . . . . 26
   3.      Requirements from Group B  . . . . . . . . . . . . . . . . 27
   3.1     Group B - Future Domain Routing Requirements . . . . . . . 27
   3.2     Underlying principles  . . . . . . . . . . . . . . . . . . 27

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   3.2.1   Inter-domain and intra-domain  . . . . . . . . . . . . . . 28
   3.2.2   Influences on a changing network . . . . . . . . . . . . . 28
   3.2.3   High level goals . . . . . . . . . . . . . . . . . . . . . 30
   3.3     High level user requirements . . . . . . . . . . . . . . . 33
   3.3.1   Organisational users . . . . . . . . . . . . . . . . . . . 33
   3.3.2   Individual users . . . . . . . . . . . . . . . . . . . . . 36
   3.4     Mandated constraints . . . . . . . . . . . . . . . . . . . 37
   3.4.1   The federated environment  . . . . . . . . . . . . . . . . 37
   3.4.2   Working with different sorts of networks . . . . . . . . . 38
   3.4.3   Delivering Diversity . . . . . . . . . . . . . . . . . . . 38
   3.4.4   When will the new solution be required?  . . . . . . . . . 39
   3.5     Assumptions  . . . . . . . . . . . . . . . . . . . . . . . 39
   3.6     Functional requirements  . . . . . . . . . . . . . . . . . 41
   3.6.1   Topology . . . . . . . . . . . . . . . . . . . . . . . . . 41
   3.6.2   Distribution . . . . . . . . . . . . . . . . . . . . . . . 42
   3.6.3   Addressing . . . . . . . . . . . . . . . . . . . . . . . . 46
   3.6.4   Statistics support . . . . . . . . . . . . . . . . . . . . 48
   3.6.5   Management requirements  . . . . . . . . . . . . . . . . . 48
   3.6.6   Provability  . . . . . . . . . . . . . . . . . . . . . . . 49
   3.6.7   Traffic engineering  . . . . . . . . . . . . . . . . . . . 50
   3.6.8   Support for mid-boxes  . . . . . . . . . . . . . . . . . . 52
   3.7     Performance requirements . . . . . . . . . . . . . . . . . 52
   3.8     Backwards compatibility (cutover) and maintainability  . . 53
   3.9     Security requirements  . . . . . . . . . . . . . . . . . . 53
   3.10    Debatable issues . . . . . . . . . . . . . . . . . . . . . 55
   3.10.1  Network modeling . . . . . . . . . . . . . . . . . . . . . 55
   3.10.2  System modeling  . . . . . . . . . . . . . . . . . . . . . 56
   3.10.3  One, two or many protocols . . . . . . . . . . . . . . . . 56
   3.10.4  Class of protocol to use . . . . . . . . . . . . . . . . . 57
   3.10.5  Map abstraction  . . . . . . . . . . . . . . . . . . . . . 57
   3.10.6  Clear identification for all entities  . . . . . . . . . . 57
   3.10.7  Robustness and redundancy: . . . . . . . . . . . . . . . . 57
   3.10.8  Hierarchy  . . . . . . . . . . . . . . . . . . . . . . . . 58
   3.10.9  Will new control mechanisms be needed? . . . . . . . . . . 58
   3.10.10 Byzantium  . . . . . . . . . . . . . . . . . . . . . . . . 58
   3.10.11 VPN support  . . . . . . . . . . . . . . . . . . . . . . . 59
   3.10.12 End to end reliability . . . . . . . . . . . . . . . . . . 59
   3.10.13 End to end transparency  . . . . . . . . . . . . . . . . . 59
   4.      Security Considerations  . . . . . . . . . . . . . . . . . 61
   5.      IANA Considerations  . . . . . . . . . . . . . . . . . . . 62
   6.      Acknowledgments  . . . . . . . . . . . . . . . . . . . . . 63
           References . . . . . . . . . . . . . . . . . . . . . . . . 65
           Authors' Addresses . . . . . . . . . . . . . . . . . . . . 68
           Intellectual Property and Copyright Statements . . . . . . 69

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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.  A group of well known routing
   experts was assembled and given the task of developing requirements
   for a new routing architecture. Their  mandate was to approach the
   problem from the blank sheet perspective.  This group was free to
   take any approach, including a revolutionary approach, in developing
   requirements for solving the problems they saw in inter domain

   Around the same time, an independent effort was started in Sweden
   with a similar goal.  In this case a team, calling itself Babylon,
   representing vendors, service providers and academia assembled to
   understand the history of inter domain routing, to do research on the
   problems seen by the service providers and to develop, from that
   study, a proposal of requirements for a follow-on to the current
   routing architecture. This group's approach required starting not
   from a blank page but from current routing architecture and practice.
   In other words the group limited itself to developing an evolutionary
   strategy. Later, the Babylon group was folded into the IRTF RRG and
   was established as Sub-Group B within the RRG.

