Network Working Group                                       H. Berkowitz
Request for Comments: 4098            Gett Communications & CCI Training
Category: Informational                                   E. Davies, Ed.
                                                        Folly Consulting
                                                                S. Hares
                                                    Nexthop Technologies
                                                         P. Krishnaswamy
                                                                 M. Lepp
                                                               June 2005

          Terminology for Benchmarking BGP Device Convergence
                          in the Control Plane

Status of This Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2005).


   This document 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
   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.

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Table of Contents

   1. Introduction ....................................................3
      1.1. Overview and Road Map ......................................4
      1.2. Definition Format ..........................................5
   2. Components and Characteristics of Routing Information ...........5
      2.1. (Network) Prefix ...........................................5
      2.2. Network Prefix Length ......................................6
      2.3. Route ......................................................6
      2.4. BGP Route ..................................................7
      2.5. Network Level Reachability Information (NLRI) ..............7
      2.6. BGP UPDATE Message .........................................8
   3. Routing Data Structures and Route Categories ....................8
      3.1. Routing Information Base (RIB) .............................8
           3.1.1. Adj-RIB-In and Adj-RIB-Out ..........................8
           3.1.2. Loc-RIB .............................................9
      3.2. Prefix Filtering ...........................................9
      3.3. Routing Policy ............................................10
      3.4. Routing Policy Information Base ...........................10
      3.5. Forwarding Information Base (FIB) .........................11
      3.6. BGP Instance ..............................................12
      3.7. BGP Device ................................................12
      3.8. BGP Session ...............................................13
      3.9. Active BGP Session ........................................13
      3.10. BGP Peer .................................................13
      3.11. BGP Neighbor .............................................14
      3.12. MinRouteAdvertisementInterval (MRAI) .....................14
      3.13. MinASOriginationInterval (MAOI) ..........................15
      3.14. Active Route .............................................15
      3.15. Unique Route .............................................15
      3.16. Non-Unique Route .........................................16
      3.17. Route Instance ...........................................16
   4. Constituent Elements of a Router or Network of Routers .........17
      4.1. Default Route, Default-Free Table, and Full Table .........17
           4.1.1. Default Route ......................................17
           4.1.2. Default-Free Routing Table .........................18
           4.1.3. Full Default-Free Table ............................18
           4.1.4. Default-Free Zone ..................................19
           4.1.5. Full Provider-Internal Table .......................19
      4.2. Classes of BGP-Speaking Routers ...........................19
           4.2.1. Provider Edge Router ...............................20
           4.2.2. Subscriber Edge Router .............................20
           4.2.3. Inter-provider Border Router .......................21
           4.2.4. Core Router ........................................21
   5. Characterization of Sets of Update Messages ....................22
      5.1. Route Packing .............................................22
      5.2. Route Mixture .............................................23
      5.3. Update Train ..............................................24

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      5.4. Randomness in Update Trains ...............................24
      5.5. Route Flap ................................................25
   6. Route Changes and Convergence ..................................25
      6.1. Route Change Events .......................................25
      6.2. Device Convergence in the Control Plane ...................27
   7. BGP Operation Events ...........................................28
      7.1. Hard Reset ................................................28
      7.2. Soft Reset ................................................29
   8. Factors That Impact the Performance of the Convergence
      Process ........................................................29
      8.1. General Factors Affecting Device Convergence ..............29
           8.1.1. Number of Peers ....................................29
           8.1.2. Number of Routes per Peer ..........................30
           8.1.3. Policy Processing/Reconfiguration ..................30
           8.1.4. Interactions with Other Protocols ..................30
           8.1.5. Flap Damping .......................................30
           8.1.6. Churn ..............................................31
      8.2. Implementation-Specific and Other Factors Affecting BGP ...31
           8.2.1. Forwarded Traffic ..................................31
           8.2.2. Timers .............................................32
           8.2.3. TCP Parameters Underlying BGP Transport ............32
           8.2.4. Authentication .....................................32
   9. Security Considerations ........................................32
   10. Acknowledgements ..............................................32
   11. References ....................................................33
       11.1. Normative References ....................................33
       11.2. Informative References ..................................34

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 'A Border Gateway Protocol
   4 (BGP-4)' [RFC1771], referred to as RFC 1771 in the remainder of the
   document.)  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.
   However, this document is primarily targeted for BGP-4 in IPv4
   networks.  IPv6 will require the use of MP-BGP [RFC2858], as
   described in RFC 2545 [RFC2545], but this document will not address
   terminology or issues specific to these extensions of BGP-4.  Also
   terminology and issues specific to the extensions of BGP that support
   VPNs as described in RFC 2547 [RFC2547] are out of scope for this

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

   o  The principal objective is to derive methodologies that
      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 these 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 in characterizing BGP convergence.

