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Versions: 00                                                            
     IRTF Routing Research Group                        F. Kastenholz,
     Internet Draft                                               (ed)
     Document <draft-irtf-routing-reqs-groupa-      Unisphere Networks
     00.txt>                                                April 2002
     Category: Informational
                     Requirements For a Next Generation
                     Routing and Addressing Architecture
                  < draft-irtf-routing-reqs-groupa-00.txt>
     Status of this Memo
        This document is an Internet-Draft and is in full conformance
        with all provisions of Section 10 of RFC2026 [1].
        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
        The list of Internet-Draft Shadow Directories can be accessed
        at http://www.ietf.org/shadow.html.
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     Table of Contents
        1 Abstract...................................................3
        2 Conventions used in this document..........................3
        3 Requirements...............................................4
         3.1  Architecture..........................................4
         3.2  Separable Components..................................5
         3.3  Scalable..............................................6
         3.4  Lots of Interconnectivity.............................7
         3.5  Random Structure......................................8
         3.6  Multi-homing..........................................9
         3.7  Multi-path............................................9
         3.8  Convergence..........................................10
         3.9  Routing System Security..............................12
         3.10 End Host Security....................................14
         3.11 Rich Policy..........................................14
          3.11.1 Routing Information Policies......................14
          3.11.2 Traffic Control Policies..........................15
         3.12 Incremental Deployment...............................16
         3.13 Mobility.............................................16
         3.14 Address Portability..................................17
         3.15 Multi-Protocol.......................................17
         3.16 Abstraction..........................................17
         3.17 Simplicity...........................................18
         3.18 Robustness...........................................18
         3.19 Media Independence...................................19
         3.20 Stand-alone..........................................19
         3.21 Safety of Configuration..............................19
         3.22 Renumbering..........................................19
         3.23 Multi-prefix.........................................19
         3.24 Cooperative Anarchy..................................19
         3.25 Network Layer Protocols and Forwarding Model.........20
         3.26 Routing Algorithm....................................20
         3.27 Positive Benefit.....................................20
         3.28 Administrative Entities and the IGP/EGP Split........20
        4 Non-Requirements..........................................21
         4.1  Forwarding Table Optimization........................21
         4.2  Traffic Engineering..................................21
         4.3  Multicast............................................22
         4.4  QOS..................................................22
         4.5  IP Prefix Aggregation................................22
         4.6  Perfect Safety.......................................23
         4.7  Dynamic Load Balancing...............................23
         4.8  Renumbering of hosts and routers.....................23
         4.9  Host Mobility........................................23
         4.10 Clean Slate..........................................24
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        5 Discussion of other Inter-Domain Routing Requirements
         5.1  Comments on "Architectural Requirements for Inter-Domain
         Routing in the Internet"..................................24
         5.2  Comments on "Future Domain Routing Requirements".....25
        6 Security Considerations...................................28
        7 IANA Considerations.......................................28
        8 References................................................28
        9 Acknowledgments...........................................28
        10           Editor's Addresses........................................29
     1  Abstract
        This note sets requirements for a new routing and addressing
        architecture for the Internet.  These requirements were
        developed by the IRTF's Routing Research Group.
        This draft is the product of Group ~B, which is one of the
        subgroups in the IRTF-Routing Research Group working on
        requirements for routing solutions for the future.  This
        document sets out requirements that we believe are important
        for a future routing architecture and routing protocols.  The
        IRTF Routing Research Group (RRG) does not endorse this set of
        requirements or any other set of requirements as the one and
        only set of requirements.
        The seemingly simple requirement is to "fix routing and
        addressing".  However, in order to "fix" it, we also need to
        understand how routing and addressing are _actually_ used
        today.  This is not a straightforward task.  Service providers
        and network administrators have many different operational and
        administrative needs.  Quite often, the only tool available to
        meet those needs is the routing system and they have proven
        amazingly crafty at using that tool in ways that were never
        envisioned.  Thus, one of the most important steps in
        developing these requirements has been to learn what the
        operational community really is doing with the routing system,
        why they are doing it, and then abstracting those tasks into
     2  Conventions used in this document
        The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
        NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and
        "OPTIONAL" in this document are to be interpreted as described
        in RFC-2119 [2].
