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Versions: 00 01 02 03 04 05 06 RFC 4098

Benchmarking Working Group                                  H. Berkowitz
Internet-Draft                                       Gett Communications
Expires: December 29, 2003                               E. Davies (ed.)
                                                         Nortel Networks
                                                                S. Hares
                                                    Nexthop Technologies
                                                         P. Krishnaswamy
                                                                    SAIC
                                                                 M. Lepp
                                                              Consultant
                                                           June 30, 2003


   Terminology for Benchmarking BGP Device Convergence in the Control
                                 Plane
                     draft-ietf-bmwg-conterm-05.txt

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that other
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   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on December 29, 2003.

Copyright Notice

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

Abstract

   This draft establishes terminology to standardize the description of
   benchmarking methodology for measuring eBGP convergence in the
   control plane of a single BGP device. Future documents will address
   iBGP convergence, the initiation of forwarding based on converged



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   control plane information and multiple interacting BGP devices. This
   terminology is applicable to both IPv4 and IPv6. Illustrative
   examples of each version are included where relevant.

Table of Contents

   1.    Introduction . . . . . . . . . . . . . . . . . . . . . . . .  4
   1.1   Overview and Roadmap . . . . . . . . . . . . . . . . . . . .  4
   1.2   Definition Format  . . . . . . . . . . . . . . . . . . . . .  5
   2.    Components and Characteristics of Routing Information  . . .  6
   2.1   (Network) Prefix . . . . . . . . . . . . . . . . . . . . . .  6
   2.2   Network Prefix Length  . . . . . . . . . . . . . . . . . . .  6
   2.3   Route  . . . . . . . . . . . . . . . . . . . . . . . . . . .  7
   2.4   BGP Route  . . . . . . . . . . . . . . . . . . . . . . . . .  7
   2.5   Network Level Reachability Information (NLRI)  . . . . . . .  8
   2.6   BGP UPDATE Message . . . . . . . . . . . . . . . . . . . . .  8
   3.    Routing Data Structures and Route Categories . . . . . . . .  9
   3.1   Routing Information Base (RIB) . . . . . . . . . . . . . . .  9
   3.1.1 Adj-RIB-In and Adj-RIB-Out . . . . . . . . . . . . . . . . .  9
   3.1.2 Loc-RIB  . . . . . . . . . . . . . . . . . . . . . . . . . .  9
   3.2   Routing Policy . . . . . . . . . . . . . . . . . . . . . . . 10
   3.3   Routing Policy Information Base  . . . . . . . . . . . . . . 10
   3.4   Forwarding Information Base (FIB)  . . . . . . . . . . . . . 11
   3.5   BGP Instance . . . . . . . . . . . . . . . . . . . . . . . . 12
   3.6   BGP Device . . . . . . . . . . . . . . . . . . . . . . . . . 12
   3.7   BGP Session  . . . . . . . . . . . . . . . . . . . . . . . . 13
   3.8   Active BGP Session . . . . . . . . . . . . . . . . . . . . . 13
   3.9   BGP Peer . . . . . . . . . . . . . . . . . . . . . . . . . . 13
   3.10  BGP Neighbor . . . . . . . . . . . . . . . . . . . . . . . . 14
   3.11  MinRouteAdvertisementInterval (MRAI) . . . . . . . . . . . . 14
   3.12  MinASOriginationInterval (MAOI)  . . . . . . . . . . . . . . 15
   3.13  Active Route . . . . . . . . . . . . . . . . . . . . . . . . 15
   3.14  Unique Route . . . . . . . . . . . . . . . . . . . . . . . . 16
   3.15  Non-Unique Route . . . . . . . . . . . . . . . . . . . . . . 16
   3.16  Route Instance . . . . . . . . . . . . . . . . . . . . . . . 16
   4.    Constituent Elements of a Router or Network of Routers . . . 18
   4.1   Default Route, Default Free Table, and Full Table  . . . . . 18
   4.1.1 Default Route  . . . . . . . . . . . . . . . . . . . . . . . 18
   4.1.2 Default Free Routing Table . . . . . . . . . . . . . . . . . 18
   4.1.3 Full Default Free Table  . . . . . . . . . . . . . . . . . . 19
   4.1.4 Default-Free Zone  . . . . . . . . . . . . . . . . . . . . . 20
   4.1.5 Full Provider-Internal Table . . . . . . . . . . . . . . . . 20
   4.2   Classes of BGP-Speaking Routers  . . . . . . . . . . . . . . 20
   4.2.1 Provider Edge Router . . . . . . . . . . . . . . . . . . . . 20
   4.2.2 Subscriber Edge Router . . . . . . . . . . . . . . . . . . . 21
   4.2.3 Inter-provider Border Router . . . . . . . . . . . . . . . . 21
   4.2.4 Core Router  . . . . . . . . . . . . . . . . . . . . . . . . 22
   5.    Characterization of Sets of Update Messages  . . . . . . . . 23



