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Network Working Group                                           A. Doria
Internet-Draft                                                      ETRI
Expires: January 17, 2005                                      E. Davies
                                                         Nortel Networks
                                                           July 19, 2004

                Analysis of IDR requirements and History

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Copyright Notice

   Copyright (C) The Internet Society (2004).  All Rights Reserved.


   This document analyses the current state of IDR routing with respect
   to RFC1026 and other IDR requirements and design efforts.  It is the
   companion document to version 03 of the inter-domain routing
   requirements draft [41], which is a discussion of requirements for
   the future routing architecture and future routing protocols.

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Table of Contents

   1.   Introduction . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1  Background . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.   Historical Perspective . . . . . . . . . . . . . . . . . . .   4
     2.1  The legacy of RFC1126  . . . . . . . . . . . . . . . . . .   4
       2.1.1  "General Requirements" . . . . . . . . . . . . . . . .   5
       2.1.2  "Functional Requirements"  . . . . . . . . . . . . . .   7
       2.1.3  "Non-Goals"  . . . . . . . . . . . . . . . . . . . . .  14
     2.2  Nimrod Requirements  . . . . . . . . . . . . . . . . . . .  16
     2.3  PNNI . . . . . . . . . . . . . . . . . . . . . . . . . . .  17
     2.4  ISO  . . . . . . . . . . . . . . . . . . . . . . . . . . .  18
     2.5  Recent Research Work . . . . . . . . . . . . . . . . . . .  18
       2.5.1  Developments in Internet Connectivity  . . . . . . . .  18
       2.5.2  Defending the End To End Principle . . . . . . . . . .  19
   3.   Existing problems of BGP and the current  EGP/IGP
        Architecture . . . . . . . . . . . . . . . . . . . . . . . .  20
     3.1  BGP and Auto-aggregation . . . . . . . . . . . . . . . . .  21
     3.2  Convergence and Recovery Issues  . . . . . . . . . . . . .  21
     3.3  Non-locality of Effects of Instability and
          Misconfiguration . . . . . . . . . . . . . . . . . . . . .  22
     3.4  Multihoming Issues . . . . . . . . . . . . . . . . . . . .  22
     3.5  AS-number exhaustion . . . . . . . . . . . . . . . . . . .  23
     3.6  Partitioned AS's . . . . . . . . . . . . . . . . . . . . .  24
     3.7  Load Sharing . . . . . . . . . . . . . . . . . . . . . . .  24
     3.8  Hold down issues . . . . . . . . . . . . . . . . . . . . .  24
     3.9  Interaction between Inter domain routing and intra
          domain routing . . . . . . . . . . . . . . . . . . . . . .  25
     3.10   Policy Issues  . . . . . . . . . . . . . . . . . . . . .  26
     3.11   Security Issues  . . . . . . . . . . . . . . . . . . . .  26
     3.12   Support of MPLS and VPNS . . . . . . . . . . . . . . . .  26
     3.13   IPv4 / IPv6 Ships in the Night . . . . . . . . . . . . .  27
     3.14   Existing Tools to Support Effective Deployment of
            Inter-Domain Routing . . . . . . . . . . . . . . . . . .  27
       3.14.1   Routing Policy Specification Language RPSL  (RFC
                2622, 2650) and RIPE NCC Database (RIPE 157) . . . .  28
   4.   Security Considerations  . . . . . . . . . . . . . . . . . .  28
   5.   Acknowledgments  . . . . . . . . . . . . . . . . . . . . . .  29
   6.   References . . . . . . . . . . . . . . . . . . . . . . . . .  29
        Authors' Addresses . . . . . . . . . . . . . . . . . . . . .  32
        Intellectual Property and Copyright Statements . . . . . . .  33

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1.  Introduction

   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.

   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.

   This draft makes a start on the analysis of domain routing in Section
   2 by revisiting the requirements for a future routing system which
   were last documented in RFC1126 - "Goals and Functional Requirements
   for Inter-Autonomous System Routing" [4] as a precursor to the design
   of BGP in 1989.  This section also looks at some other work that has
   been carried out since RFC1126 was published in order to flesh out
   the historical perspective.  Some of the requirements for new routing
   architectures derive from the problems that are currently being
   experienced in the Internet today.  These will be discussed in
   Section 3.

1.1  Background

   Today's Internet uses an addressing and routing structure that has
   developed in an ad hoc, more or less upwards-compatible fashion.  It
   has progressed from handling a single domain, non-commercial Internet
   to a solution that is just about controlling today's multi-domain,
   federated, combination commercial and not-for-profit Internet.  The
   result is not ideal, particularly as regards inter-domain routing
   mechanisms that have to implement a host of domain specific routing

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   policies for competing, communicating domains, but it does a pretty
   fair job at its primary goal of providing any-to-any connectivity to
   many millions of computers.

   Based on a large body of anecdotal evidence, but also on a growing
   body of experimental evidence [11] and analytic work on the stability
   of BGP under certain policy specifications [12], the main Internet
   inter-domain routing protocol, BGP4, appears to have a number of
   problems that need to be resolved.  Additionally, the hierarchical
   nature of the inter-domain routing problem appears to be changing as
   the connectivity between domains becomes increasingly meshed [13]
   which alters some of the scaling and structuring assumptions on which
   BGP4 is built.  Patches and fix-ups may relieve some of these
   problems but others may require a new architecture and new protocols.

   Since the original version of this draft was published a number of
   the initiatives mentioned (such as the DARPA NewArch project
   described in Section 2.5.2) have continued researching the way
   forwards for the Internet.  There have also been continuing efforts
   in the IETF multi6 working group to resolve the problems of
   multihoming especially in IPv6.  Some of the explosive growth of the
   routing tables has been quenched by the economic downturn since the
   end of 2000, but this has not resolved the problems that existed with
   inter-domain routing.  The contents of this draft remain relevant to
   the Internet today and the intention is to provide further updates to
   document the research efforts that have been going on over the last
   couple of years.

2.  Historical Perspective

2.1  The legacy of RFC1126

   RFC1126 outlined a set of requirements that were to guide the
   development of BGP.  While the network is definitely different then
   it was in 1989, many of the same requirements remain.  As a first
   step in setting requirements for the future, we need to understand
   the requirements that were originally set for the current protocols.
   And in charting a future architecture we must first be sure to do no
   harm.  This means a future domain routing has to support as its base
   requirement, the level of function that is available today.

   The following sections each relate to a requirement, or non-
   requirement listed in RFC1126.  In fact the section names are direct
   quotes from the document.  The discussion of these requirements
   covers the following areas:

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   Explanation:       Optional interpretation for today's audience of
                      the original intent of the requirement
   Relevance:         Is the requirement of RFC1126 still relevant, and
                      to what degree? Should it be understood
                      differently in today's environment?
   Current practice:  How well is the requirement met by current
                      protocols and practice?