   For path-vector protocols, such as BGP, the primary initial focus
   will therefore be on network and system control-plane [RFC3654]
   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 at their default
   setting unless the test specifies otherwise.

   Subsequent documents 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 Device Under Test
   (DUT), and other realistic performance modifiers.  Convergence of
   Interior Gateway Protocols (IGPs) will also be considered in separate

1.1.  Overview and Road Map

   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
   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

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   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

1.2.  Definition Format

   The definition format is equivalent to that defined in 'Requirements
   for IP Version 4 Routers' [RFC1812], and is repeated here for

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

      One or more sentences forming the body of the definition.

      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.  This item may
      not be applicable (N.A.).

      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.

2.  Components and Characteristics of Routing Information

2.1.  (Network) Prefix

      "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,
      "Classless Inter Domain Routing (CIDR)", of RFC 1812.)

      In the CIDR context, the network prefix is the network component
      of an IP address.  In IPv4 systems, the network component of a
      complete address is known as the 'network part', and the remaining
      part of the address is known as the 'host part'.  In IPv6 systems,

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      the network component of a complete address is known as the
      'subnet prefix', and the remaining part is known as the 'interface

   Measurement units: N.A.


   See also:

2.2.  Network Prefix Length

      The network prefix length is the number of bits, out of the total
      constituting the address field, that define the network prefix
      portion of the address.

      A common alternative to using a bit-wise mask to communicate this
      component is the use of slash (/) notation.  This binds the notion
      of network prefix length in bits to an IP address.  For example, indicates that 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:


   See also:
      Network Prefix.

2.3.  Route

      In general, a 'route' is the n-tuple .  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 toward 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.

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      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.


   See also:
      BGP Route.

2.4.  BGP Route

      A BGP route is an n-tuple .

      BGP Attributes, such as Nexthop or AS path, are defined in RFC
      1771, where they are known as Path Attributes, and they 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.


   See also:
      Route, Prefix, Adj-RIB-In, Network Level Reachability Information

2.5.  Network Level Reachability Information (NLRI)

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

      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

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   Measurement units: N.A.


   See also:
      Route Packing, Network Prefix, BGP Route, NLRI.

2.6.  BGP UPDATE Message

      An UPDATE message contains an advertisement of a single NLRI
      field, possibly containing multiple prefixes, and multiple
      withdrawals of unfeasible routes.  See RFC 1771 for details.

      From RFC 1771: "A variable length sequence of path attributes is
      present in every UPDATE.  Each path attribute is a triple
       of variable

   Measurement units: N.A.

   See also:

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

   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

      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.

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      The Adj-RIB-Out contains the information the DUT will advertise to
      the peer.  See RFC 1771.



   Measurement units:
      Number of route instances.

   See also:
      Route, BGP Route, Route Instance, Loc-RIB, FIB.

3.1.2.  Loc-RIB

      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.

      The separation implied among 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.


   Measurement units:
      Number of routes.

   See also:
      Route, BGP Route, Route Instance, Adj-RIB-In, Adj-RIB-Out, FIB.

3.2.  Prefix Filtering

      Prefix Filtering is a technique for eliminating routes from
      consideration as candidates for entry into a RIB by matching the
      network prefix in a BGP Route against a list of network prefixes.

      A BGP Route is eliminated if, for any filter prefix from the list,
      the Route prefix length is equal to or longer than the filter
      prefix length and the most significant bits of the two prefixes

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      match over the length of the filter prefix.  See 'Cooperative
      Route Filtering Capability for BGP-4' [BGP-4] for examples of

   Measurement units:
      Number of filter prefixes; lengths of prefixes.