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   5.1   Route Packing  . . . . . . . . . . . . . . . . . . . . . . . 23
   5.2   Route Mixture  . . . . . . . . . . . . . . . . . . . . . . . 23
   5.3   Update Train . . . . . . . . . . . . . . . . . . . . . . . . 24
   5.4   Randomness in Update Trains  . . . . . . . . . . . . . . . . 25
   5.5   Route Flap . . . . . . . . . . . . . . . . . . . . . . . . . 26
   6.    Route Changes and Convergence  . . . . . . . . . . . . . . . 27
   6.1   Route Change Events  . . . . . . . . . . . . . . . . . . . . 27
   6.2   Device Convergence in the Control Plane  . . . . . . . . . . 28
   7.    BGP Operation Events . . . . . . . . . . . . . . . . . . . . 30
   7.1   Hard Reset . . . . . . . . . . . . . . . . . . . . . . . . . 30
   7.2   Soft Reset . . . . . . . . . . . . . . . . . . . . . . . . . 30
   8.    Factors that Impact the Performance of the Convergence
         Process  . . . . . . . . . . . . . . . . . . . . . . . . . . 32
   8.1   General Factors Affecting Device Convergence . . . . . . . . 32
   8.1.1 Number of Peers  . . . . . . . . . . . . . . . . . . . . . . 32
   8.1.2 Number of Routes per Peer  . . . . . . . . . . . . . . . . . 32
   8.1.3 Policy Processing/Reconfiguration  . . . . . . . . . . . . . 32
   8.1.4 Interactions with Other Protocols  . . . . . . . . . . . . . 32
   8.1.5 Flap Damping . . . . . . . . . . . . . . . . . . . . . . . . 33
   8.1.6 Churn  . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
   8.2   Implementation-specific and other Factors Affecting BGP
         Convergence  . . . . . . . . . . . . . . . . . . . . . . . . 34
   8.2.1 Forwarded Traffic  . . . . . . . . . . . . . . . . . . . . . 34
   8.2.2 Timers . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
   8.2.3 TCP Parameters Underlying BGP Transport  . . . . . . . . . . 34
   8.2.4 Authentication . . . . . . . . . . . . . . . . . . . . . . . 34
   9.    Security Considerations  . . . . . . . . . . . . . . . . . . 35
   10.   Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . 36
         Normative References . . . . . . . . . . . . . . . . . . . . 37
         Informative References . . . . . . . . . . . . . . . . . . . 38
         For Internet Draft consistency purposes only . . . . . . . . 39
         Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 39
         Intellectual Property and Copyright Statements . . . . . . . 41


















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1. Introduction

   This document defines terminology for use in characterizing the
   convergence performance of BGP processes in routers or other devices
   that instantiate BGP functionality (see RFC1771 [1]). It is the first
   part of a two document series, of which the subsequent document will
   contain the associated tests and methodology. This terminology is
   applicable to both IPv4 and IPv6. Illustrative examples of each
   version are included where relevant. Although IPv6 will require the
   use of MP-BGP, we will not deal with issues related to RFC 2283 [17]
   in this draft.

   The following observations underlie the approach adopted in this, and
   the companion document:

   o  The principal objective is to derive methodologies to standardize
      conducting and reporting convergence-related measurements for BGP.

   o  It is necessary to remove ambiguity from many frequently used
      terms that arise in the context of such measurements.

   o  As convergence characterization is a complex process, it is
      desirable to restrict the initial focus in this set of documents
      to specifying how to take basic control plane measurements as a
      first step to characterizing BGP convergence.

   For path vector protocols, such as BGP, the primary initial focus
   will therefore be on network and system control-plane activity
   consisting of the arrival, processing, and propagation of routing
   information.

   We note that for testing purposes all optional parameters should be
   turned off.  All variable parameters should be in their default
   setting unless specified by the test.

   Subsequent drafts will explore the more intricate aspects of
   convergence measurement, such as the impacts of the presence of
   Multiprotocol Extensions for BGP-4, policy processing, simultaneous
   traffic on the control and data paths within the Cevice Under Test
   (DUT), and other realistic performance modifiers. Convergence of
   Interior Gateway Protocols will also be considered in separate
   drafts.

1.1 Overview and Roadmap

   Characterizations of the BGP convergence performance of a device must
   take into account all distinct stages and aspects of BGP
   functionality. This requires that the relevant terms and metrics be



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   as specifically defined as possible. Such definition is the goal of
   this document.

   The necessary definitions are classified into separate categories:

   o  Components and characteristics of routing information

   o  Routing data structures and route categories

   o  Descriptions of the constituent elements of a network or a router
      that is undergoing convergence

   o  Characterization of sets of update messages, types of route change
      events, as well as some events specific to BGP operation

   o  Descriptions of factors that impact the performance of
      convergence processes


1.2 Definition Format

   The definition format is equivalent to that defined in [3], and is
   repeated here for convenience:

   X.x Term to be defined. (e.g., Latency)

   Definition:
      One or more sentences forming the body of the definition.

   Discussion:
      A brief discussion of the term, its application and any
      restrictions that there might be on measurement procedures.

   Measurement units:
      The units used to report measurements of this term, if applicable.

   Issues:
      List of issues or conditions that could affect this term.

   See Also:
      List of related terms that are relevant to the definition or
      discussion of this term.









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2. Components and Characteristics of Routing Information

2.1 (Network) Prefix

   Definition:
      "A network prefix is a contiguous set of bits at the more
      significant end of the address that collectively designates the
      set of systems within a network; host numbers select among those
      systems." (This definition is taken directly from section 2.2.5.2,
      "Classless Inter Domain Routing (CIDR)", in [3].)

   Discussion:
      In the CIDR context, the network prefix is the network component
      of an IP address.

   Measurement Units: N.A.

   Issues:

   See Also:


2.2 Network Prefix Length

   Definition:
      The network prefix length is the number of bits out of the total
      available in the address field, used to define the network prefix.

   Discussion:
      A common alternative to using a bit-wise mask to communicate this
      component is the use of "slash (/) notation." Slash notation binds
      the notion of network prefix length in bits to an IP address.
      E.g., 141.184.128.0/17 indicates the network component of this
      IPv4 address is 17 bits wide. Similar notation is used for IPv6
      network prefixes e.g. 2001:db8:719f::/48

      When referring to groups of addresses, the network prefix length
      is often used as a means of describing groups of addresses as an
      equivalence class.  For example, 'one hundred /16 addresses'
      refers to 100 addresses whose network prefix length is 16 bits.

   Measurement units: bits

   Issues:

   See Also:  network prefix





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2.3 Route

   Definition:
      In general, a 'route' is the n-tuple
      <prefix, nexthop [, other routing or non-routing protocol
      attributes]>

      A route is not end-to-end, but is defined with respect to a
      specific next hop that should take packets on the next step
      towards their destination as defined by the prefix. In this usage,
      a route is the basic unit of information about a target
      destination distilled from routing protocols.

   Discussion:
      This term refers to the concept of a route common to all routing
      protocols. With reference to the definition above, typical
      non-routing-protocol attributes would be associated with diffserv
      or traffic engineering.

   Measurement Units: N.A.

   Issues: None.