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        We believe that we have captured the essential requirements for
        one possible future routing and addressing architecture for the
        Internet.  We do not consider features, functions, or
        capabilities not described in this note to be critically
        important for a future routing and addressing architecture and
        they should be considered optional.  A specific architecture
        MAY include OR exclude them without conflicting with this note.
        There are many IETF documents that define specific terms.  We
        generally choose not to use these strict, well-crafted,
        definitions.  They were made with the current architecture and
        protocols in mind.  A goal of this work is to foster
        development of new and different architectures.  By using the
        "old" terms we may inadvertently limit or constrain avenues of
        enquiry and investigation, possibly preventing consideration of
        promising architectures.
     3  Requirements
        This chapter presents the requirements.
        The requirements presented in this section are NOT presented in
        any order.  A later version of this note may order the
        requirements in some kind of priority.
     3.1 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 used.
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     3.2 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 available.
        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 use 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.
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     3.3 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.
        1.   We do not  know how big the Internet will grow over that
             time, and
        2.   The architecture developed from these requirements may
             change the fundamental structure of the Internet, and
             therefore its growth patterns.  This change makes it
             difficult to predict future growth patterns of the
        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 shortsighted.
        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
        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.
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        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 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
     3.4 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
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        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
        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 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
        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
     3.5 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 structure.
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     3.6 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
        The term "multihoming" may be interpreted in its broadest sense
        -- one "place" has multiple connections or links to another
        The architecture MUST NOT limit the number of alternate paths
        to a 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.
     3.7 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 automatic.
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        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, 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.
     3.8 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
        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
        This is not to say that all routers are constantly processing
        changes.  The effects of changes are like ripples in a pond.
        They spread outward from where they occur.  Some routers will
        be processing just C1, others C2, others both C1 and C2, and
        others neither.
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        We have two separate scopes over which we can set requirements
        with respect to convergence:
        1. Single Change
           In this requirement a single change of any type (link
           addition or deletion, router failure or restart, etc.) is
           introduced into a stabilized system.  No additional changes
           are introduced.  The system must restabilize within TBDms.
           This requirement is a fairly abstract one as it would be
           impossible to test in a real network.
        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
               -  Within any scope, S, network changes are constantly
                  occurring and the average inter-change interval is Tc
               -  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.
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        The growth rate of the convergence time MUST NOT be related to
        the growth rate of the Internet as a whole.  This implies that
        the convergence time either
        1. Not be a function of basic network elements (such as
           prefixes and links/paths), and/or
        2. That the Internet be continuously divisible into chunks that
           limit the scope and effect of a change, thereby limiting the
           number of routers, prefixes, links, and so on involved in
           the new calculations.
     3.9 Routing System Security
        The security of the Internet's routing system is paramount.  If
        the routing system is compromised or attacked, the entire
        Internet can fail.  This is unacceptable.  Any new Architecture
        must be secure.
        Architectures by themselves are not secure.  It is the
        implementation of an architecture; its protocols, algorithms,
        and data structures, that are secure.  These requirements apply
        primarily to the implementation.  The architecture MUST provide
        the elements that the implementation needs to meet these
        security requirements.  Also, the architecture MUST NOT prevent
        these security requirements from being met.
        Security means different things to different people.  In order
        for this requirement to be useful, we must define what we mean
        by security.  We do this by identifying the attackers and
        threats we wish to protect against.  They are:
           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 traffic.
        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 traffic.
            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
           Therefore, we believe that the option to encrypt routing
           protocol traffic is required.
        Data Consistency
           A router should be able to detect and recover from any data
           that is received from other routers which is inconsistent.
           That is, it MUST NOT be possible for data from multiple
           routers, none of which is malicious, to "break" another
        Where security mechanisms are provided, they must use methods
        that are considered to be cryptographically secure (e.g. using
        cryptographically strong encryption and signatures -- no clear
        text passwords!).
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        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.
     3.10    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).
     3.11    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 software.
        The main motivators for influencing path and next-hop selection
        seem to be transit rules, business decisions and load
        The new Architecture must support rich policy mechanisms.
        Furthermore, the policy definition and dissemination
        mechanismsshould be separated from the network topology and
        connectivity dissemination mechanisms.  Policy provides input
        to and controls the generation of the forwarding table and the
        abstraction, filtering, aggregation, and dissemination of
        topology information.