   One of the questions that arose while the groups were working in
   isolation was whether there would be many similarities between the
   set 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 set of
   requirements, there were many areas of fundamental agreement, and
   some areas of disagreement.

   There were suggestions within the RRG that the two teams should work
   together to bring the requirements sets together into one set of
   requirements. Since these requirements are only guidelines to future
   work, however, it was felt by some that doing so would lose 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
   take these requirements as written and go create an architecture that
   met these requirements. Rather, the requirements, were really 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 both of the requirements sets produced by the
   teams. They have only been modified slightly, all editorial, from the
   final versions submitted as individual internet drafts. The
   requirements have been left unaltered.

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   In reading this document it is important to keep in mind that all of
   these requirements are in fact just suggestions. As an informational
   document, these suggestions are laid out to assist those interested
   in working on 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 is no guarantee. So,
   one last, or rather first, suggestion to anyone reading this
   document, do not treat what it says as absolute, and do not 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.

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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

   The requirements presented in this section are NOT presented in any

2.1.1 Architecture

   The new routing and addressing protocols, data structures, and
   algorithms MUST 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

2.1.2 Separable Components

   The architecture MUST place different functions into separate

   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

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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.

   o  Making policy definition and application a separate subsystem,
      layered overtop of 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 overtop
   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

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

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   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 ASes and

   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 to 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
   is also a significant factor.  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

   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:

   1.  The computational power and memory sizes required to execute the
       routing protocol software and to contain the tables must be less
       than the growth in hardware capabilities described by Moore's
       Law, which has hardware capabilities doubling every 18 months or
       so.  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 40gbits (OC768).  We should not expect raw network
       link speed to grow much beyond OC768. In addition, for economic
       reasons, large swathes of the core of the Internet will still

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       operate at lower speeds, possibly as slow as DS3.

       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

   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 up to more
   "other things".  Company's multi-home to multiple ISPs, ISPs peer
   with more ISPs, and so on.  These connections are made for many

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   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
   "meshier".  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.  When there are
   multiple valid, loop free, paths available, all such paths MUST be
   available for forwarding traffic.

   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 make any constraints
   on or assumptions about the topology or connectedness of the elements
   comprising the Internet.  The routing 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

2.1.6 Multi-homing

   The Architecture MUST provide multi-homing for all elements of the
   Internet.  That is, multihoming 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 "multihoming" 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

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   multi-homed site.

   When multi-homing, 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 multihoming leads to undue
   increases in the size of the BGP routing tables.  The new
   architecture MUST support multi-homing without causing 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 use in specifying the rules for
   classifying the traffic and assigning classes of traffic to different
   paths (or prohibiting it from certain paths).  The rules for
   classification should allow traffic to be classified based on

   o  IPv6 FlowIDs

   o  TOS byte

   o  Source and/or Destination prefixes

   o  Random selections at some probability

   o  ...

   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

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

   Past experience with dynamic load-balancing and management over
   multiple paths has been bad. Typically, traffic would oscillate,

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   first all traffic would go over one path, then it would all be
   'migrated' to a different path, and then back again.  Significant
   research is needed in this area.

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 come up with 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
   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

   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

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       deletion, router failure or restart, etc.) is introduced into a
       stabilized system.  No additional changes are introduced.  The
       system must restabilize within TBDms. This requirement is a
       fairly abstract one as it would be impossible to test in a real

   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.

   -  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, thought perhaps not by the optimal path -- this allows some
      'hunting' for the optimal solution)

      X, Y, Z, ARE TBD

   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

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   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

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

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

   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 DDOS attacks.

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

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       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

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

       By "privacy" we mean privacy of the routing protocol exchanges
       between routers.  In the past this has not been considered
       important for routing protocols.