2.1.1  "General Requirements"  "Route to Destination"

   Timely routing to all reachable destinations, including multihoming
   and multicast.
   Relevance:         Valid, but requirements for multihoming need
                      further discussion and elucidation.  The
                      requirement should include multiple source
                      multicast routing.
   Current practice:  Multihoming is not efficient and the proposed
                      inter-domain multicast protocol BGMP is an add-on
                      to BGP following many of the same strategies but
                      not integrated into the BGP framework [23].  "Routing is Assured"

   This requires that a user be notified within a reasonable time period
   of attempts, about inability to provide a service.
   Relevance:         Valid
   Current practice:  There are ICMP messages for this, but in many
                      cases they are not used, either because of fears
                      about creating message storms or uncertainty about
                      whether the end system can do anything useful with
                      the resulting information.  "Large System"

   The architecture was designed to accommodate the growth of the
   Relevance:         Valid.  Properties of Internet topology might be
                      an issue for future scalability (topology varies
                      from very sparse to quite dense at present).
                      Instead of setting growth in a time-scale,
                      indefinite growth should be accommodated.  On the
                      other hand, such growth has to be accommodated
                      without making the protocols too expensive -
                      trade-offs may be necessary.

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   Current practice:  Scalability of the current protocols will not be
                      sufficient under the current rate of growth.
                      There are problems with BGP convergence for large
                      dense topologies, problems with routing
                      information propagation between routers in transit
                      domain, limited support for hierarchy, etc.  "Autonomous Operation"
   Relevance:         Valid.  There may need to be additional
                      requirements for adjusting policy decisions to the
                      global functionality and for avoiding
                      contradictory policies.  This would decrease the
                      possibility of unstable routing behavior.
                      There is a need for handling various degrees of
                      trust in autonomous operations, ranging from no
                      trust (e.g., between separate ISPs) to very high
                      trust where the domains have a common goal of
                      optimizing their mutual policies.
                      Policies for intra domain operations should in
                      some cases be revealed, using suitable
   Current practice:  Policy management is in the control of network
                      managers, as required, but there is little support
                      for handling policies at an abstract level for a
                      Cooperating administrative entities decide about
                      the extent of cooperation independently.  Lack of
                      coordination combined with global range of effects
                      results in occasional melt-down of Internet
                      routing.  "Distributed System"

   The routing environment is a distributed system.  The distributed
   routing environment supports redundancy and diversity of nodes and
   links.  Both data and operations are distributed.
   Relevance:         Valid.  RFC1126 is very clear that we should not
                      be using centralized solutions, but maybe we need
                      a discussion on trade-offs between common
                      knowledge and distribution (i.e., to allow for
                      uniform policy routing, e.g., GSM systems are in a
                      sense centralized, but with hierarchies)
   Current practice:  Routing is very distributed, but lacking abilities
                      to consider optimization over several hops or

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Internet-Draft                IDR History                      July 2004  "Provide A Credible Environment"

   Routing mechanism information must be integral and secure (credible
   data, reliable operation).  Security from unwanted modification and
   influence is required.
   Relevance:         Valid.
   Current practice:  BGP provides a mechanism for authentication and
                      There are however security problems with current
                      practice.  "Be A Managed Entity"

   Requires that a manager should get enough information on a state of
   network so that s/he could make informed decisions.
   Relevance:         The requirement is reasonable, but we might need
                      to be more specific on what information should be
                      available, e.g.  to prevent routing oscillations.
   Current practice:  All policies are determined locally, where they
                      may appear reasonable but there is limited global
                      coordination through the routing policy databases
                      operated by the Internet registries (ARIN, RIPE,
                      APNIC etc).
                      Operators are not required to register their
                      policies; even when policies are registered, it is
                      difficult to check that the actual policies in use
                      match the declared policies and therefore a
                      manager cannot guarantee to make a globally
                      consistent decision.  "Minimize Required Resources"
   Relevance:         Valid, however, the paragraph states that
                      assumptions on significant upgrades shouldn't be
                      made.  Although this is reasonable, a new
                      architecture should perhaps be prepared to use
                      upgrades when they occur.
   Current practice:  Most bandwidth is consumed by the exchange of the
                      NLRI.  Usage of CPU depends on the stability of
                      the Internet.  Both phenomena have a local nature,
                      so there are not scaling problems with bandwidth
                      and CPU usage.  Instability of routing increases
                      the consumption of resources in any case.  The
                      number of networks in the Internet dominates
                      memory requirements - this is a scaling problem.

2.1.2  "Functional Requirements"

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Internet-Draft                IDR History                      July 2004  "Route Synthesis Requirements"  "Route around failures dynamically"
   Relevance:         Valid.  Should perhaps be stronger.  Only
                      providing a best- effort attempt may not be enough
                      if real-time services are to be provided for.
                      Detections may need to be faster than 100ms to
                      avoid being noticed by end-users.
   Current practice:  latency of fail-over is too high; sometimes
                      minutes or longer.  "Provide loop free paths"
   Relevance:         Valid.  Loops should occur only with negligible
                      probability and duration.
   Current practice:  both link-state intra domain routing and BGP
                      inter- domain routing (if correctly configured)
                      are forwarding- loop free after having converged.
                      However, convergence time for BGP can be very long
                      and poorly designed routing policies may result in
                      a number of BGP speakers engaging in a cyclic
                      pattern of advertisements and withdrawals which
                      never converges to a stable result [20].  Perhaps
                      this is one context in which the need for global
                      convergence needs to be reviewed.  "Know when a path or destination is unavailable"
   Relevance:         Valid to some extent, but there is a trade-off
                      between aggregation and immediate knowledge of
                      reachability.  It requires that routing tables
                      contain enough information to determine that the
                      destination is unknown or a path cannot be
                      constructed to reach it.
   Current practice:  Knowledge about lost reachability propagates
                      slowly through the networks due to slow
                      convergence for route withdrawals.  "Provide paths sensitive to administrative policies"
   Relevance:         Valid.  Policy control of routing is of
                      increasingly importance as the Internet has turned
                      into business.
   Current practice:  Supported to some extent.  Policies are only
                      possible to apply locally in an AS and not
                      globally.  At least there is a very small
                      probability of affecting policies in other AS's.
                      Furthermore, only static policies are supported;
                      between static policies and `policies dependent
                      upon volatile events of great celerity` there
                      should exist events that routing should be aware