   See Also: BGP route


2.4 BGP Route

   Definition:
      A BGP route is an n-tuple
      <prefix, nexthop, ASpath [, other BGP attributes]>.

   Discussion:
      BGP Attributes, such as Nexthop or AS path are defined in RFC
      1771[1], where they are known as Path Attributes, and are the
      qualifying data that define the route.

      From RFC 1771: "For purposes of this protocol a route is defined
      as a unit of information that pairs a destination with the
      attributes of a path to that destination"

   Measurement Units: N.A.

   Issues:

   See Also: Route, prefix, Adj-RIB-in, NLRI.





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2.5 Network Level Reachability Information (NLRI)

   Definition:
      The NLRI consists of one or more network prefixes with the same
      set of path attributes.

   Discussion:
      Each prefix in the NLRI is combined with the (common) path
      attributes to form a BGP route. The NLRI encapsulates a set of
      destinations to which packets can be routed (from this point in
      the network) along a common route described by the path
      attributes.

   Measurement Units: N.A.

   Issues:

   See Also:  Route Packing, Network Prefix, BGP Route, NLRI


2.6 BGP UPDATE Message

   Definition:
      An UPDATE message contains an advertisement of a single NLRI
      field, possibly containing multiple prefixes, and multiple
      withdrawals of unfeasible routes.  See RFC 1771 ([1]) for details.

   Discussion:
      From RFC 1771: "A variable length sequence of path attributes is
      present in every UPDATE.  Each path attribute is a triple
      <attribute type, attribute length, attribute value> of variable
      length."

   Measurement Units: N.A.

   See Also















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3. Routing Data Structures and Route Categories

3.1 Routing Information Base (RIB)

   The RIB collectively consists of a set of logically (not necessarily
   physically) distinct databases, each of which is enumerated below.
   The RIB contains all destination prefixes to which the router may
   forward, and one or more currently reachable next hop addresses for
   them.

   Routes included in this set potentially have been selected from
   several sources of information, including hardware status, interior
   routing protocols, and exterior routing protocols. RFC 1812 contains
   a basic set of route selection criteria relevant in an all-source
   context. Many implementations impose additional criteria.  A common
   implementation-specific criterion is the preference given to
   different routing information sources.

3.1.1 Adj-RIB-In and Adj-RIB-Out

   Definition:
      Adj-RIB-In and Adj-RIB-Out are "views" of routing information from
      the perspective of individual peer routers.

      The Adj-RIB-In contains information advertised to the DUT by a
      specific peer.  The Adj-RIB-Out contains the information the DUT
      will advertise to the peer.

      See RFC 1771[1].

   Discussion:

   Issues:

   Measurement Units: Number of route instances

   See Also:
      Route, BGP Route, Route Instance, Loc-RIB, FIB


3.1.2 Loc-RIB

   Definition:
      The Loc-RIB contains the set of best routes selected from the
      various Adj-RIBs, after applying local policies and the BGP route
      selection algorithm.





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   Discussion:
      The separation implied between the various RIBs is logical. It
      does not necessarily follow that these RIBs are distinct and
      separate entities in any given implementation.

      Types of routes that need to be considered include internal BGP,
      external BGP, interface, static and IGP routes.

   Issues:

   Measurement Units: Number of routes

   See Also:
      Route, BGP Route, Route Instance, Adj-RIB-in, Adj-RIB-out, FIB


3.2 Routing Policy

   Definition:
      Routing Policy is "the ability to define conditions for accepting,
      rejecting, and modifying routes received in advertisements"[9].

   Discussion:
      RFC 1771 [1] further constrains policy to be within the hop-by-hop
      routing paradigm. Policy is implemented using filters and
      associated policy actions.  Many AS's formulate and document their
      policies using the Routing Policy Specification Language (RPSL)
      [6] and then automatically generate configurations for the BGP
      processes in their routers from the RPSL specifications.

   Measurement Units: Number of policies; length of policies

   Issues:

   See Also: Routing Policy Information Base.


3.3 Routing Policy Information Base

   Definition:
      A routing policy information base is the set of incoming and
      outgoing policies.

   Discussion:
      All references to the phase of the BGP selection process below are
      made with respect to RFC 1771 [1] definition of these phases.





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      Incoming policies are applied in Phase 1 of the BGP selection
      process [1] to the Adj-RIB-In routes to set the metric for the
      Phase 2 decision process.  Outgoing Policies are applied in Phase
      3 of the BGP process to the Adj-RIB-Out routes preceding route
      (prefix and path attribute tuple) announcements to a specific
      peer.

      Policies in the Policy Information Base have matching and action
      conditions.  Common information to match include route prefixes,
      AS paths, communities, etc.  The action on match may be to drop
      the update and not pass it to the Loc-RIB, or to modify the update
      in some way, such as changing local preference (on input) or MED
      (on output), adding or deleting communities, prepending the
      current AS in the AS path, etc.

      The amount of policy processing (both in terms of route maps and
      filter/access lists) will impact the convergence time and
      properties of the distributed BGP algorithm. The amount of policy
      processing may vary from a simple policy which accepts all routes
      and sends all routes to complex policy with a substantial fraction
      of the prefixes being filtered by filter/access lists.

   Measurement Units: Number and length of policies

   Issues:

   See Also:


3.4 Forwarding Information Base (FIB)

   Definition:
      As according to the definition in Appendix B of [4]: "The table
      containing the information necessary to forward IP Datagrams is
      called the Forwarding Information Base. At minimum, this contains
      the interface identifier and next hop information for each
      reachable destination network prefix."

   Discussion:
      The forwarding information base describes a database indexing
      network prefixes versus router port identifiers.

      The forwarding information base is distinct from the "routing
      table" (the Routing Information Base or RIB), which holds all
      routing information received from routing peers. It is a data
      plane construct and used for the forwarding of each packet. The
      Forwarding Information Base is generated from the RIB. For the
      purposes of this document, the FIB is effectively the subset of



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      the RIB used by the forwarding plane to make per-packet forwarding
      decisions.

      Most current implementations have full, non-cached FIBs per router
      interface. All the route computation and convergence occurs before
      entries are downloaded into a FIB.