       When the routers are on point-to-point links, with routers at
       each end, there is no need to encrypt the routing protocol
       traffic; there is no possibility of a third party intercepting
       the traffic, and if one of the two routers are compromised then
       it doesn't matter.  This is not sufficient. We believe 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

       2.  When two routers are exchanging information "at a distance"
           (over intervening routers and, possibly, administrative
           domains).  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

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       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

   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, we define policy as

   Policy is the set of administrative influences that alter the path
   determination and next-hop selection procedures of the routing

   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

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   traffic is classified and assigned to routes. 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 others 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

   -  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.

   -  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 "provisional" in the sense of
      "accept routes that traverse "foo" only if there are no others

   -  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.

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   -  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. 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, DSCP values, and MPLS
   labels) .

   - The ability to 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
   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  TOS/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
   cutover from one architecture and protocol to another. This means
   that any new architecture and protocol MUST be incrementally

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   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

   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.

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 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.

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   The architecture MUST NOT assume that all topological elements have
   IPv4 addresses/prefixes, nor can it assume that they have IPv6

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

   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 to for network designers and
   operators to

   o  Group elements together for administrative control purposes,

   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

   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 Radia Perlman can
   explain all the important concepts in less than an hour.

   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".

   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

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   and whistles, then there are fewer things that need to be

   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

   o  Defective (even malicious) trusted routers.

   o  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.

         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

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   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.

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 (no dialup 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[44] 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

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   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 with
   regard to using link-state, distance-vector, or path-vector routing

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

   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).

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   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.

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 a
   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 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 you ask N people what traffic engineering is, you 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 has said (roughly)

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      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 QOS

   The Architecture concerns itself primarily with disseminating network
   topology information so that routers may select paths to destinations
   and build appropriate forwarding tables.  QOS is not a part of this
   function and we make no requirements with respect 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 misconfigure 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.

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   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.

   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 [45].  Traffic destined for
   a mobile-host is explicitly forwarded by dedicated relay agents.
   Mobile-IP [45] 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

2.2.10 Clean Slate

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

   Various developments 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 advent of IPv6 and the application of IP mechanisms to private
   commercial networks offering specific service guarantees as an
   improvement over the best efforts services of the Public Internet
   epitomize the kind of radical changes which have to be accommodated:
   Major changes to the inter-domain routing system are inevitable if it
   is to provide an efficient underpinning for the radically changed and
   increasingly, commercially-based networks which 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, means that we should consider the whole area of routing as an
   integrated system. This is done for 2 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 the name Future Domain Routing(FDR) is
      being used in this document,

   -  As an acknowledgment of how intertwined inter-domain and intra-
      domain routing are within today's routing architecture.

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   We are aware that using the term Domain Routing is already fraught
   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 expansion on the scope of

   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 context is
   very similar to the concept of Region that was put forth by John
   Wroclawski in his Metanet model [10]. The idea includes the notion
   that within a domain certain system attributes will characterize the
   behavior of the systems in the domain and that there will be borders
   between domains.  The idea of domain presented does not inherently
   presuppose that the identifying behaviors between two domains are to
   be the same.  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 a subset of all
   domains as conceived of in this document, there has been no attempt
   to create a new term.

   Current practice stresses the need to separate the concerns of the
   control plane in a router and the forwarding plane:  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 document the terms intra-domain and inter-domain will
   be used.  These terms SHOULD NOT be understood to imply that there is
   one intra-domain and one inter-domain.  Rather these SHOULD be
   understood as relative terms.  In all case of domains there will be a
   set of network systems that are within that domain and 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 same routing activities can be
   viewed as intra-domain from one perspective and 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

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   changes that will affect the organization and the usage of the
   network, including:

   -  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

   -  Potential addition of a second IP addressing technique through

   -  The use of VPNs and private address space with IPv4, and possibly

   -  Evolution of the end-to-end principle to deal with the expanded
      role of the Internet as discussed in [32]]. This paper discusses
      the possibility that the range of new requirements, especially the
      social and techno-political ones, which are being placed on the
      future Internet, 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.  The 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 [24] and GMPLS
      environments [25].

   -  Integrating additional constraints into route determination from
      interactions with other layers (e.g. Shared Risk Link Groups [31])

   -  Support for alternative and multiple routing techniques that are
      better suited to delivering types of content organised 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
   which, for the present, is mostly not explicitly discussed:

   -  How will we know when we have succeeded? 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 which it is
   trying to support.  It is our goal to develop a routing architecture
   where even 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. 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 efforts service in
   the Public Internet.  On the other hand, with, for example, DiffServ
   it is possible to 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 should be possible to
   construct services such as Virtual Wire [18] and Assured Rate [19].