        Note that if the architecture is properly divided into
        subsystems then at a later time, new policy subsystems that
        include new features and capabilities could be developed and
        installed as needed.
        We divide the general area of policy into two sub-categories,
        routing information and traffic control.  Routing Information
        Policies control what routing information is disseminated or
        accepted, how it is disseminated, and how routers determine
        paths and next-hops from the received information.  Traffic
        Control Policies determine how traffic is classified and
        assigned to routes.
     3.11.1  Routing Information Policies
        There must be mechanisms to allow network administrators,
        operators, and designers to control receipt and dissemination
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        of routing information.  These controls include, but are not
        limited to:
        - Selecting to which others routing information will be
        - Specifying the "granularity" and type of transmitted
          information.  The length of IPv4 prefixes is an example of
        - Selection and filtering of topology and service information
          that is transmitted.  This gives different 'views' of
          internal structure and topology to different peers.
        - Selecting the level of security and authenticity for
          transmitted information
        - Being able to cause the level of detail that is visible for
          some portion of the network to reduce the farther you get
          from that part of the network.
        - 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 available".
        - Selecting the desired level of "granularity" for received
          routing information (this would include, but is not limited
          to, things similar in nature to the prefix-length filters
          widely used in the current routing and addressing system).
        - Selecting the level of security and authenticity of received
          information in order for that information to be accepted.
        - Determining the treatment of received routing information
          based on attributes supplied with the information.
        - Applying attributes to routing information that is to be
          transmitted and then determining treatment of information
          (eg, sending it "here" but not "there") based on those tags.
        - Selection and filtering of topology and service information
          that is received.
     3.11.2  Traffic Control Policies
        The architecture SHOULD provide mechanisms that allow network
        operators to manage and control the flow of traffic.  The
        traffic controls should include, but are not limited to:
        - The ability to detect and eliminate congestion points in the
          network (by re-directing traffic around those points) .
        - The ability to develop multiple paths through the network
          with different attributes and then assign traffic to those
          paths based on some discriminators within the packets
          (discriminators include, but are not limited to, IP Addresses
          or prefixes, DSCP values, and MPLS labels) .
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        - 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
          o Traffic matrices (e.g., traffic from prefix X and to
             prefix Y).
     3.12    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 deployable; ISPs must be able to set up small
        sections of the new architecture, check it out, and then slowly
        grow the sections.  Eventually, these sections will "touch" and
        "squeeze out" the old architecture.
        The protocols that implement the Architecture MUST be able to
        interoperate at "production levels" with currently existing
        routing protocols.  Furthermore, the protocol specifications
        MUST define how the interoperability is done.
        We also believe that sections of the Internet will never
        convert over to the new architecture.  Thus, it is important
        that the new architecture and its protocols be able to
        interoperate with "old architecture" regions of the network
        The architecture's addressing system MUST NOT force existing
        address allocations to be redone: no renumbering!
     3.13     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.
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     3.14     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.
     3.15    Multi-Protocol
        The Internet is expected to be "multi-protocol" for at least
        the next several years.  IPv4 and IPv6 will co-exist in many
        different ways during a transition period.  The architecture
        MUST be able to handle both IPv4 and IPv6 addresses.
        Furthermore, protocols that supplant IPv4 and IPv6 may be
        developed and deployed during the lifetime of the architecture.
        The architecture MUST be flexible and extensible enough to
        handle new protocols as they arise.
        Furthermore, the architecture MUST NOT assume any given
        relationships between a topological element's IPv4 address and
        its IPv6 address.  The architecture MUST NOT assume that all
        topological elements have IPv4 addresses/prefixes, nor can it
        assume that they have IPv6 addresses/prefixes.
        The architecture SHOULD allow different paths to the same
        destination to be used for different protocols, even if all
        paths can carry all protocols.
        In addition to the addressing technology, the architecture need
        not be restricted to only packet  based
        multiplexing/demultiplexing technology (such as IP); support
        for other multiplexing/ demultiplexing technologies MAY be
     3.16    Abstraction
        The architecture must provide mechanisms to for network
        designers and operators to
          o Group elements together for administrative control
          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.