   Measurement units: N.A.

   Issues:

   See Also: Route, RIB


3.5 BGP Instance

   Definition:
      A BGP instance is a process with a single Loc-RIB.

   Discussion:
      For example, a BGP instance would run in routers or test
      equipment. A test generator acting as multiple peers will
      typically run more than one instance of BGP. A router would
      typically run a single instance.

   Measurement units: N/A

   Issues:

   See Also:


3.6 BGP Device

   Definition:
      A BGP device is a system that has one or more BGP instances
      running on it, each of which is responsible for executing the BGP
      state machine.

   Discussion:
      We have chosen to use "device" as the general case, to deal with
      the understood [e.g. [9]] and yet-to-be-invented cases where the
      control processing may be separate from forwarding [12].  A BGP
      device may be a traditional router, a route server, a BGP-aware
      traffic steering device or a non forwarding route reflector.  BGP
      instances such as route reflectors or servers, for example, never
      forwards traffic, so forwarding-based measurements would be
      meaningless for it.



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   Measurement units: N/A

   Issues:

   See Also:


3.7 BGP Session

   Definition:
      A BGP session is a session between two BGP instances.

   Discussion:

   Measurement units: N/A

   Issues:

   See Also:


3.8 Active BGP Session

   Definition:
      An active BGP session is one which is in the established state.
      (See RFC 1771 [1]).

   Discussion:

   Measurement units: N/A

   Issues:

   See Also:


3.9 BGP Peer

   Definition:
      A BGP peer is another BGP instance to which the DUT is in the
      Established state. (See RFC 1771 [1]).

   Discussion:
      In the test scenarios in the methodology discussion that will
      follow this draft, peers send BGP advertisements to the DUT and
      receive DUT-originated advertisements.  We recommend that the
      peering relation be established before tests are begun.  It might
      also be interesting to measure the time required to reach the



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      established state.

      This is a protocol-specific definition, not to be confused with
      another frequent usage, which refers to the business/economic
      definition for the exchange of routes without financial
      compensation.

      It is worth noting that a BGP peer, by this definition is
      associated with a BGP peering session, and there may be more than
      one such active session on a router or on a tester.  The peering
      sessions referred to here may exist between various classes of BGP
      routers (see Section 4.2).

   Measurement units: number of BGP peers

   Issues:

   See Also:


3.10 BGP Neighbor

   Definition:
      A BGP neighbor is a device that can be configured as a BGP peer.

   Discussion:

   Measurement units:

   Issues:

   See Also:


3.11 MinRouteAdvertisementInterval (MRAI)

   Definition:
      (Paraphrased from 1771[1]) The MRAI timer determines the minimum
      time between advertisements of routes to a particular destination
      (prefix) from a single BGP device. The timer is applied on a
      pre-prefix basis, although the timer is set on a per BGP device
      basis.

   Discussion:
      Given that a BGP instance may manage in excess of 100,000 routes,
      RFC 1771 allows for a degree of optimization in order to limit the
      number of timers needed. The MRAI does not apply to routes
      received from BGP speakers in the same AS or to explicit



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      withdrawals.

      RFC 1771 also recommends that random jitter is applied to MRAI in
      an attempt to avoid synchronization effects between the BGP
      instances in a network.

      In this document we define routing plane convergence by measuring
      the time an NLRI is advertised to the DUT to the time it is
      advertised from the DUT.  Clearly any delay inserted by the MRAI
      will have a significant effect on this measurement.

   Measurement Units: seconds.

   Issues:

   See Also:  NLRI, BGP route


3.12 MinASOriginationInterval (MAOI)

   Definition:
      The MAOI specifies the minimum interval between advertisements of
      locally originated routes from this BGP instance.

   Discussion:
      Random jitter is applied to MAOI in an attempt to avoid
      synchronization effects between BGP instances in a network.

   Measurement Units: seconds

   Issues:
      It is not known what, if any relationship exists between the
      settings of MRAI and MAOI.

   See Also: MRAI, BGP route


3.13 Active Route

   Definition:
      Route for which there is a FIB entry corresponding to a RIB entry.

   Discussion:

   Measurement Units: Number of routes.






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   Issues:

   See also: RIB.


3.14 Unique Route

   Definition:
      A unique route is a prefix for which there is just one route
      instance across all Adj-Ribs-In.

   Discussion:

   Measurement Units: N.A.

   Issues:

   See Also: route, route instance




3.15 Non-Unique Route

   Definition:
      A Non-unique route is a prefix for which there is at least one
      other route in a set including more than one Adj-RIB-in.

   Discussion:

   Measurement Units: N.A.

   Issues:

   See Also:
      route, route instance, unique active route.


3.16 Route Instance

   Definition:
      A route instance is one of several possible occurrences of a route
      for a particular prefix.

   Discussion:
      When a router has multiple peers from which it accepts routes,
      routes to the same prefix may be received from several peers. This
      is then an example of multiple route instances.



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      Each route instance is associated with a specific peer. The BGP
      algorithm that arbitrates between the available candidate route
      instances may reject a specific route instance due to local
      policy.

   Measurement Units: Number of route instances

   Issues:
      The number of route instances in the Adj-RIB-in bases will vary
      based on the function to be performed by a router. An
      inter-provider border router, located in the default-free zone
      (see Section 4.1.4) will likely receive more route instances than
      a provider edge router, located closer to the end-users of the
      network.

   See Also:



































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4. Constituent Elements of a Router or Network of Routers

   Many terms included in this list of definitions were originally
   described in previous standards or papers. They are included here
   because of their pertinence to this discussion. Where relevant,
   reference is made to these sources. An effort has been made to keep
   this list complete with regard to the necessary concepts without over
   definition.

4.1 Default Route, Default Free Table, and Full Table

   An individual router's routing table may not necessarily contain a
   default route.  Not having a default route, however, is not
   synonymous with having a full default-free table(DFT).  Also, a
   router which has a full set of routes as in a DFT but also has a
   'discard' rule for a default route would not be considered as default
   free.