   Providers today offer rudimentary promises about how traffic will be
   handled in the network, for example delay and long-term packet loss
   guarantees, and this will probably be even more relevant in the
   future. 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

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

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   current common denominator. Scaleable well beyond current predictable needs

   Any proposed new FDR system should scale beyond the size and
   performance we can foresee for the next ten years.  The previous IDR
   proposal has, with some massaging, held up for somewhat over ten
   years in which time the Internet has grown far beyond the predictions
   that were made in the requirements that were placed on it originally.

   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! Supporting alternative forwarding mechanisms

   With the advent of circuit based technologies (e.g., MPLS [24] used
   for RSVP-TE or CR-LDP for traffic engineering, GMPLS [25]) 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. Supporting separation of topology map and connectivity service

   It is envisioned that an organization can support multiple services
   on top of a single network. These services can, for example, be of
   different quality, of different type of connectivity, or 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. Achieving 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

   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

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   avoid building this sharing in as an assumption in the FDR.

   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). Providing for use of different routing paradigms in different
        areas of the same network

   A number of different routing paradigms have been used or researched
   in addition to conventional shortest path hop-by-hop 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. Preventing 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. Providing provable convergence with verifiable policy

   It has been shown both analytically by Griffin et al (see [12]) and
   practically (see [20]) that BGP will not converge stably or is only
   meta-stable (i.e. will not reconverge 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 that could be
   applied to a policy free implementation.

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

   A goal of the FDR should be to achieve provable convergence of the
   protocols used which may involve constraining the topologies and

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   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. Providing robustness despite errors and failures

   From time to time in the history of the Internet there have been
   occurrences where people misconfiguring routers have destroyed global
   connectivity. This should never be possible.

   A goal of the FDR is to be 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. Simplicity in management

   With the policy work ([26], [27] and [28]) that has been done at IETF
   there exists 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. The legacy of RFC1126

   RFC1126 outlined a set of requirements that were used to guide the
   development of BGP. While the network is definitely different then it
   was in 1989, many of the same requirements remain.  A future domain
   routing has to support as its base requirement, the level of function
   that is available today.  A detailed discussion of RFC1126 and its
   requirements can be found in [41].  Those requirements, while
   specifically spelled out in that document are to be 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, which 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 [4] was published.  In
   particular a major part of the network are now owned by commercial

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   service provider organizations in the business of making profits from
   carrying data traffic. Commercial service providers

   The routing system must take into account the commercial service
   provider's for commercial 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 also offer contracts to their customers
   in the form of Service Level Agreements (SLAs) and the routing system
   must allow the providers to support these SLAs through traffic
   engineering and load balancing, as well as multihoming, allowing them
   to achieve the degree of resilience and robustness that they need.

   Service providers can be categorized as

   -  Global Service Providers (GSPs) with networks that have a global
      reach.  Such providers may, and usually will, wish to constrain
      traffic between their customers to run entirely on their networks.
      Such providers will interchange traffic at multiple peering points
      with other GSPs and 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.

   -  National Service Providers (NSPs) that are similar to GSPs but
      typically cover one country.  Such organizations 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 and
      will typically purchase transit capacity from NSPs or GSPs to
      provide global connectivity, but may also peer with neighbouring

   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

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   Service providers will need to be involved in accounting for Internet
   usage, monitoring the traffic, and 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. 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 with some multi-national companies owning
   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, whilst effectively supporting the larger

   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

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

   Enterprises will wish to be able to multihome to one or more
   providers as one possible means of enhancing the resilience of their

   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. 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 of the routing system.

   The routing system must support dial-up users. Internet exchange points

   Peering of service providers, academic networks and larger
   enterprises is increasingly happening at specific Internet Exchange

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   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 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. 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. All end users

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

   End user applications should be able to request, or have requested on
   their behalf by agents and policy mechanisms, end-to-end
   communication services with different QoS characteristics as compared
   with the best efforts 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. Network planners

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

   The routing system should, so far as is possible, be simple to

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   configure operate and troubleshoot, behave in a predictable, stable
   fashion and deliver appropriate statistics and events to allow the
   network to be managed and upgraded in an efficient and timely
   fashion. 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 requirement 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 and 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

   -  Technological factors such as the prevalence of different levels
      of technology in the developed world as opposed to in the
      developing or undeveloped world.