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                      of.  Lastly, there is no support for policies
                      other than route- properties (such as AS-origin,
                      AS-path, destination prefix, MED-values etc).  "Provide paths sensitive to user policies"
   Relevance:         Valid to some extent, as they may conflict with
                      the policies of the network administrator.  It is
                      likely that this requirement will be met by means
                      of different bit transport services offered by an
                      operator, but at the cost of adequate
                      provisioning, authentication and policing when
                      utilizing the service.
   Current practice:  not supported in normal routing.  Can be
                      accomplished to some extent with loose source
                      routing, resulting in inefficient forwarding in
                      the routers.  The various attempts to introduce
                      QoS (Integrated Services and DiffServ) can also be
                      seen as means to support this requirement but they
                      have met with limited success.  "Provide paths which characterize user quality-of-service
   Relevance:         Valid to some extent, as they may conflict with
                      the policies of the operator.  It is likely that
                      this requirement will be met by means of different
                      bit transport services offered by an operator, but
                      at the cost of adequate provisioning,
                      authentication and policing when utilizing the
                      service.  It has become clear that offering to
                      provide a particular QoS to any arbitrary
                      destination from a particular source is generally
                      impossible:  QoS except in very 'soft' forms such
                      as overall long term average packet delay, is
                      generally associated with connection oriented
   Current practice:  Creating routes with specified QoS is not
                      generally possible at present.  "Provide autonomy between inter- and intra-autonomous system
          route synthesis"
   Relevance:         Inter and intra domain routing should stay
                      independent, but one should notice that this to
                      some extent contradicts the previous three
                      requirements.  There is a trade-off between
                      abstraction and optimality.

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   Current practice:  inter-domain routing is performed independently of
                      intra-domain routing.  Intra-domain routing is,
                      especially in transit domains, very interrelated
                      to inter-domain routing.  "Forwarding Requirements"  "Decouple inter- and intra-autonomous system forwarding
   Relevance:         Valid.
   Current practice:  As explained in, intra-domain forwarding
                      in transit domains is codependent with
                      inter-domain forwarding decisions.  "Do not forward datagrams deemed administratively
   Relevance:         Valid, and increasingly important in the context
                      of enforcing policies correctly expressed through
                      routing advertisements but flouted by rogue peers
                      which send traffic for which a route has not been
                      advertised.  On the other hand, packets that have
                      been misrouted due to transient routing problems
                      perhaps should be forwarded to reach the
                      destination, although along an unexpected path.
   Current practice:  at stub domains there is packet filtering, e.g.,
                      to catch source address spoofing on outgoing
                      traffic or to filter out unwanted incoming
                      traffic.  Filtering can in particular reject
                      traffic (such as unauthorized transit traffic)
                      that has been sent to a domain even when it has
                      not advertised a route for such traffic on a given
                      interface.  The growing class of 'mid boxes' (e.g.
                      NATs) is quite likely to apply administrative
                      rules that will prevent forwarding of packets.
                      Note that security policies may deliberately hide
                      administrative denials.  In the backbone,
                      intentional packet dropping based on policies is
                      not common.  "Do not forward datagrams to failed resources"
   Relevance:         Unclear, although it is clearly desirable to
                      minimise waste of forwarding resources by
                      discarding datagrams which cannot be delivered at
                      the earliest opportunity.  There is a trade-off
                      between scalability and keeping track of
                      unreachable resources.  Equipment closest to a
                      failed node has the highest motivation to keep
                      track of failures so that waste can be minimised.

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   Current practice:  routing protocols use both internal adjacency
                      management sub-protocols (e.g.  Hello protocols)
                      and information from equipment and lower layer
                      link watchdogs to keep track of failures in
                      routers and connecting links.  Failures will
                      eventually result in the routing protocol
                      reconfiguring the routing to avoid (if possible) a
                      failed resource, but this is generally very slow
                      (30s or more).  In the meantime datagrams may well
                      be forwarded to failed resources.  In general
                      terms, end hosts and some non- router midboxes do
                      not participate in these notifications and
                      failures of such boxes will not affect the routing
                      system.  "Forward datagram according to its characteristics"
   Relevance:         Valid.  This is necessary in enabling
                      differentiation in the network, based on QoS,
                      precedence, policy or security.
   Current practice:  ingress and egress filtering can be done based on
                      policy.  "Information Requirements"  "Provide a distributed and descriptive information base"
   Relevance:         Valid, however hierarchical information bases
                      might provide more possibilities.
   Current practice:  the information base is distributed, it is unclear
                      whether they support all necessary routing
                      functionality.  "Determine resource availability"
   Relevance:         Valid.  It should be possible for resource
                      availability and levels of resource availability
                      to be determined.  This prevents needing to
                      discover unavailability through failure.  Resource
                      location and discovery is arguably a separate
                      concern that could be addressed outside the core
                      routing requirements.
   Current practice:  Resource availability is predominantly handled
                      outside of the routing system.  "Restrain transmission utilization"
   Relevance:         Valid.  However certain requirements in the
                      control plane, such as fast detection of faults
                      may be worth consumption of more resources.
                      Similarly, simplicity of implementation may make
                      it cheaper to 'back haul' traffic to central

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                      locations to minimise the cost of routing if
                      bandwidth is cheaper than processing.
   Current practice:  BGP messages probably do not ordinarily consume
                      excessive resources, but might during erroneous
                      conditions.  In the data plane, the near universal
                      adoption of shortest path protocols could be
                      considered to result in minimization of
                      transmission utilization.  "Allow limited information exchange"
   Relevance:         Valid.  But perhaps routing could be improved if
                      certain information could be available either
                      globally or at least for a wider defined locality.
   Current practice:  Policies are used to determine which reachability
                      information that is exported.  "Environmental Requirements"  "Support a packet-switching environment"
   Relevance:         Valid but routing system should not be limited to
                      this exclusively.
   Current practice:  supported.  "Accommodate a connection-less oriented user  transport
   Relevance:         Valid, but routing system should not be limited to
                      this exclusively.
   Current practice:  accommodated.  "Accommodate 10K autonomous systems and 100K networks"
   Relevance:         No longer valid.  Needs to be increased
                      potentially indefinitely.  It is extremely
                      difficult to foresee the future size expansion of
                      the Internet so that the utopian solution would be
                      to achieve an Internet whose architecture is scale
                      invariant.  Regrettably, this may not be
                      achievable without introducing undesirable
                      complexity and a suitable trade off between
                      complexity and scalability is likely to be
   Current Practice:  Supported but perhaps reaching its limit.  "Allow for arbitrary interconnection of autonomous systems"
   Relevance:         Valid.  However perhaps not all interconnections
                      should be accessible globally.