   It should be noted that the references to number of routes in this
   section document are to routes installed in the loc-RIB and are
   therefore unique routes, not route instances, and that the total
   number of route instances may be 4 to 10 times the number of routes.

4.1.1 Default Route

   Definition:
      A Default Route can match any destination address. If a router
      does not have a more specific route for a particular packet's
      destination address, it forwards this packet to the next hop in
      the default route entry, provided its Forwarding Table (Forwarding
      Information Base (FIB) contains one). The notation for a default
      route for IPv4 is 0.0.0.0/0 and for IPv6 it is 0:0:0:0:0:0:0:0 or
      ::/0.

   Discussion:

   Measurement units: N.A.

   Issues:

   See Also: default free routing table, route, route instance


4.1.2 Default Free Routing Table







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   Definition:
      A default free routing table has no default routes and is
      typically seen in routers in the core or top tier of routers in
      the network.

   Discussion:
      The term originates from the concept that routers at the core or
      top tier of the Internet will not be configured with a default
      route (Notation in IPv4 0.0.0.0/0 and in IPv6 0:0:0:0:0:0:0:0 or
      ::/0). Thus they will forward every packet to a specific next hop
      based on the longest match between  the  destination IP addresse
      and the routes in the forwarding table.

      Default free routing table size is commonly used as an indicator
      of the magnitude of reachable Internet address space. However,
      default free routing tables may also include routes internal to
      the router's AS.

   Measurement Units: The number of routes

   See Also: Full Default Free, Default Route


4.1.3 Full Default Free Table

   Definition:
      A full default free table is the union of all sets of default free
      BGP routes collectively announced by the complete set of
      autonomous systems making up the public Internet.  Due to the
      dynamic nature of the Internet, the exact size and composition of
      this table may vary slightly depending where and when it is
      observed.

   Discussion:
      It is generally accepted that a full table, in this usage, does
      not contain the infrastructure routes or individual sub-aggregates
      of routes that are otherwise aggregated by the provider before
      announcement to other autonomous systems.

   Measurement Units: number of routes

   Issues:

   See Also: Routes, Route Instances, Default Route







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4.1.4 Default-Free Zone

   Definition:
      The default-free zone is that part of the Internet backbone that
      does not have a default route.

   Discussion:

   Measurement Units:

   Issues:

   See Also: Default Route


4.1.5 Full Provider-Internal Table

   Definition:
      A full provider-internal table is a superset of the full routing
      table that contains infrastructure and non- aggregated routes.

   Discussion:
      Experience has shown that this table might contain 1.3 to 1.5
      times the number of routes in the externally visible full table.
      Tables of this size, therefore, are a real-world requirement for
      key internal provider routers.

   Measurement Units: number of routes

   Issues:

   See Also: Routes, Route Instances, Default Route


4.2 Classes of BGP-Speaking Routers

   A given router may perform more than one of the following functions,
   based on its logical location in the network.

4.2.1 Provider Edge Router

   Definition:
      A provider edge router is a router at the edge of a provider's
      network that speaks eBGP to a BGP speaker in another AS.

   Discussion:
      The traffic that transits this router may be destined to, or
      originate from non-adjacent autonomous systems.  In particular the



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      MED values used in the Provider Edge Router would not be visible
      in the non-adjacent autonomous systems.

      Such a router will always speak eBGP and may speak iBGP.

   Measurement units:

   Issues:

   See Also:


4.2.2 Subscriber Edge Router

   Definition:
      A subscriber edge router is router at the edge of the subscriber's
      network that speaks eBGP to its provider's AS(s).

   Discussion:
      The router belongs to an end user organization that may be multi-
      homed, and which carries traffic only to and from that end user
      AS.

      Such a router will always speak eBGP and may speak iBGP.

   Measurement units:

   Issues:
      This definition of an enterprise border router (which is what most
      Subscriber Edge Routers are) is practical rather than rigorous. It
      is meant to draw attention to the reality that many enterprises
      may need a BGP speaker that advertises their own routes and
      accepts either default alone or partial routes. In such cases,
      they may be interested in benchmarks that use a partial routing
      table, to see if a smaller control plane processor will meet their
      needs.

   See Also:


4.2.3 Inter-provider Border Router

   Definition:
      An inter-provider border router is a BGP speaking router which
      maintains BGP sessions with other BGP speaking routers in other
      providers' ASs.





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   Discussion:
      Traffic transiting this router may be originated in or destined
      for another AS that has no direct connectivity with this
      provider's AS.

      Such a router will always speak eBGP and may speak iBGP.

   Measurement units:

   Issues:

   See Also:


4.2.4 Core Router

   Definition:
      An core router is a provider router Internal to the provider's
      net, speaking iBGP to that provider's edge routers, other intra-
      provider core routers, or the provider's inter-provider border
      routers.

   Discussion:
      Such a router will always speak iBGP and may speak eBGP.

   Measurement units:

   Issues:
      Then by this definition the DUT's which are eBGP routers aren't
      core routers.

   See Also:



















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5. Characterization of Sets of Update Messages

   This section contains a sequence of definitions that build up to the
   definition of an Update Train. The Packet train concept was
   originally introduced by Jain and Routhier [11]. It is here adapted
   to refer to a train of packets of interest in BGP performance
   testing.

   This is a formalization of the sort of test stimulus that is expected
   as input to a DUT running BGP. This data could be a
   well-characterized, ordered and timed set of hand-crafted BGP UPDATE
   packets.  It could just as well be a set of BGP UPDATE packets that
   have been captured from a live router.

   Characterization of route mixtures and Update Trains is an open area
   of research.  The particular question of interest for this work is
   the identification of suitable Update Trains, modeled or taken from
   live traces that reflect realistic sequences of UPDATEs and their
   contents.

5.1 Route Packing

   Definition:
      Route packing is the number of route prefixes accommodated in a
      single Routing Protocol UPDATE Message either as updates
      (additions or modifications) or withdrawals.

   Discussion:
      In general, a routing protocol update may contain more than one
      prefix.  In BGP, a single UPDATE may contain two sets of multiple
      network prefixes: one set of additions and updates with identical
      attributes (the NLRI) and one set of unfeasible routes to be
      withdrawn.