   See also:
      BGP Route, Network Prefix, Network Prefix Length, Routing Policy,
      Routing Policy Information Base.

3.3.  Routing Policy

      Routing Policy is "the ability to define conditions for accepting,
      rejecting, and modifying routes received in advertisements"

      RFC 1771 further constrains policy to be within the hop-by-hop
      routing paradigm.  Policy is implemented using filters and
      associated policy actions such as Prefix Filtering.  Many ASes
      formulate and document their policies using the Routing Policy
      Specification Language (RPSL) [RFC2622] and then automatically
      generate configurations for the BGP processes in their routers
      from the RPSL specifications.

   Measurement units:
      Number of policies; length of policies.


   See also:
      Routing Policy Information Base, Prefix Filtering.

3.4.  Routing Policy Information Base

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

      All references to the phase of the BGP selection process below are
      made with respect to RFC 1771 definition of these phases.
      Incoming policies are applied in Phase 1 of the BGP selection
      process to the Adj-RIB-In routes to set the metric for the Phase 2

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      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 includes route prefixes,
      AS paths, communities, etc.  The action on match may be to drop
      the update and not to 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 that accepts all routes and sends them according to a
      complex policy with a substantial fraction of the prefixes being
      filtered by filter/access lists.

   Measurement units:
      Number and length of policies.


   See also:

3.5.  Forwarding Information Base (FIB)

      According to the definition in Appendix B of RIPE-37 [RIPE37]:
      "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."

      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 is
      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 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.

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   Measurement units: N.A.


   See also:
      Route, RIB.

3.6.  BGP Instance

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

      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.


   See also:

3.7.  BGP Device

      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.

      We have chosen to use "device" as the general case, to deal with
      the understood (e.g., [GLSSRY]) and yet-to-be-invented cases where
      the control processing may be separate from forwarding [RFC2918].
      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 forward traffic, so forwarding-based measurements
      would be meaningless for them.

   Measurement units: N.A.


   See also:

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3.8.  BGP Session

      A BGP session is a session between two BGP instances.


   Measurement units: N.A.


   See also:

3.9.  Active BGP Session

      An active BGP session is one that is in the established state.
      (See RFC 1771.)


   Measurement units: N.A.


   See also:

3.10.  BGP Peer

      A BGP peer is another BGP instance to which the DUT is in the
      Established state.  (See RFC 1771.)

      In the test scenarios for the methodology discussion that will
      follow this document, peers send BGP advertisements to the DUT and
      receive DUT-originated advertisements.  We recommend that the
      peering relation be established before tests begin.  It might also
      be interesting to measure the time required to reach the
      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).

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   Measurement units:
      Number of BGP peers.


   See also:

3.11.  BGP Neighbor

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


   Measurement units:


   See also:

3.12.  MinRouteAdvertisementInterval (MRAI)

      (Paraphrased from RFC 1771) 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

      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
      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 from 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:

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   See also:
      NLRI, BGP Route.

3.13.  MinASOriginationInterval (MAOI)

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

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

   Measurement units:

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

   See also:
      MRAI, BGP Route.

3.14.  Active Route

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


   Measurement units:
      Number of routes.


   See also:

3.15.  Unique Route

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

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   Measurement units: N.A.


   See also:
      Route, Route Instance.

3.16.  Non-Unique Route

      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.


   Measurement units: N.A.


   See also:
      Route, Route Instance, Unique Active Route.

3.17.  Route Instance

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

      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.  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.

      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

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   See also:

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

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 that has a full set of routes as in a DFT, but that also has a
   'discard' rule for a default route would not be considered default

   Note that in this section the references to number of routes are to
   routes installed in the loc-RIB, which are therefore unique routes,
   not route instances.  Also note that the total number of route
   instances may be 4 to 10 times the number of routes.

4.1.1.  Default Route

      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 that its Forwarding Table
      (Forwarding Information Base, or FIB, contains one).  The notation
      for a default route for IPv4 is and for IPv6 it is
      0:0:0:0:0:0:0:0 or ::/0.


   Measurement units: N.A.


   See also:
      Default-Free Routing Table, Route, Route Instance.

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4.1.2.  Default-Free Routing Table

      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.

      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 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 address 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 Table, Default Route.