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   Current practice:  BGP-4 allows for arbitrary interconnections.  "General Objectives"  "Provide routing services in a timely manner"
   Relevance:         Valid, as stated before.  The more complex a
                      service is the longer it should be allowed to
                      take, but the implementation of services requiring
                      (say) NP-complete calculation should be avoided.
   Current practice:  More or less, with the exception of convergence
                      and fault robustness.  "Minimize constraints on systems with limited resources"
   Relevance:         Valid
   Current practice:  Systems with limited resources are typically stub
                      domains that advertise very little information.  "Minimize impact of dissimilarities between  autonomous
   Relevance:         Important.  This requirement is critical to a
                      future architecture.  In a domain routing
                      environment where the internal properties of
                      domains may differ radically, it will be important
                      to be sure that these dissimilarities are
                      minimized at the borders.
   Current: practice: For the most part this capability isn't required
                      in today's networks since the intra-domain
                      attribute are nearly identical to start with.  "Accommodate the addressing schemes and protocol mechanisms
          of the autonomous systems"
   Relevance:         Important, probably more so than when RFC1126 was
                      originally developed because of the potential
                      deployment of IPv6, wider usage of MPLS and the
                      increasing usage of VPNs.
   Current practice:  Largely only one global addressing scheme is
                      supported in most autonomous systems.  "Must be implementable by network vendors"
   Relevance:         Valid, but note that what can be implemented today
                      is different from what was possible when RFC1126
                      was written: a future domain routing architecture
                      should not be unreasonably constrained by past
   Current practice:  BGP was implemented.

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2.1.3  "Non-Goals"

   RFC1126 also included a section discussing non-goals.  To what extent
   are these still non-goals?  Does the fact that they were non-goals
   adversely affect today's IDR system?  "Ubiquity"

   In a sense this 'non-goal' has effectively been achieved by the
   Internet and IP protocols.  This requirement reflects a different
   worldview where there was serious competition for network protocols,
   which is really no longer the case.  Ubiquitous deployment of inter-
   domain routing in particular has been achieved and must not be undone
   by any proposed future domain routing architecture.  On the other
   -  ubiquitous connectivity cannot be reached in a policy sensitive
      environment and should not be an aim,
   -  it must not be required that the same routing mechanisms are used
      throughout provided that they can interoperate appropriately
   -  the information needed to control routing in a part of the network
      should not necessarily be ubiquitously available and it must be
      possible for an operator to hide commercially sensitive
      information that is not needed outside a domain.
   Relevance:         De facto essential for a future domain routing
                      architecture, but what is required is ubiquity of
                      the routing system rather than ubiquity of
   Current practice:  de facto ubiquity achieved.  "Congestion control"
   Relevance:         It is not clear if this non-goal was to be applied
                      to routing or forwarding.  It is definitely a
                      non-goal to adapt the choice of route at transient
                      congestion.  However, to add support for
                      congestion avoidance (e.g., ECN and ICMP messages)
                      in the forwarding process would be a useful
                      addition.  There is also extensive work going on
                      in traffic engineering which should result in
                      congestion avoidance through routing as well as in
   Current practice:  Some ICMP messages (e.g.  source quench) exist to
                      deal with congestion control but these are not
                      generally used as they either make the problem
                      worse or there is no mechanism to reflect the
                      message into the application which is providing
                      the source.

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Internet-Draft                IDR History                      July 2004  "Load splitting"
   Relevance:         This should neither be a non-goal, nor an explicit
                      goal.  It might be desirable in some cases and
                      should be considered as an optional architectural
   Current practice:  Can be implemented by exporting different prefixes
                      on different links, but this requires manual
                      configuration and does not consider actual load.  "Maximizing the utilization of resources"
   Relevance:         Valid.  Cost-efficiency should be strived for;
                      maximizing resource utilization does not always
                      lead to greatest cost-efficiency.
   Current practice:  Not currently part of the system, though often a
                      'hacked in' feature done with manual
                      configuration.  "Schedule to deadline service"

   This non-goal was put in place to ensure that the IDR did not have to
   meet real time deadline goals such as might apply to CBR services in
   Relevance:         The hard form of deadline services is still a
                      non-goal for the future domain routing
                      architecture but overall delay bounds are much
                      more of the essence than was the case when RFC1126
                      was written.
   Current Practice:  Service providers are now offering overall
                      probabilistic delay bounds on traffic contracts.
                      To implement these contracts there is a
                      requirement for a rather looser form of delay
                      sensitive routing.  "Non-interference policies of resource utilization"

   The requirement in RFC1126 is somewhat opaque, but appears to imply
   that what we would today call QoS routing is a non-goal and that
   routing would not seek to control the elastic characteristics of
   Internet traffic whereby a TCP connection can seek to utilize all the
   spare bandwidth on a route, possibly to the detriment of other
   connections sharing the route or crossing it.
   Relevance:         Open Issue.  It is not clear whether dynamic QoS
                      routing can or should be implemented.  Such a
                      system would seek to control the admission and
                      routing of traffic depending on current or recent
                      resource utilization.  This would be particularly
                      problematic where traffic crosses an ownership
                      boundary because of the need for potentially

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                      commercially sensitive information to be made
                      available outside the ownership boundary.
   Current practice:  Routing does not consider dynamic resource
                      availability.  Forwarding can support service

2.2  Nimrod Requirements

   Nimrod as expressed by Noel Chiappa in his early document, "A New IP
   Routing and Addressing Architecture" (1991) and later in the NIMROD
   Working Group documents RFC 1753 and RFC1992 established a number of
   requirements that need to be considered by any new routing
   architecture.  The Nimrod requirements took RFC1126 as a starting
   point and went further.

   The goals of Nimrod, quoted from RFC1992, were as follows
   1.  To support a dynamic internetwork of *arbitrary size* (our
       emphasis) by providing mechanisms to control the amount of
       routing information that must be known throughout an
   2.  To provide service-specific routing in the presence of multiple
       constraints imposed by service providers and users.
   3.  To admit incremental deployment throughout an internetwork.
   -  As discussed in other sections of this document the amount of
      information needed to maintain the routing system is growing at a
      rate that does not scale.  And yet, as the services and
      constraints upon those services grow there is a need for more
      information to be maintained by the routing system.  One of the
      key terms in the first requirements is 'control'.  While
      increasing amounts of information need to be known and maintained
      in the Internet, the amounts and kinds of information that are
      distributed can be controlled.  This goal should be reflected in
      the requirements for the future domain architecture.
   -  If anything, the demand for specific services in the Internet has
      grown since 1996 when the Nimrod architecture was published.
      Additionally the kinds of constraints that service providers need
      to impose upon their networks and that services need to impose
      upon the routing have also increased.  Any changes made to the
      network in the last half-decade have not significantly improved
      this situation.
   -  The ability to incrementally deploy any new routing architecture
      within the Internet is still a absolute necessity.  It is
      impossible to imagine that a new routing architecture could
      supplant the current architecture on a flag day

   At one point in time Nimrod, with its addressing and routing
   architectures was seen as a candidate for IPng.  History shows that
   it was not accepted as the IPng, having been ruled out of the

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   selection process by the IESG in 1994 on the grounds that it was 'too
   much of a research effort' [35], although input for the requirements
   of IPng was explicitly solicited from Chiappa [8].  Instead IPv6 has
   been put forth as the IPng.  Without entering a discussion of the
   relative merits of IPv6 versus Nimrod, it is apparent that IPv6,
   while it may solve many problems, does not solve the critical routing
   problems in the Internet today.  In fact in some sense it exacerbates
   them by adding a requirements for support of two internet protocols
   and their respective addressing methods.  In many ways the addition
   of IPv6 to the mix of methods in today's Internet only points to the
   fact that the goals, as set forth by the Nimrod team, remain as
   necessary goals.