   Measurement Units:
      Number of prefixes.

   Issues:

   See Also:
      route, BGP route, route instance, update train, NLRI.


5.2 Route Mixture







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   Definition:
      A route mixture is the demographics of a set of routes.

   Discussion:
      A route mixture is the input data for the benchmark.  The
      particular route mixture used as input must be selected to suit
      the question being asked of the benchmark. Data containing simple
      route mixtures might be suitable to test the performance limits of
      the BGP device.

      Using live data, or input that simulates live data, should improve
      understanding of how the BGP device will operate in a live
      network. The data for this kind of test must be route mixtures
      that model the patterns of arriving control traffic in the live
      Internet.

      To accomplish that kind of modeling it is necessary to identify
      the key parameters that characterize a live Internet route
      mixture.  The parameters and how they interact is an open research
      problem.  However, we identify the following as affecting the
      route mixture:

      *  Path length distribution

      *  Attribute distribution

      *  Prefix length distribution

      *  Packet packing

      *  Probability density function of inter-arrival times of
         UPDATES

      Each of the items above is more complex than a single number.  For
      example, one could consider the distribution of prefixes by AS or
      distribution of prefixes by length.

   Measurement Units: Probability density functions

   Issues:

   See Also:  NLRI, RIB.


5.3 Update Train






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   Definition:
      An update train is a set of Routing Protocol UPDATE messages sent
      by a router to a BGP peer.

   Discussion:
      The arrival pattern of UPDATEs can be influenced by many things,
      including TCP parameters, hold-down timers, upsteam processing, a
      peer coming up or multiple peers sending at the same time.
      Network conditions such as a local or remote peer flapping a link
      can also affect the arrival pattern.

   Measurement units:
      Probability density function for the inter-arrival times of UPDATE
      packets in the train.

   Issues:
      Characterizing the profiles of real world UPDATE trains is a
      matter for future research.  In order to generate realistic UPDATE
      trains as test stimuli a formal mathematical scheme or a proven
      heuristic is needed to drive the selection of prefixes. Whatever
      mechanism is selected it must generate Update trains that have
      similar characteristics to those measured in live networks.

   See Also:  Route Mixture, MRAI, MAOI


5.4 Randomness in Update Trains

   As we have seen from the previous sections, an update train used as a
   test stimulus has a considerable number of parameters that can be
   varied, to a greater or lesser extent, randomly and independently.

   A random Update Train will contain:

   o  A route mixture randomized across

      *  NLRIs

      *  updates and withdrawals

      *  prefixes

      *  inter-arrival times of the UPDATEs

         and possibly across other variables.

   This is intended to simulate the unpredictable asynchronous nature of
   the network, whereby UPDATE packets may have arbitrary contents and



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   be delivered at random times.

   It is important that the data set be randomized sufficiently to avoid
   favoring one vendor's implementation over another's. Specifically,
   the distribution of prefixes could be structured to favor the
   internal organization of the routes in a particular vendor's
   databases. This is to be avoided.

5.5 Route Flap

   Definition:
      A route flap ia a change of state (withdrawal, announcement,
      attribute change) for a route.

   Discussion:
      Route flapping can be considered a special and pathological case
      of update trains. A practical interpretation of what may be
      considered excessively rapid is the RIPE 229 [7], which contains
      current guidelines on flap damping parameters.

   Measurement units: Flapping events per unit time.

   Issues:
      Specific Flap events can be found in Section 6.1. A bench-marker
      should use a mixture of different route change events in testing.

   See Also: Route change events, flap damping, packet train
























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6. Route Changes and Convergence

   The following two definitions are central to the benchmarking of
   external routing convergence, and so are singled out for more
   extensive discussion.

6.1 Route Change Events

   A taxonomy characterizing routing information changes seen in
   operational networks is proposed in [4] as well as Labovitz et al[5].
   These papers describe BGP protocol-centric events, and event
   sequences in the course of an analysis of network behavior. The
   terminology in the two papers categorizes similar but slightly
   different behaviors with some overlap. We would like to apply these
   taxonomies to categorize the tests under definition where possible,
   because these tests must tie in to phenomena that arise in actual
   networks. We avail ourselves of, or may extend, this terminology as
   necessary for this purpose.

   A route can be changed implicitly by replacing it with another route
   or explicitly by withdrawal followed by the introduction of a new
   route. In either case the change may be an actual change, no change,
   or a duplicate. The notation and definition of individual
   categorizable route change events is adopted from [5] and given
   below.

   1.  AADiff: Implicit withdrawal of a route and replacement by a route
       different in some path attribute.

   2.  AADup: Implicit withdrawal of a route and replacement by route
       that is identical in all path attributes.

   3.  WADiff: Explicit withdrawal of a route and replacement by a
       different route.

   4.  WADup: Explicit withdrawal of a route and replacement by a route
       that is identical in all path attributes.

   To apply this taxonomy in the benchmarking context, we need both
   terms to describe the sequence of events from the update train
   perspective, as listed above, and event indications in the time
   domain so as to be able to measure activity from the perspective of
   the DUT. With this in mind, we incorporate and extend the definitions
   of [5] to the following:

   1.  Tup (TDx): Route advertised to the DUT by Test Device x

   2.  Tdown(TDx): Route being withdrawn by Device x



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   3.  Tupinit(TDx): The initial announcement of a route to a unique
       prefix

   4.  TWF(TDx): Route fail over after an explicit withdrawal.

   But we need to take this a step further. Each of these events can
   involve a single route, a "short" packet train, or a "full" routing
   table. We further extend the notation to indicate how many routes are
   conveyed by the events above:

   1.  Tup(1,TDx) means Device x sends 1 route

   2.  Tup(S,TDx) means Device x sends a train, S, of routes

   3.  Tup(DFT,TDx) means Device x sends an approximation of a full
       default-free table.

   The basic criterion for selecting a "better" route is the final
   tiebreaker defined in RFC1771, the router ID. As a consequence, this
   memorandum uses the following descriptor events, which are routes
   selected by the BGP selection process rather than simple updates:

   1.  Tbest   -- The current best path.

   2.  Tbetter -- Advertise a path that is better than Tbest.

   3.  Tworse  -- Advertise a path that is worse than Tbest.


6.2 Device Convergence in the Control Plane

   Definition:
      A routing device is said to have converged at the point in time
      when the DUT has performed all actions in the control plane needed
      to react to changes in topology in the context of the test
      condition.