3.4.1 The federated environment

   The graph of the Internet network with routers and other control
   boxes at the nodes and communication links along 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

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   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.  Consideration needs to be given to the degree
   and nature of interchange of information between the layers that is
   desirable.  In particular, the need for robustness through diverse
   routing implies knowledge of the underlying networks to be able to
   guarantee the robustness.

   Mobile access networks may also impose extra requirements on Layer 3

3.4.3 Delivering Diversity

   The routing system is operating 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 provide diversity buys layer 2 services from two
   separate providers who in turn buy wayleaves from the same provider:

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

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   [31].  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 largely not
   provable at this time.

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:

   1.   The number of hosts today is somewhere in the area of 100
        Million. With dial in and NATs this is likely to turn into up to
        500 Million users (see [30]). 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

   2.   NATs, firewalls and other mid-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.   As of 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.[43]  This is down from a previously reported growth rate
        of 51% per year.[13].  Future growth rates are difficult to

   5.   In contrast to the number of operators, the number of domains is

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        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 ASes,
        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. A
        domain 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
        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
        only have 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

   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 ócircuitsó 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,

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        as multi-homing becomes important. Also traffic will become more
        locally distributed, which will drive the demand for local

   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.  As discussed in section 2.3.12 a
   new architecture must build upon the requirements of the past routing
   framework and must, and MUST not reduce the functionality of the
   network.  A discussion and analysis of the RFC1126 requirements can
   be found in [41].

3.6.1 Topology Routers should be able to know and 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)[36] utilized a
   capability which allowed a collection of topologically related
   domains to be replaced by a domain collection object in a similar way
   to the Nimrod[9] domain hierarchies, allowing a route to be more
   compactly represented by a single collection in place 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. The same topology information should support different path
        selection ideas

   The same topology information needs to provide a more flexible
   spectrum of path selection methods that we might expect to find in a

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   future Internet, including, amongst others, both 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 (Open
   constraints should be allowed).  Allowing different path selection
   techniques to be used 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.

   R(5)  Routers MUST be capable of supporting a small number of
         different path selection algorithms Separation of the routing information topology from the data
        transport topology.

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

   Physically, the two functional 'planes' can reside in the same nodes
   and share the same links, but this is not the only possibility. Other
   options can also be feasible, and 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 where there are multiple links between two routers, and all the
   links are used for data forwarding, but only one is used for carrying
   the routing session.

3.6.2 Distribution 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 change has 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.

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   R(10) The router MUST be able to acquire and store additional static
         and dynamic information relating to the capabilities of the
         topology and its component nodes and links, which 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 path.

   R(11) The Routing System MUST support service specifications, e.g.
         the Service Level Specifications (SLSs) developed by the
         Differentiated Services working group. [42]

   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

   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.  Also 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 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.

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       (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.

   -   security information

      Security characteristics of other domains (in the path or in the
      map) can allow the routing entity to choose routing decision based
      on some political reasons. The information itself is assumed to be
      so secure that you can trust it.

   -   usage and cost information

      This can be used for billing and traffic engineering purpose. 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 cheap or an expensive route from an economic

   -   monitored performance

      Some performance information such as delay and drop frequency can
      be carried. (This is 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 necessary 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.

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   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
   remains a research topic. Restricting the requirement for convergence
   to localities will have an effect on all of the other requirements in
   this section.

   R(18) The distribution, and the rate of distribution of changes MUST
         NOT affect the stability of the routing information, e.g. by
         commencing redistribution of a change before the previous one
         had settled. Avoiding routing oscillations

   R(19) The routing system MUST minimize oscillations in route
         advertisements. Providing loop free routing and forwarding

   In line with the separation of concerns of routing and forwarding:

   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. Detection, notification and repair of failures

   R(22) The routing system MUST provide means for detecting failures of
         both node equipment and communication links.

   R(23) The routing system SHOULD be able to coordinate responses to
         failure detection indications from layer 3 mechanisms and nodal
         mechanisms built into the routing system and from lower layer
         mechanisms that are propagated 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

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         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 (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:
   Interactions between (say) 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 make provision to allow the
         rate of transmission of these keepalives to be configured,
         including the capability to turn them off altogether where
         links 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 Support mix of IPv4, IPv6 and other types of addresses

   R(26) The routing system MUST support a mix of different kinds of

   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.

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

   This capability would minimise the protocol overhead when exchanging
   routes. Support for domain renumbering/readdressing

   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 [39], [40]. 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.