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        Mapping mechanisms, algorithms, and techniques MUST be
     3.17    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 and whistles, then there are fewer things that need to
           be implemented.
        2. More reliable implementations.  With fewer components, there
           is less code, reducing bug counts, and fewer interactions
           between components that could lead to unforeseen and
           incorrect behavior.
     3.18     Robustness
        The architecture, and the protocols implementing it, should be
        robust.  Robustness comes in many different flavors.  Some
        considerations with regard to robustness include (but are not
        limited to):
          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
        EDITOR'S NOTE:
               Some of the contributors to this note 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 breakins" and
               "authenticating and encrypting data".  This requirement
               goes beyond those views.
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     3.19    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 towards any "routing" or
        "topology" services that are offered by the medium over which
        IP is operating.  That is, the new architecture MUST NOT be
        designed to integrate with any media-specific topology
        management or routing scheme.
        The routing architecture must assume, and must work over, the
        simplest possible media.
        The routing and addressing architecture can certainly make use
        of lower-layer information and services, when and where
        available, and to the extent that IP routing wishes.
     3.20     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.
     3.21    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!)
     3.22    Renumbering
        The routing system MUST allow topological entities to be
     3.23    Multi-prefix
        The architecture MUST allow topological entities to have
        multiple prefixes (or the equivalent under the new
     3.24    Cooperative Anarchy
        As RFC1726[5] said:
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          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.
     3.25    Network Layer Protocols and Forwarding Model
        For the purposes of backward compatibility, any new routing and
        addressing architecture and protocols MUST work with IPv4 and
        IPv6 using the traditional "hop by hop" forwarding and packet-
        based multiplex/demultiplex models.  However, the architecture
        need not be restricted to these models.  Additional forwarding
        and multiplex/demultiplex models MAY be added.
     3.26     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 algorithms.
     3.27     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.
     3.28    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
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        authorities, the administrative authority boundaries may be
        complex and overlapping, rather than being a strict hierarchy.
        Furthermore, there may be multiple levels of administration,
        each with its own level of policy and control.  For example, a
        large network might have "continental-level" administrations
        covering its European and Asian operations, respectively.
        There would also be that network's "inter-continental"
        administration covering the Europe-to-Asia links.  Finally,
        there would be the "Internet" level in the administrative
        structure (analogous to the "exterior" concept in the current
        routing architecture).
        Thus, we believe that the administrative structure of the
        Internet must be extensible to many levels (more than the two
        provided by the current IGP/EGP split).  The interior/exterior
        property is not absolute.  The interior/exterior property of
        any point in the network is relative; a point on the network is
        interior with respect to some points on the network and
        exterior with respect to others.
        Administrative entities may not trust each other; some may be
        almost actively hostile towards each other.  The architecture
        MUST accommodate these models.  Furthermore, the architecture
        MUST NOT require any particular level of trust among
        administrative entities.
     4  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.
     4.1 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
     4.2 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
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        intent is when operators "traffic engineer" their networks and
        then make those capabilities an inherent part of the system.
     4.3 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
        We do note however that one respected network sage has said
               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...
     4.4 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 towards 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.
     4.5 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.
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        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.
     4.6 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
        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.
     4.7 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.
     4.8 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.
     4.9 Host Mobility
        In the Internet Architecture, host-mobility is handled on a
        per-host basis by a dedicated, Mobile-IP protocol [6].  Traffic
        destined for a mobile-host is explicitly forwarded by dedicated
        relay agents.  Mobile-IP [6] adequately solves the host-
        mobility problem and we do not see a need for any additional
        requirements in this area.  Of course, the new architecture
        MUST NOT impede or conflict with Mobile-IP.
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     4.10    Clean Slate
        For the purposes of development of the architecture, we assume
        that there is a 'clean slate'.  Unless specified in section 3,
        we have no explicit requirements that elements, concepts or
        mechanisms of the current routing architecture are carried
        forward into the new one.
     5  Discussion of other Inter-Domain Routing Requirements documents
        Recently, two other Internet Drafts have been published that
        set out some requirements for a new Inter-Domain routing
        architecture.  These drafts are "Future Domain Routing
        Requirements" by Elwyn Davies, et al [3], and "Architectural
        Requirements for Inter-Domain Routing in the Internet" by Geoff
        Huston [4].