   There is another sense in which study of Nimrod and its architecture
   may be important to deriving a future domain routing architecture.
   Nimrod can be said to have two derivatives:
   -  MPLS in that it took the notion of forwarding along well known
   -  PNNI in that it took the notion of abstracting topological
      information and using that information to create connections for

   It is important to note, that whilst MPLS and PNNI borrowed ideas
   from Nimrod, neither of them can be said to be an implementation of
   this architecture.

2.3  PNNI

   PNNI was developed under the ATM Forum's auspices as a hierarchical
   route determination protocol for ATM, a connection oriented
   architecture.  It is reputed to have developed several of it methods
   from a study of the Nimrod architecture.  What can be gained from an
   analysis of what did and did not succeed in PNNI?

   The PNNI protocol includes the assumption that all peer groups are
   willing to cooperate, and that the entire network is under the same
   top administration.  Are there limitations that stem from this 'world
   node' presupposition?  As discussed in [13], the Internet is no
   longer a clean hierarchy and there is a lot of resistance to having
   any sort of 'ultimate authority' controlling or even brokering

   PNNI is the first deployed example of a routing protocol that uses
   abstract map exchange (as opposed to distance vector or link state
   mechanisms) for inter-domain routing information exchange.  One
   consequence of this is that domains need not all use the same
   mechanism for map creation.  What were the results of this
   abstraction and source based route calculation mechanism?

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   Since the authors of this document do not have experience running a
   PNNI network, the comments above are from a theoretical perspective.
   Information on these issues, and any other relevant issues, is
   solicited from those who do have such operational experience.  Any

2.4  ISO

   Note: [At IETF52, a long time ago now a presentation on this draft
   was made to the IETF routing group was made.  I was reminded that ISO
   had already tackled this problem as well, and that their efforts
   should be reviewed as well.  That work is still pending a year later.
   Any volunteers to write this section?]

2.5  Recent Research Work

2.5.1  Developments in Internet Connectivity

   The recent work commissioned from Geoff Huston by the Internet
   Architecture Board [13] draws a number of conclusions from analysis
   of BGP routing tables and routing registry databases:
   -  The connectivity between provider ASs is becoming more like a
      dense mesh than the tree structure that was commonly assumed to be
      commonplace a couple of years ago.  This has been driven by the
      increasing amounts charged for peering and transit traffic by
      global service providers.  Local direct peering and internet
      exchanges are becoming steadily more common as the cost of local
      fibre connections drops.
   -  End user sites are increasingly resorting to multi-homing onto two
      or more service providers as a way of improving resiliency.  This
      has a knock-on effect of spectacularly fast depletion of the
      available pool of AS numbers as end user sites require public AS
      numbers to become multi-homed and corresponding increase in the
      number of prefixes advertised in BGP.
   -  Multi-homed sites are using advertisement of longer prefixes in
      BGP as a means of traffic engineering to load spread across their
      multiple external connections with further impact on the size of
      the BGP tables.
   -  Operational practices are not uniform, and in some cases lack of
      knowledge or training is leading to instability and/or excessive
      advertisement of routes by incorrectly configured BGP speakers.
   -  All these factors are quickly negating the advantages in limiting
      the expansion of BGP routing tables that were gained by the
      introduction of CIDR and consequent prefix aggregation in BGP.  It
      is also now impossible for IPv6 to realize the world view in which
      the default free zone would be limited to perhaps 10,000 prefixes.

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   -  The typical 'width' of the Internet in AS hops is now around five,
      and much less in many cases.

   These conclusions have a considerable impact on the requirements for
   the future domain routing architecture:
   -  Topological hierarchy (e.g.  mandating a tree structured
      connectivity) cannot be relied upon to deliver scalability of a
      large Internet routing system
   -  Aggregation cannot be relied upon to constrain the size of routing
      tables for an all-informed routing system

2.5.2  Defending the End To End Principle

   DARPA is funding a project to think about a new architecture for
   future generation Internet, called NewArch
   (http://www.isi.edu/newarch/).  Work started in the first half of
   2000.  When this draft was originally published, work was only just
   getting under way and little in the way of results had been
   published.  Since then significant work has been done both on
   addressing architectures and a novel routing paradigm.

   The main conclusion of the the initial work was that as the Internet
   becomes mainstream infrastructure, fewer and fewer of the
   requirements are truly global but may apply with different force or
   not at all in certain parts of the network.  This (it is claimed)
   makes the compilation of a single, ordered list of requirements
   deeply problematic.  Instead we may have to produce multiple
   requirement sets with support for differing requirement importance at
   different times and in different places.  This 'meta-requirement'
   significantly impacts architectural design.

   Potential new technical requirements identified included:
   -  Commercial environment concerns such as richer inter-provider
      policy controls and support for a variety of payment models
   -  Trustworthiness
   -  Ubiquitous mobility
   -  Policy driven self-organisation ('deep auto configuration')
   -  Extreme short-time-scale resource variability
   -  Capacity allocation mechanisms
   -  Speed, propagation delay and Delay/BandWidth Product issues

   Non-technical or political 'requirements' include:
   -  Legal and Policy drivers such as
      o  Privacy and free/anonymous speech
      o  Intellectual property concerns

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      o  Encryption export controls
      o  Law enforcement surveillance regulations
      o  Charging and taxation issues
   -  Reconciling national variations and consistent operation in a
      world wide infrastructure

   One of the participants in this work (Dave Clark) with one of his
   associates has also published a very interesting paper analyzing the
   impact of some of these new requirements on the end-to-end principle
   that has guided the development of the Internet to date [32].  Their
   primary conclusion is that the loss of trust between the users at the
   ends of end to end has the most fundamental effect on the Internet.
   This is clear in the context of the routing system, where operators
   are unwilling to reveal the inner workings of their networks for
   commercial reasons.  Similarly, trusted third parties and their
   avatars (mainly mid-boxes of one sort or another) have a major impact
   on the end-to-end principles and the routing mechanisms that went
   with them.  Overall, the end to end principles should be defended so
   far as is possible - some changes are already too deeply embedded to
   make it possible to go back to full trust and openness - at least
   partly as a means of staving off the day when the network will ossify
   into an unchangeable form and function (much as the telephone network
   has done).  The hope is that by that time a new Internet will appear
   to offer a context for unfettered innovation.