   It is still an open question as to whether it is possible or useful
   to support anycast addressing between cooperating domains. Address scoping

   R(31) The routing system MUST support scoping of unicast addresses,
         and SHOULD support scoping of multicast and anycast address

   For unicast address scoping, as is being designed for IPv6, does not
   seem to cause any special problems with respect to routing. IPv6
   Inter-domain routing handles only IPv6 global addresses, while intra-
   domain routing also needs to be aware of site-local addresses. Link-
   local addresses are never routed at all.

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

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   R(32) The routing system MUST support system mobility (and
         movability, and portability, whatever the differences may be).
         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
   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. Simple policy management

   The basic aims of this specification are:

   -  to require less manual configuration than today

   -  to satisfy both the requirements for easy handling, and maximum
      control, i.e.

      -  All the information should be available

      -  But should not be visible except for when desired.

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

      -  Provide Policy conflict Resolution

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   R(35) The routing system MUST provide for management of the system by
         means of policies; e.g. 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.

   R(36) The distribution of policies MUST be amenable to scoping, to
         protect proprietary policies that are not of relevance beyond
         the local set of domains from distribution. 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 need 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
         will minimize the disruption to the network caused by
         maintenance and upgrades of software and hardware.  It is
         recognized that some of the capabilities needed are outside the
         scope of the routing architecture (e.g. minimum impact software
         upgrade) but the routing system SHOULD provide the necessary
         support for such capabilities.

3.6.6 Provability

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

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

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   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
   divergence. A domain or group of domains in a system is defined as
   being convergent if and only if, after an exchange of routing
   information, routing tables reach a stable state that does not change
   until routing policies or topology changes.

   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 is possible.

   Tools are required that verify the stability characteristics of the
   routing system in specified parts of 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 a source of oscillations that arise
   from policy conflicts. Research is needed to prove that there is an
   efficient solution to the dynamic checking of oscillations.

3.6.7 Traffic engineering

   The ability to do traffic engineering and get the feedback from the
   network that enables traffic engineering are capabilities that should
   be included in the future domain architecture.  Traffic engineering
   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 under 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

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   At present there is an almost total lack of effective traffic
   engineering tools, whether on-line at all times for network control
   or off-line for network planning.  The routing system should
   encourage the 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 both in real time and for off-line
         planning and management. 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 on to a single path when the multiple paths
         are not needed.

   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 these
         peer routes so that traffic can be readily constrained to
         travel as the network operators desire and they can
         consequentially make optimal use of the available connectivity.

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3.6.8 Support for mid-boxes

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

   R(48) The routing system SHOULD work in conjunction with mid- boxes,
         e.g. NAT, to aid in bi-directional connectivity without
         compromising the additional opacity and privacy that the
         mid-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.  Currently the required values
   for these performance requirements are left for further discussion.

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

   R(50) Local convergence SHOULD occur within X units of time.

   R(51) The routing system MUST be 99.99x?% available.

   R(52) The routing system MUST be reliable as measured by TBD.

   R(53) The routing system MUST be locally stable as measured by TBD.

   R(54) The routing system MUST be globally stable as measured by TBD.

   R(55) The routing system SHOULD scale to an indefinitely large number
         of domains.

   In many cases there has been very little data or statistical evidence
   for many of the performance claims being made.  In recent years
   several efforts have been initiated to gather data and do the
   analyses required to make scientific assessments of the 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

   R(56) The introduction of the routing system MUST NOT require any
         flag days

   R(57) The network currently in place MUST continue to run at least as
         well as it does now while the new network is being brought in
         around it.

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

   R(58) The new architecture MUST NOT be limited by the restrictions
         that plague today's network.  [It has to be admitted that this
         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 whilst providing an
   architecture which will eventually allow them to be removed.

   These three requirements have significance not only for the
   transition strategy, but for the architecture itself implying that it
   must be possible for an internet such as today's BGP controlled
   network, or one of its ASes, to exist as a domain within the new FDR.

3.9 Security requirements

   As previously discussed, one of the major changes to have 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(59) The communicating entities MUST be able to identify who sent
         and who received the information (authentication)

   R(60) 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 to the other domains, then in intra-domain routing
   since 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

   R(61) 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(62) The routing communication mechanism MUST be robust against
         denial-of-service attacks.

   Further considerations that may impose requirements include:

   -  Whether no one else but the intended recipient must be able to
      access (privacy) or understand (confidentiality) the information.