4.1.3.  Full Default-Free Table

      A full default-free table is the union of all sets of BGP routes
      taken from all the default-free BGP routing tables 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 on where and when it is observed.

      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.

      The full default-free routing table is not the same as the union
      of all reachable unicast addresses.  The table simply does not

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      contain the default prefix (0/0) and does contain the union of all
      sets of BGP routes from default-free BGP routing tables.

   See also:
      Routes, Route Instances, Default Route.

4.1.4.  Default-Free Zone

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


   Measurement units:


   See also:
      Default Route.

4.1.5.  Full Provider-Internal Table

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

      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.


   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.

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4.2.1.  Provider Edge Router

      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.

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


   See also:

4.2.2.  Subscriber Edge Router

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

      The router belongs to an end user organization that may be multi-
      homed, and that carries traffic only to and from that end user AS.
      Such a router will always speak eBGP and may speak iBGP.

   Measurement units:

      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 whether a smaller control plane processor will meet
      their needs.

   See also:

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4.2.3.  Inter-provider Border Router

      An inter-provider border router is a BGP speaking router that
      maintains BGP sessions with other BGP speaking routers in other
      providers' ASes.

      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

   Measurement units:


   See also:

4.2.4.  Core Router

      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

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

   Measurement units:

      By this definition, the DUTs that are eBGP routers aren't core

   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 [PKTTRAIN].  It is here
   adapted to refer to a train of packets of interest in BGP performance

   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 on or taken
   from live traces that reflect realistic sequences of UPDATEs and
   their contents.

5.1.  Route Packing

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

      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

   Measurement units:

   Number of prefixes.


   See also:
      Route, BGP Route, Route Instance, Update Train, NLRI.

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5.2.  Route Mixture

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

      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
      will 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 this 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 by

   Measurement units:
      Probability density functions.


   See also:
      NLRI, RIB.

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5.3.  Update Train

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

      The arrival pattern of UPDATEs can be influenced by many things,
      including TCP parameters, hold-down timers, upstream 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.

      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 a route mixture randomized across:

   *  NLRIs

   *  updates and withdrawals

   *  prefixes

   *  inter-arrival times of the UPDATEs and possibly across other

   This is intended to simulate the unpredictable asynchronous nature of
   the network, whereby UPDATE packets may have arbitrary contents and
   be delivered at random times.

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   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

      A route flap is a change of state (withdrawal, announcement,
      attribute change) for a route.

      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 [RIPE229], which
      contains current guidelines on flap-damping parameters.

   Measurement units:
      Flapping events per unit time.

      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

6.  Route Changes and Convergence

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

6.1.  Route Change Events

   A taxonomy characterizing routing information changes seen in
   operational networks is proposed in RIPE-37 [RIPE37] and Labovitz et
   al [INSTBLTY].  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.

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   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 [INSTBLTY] 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 terms to
   describe the sequence of events from the update train perspective, as
   listed above, and event indications in the time domain in order to
   measure activity from the perspective of the DUT.  With this in mind,
   we incorporate and extend the definitions of [INSTBLTY] to the

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

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

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

   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.

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   The basic criterion for selecting a "better" route is the final
   tiebreaker defined in RFC 1771, 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

   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

      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

      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 are advertised onward.
      The convergence process, in general, can be subdivided into three
      distinct phases:

      *  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
      that we describe herein and in 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 (as far as is possible) to exclude any

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      additional time needed to download and install the
      forwarding information base in the data plane.  This definition is
      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.


   See also:

7.  BGP Operation Events

   The BGP process(es) in a device might restart because operator
   intervention or a power failure caused a complete shutdown.  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

7.1.  Hard Reset

      An event that 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.


   Measurement units: N.A.


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   See also:

7.2.  Soft Reset

      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.

      There are two methods of performing a soft reset: (1) graceful
      restart [GRMBGP], wherein the BGP device that has lost a
      peer continues to forward traffic for a period of time before
      tearing down the peer's routes and (2) soft
      refresh [RFC2918], wherein a BGP device can request a peer's

   Measurement units: N.A.


   See also:

8.  Factors That Impact the Performance of the Convergence Process

   Although this is not a complete list, all the items discussed below
   have a significant effect 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 generated by each
   additional peer.  Increasing the number of peers also increases the
   processing workload for TCP and BGP keepalives.