   In line with a number of other research and discussion streams, the
   NewArch project appears to be embracing the necessity of separating
   the locator and identifier functions of today's IP addresses with the
   resultant consequences for the inter-domain routing system.  A number
   of interesting papers have now been published covering possible
   modifications to the addressing architecture (FARA) and an
   alternative inter-domain routing scheme (NIRA).  Pointers to these
   papers can be found on the NewArch website.

3.  Existing problems of BGP and the current  EGP/IGP Architecture

   Although most of the people who have to work with BGP today believe
   it to be a useful, working protocol, discussions have brought to
   light a number of areas where BGP or the relationship between BGP and
   the IGPs in use today could be improved.  This section is, to a large
   extent, a wish list for the future domain routing architecture based
   on those areas where BGP is seen to be lacking, rather than simply a
   list of problems with BGP.  The shortcomings of today's inter-domain
   routing system have also been extensively surveyed in 'Architectural
   Requirements for Inter-Domain Routing in the Internet' [13],
   particularly with respect to its stability and the problems produced
   by explosions in the size of the Internet.

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3.1  BGP and Auto-aggregation

   The stability and later linear growth rates of the number of routing
   objects (prefixes) that was achieved by the introduction of CIDR
   around 1994, has now been once again been replaced by near-
   exponential growth of number of routing objects.  The granularity of
   many of the objects advertised in the default free zone is very small
   (prefix length of 22 or longer):  This granularity appears to be a
   by-product of attempts to perform precision traffic engineering
   related to increasing levels of multi-homing.  At present there is no
   mechanism in BGP that would allow an AS to aggregate such prefixes
   without advance knowledge of their existence, even if it was possible
   to deduce automatically that they could be aggregated.  Achieving
   satisfactory auto-aggregation would also significantly reduce the
   non-locality problems associated with instability in peripheral ASs.

   On the other hand, it may be that alterations to the connectivity of
   the net as described in [13] and Section 2.5.1 may limit the
   usefulness of auto-aggregation

3.2  Convergence and Recovery Issues

   BGP today is a stable protocol under most circumstances but this has
   been achieved at the expense of making the convergence time of the
   inter-domain routing system very slow under some conditions.  This
   has a detrimental effect on the recovery of the network from

   The timers that control the behavior of BGP are typically set to
   values in the region of several tens of seconds to a few minutes,
   which constrains the responsiveness of BGP to failure conditions.

   In the early days of deployment of BGP, poor network stability and
   router software problems lead to storms of withdrawals closely
   followed by re-advertisements of many prefices.  To control the load
   on routing software imposed by these 'route flaps', route flap
   damping was introduced into BGP.  Most operators have now implemented
   a degree of route flap damping in their deployments of BGP.  This
   restricts the number of times that the routing tables will be rebuilt
   even if a route is going up and down very frequently.  Unfortunately,
   the effect of route flap damping is exponential in its behavior that
   can result in some parts of the Internet being inaccessible for hours
   at a time.

   There is evidence ([13] and our own measurements - results yet to be
   published) that in today's network route flap is disproportionately
   associated with the fine grain prefices (length 22 or longer)
   associated with traffic engineering at the periphery of the network.

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   Auto-aggregation as previously discussed would tend to mask such
   instability and prevent it being propagated across the whole network.
   Another question that needs to be studied is the continuing need for
   an architecture that requires global convergence.  Some of our
   studies (yet to be published) show that, in some localities at least,
   the network never actually reaches stability; i.e.  never really
   globally converges.  Can a global, and beyond, network be designed
   with the requirement of global convergence?

3.3  Non-locality of Effects of Instability and Misconfiguration

   There have been a number of instances, some of which are well
   documented of a mistake in BGP configuration in a single peripheral
   AS propagating across the whole Internet and resulting in misrouting
   of most of the traffic in the Internet.

   Similarly, route flap in a single peripheral AS can require route
   table recalculation across the entire Internet.

   This non-locality of effects is highly undesirable, and it would be a
   considerable improvement if such effects were naturally limited to a
   small area of the network around the problem.  This is another
   argument for an architecture that does not require global

3.4  Multihoming Issues

   As discussed previously, the increasing use of multi-homing as a
   robustness technique by peripheral ASs requires that multiple routes
   have to be advertised for such domains.  These routes must not be
   aggregated close in to the multi-homed domain as this would defeat
   the traffic engineering implied by multi-homing and currently cannot
   be aggregated further away from the multi-homed domain due to the
   lack of auto-aggregation capabilities.  Consequentially the default
   free zone routing table is growing exponentially, as it was before

   The longest prefix match routing technique introduced by CIDR, and
   implemented in BGP4, when combined with provider address allocation
   is an obstacle to effective multi-homing if load sharing across the
   multiple links is required:  If an AS has been allocated its
   addresses from an upstream provider, the upstream provider can
   aggregate those addresses with those of other customers and need only
   advertise a single prefix for a range of customers.  But, if the
   customer AS is also connected to another provider, the second
   provider is not able to aggregate the customer addresses because they
   are not taken from his allocation, and will therefore have to
   announce a more specific route to the customer AS.  The longest match

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   rule will then direct all traffic through the second provider, which
   is not as required.

   AS3 has received its addresses from AS1, which means AS1 can
   aggregate.  But if AS3 want its traffic to be seen equally both ways,
   AS1 is forced to announce both the aggregate and the more specific
   route to AS3.

                    \       /
                   AS1     AS2
                      \   /

    This problem has induced many ASs to apply for their own address
   allocation even though they could have been allocated from an
   upstream provider further exacerbating the default free zone route
   table size explosion.  This problem also interferes with the desire
   of many providers in the default free zone to route only prefixes
   that are equal to or shorter than 20 or 19 bits.

   Note that some problems which are referred to as multihoming issues
   are not and should not solvable through the routing system (e.g.
   where a TCP load distributor is needed), and multihoming is not a
   panacea for the general problem of robustness in a routing system

   Since the original publication of this draft the IETF multi6 working
   group has been struggling to determine how to provide a mechanism to
   allow multihoming with IPv6 while maintaining the beneficial effects
   that strict provider addressing brings to the size of the core
   routing tables.  The process has been long and difficult and a full
   resolution is not yet in sight.  The main conclusion has been, as
   with the NewArch group, that the locator and identifier functions of
   the IP address will need to be decoupled which was one of the major
   proposals of the Nimrod project Section 2.2.  One major difficulty is
   that it is not clear how to solve the problem in such a way that the
   basic structure of IP in general and IPv6 in particular is not
   compromised.  Many of the proposals considered effectively provide an
   overlay on IP which may not be the most desirable solution but the
   alternatives might mean designing yet another new version of IP
   before IPv6 has been fully deployed.