        Rather than use these documents, we decided to develop our own
        set of requirements for a future inter-domain routing
        architecture.  The reasons are
        1.   There are requirements in [3] and [4] with which we do not
             agree, plus we have additional requirements that are not
             in those documents.
        2.   We do not agree with the methodology in [3] and [4].  In
             particular, [3]'s list of requirements seems to us like an
             exhaustive list of things, falling dangerously close to
             the "My Layer MUST solve all of networking's problems"
             disease.  One of the hardest parts of setting requirements
             is to determine what problems will NOT be solved.
        [3] and [4] each provide excellent historical background
        information.  Rather than repeat the information here, readers
        are encouraged to consult those documents.
        Discussions and commentary on each internet-draft follow.
     5.1 Comments on "Architectural Requirements for Inter-Domain
         Routing in the Internet"
        The IAB have developed an internet-draft titled "Architectural
        Requirements for Inter-Domain Routing in the Internet" [4].
        Rather than using [4], we have produced our own document.
        A good part of [4] is a detailed explanation of the current
        problems in routing and addressing.  This work is valuable.  We
        chose not to replicate it in this note.
        The main reason we decided not to use [4] is that it is too
        rooted in the current BGP/AS model.  We believe that the
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        charter for the Routing Research Group is to work on longer-
        term futures, including the possibility of replacing that
        model.  We wish to develop our requirements in a forward-
        looking manner and using requirements rooted in the old model
        may cause us to unwittingly constrain our thinking.
        [4] Enumerates four requirements for a new routing
        architecture.  These requirements are fairly broad and loose.
        They are:
            We agree.  The new architecture must be scalable.  We have
            included a requirement for scalability.
        Stability and Predictability
            Yes, the routing and addressing architecture should be
            stable and predictable.  However, we are not sure that
            overall this is possible.
            Fast convergence would be nice.  However, the size and
            complexity of the Internet are such that we do not believe
            that the entire net can ever converge.  Changes with global
            impact will always be happening and their effects will be
            constantly propagating through the network.  We expect that
            any routing system will, at best, be able to converge
            incrementally.  That is, in any one place, convergence with
            respect to one change can occur, but before the entire net
            converges, another change will occur, requiring a new set
            of calculations and a "new" convergence.
            We prefer to believe that convergence at any single point
            and after any single change must occur quickly.  Also,
            since we expect that the network will constantly by (re-
            converging, so the load of those attempts must be minimal.
        Routing Overhead
            Routing overhead should be minimized.  True.
     5.2 Comments on "Future Domain Routing Requirements"
        A separate group is developing a document titled "Future Domain
        Routing Requirements" [3].
        Rather than using [3], we have produced our own document.  As
        with [4] we believe that this document is too rooted in the
        current BGP/AS model, which is not a useful context for
        developing long-term future architectures.
        We have a number of observations on [3], in no particular
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          1. The introductory/historical/background is fine.  In fact,
             that material should be considered "required reading" to
             understand the background and current problems of Internet
             Routing.  We commend the authors of [3] for putting this
             material together.
          2. The "goals" section (1.2) seems to be heavily oriented to
             specific issues and tasks that network designers and
             administrators face today.  Our charter calls for us to
             consider the very long term.  Thus, it is hard to say what
             specific tasks the operations community needs to perform.
             Therefore, we prefer to take a broader view of what
             routing should do and have written our document
          3. [3] Seems still wedded to the old BGP/AS model of doing
             inter-domain routing.  That may well be an adequate model.
             However, the Routing Research Group's charter is to
             consider and develop long-term future directions in
             routing.  We prefer to develop our own document, trying to
             avoid falling into the "traps" of the past.
          4. The document seems to be an exhaustive wish list of
             things.  The hardest part of doing requirements is to
             figure out what not to require.  Coincident with that
             observation, there were a couple of "would be nice" and
             "might be needed" sorts of things.  The fear is that they
             fell into the trap of "All problems must be solved in our
             layer", which leads to very poor architectures and
          5. They call for "support for NATs and other mid-boxes".  If
             the Routing and Addressing architecture is "right" then
             there is no need for them, at least as far as Routing and
             Addressing are concerned.
             Also, we are confused as to what "support for NATs..."
             actually means.