   -  Whether it is possible to verify that all the information has been
      received (non-repudiation).

   -  Whether there is a need to separate security of routing from
      security of forwarding.

   -  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 if 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
   authentication and integrity of the information end-to-end.  This
   information includes both routes and addresses. There has been
   interest in having digital signatures both on originated routes, but
   also countersignatures by address authorities to confirm that the

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   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 straight to an address registry.  Where a
   prefix delegated by a provider is being advertised though 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
         mid-boxes whenever possible.

   This is likely to involve further requirements for abstraction of
   information, as, for example, the firewall 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 [32].

   R(64) The routing system MUST be capable of complying with local
         legal requirement 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-

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.  The model 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 the 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
   routing for traffic engineering.

   The naturalness of this network model and the 'fit' of the graph

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   theoretical methods may have tended to blind us to alternative
   representations and inhibited us from seeking out 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 effort to object model 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 in the best of
   all possible worlds, it might be best to have one protocol that
   handles all situations, this seems improbable in this less then best
   of all possible worlds.  On the other hand, maintaining the 'strict'
   division evident in the network today between the IGP and EGP has
   been effectively argued elsewhere as being 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, yes, a new protocol will need
   to be designed.

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3.10.4 Class of protocol to use

   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 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

   -  If we summarise too little, then more information then 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. Of course 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 ASes, domains, areas, and regions,
   need to be clearly identified and defined to avoid mixing from each

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

3.10.7 Robustness and redundancy:

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   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 for scaling control.

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

3.10.9 Will new control mechanisms be needed?

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

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

   At best, it might be possible to construct a new totally dynamical
   routing protocol solely on a control theoretic basis as opposed to
   the current protocols which are based in graph theory and static in

3.10.10 Byzantium

   Is solution to the Byzantine Generals problem a requirement?  This is
   the problem of reaching a consensus among distributed units if some

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   of them give misleading answers. The current intra-domain routing
   system is, at one level, totally intolerant of misleading
   information, but the effect of different sorts of misleading or
   incorrect information has vastly varying results, from total collapse
   through to purely local disconnection of a single domain.  This sort
   of behavior is not very desirable.

   What are some of the other network robustness issues that must be

3.10.11 VPN support

   Today BGP is also used for VPN and other stuff for example as
   described in RFC2547 [16].

   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 any 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
   currently are silent on this issue.

3.10.12 End to end reliability

   The existing Internet architecture neither requires or provides end-
   to-end reliability of control information dissemination.  For
   example, in distributing VPN information there is, however, a
   requirement for end to end reliability of control information, i.e.
   the ends of the VPN established need to have a 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
   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

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   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 in the rest of the

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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".

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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

   Group A Acknolwedgements

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

           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

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

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      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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   [1]   Clark, D., "Policy Routing in Internet Protocols", RFC 1102,
         May 1989.

   [2]   Estrin, D., "Requirements for Policy Based Routing in the
         Research Internet", RFC 1125, Nov 1989.

   [3]   Steenstrup, M., "An Architecture for Inter-Domain Policy
         Routing", RFC 1478, Jun 1993.

   [4]   Little, M., "Goals and Functional Requirements for
         Inter-Autonomous System Routing", RFC 1126, Jul 1989.

   [5]   Perlman, R., "Interconnections Second Edition", Addison Wesley
         Longman Inc., 1999.

   [6]   Perlman, R., "Network Layer Protocols with Byzantine
         Robust-ness", Ph.D Thesis, Department of Electrical Engineering
         and Computer Science, MIT, Aug 1988.

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

   [8]   Chiappa, N., "IPng Technical Requirements of the Nimrod Routing
         and Addressing Architecture", RFC 1753, Dec 1994.

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

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

   [11]  Labovitz, C., Ahuja, A., Farnam, J. and A. Bose, "Experimental
         Measurement of Delayed Convergence", Apricot , Mar 2000,

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

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

   [14]  Alaettinoglu, C., Jacobson, V. and H. Yu, "",
         draft-alaettinoglu-isis-convergence-00 (work in progress), Nov

   [15]  Sandick, H., Squire, M., Cain, B., Duncan, I. and B. Haberman,

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         "Fast LIveness Protocol (FLIP)", draft-sandiick-flip-00 (work
         in progress), Feb 2000.

   [16]  Rosen, E. and Y. Rekhter, "BGP/MPLS VPNs", RFC 2547, Mar 1999.