3.5  AS-number exhaustion

   The domain identifier or AS-number is a 16-bit number.  Allocation of

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   AS-numbers is currently increasing 51% a year [13] with the result
   that exhaustion is likely around 2005.  The IETF is currently
   studying proposals to increase the available range of AS-numbers to
   32 bits, but this will present a deployment challenge during

3.6  Partitioned AS's

   Tricks with discontinuous ASs are used by operators, for example, to
   implement anycast.  Discontinuous ASs may also come into being by
   chance if a multi-homed domain becomes partitioned as a result of a
   fault and part of the domain can access the Internet through each
   connection.  It may be desirable to make support for this kind of
   situation more transparent than it is at present.

3.7  Load Sharing

   Load splitting or sharing was not a goal of the original designers of
   BGP and it is now a problem for today's network designers and
   managers.  Trying to fool BGP into load sharing between several links
   is a constantly recurring exercise for most operators today.  Traffic
   engineering extensions to the future domain routing architecture that
   will facilitate load sharing should be considered.

3.8  Hold down issues

   As with the interval between 'hello' messages in OSPF, the typical
   size and defined granularity (seconds to tens of seconds) of the
   'keep-alive' time negotiated at start-up for each BGP connection
   constrains the responsiveness of BGP to link failures.

   The recommended values and the available lower limit for this timer
   were set to limit the overhead caused by keep-alive messages when
   link bandwidths were typically much lower than today.  Analysis and
   experiment ([14], [15] & [33]) indicate that faster links could
   sustain a much higher rate of keep-alive messages without
   significantly impacting normal data traffic.  This would improve
   responsiveness to link and node failures but with a corresponding
   increase in the risk of instability, if the error characteristics of
   the link are not taken properly into account when setting the
   keep-alive interval.

   An additional problem with the hold-down mechanism in BGP is the
   amount of information that has to be exchanged to re-establish the
   database of route advertisements on each side of the link when it is
   re-established after a failure.  Currently any failure, however brief
   forces a full exchange which could perhaps be constrained by
   retaining some state across limited time failures and using revision

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   control, transaction and replication techniques to re-synchonise the
   databases.  Various techniques have been implemented to try to reduce
   this problem but they have not yet been standardised.

3.9  Interaction between Inter domain routing and intra domain routing

   Today, many operators' backbone routers run both I-BGP and an IGP
   maintain the routes that reach between the borders of the domain.
   Exporting routes from BGP into IGP and bringing them back up to BGP
   is not recommended [29], but it is still necessary for all backbone
   routers to run both protocols.  BGP is used to find the egress point
   and IGP to find the path (next hop router) to the egress point across
   the domain.  This is not only a management problem but may also
   create other problems:
   -  BGP is a distance vector protocol, as compared with most IGPs,
      which are link state protocols, and as such it is not optimised
      for convergence speed although they generally require less
      processing power.  Incidentally, more efficient distance vector
      algorithms are available such as [34].
   -  The metrics used in BGP and the IGP are rarely comparable or
      combinable.  Whilst there are arguments that the optimizations
      inside a domain may be different from those for end-to-end paths,
      there are occasions, such as calculating the 'topologically
      nearest' server when computable or combinable metrics would be of
   -  The policies that can be implemented using BGP are designed for
      control of traffic exchange between operators, not for controlling
      paths within a domain.  Policies for BGP are most conveniently
      expressed in RPSL and this could be extended if thought desirable
      to include additional policy information.
   -  If the NEXT HOP destination for a set of BGP routes becomes
      inaccessible because of IGP problems, the routes using the
      vanished next hop have to be invalidated at the next available
      UPDATE.  Subsequently, if the next hop route reappears, this would
      normally lead to the BGP speaker requesting a full table from its
      neighbour(s).  Current implementations may attempt to circumvent
      the effects of IGP route flap by caching the invalid routes for a
      period in case the next hop is restored.
   -  Synchronization between IGP and EGP is a problem as long as we use
      different protocols for IGP and EGP, which will most probably be
      the case even in the future because of the differing requirements
      in the two situations.  Some sort of synchronization between those
      two protocols would be useful.  In the draft 'OSPF Transient
      Blackhole Avoidance' [22], the IGP side of the story is covered.
   -  Synchronizing in BGP means waiting for the IGP to know about the
      same networks as the EGP, which can take a significant period of
      time and slows down the convergence of BGP by adding the IGP
      convergence time into each cycle.

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3.10  Policy Issues

   There are several classes of issue with current BGP policy:
   -  - Policy is installed in an ad-hoc manner in each autonomous
      system.  There isn't a method for ensuring that the policy
      installed in one router is coherent with policies installed in
      other routers.
   -  - As described in Griffin [12] and in McPherson [20] it is
      possible to create policies for ASs, and instantiate them in
      routers, that will cause BGP to fail to converge in certain types
      of topology
   -  - There is no available network model for describing policy in a
      coherent manner.

   Policy management is extremely complex and mostly done without the
   aid of any automated procedures.  The extreme complexity means that a
   highly qualified specialist is required for policy management of
   border routers.  The training of these specialists is quite lengthy
   and needs to involve long periods of hands-on experience.  There is,
   therefore, a shortage of qualified staff for installing and
   maintaining the routing policies.  Also many training courses cover
   only the basic configuration aspects and do not cover policy issues.

3.11  Security Issues

   While many of the issues with BPG security have been traced either to
   implementation issues or to operational issues, BGP is vulnerable to
   DDOS attacks.  Additionally routers can be used as unwitting
   forwarders in DDOS attacks on other systems.

   Though DDOS attacks can be fought in a variety of ways, most
   filtering methods, it is takes constant vigilance.  There is nothing
   in the current architecture or in the protocols that serves to
   protect the forwarders from these attacks.

3.12  Support of MPLS and VPNS

   Recently BGP has been modified to function as a signaling protocol
   for MPLS and for VPNs [16].  Some people see this over-loading of the
   BGP protocol as a boon whilst others see it as a problem.  While it
   was certainly convenient as a vehicle for vendors to deliver extra
   functionality for to their products, it has exacerbated some of the
   performance and complexity issues of BGP.  Two important problems
   are, the additional state that must be retained and refreshed to
   support VPN tunnels and that BGP does not provide end-to-end
   notification making it difficult to confirm that all necessary state
   has been installed or updated.