   Discussion:
      For example, when considering BGP convergence, the convergence
      resulting from a change that alters the best route instance for a
      single prefix at a router would be deemed to have occurred when
      this route is advertised to its downstream peers.  By way of
      contrast, OSPF convergence concludes when SPF calculations have
      been performed and the required link states advertised onwards.

      The convergence process, in general, can be subdivided into three
      distinct phases:




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      *  convergence across the entire Internet,

      *  convergence within an Autonomous System,

      *  convergence with respect to a single device.

      Convergence with respect to a single device can be

      *  convergence with regard to data forwarding process(es)

      *  convergence with regard to the routing process(es), the focus
         of this document.

      It is the latter, convergence with regard to the routing process,
      that we describe in this and the methodology documents.

      Because we are trying to benchmark the routing protocol
      performance which is only a part of the device overall, this
      definition is intended (so far as is possible) to exclude any
      additional time such as is needed to download and install the
      forwarding information base in the data plane.  This definition
      should be usable for different families of protocols.

      It is of key importance to benchmark the performance of each phase
      of convergence separately before proceeding to a composite
      characterization of routing convergence, where
      implementation-specific dependencies are allowed to interact.

      Care also needs to be taken to ensure that the convergence time is
      not influenced by policy processing on downstream peers.

      The time resolution needed to measure the device convergence
      depends to some extent on the types of the interfaces on the
      router.  For modern routers with gigabit or faster interfaces, an
      individual UPDATE may be processed and re-advertised in very much
      less than a millisecond so that time measurements must be made to
      a resolution of hundreds to tens of microseconds or better.

   Measurement Units:
      Time period.

   Issues:

   See Also:







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7. BGP Operation Events

   The BGP process(es) in a device might restart because operator
   intervention or a power failure caused a complete shut-down.  In this
   case a hard reset is needed. A peering session could be lost, for
   example, because of action on the part of the peer or a dropped tcp
   session.  A device can reestablish its peers and re-advertise all
   relevant routes in a hard reset.  However,  if a peer is lost, but
   the BGP process has not failed, BGP has mechanisms for a "soft
   reset."

7.1 Hard Reset

   Definition:
      An event which triggers a complete re-initialization of the
      routing tables on one or more BGP sessions, resulting in exchange
      of a full routing table on one or more links to the router.

   Discussion:

   Measurement Units: N/A

   Issues:

   See Also:


7.2 Soft Reset

   Definition:
      A soft reset is performed on a per-neighbor basis; it does not
      clear the BGP session while re-establishing the peering relation
      and does not stop the flow of traffic.

   Discussion:
      There are two methods of performing a soft reset: Graceful restart
      [13] where the BGP device that has lost a peer but continues to
      forward traffic for a period of time before tearing down the
      peer's routes.  The alternative method is soft refresh [12], where
      a BGP device can request a peer's Adj-RIB-Out.

   Measurement Units: N/A

   Issues:

   See Also:





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8. Factors that Impact the Performance of the Convergence Process

   While this is not a complete list, all of the items discussed below
   have a significant affect on BGP convergence.  Not all of them can be
   addressed in the baseline measurements described in this document.

8.1 General Factors Affecting Device Convergence

   These factors are conditions of testing external to the router Device
   Under Test (DUT).

8.1.1 Number of Peers

   As the number of peers increases, the BGP route selection algorithm
   is increasingly exercised. In addition, the phasing and frequency of
   updates from the various peers will have an increasingly marked
   effect on the convergence process on a router as the number of peers
   grows, depending on the quantity of updates that is generated by each
   additional peer. Increasing the number of peers also increases the
   processing workload for TCP and BGP keepalives.

8.1.2 Number of Routes per Peer

   The number of routes per BGP peer is an obvious stressor to the
   convergence process. The number, and relative proportion, of multiple
   route instances and distinct routes being added or withdrawn by each
   peer will affect the convergence process, as will the mix of
   overlapping route instances, and IGP routes.

8.1.3 Policy Processing/Reconfiguration

   The number of routes and attributes being filtered, and set, as a
   fraction of the target route table size is another parameter that
   will affect BGP convergence.

   Extreme examples are

   o  Minimal Policy: receive all, send all,

   o  Extensive policy: up to 100% of the total routes have applicable
      policy.


8.1.4 Interactions with Other Protocols

   There are interactions in the form of precedence, synchronization,
   duplication and the addition of timers, and route selection criteria.
   Ultimately, understanding BGP4 convergence must include understanding



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   of the interactions with both the IGPs and the protocols associated
   with the physical media, such as Ethernet, SONET, DWDM.

8.1.5 Flap Damping

   A router can use flap damping to respond to route flapping.   Use of
   flap damping is not mandatory, so the decision to enable the feature,
   and to change parameters associated with it, can be considered a
   matter of routing policy.

   The timers are defined by RFC 2439 [2] and discussed in RIPE-229 [7].
   If this feature is in effect, it requires that the device keep
   additional state to carry out the damping, which can have a direct
   impact on the control plane due to increased processing.  In
   addition, flap damping may delay the arrival of real changes in a
   route, and affect convergence times

8.1.6 Churn

   In theory, a BGP device could receive a set of updates that
   completely defined the Internet, and could remain in a steady state,
   only sending appropriate keepalives.  In practice, the Internet will
   always be changing.

   Churn refers to control plane processor activity caused by
   announcements received and sent by the router.  It does not include
   keepalives and TCP processing.

   Churn is caused by both normal and pathological events.  For example,
   if an interface of the local router goes down and the associated
   prefix is withdrawn, that withdrawal is a normal activity, although
   it contributes to churn.  If the local device receives a withdrawal
   of a route it already advertises, or an announcement of a route it
   did not previously know, and re-advertises this information, again
   these are normal constituents of churn. Routine updates can range
   from single announcement or withdrawals, to announcements of an
   entire default-free table.  The latter is completely reasonable as an
   initialization condition.