   [17]  Clark, D., Chapin, L., Cerf, V., Braden, R. and R. Hobby,
         "Towards the Future Internet Architecture", RFC 1287, Dec 1991.

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

   [19]  Seddigh, N., Nandy, B. and J. Heinanen, "An Assured Rate
         Per-Domain Behaviour for Differentiated Services",
         draft-ietf-diffserv-pdb-ar-00 (work in progress), Feb 2001.

   [20]  McPherson, D., Gill, V., Walton, D. and A. Retana, "BGP
         Persistent Route Oscillation Condition",
         draft-mcpherson-bgp-route-oscillation-00 (work in progress),
         Dec 2000.

   [21]  Hain, T., "Architectural Implications of NAT", RFC 2993, Nov

   [22]  McPherson, D. and T. Przygienda, "OSPF Transient Blackhole
         Avoidance", draft-mcpherson-ospf-transient-00 (work in
         progress), Jul 2000.

   [23]  Thaler, D., Estrin, D. and D. Meyer, "Border Gateway Multicast
         Protocol (BGMP): Protocol Specification",
         draft-ietf-bgmp-spec-02 (work in progress), Nov 2000.

   [24]  Rosen, E., "Multiprotocol Label Switching Architecture", RFC
         3031, Jan 2001.

   [25]  Ashwood-Smith, P., "Generalized MPLS - Signaling Functional
         Description", draft-ietf-mpls-generalized-signaling-01 (work in
         progress), Nov 2000.

   [26]  "IETF Resource Allocation Protocol working group",  , 2002,

   [27]  "IETF Configuration management with SNMP working group",  ,
         2002, <http://www.ietf.org/html.charters/

   [28]  "IETF Policy working group",  , 2002, <http://www.ietf.org/

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   [29]  Yu, J., "Scalable Routing Design Principles", RFC 2791, Jul

   [30]  "Telcordia Technologies Netsizer web site",  , 2002, <http://

   [31]  "Inference of Shared Risk Link Groups",
         draft-many-inference-srlg-00 (work in progress), Feb 2001.

   [32]  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>.

   [33]  Lang, J., "Link Management Protocol", draft-lang-mpls-lmp-02
         (work in progress), Jul 2000.

   [34]  Xu, Z., Dai, S. and J. Garcia-Luna-Aceves, "A More Efficient
         Distance Vector Routing Algorithm", Proc IEEE MILCOM 97,
         Monterey, California, Nov 1997, <http://www.cse.ucsc.edu/

   [35]  Bradner, S. and A. Mankin, "The Recommendation for the IP Next
         Generation Protocol", RFC 1752, Jan 1995.

   [36]  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.

   [37]  Bates, T., Rekhter, Y., Chandra, R. and D. Katz, "Multiprotocol
         Extensions to BGP-4", RFC 2858, Jun 2000.

   [38]  Berkowitz, H. and D. Krioukov, "To Be Multihomed: Requirements
         and Definitions", draft-berkowitz-multirqmt-02 (work in
         progress), Oct 1999.

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

   [40]  Berkowitz, H., "Router Renumbering Guide", RFC 2072, Jan 1997.

   [41]  Doria, A., "Analysis of IDR requirements and History",
         draft-groupb-irtf-rr-history-00 (work in progress), Feb 2002.

   [42]  Grossman, D., "New Terminology and Clarifications for
         Diffserv", draft-ietf-diffserv-new-terms-08 (work in progress),
         Jan 2002.

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   [43]  Broido, A., Nemeth, E., Claffy, K. and C. Elves, "Internet
         Expansion, Refinement and Churn", Presentation at Nanog , Feb

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

   [45]  Perkins, C., "IP Mobility Support.", RFC 2002, Oct 1996.

Authors' Addresses

   Avri Doria
   161 Gajeong-dong
   Daejeon, RI  305-350

   Phone: +82 16 9608 5024
   EMail: avri@acm.org

   Elwyn B. Davies
   Nortel Networks
   Harlow Laboratories
   London Road
   Harlow, Essex  CM17 9NA

   Phone: +44 1279 405 498
   Fax:   +44 1279 405 514
   EMail: elwynd@nortelnetworks.com

   Frank Kastenholz
   Juniper Networks
   10 Technology Park
   Westford, MA  01886

   Phone: +1 978 589 0286
   EMail: fkastenholz@juniper.net

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