          6. The authors of [3] talk a fair bit about some low-level
             things they want.  Our opinion is that we are looking "too
             far out" to talk about detailed, low-level requirements.
             We  don't know what the operators of 2007 will want.
             Besides solving the basic problem of getting topological
             and addressing information "around", we need to think more
             about how to keep the architecture (and design and
             implementation) flexible and open so that in 2006 when
             someone says "We need a gonkulator!" we can say "Easy, it
             gets plugged in here..."
          7. Multicast/Anycast
             We do not believe that multicast routing is a part of our
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             Anycast is a fairly nebulous technology.  To require that
             routing "support" it at this stage in its development is
             premature.  To require that routing support anycast means,
             in effect, that we first define what it is.
          8. Support for renumbering
             We take this to mean either that
               o The routing-and-addressing system actually does the
                  renumbering, to which we reply "Is this really
                  something for routing to do?", or
               o The routing-and-addressing system must continue to
                  operate when elements of the network are renumbered.
                  We have a requirement for this
          9. Statistics support
             This seems to us to be a low-level protocol issue.  Yes
             the protocol needs a MIB.  But we do not believe that this
             is an architectural or requirements issue.
             This also indicates to us that [3] is more concerned with
             lower-level protocol and implementation issues rather than
             taking the proverbial "step back" to look at "the big
          10. There were some comments about convergence that
             seemed to indicate that the authors of [3] are thinking of
             global convergence.  We have observed that global
             convergence is probably not doable anymore.  We believe
             that "permanent change" is the order of the day...
          11. One of their open-issues indicates that the
             authors of [3] are thinking about whether the EGP/IGP
             split is good or not.  It's good they are thinking about
             it.  It's bad that they consider it open.  We consider
             this split to be A Bad Thing -- there should be no such
             split in the architecture.
          12. One example of the too fine a level of detail they
             are getting into is that in 7.2.2 they talk about having a
             number of specific path attributes.  But, if say in 2007
             we discover a need for a gonkulation attribute, it's not
             in the list in [3].  Perhaps we are taking their document
             too literally, but someone taking [3] and designing to it
             would maybe make attributes TLV's and leave it at that.
             They wouldn't consider the effects of unconsidered new
             attributes.  We prefer to think of things in the reverse
                We know we need attributes, but we don't know what they
                all are.  Therefore the attribute mechanism must be
                flexible and allow growth in weird new directions
                without causing problems on the rest of the system --
                so how do we do that.
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     6  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".
     7  IANA Considerations
        This document is a set of requirements from which a new routing
        and addressing architecture will be developed.  From that
        architecture, a new protocol, or set of protocols, may be
        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.
     8  References
        [1] Bradner, S., "The Internet Standards Process û Revision 3",
            BCP9, RFC2026, October 1996.
        [2] Bradner, S., "Key words for use in RFCs to Indicate
            Requirements Levels", BCP 14 RFC 2119, March 1997.
        [3] Davies, E., et al, "Future Domain Routing Requirements",
            draft-davies-fdr-reqs-01.txt, July 2001, Work In Progress.
        [4] Huston, G., "Architectural Requirements for Inter-Domain
            Routing in the Internet" draft-iab-bgparch-01.txt, May
            2001, Work In Progress.
        [5] Partridge, C., and F. Kastenholz, "Technical Criteria for
            Choosing IP The Next Generation (IPng)", RFC 1726. December
        [6] Perkins, C., "IP Mobility Support."  RFC2002, October 1996.
     9  Acknowledgments
        This originated in the  IRTF Routing Research GroupÆs sub-group
        on Inter-domain routing requirements.  The members of the group
        Abha Ahuja                      Danny McPherson
        J. Noel Chiappa                 David Meyer
        Sean Doran                      Mike OÆDell
        JJ Garcia-Luna-Aceves           Andrew Partan
        Susan Hares                     Radia Perlman
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                       Inter-domain Routing Requirements     March 2002
        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
     10 Editor's Addresses
        Frank Kastenholz
        Unisphere Networks
        10 Technology Park
        Westford, MA, 01886, USA
        Phone: +1 978 589 0286
        Email: fkastenholz@unispherenetworks.com
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                       Inter-domain Routing Requirements     March 2002
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