   Flapping routes are a pathological contributor to churn, as is MED
   oscillation [16].  The goal of flap damping is to reduce the
   contribution of flapping to churn.

   The effect of churn on overall convergence depends on the processing
   power available to the control plane, and whether the same
   processor(s) are used for forwarding and for control.





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8.2 Implementation-specific and other Factors Affecting BGP Convergence

   These factors are conditions of testing internal to the Device Under
   Test (DUT), although they may affect its interactions with test
   devices.

8.2.1 Forwarded Traffic

   The presence of actual traffic in the device may stress the control
   path in some fashion if both the offered load due to data and the
   control traffic (FIB updates and downloads as a consequence of flaps)
   are excessive. The addition of data traffic presents a more accurate
   reflection of realistic operating scenarios than if only control
   traffic is present.

8.2.2 Timers

   Settings of delay and hold-down timers at the link level as well as
   for BGP4, can introduce or ameliorate delays.  As part of a test
   report, all relevant timers should be reported if they use non-
   default value.

8.2.3 TCP Parameters Underlying BGP Transport

   Since all BGP traffic and interactions occur over TCP, all relevant
   parameters characterizing the TCP sessions should be provided: e.g.
   Slow start, max window size, maximum segment size, or timers.

8.2.4 Authentication

   Authentication in BGP is currently done using the TCP MD5 Signature
   Option [8].  The processing of the MD5 hash, particularly in devices
   with a large number of BGP peers and a large amount of update traffic
   can have an impact on the control plane of the device.

















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9. Security Considerations

   The document explicitly considers authentication as a performance-
   affecting feature, but does not consider the overall security of the
   routing system.














































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10. Acknowledgments

   Thanks to Francis Ovenden for review and Abha Ahuja for
   encouragement. Much appreciation to Jeff Haas, Matt Richardson, and
   Shane Wright at Nexthop for comments and input. Debby Stopp and Nick
   Ambrose contributed the concept of route packing.

   Alvaro Retana was a key member of the team that developed this
   document, and made significant technical contributions regarding
   route mixes.  The team thanks him and regards him as a co-author in
   spirit.








































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Normative References

   [1]   Rekhter, Y. and T. Li, "A Border Gateway Protocol 4 (BGP-4)",
         RFC 1771, March 1995.

   [2]   Villamizar, C., Chandra, R. and R. Govindan , "BGP Route Flap
         Damping", RFC 2439, November 1998.

   [3]   Baker, F., "Requirements for IP Version 4 Routers", RFC 1812,
         June 1995.

   [4]   Ahuja, A., Jahanian, F., Bose, A. and C. Labovitz, "An
         Experimental Study of Delayed Internet Routing Convergence",
         RIPE-37 Presentation to Routing WG, November 2000, <http://
         www.ripe.net/ripe/meetings/archive/ripe-37/presentations/
         RIPE-37-convergence/>.

   [5]   Labovitz, C., Malan, G. and F. Jahanian, "Origins of Internet
         Routing Instability", Infocom 99, August 1999.

   [6]   Alaettinoglu, C., Villamizar, C., Gerich, E., Kessens, D.,
         Meyer, D., Bates, T., Karrenberg, D. and M. Terpstra, "Routing
         Policy Specification Language (RPSL)", RFC 2622, June 1999.

   [7]   Panigl , C., Schmitz , J., Smith , P. and C. Vistoli, "RIPE
         Routing-WG Recommendation for coordinated route-flap damping
         parameters, version 2", RIPE 229, October 2001.

   [8]   Heffernan, A., "Protection of BGP Sessions via the TCP MD5
         Signature Option", RFC 2385, August 1998.

   [9]   Juniper Networks, "Junos(tm) Internet Software Configuration
         Guide Routing and Routing Protocols, Release 4.2", Junos 4.2
         and other releases, September 2000, <http://www.juniper.net/
         techpubs/software/junos42/swconfig-routing42/html/
         glossary.html#1013039>.

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

   [11]  Jain, R. and S. Routhier, "Packet trains -- measurement and a
         new model for computer network traffic",  IEEE Journal on
         Selected Areas in Communication 4(6), September 1986.








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Informative References

   [12]  Chen, E., "Route Refresh for BGP-4", RFC 2918, September 2000.

   [13]  Sangli, S., Rekhter, Y., Fernando, R., Scudder, J. and E. Chen,
         "Graceful Restart Mechanism for BGP", draft-ietf-idr-restart-06
         (work in progress), January 2003.

   [14]  Chen, E. and Y. Rekhter, "Cooperative Route Filtering
         Capability for BGP-4", draft-ietf-idr-route-filter-08 (work in
         progress), January 2003.

   [15]   Anderson, T. and H. Khosravi, "Requirements for Separation of
         IP Control and Forwarding", draft-ietf-forces-requirements-08
         (work in progress), January 2003.

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

   [17]  Bates, T.,  Rekhter, Y., Chandra, R. and D. Katz,
         "Multiprotocol Extensions for BGP-4", RFC 2283.





























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For Internet Draft consistency purposes only

   [18]  Bradner, S., "The Internet Standards Process -- Revision 3",
         RFC 2026, BCP 9, October 1996.


Authors' Addresses

   Howard Berkowitz
   Gett Communications
   5012 S. 25th St
   Arlington, VA  22206
   USA

   Phone: +1 703 998-5819
   Fax:   +1 703 998-5058
   EMail: hcb@gettcomm.com


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

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


   Susan Hares
   Nexthop Technologies
   517 W. William
   Ann Arbor, MI  48103
   USA

   EMail: skh@nexthop.com


   Padma Krishnaswamy
   SAIC
   331 Newman Springs Road
   Red Bank, New Jersey  07701
   USA

   EMail: kri1@earthlink.net





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   Marianne Lepp
   Consultant

   EMail: mlepp@lepp.com















































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Intellectual Property Statement

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   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
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