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   In creating the future domain routing architecture, serious
   consideration must be given to the argument that VPN signaling
   protocols should remain separate from the route determination

3.13  IPv4 / IPv6 Ships in the Night

   The fact that service providers would need to maintain two completely
   separate networks; one for IPv4 and one for IPv6 has been a real
   hindrance to the introduction of IPv6.  When IPv6 does get widely
   deployed it will do so without causing the disappearance of IPv4.
   This means that unless something is done, service providers would
   need to maintain the two networks in, relative, perpetuity.

   It is possible to use a single set of BGP speakers with multiprotocol
   extensions [37] to exchange information about both IPv4 and IPv6
   routes between domains, but the use of TCP as the transport protocol
   for the information exchange results in an asymmetry when choosing to
   use one of TCP over IPv4 or TCP over IPv6.  Successful information
   exchange confirms one of IPv4 or IPv6 reachability between the
   speakers but not the other, making it possible that reachability is
   being advertised for a protocol for which it is not present.

   Also, current implementations do not allow a route to be advertised
   for both IPv4 and IPv6 in the same UPDATE message, because it is not
   possible to explicitly link the reachability information for an
   address family to the corresponding next hop information.  This could
   be improved, but currently results in independent UPDATEs being
   exchanged for each address family.

3.14  Existing Tools to Support Effective Deployment of Inter-Domain

   The tools available to network operators to assist in configuring and
   maintaining effective inter-domain routing in line with their defined
   policies are limited, and almost entirely passive.
   -  There are no tools to facilitate the planning of the routing of a
      domain (either intra- or inter-domain); there are a limited number
      of display tools that will visualize the routing once it has been
   -  There are no tools to assist in converting business policy
      specifications into the RPSL language; there are limited tools to
      convert the RPSL into BGP commands and to check, post-facto, that
      the proposed policies are consistent with the policies in adjacent
      domains (always provided that these have been revealed and
      accurately documented).

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   -  There are no tools to monitor BGP route changes in real time and
      warn the operator about policy inconsistencies and/or

   The following section summarises the tools that are available to
   assist with the use of RPSL.  Note they are all batch mode tools used
   off-line from a real network.  These tools will provide checks for
   skilled inter-domain routing configurers but limited assistance for
   the novice.

3.14.1  Routing Policy Specification Language RPSL  (RFC 2622, 2650) and
       RIPE NCC Database (RIPE 157)

   Routing Policy Specification Language RPSL enables a network operator
   to describe routes, routers and autonomous systems ASs that are
   connected to the local AS.

   Using the RPSL language a distributed database is created to describe
   routing policies in the Internet as described by each AS
   independently.  The database can be used to check the consistency of
   routing policies stored in the database.

   Tools exist (RIPE 81, 181, 103) that can be applied on the database
   to answer requests of the form, e.g.
   -  Flag when two neighboring network operators specify conflicting or
      inconsistent routing information exchanges with each other and
      also detect global inconsistencies where possible;
   -  Extract all AS-paths between two networks that are allowed by
      routing policy from the routing policy database; display the
      connectivity a given network has according to current policies.

   The database queries enable a partial static solution to the
   convergence problem.  They analyze routing policies of very limited
   part of Internet and verify that they do not contain conflicts that
   could lead to protocol divergence.  The static analysis of
   convergence of the entire system has exponential time complexity, so
   approximation algorithms would have to be used.

4.  Security Considerations

   As this is an informational draft  on the history of requirements in
   IDR and on the problems facing the current Internet IDR architecture,
   it does not as such create any security problems.  On the other hand,
   some of the problems with today's Internet routing architecture do
   create security problems and these have been discussed in the text

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5.  Acknowledgments

   The draft is derived from work originally produced by Babylon.
   Babylon was a loose association of individuals from academia, service
   providers and vendors whose goal was to discuss issues in Internet
   routing with the intention of finding solutions for those problems.
   The individual members who contributed materially to this draft are:
   Anders Bergsten, Howard Berkowitz, Malin Carlzon, Lenka Carr
   Motyckova, Elwyn Davies, Avri Doria, Pierre Fransson, Yong Jiang,
   Dmitri Krioukov, Tove Madsen, Olle Pers, and Olov Schelen.
   Thanks also go to the members of Babylon and others who did
   substantial reviews of this material.  Specifically we would like to
   acknowledge the helpful comments and suggestions of the following
   individuals:  Loa Andersson, Tomas Ahlstrom, Erik Aman, Thomas
   Eriksson, Niklas Borg, Nigel Bragg, Thomas Chmara, Krister Edlund,
   Owe Grafford, Torbjorn Lundberg, Jasminko Mulahusic, Florian-Daniel
   Otel, Bernhard Stockman, Tom Worster, Roberto Zamparo.
   In addition, the authors are indebted to the folks who wrote all the
   references we have consulted in putting this paper together.  This
   includes not only the references explicitly listed below, but also
   those who contributed to the mailing lists we have been participating
   in for years.
   Finally, it is the editors who are responsible for any lack of
   clarity, any errors, glaring omissions or misunderstandings.

6  References

   [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.

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   [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"",
         , 2002.

   [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", NANOG , 2002.

   [12]  Griffin, T. and G. Wilfong, "An Analysis of BGP Convergence
         Properties",  , 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,
         "Fast LIveness Protocol (FLIP)", draft-sandick-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", RFC 3345, Aug 2002.

   [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.

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   [23]  Thaler, D., Estrin, D. and D. Meyer, "Border Gateway Multicast
         Protocol (BGMP): Protocol Specification",
         draft-ietf-bgmp-spec-06 (work in progress), Nov 2000.

   [24]  Rosen, E., "Multiprotocol Label Switching Architecture", RFC
         3031, 2004.

   [25]  Ashwood-Smith, P., "Generalized MPLS - Signaling Functional
         Description", draft-ietf-mpls-generalized-signaling-09 (work in
         progress), 2002.

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

   [27]  "IETF Configuration management with SNMP working group",  ,

   [28]  "IETF Policy working group",  , 2002,

   [29]  Yu, J., "Scalable Routing Design Principles", RFC 2791, 2002.

   [30]  "Telcordia Technologies Netsizer web site
         http://www.netsizer.com/",  , 2002.

   [31]  "Inference of Shared Risk Link Groups",
         draft-many-inference-srlg-02 (work in progress), 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, "Link Management Protocol", draft-lang-mpls-lmp-02 (work
         in progress), 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,

   [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 , 1993.

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   [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), 2002.

   [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, "Requirements for Inter-Domain Routing",
         draft-irtf-routing-reqs-03 (work in progress), 2004.

Authors' Addresses

   Avri Doria
   161 Gajeong-dong
   Daejeon  305-350

   Phone: +1 401 663 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

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