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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.

   The following are extreme examples:

   o  Minimal policy: receive all, send all.

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

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 an
   understanding of the interactions with both the IGPs and the
   protocols associated with the physical media, such as Ethernet,
   SONET, and 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 [RFC2439] and discussed in RIPE-
   229 [RIPE229].  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.

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8.1.6.  Churn

   In theory, a BGP device could receive a set of updates that
   completely define 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 it re-advertises this information, these
   are normal constituents of churn.  Routine updates can range from
   single announcements 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 [RFC3345].  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 on whether the same
   processor(s) are used for forwarding and control.

8.2.  Implementation-Specific and Other Factors Affecting BGP

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

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 would be presented
   if only control traffic were present.

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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 MUST be reported if they use non-default

8.2.3.  TCP Parameters Underlying BGP Transport

   Because all BGP traffic and interactions occur over TCP, all relevant
   parameters characterizing the TCP sessions MUST 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 [RFC2385].  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.

9.  Security Considerations

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

10.  Acknowledgements

   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

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11.  References

11.1.  Normative References

   [RFC1771]    Rekhter, Y. and T. Li, "A Border Gateway Protocol 4
                (BGP-4)", RFC 1771, March 1995.

   [RFC2439]    Villamizar, C., Chandra, R., and R. Govindan, "BGP Route
                Flap Damping", RFC 2439, November 1998.

   [RFC1812]    Baker, F., "Requirements for IP Version 4 Routers", RFC
                1812, June 1995.

   [RIPE37]     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,
   [INSTBLTY]   Labovitz, C., Malan, G., and F. Jahanian, "Origins of
                Internet Routing Instability", Infocom 99, August 1999.

   [RFC2622]    Alaettinoglu, C., Bates, T., Gerich, E., Karrenberg, D.,
                Meyer, D., Terpstra, M., and C. Villamizar, "Routing
                Policy Specification Language (RPSL)", RFC 2280, January

   [RIPE229]    Panigl, C., Schmitz, J., Smith, P., and C. Vistoli,
                "RIPE Routing-WG Recommendation for coordinated route-
                flap damping parameters, version 2", RIPE 229, October

   [RFC2385]    Heffernan, A., "Protection of BGP Sessions via the TCP
                MD5 Signature Option", RFC 2385, August 1998.

   [GLSSRY]     Juniper Networks, "Junos(tm) Internet Software
                Configuration Guide Routing and Routing Protocols,
                Release 4.2", Junos 4.2 and other releases, September
   [RFC2547]    Rosen, E. and Y. Rekhter, "BGP/MPLS VPNs", RFC 2547,
                March 1999.

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   [PKTTRAIN]   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.

11.2.  Informative References

   [RFC2918]    Chen, E., "Route Refresh Capability for BGP-4", RFC
                2918, September 2000.

   [GRMBGP]     Sangli, S., Rekhter, Y., Fernando, R., Scudder, J., and
                E. Chen, "Graceful Restart Mechanism for BGP", Work in
                Progress, June 2004.

   [BGP-4]      Chen, E. and Y. Rekhter, "Cooperative Route Filtering
                Capability for BGP-4", Work in Progress, March 2004.

   [RFC3654]    Khosravi, H. and T. Anderson, "Requirements for
                Separation of IP Control and Forwarding", RFC 3654,
                November 2003.

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

   [RFC2858]    Bates, T., Rekhter, Y., Chandra, R., and D. Katz,
                "Multiprotocol Extensions for BGP-4", RFC 2858, June

   [RFC2545]    Marques, P. and F. Dupont, "Use of BGP-4 Multiprotocol
                Extensions for IPv6 Inter-Domain Routing", RFC 2545,
                March 1999.

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Authors' Addresses

   Howard Berkowitz
   Gett Communications & CCI Training
   5012 S. 25th St
   Arlington, VA  22206

   Phone: +1 703 998-5819
   Fax:   +1 703 998-5058

   Elwyn B. Davies
   Folly Consulting
   The Folly
   Cambs, CB7 5AW

   Phone: +44 7889 488 335

   Susan Hares
   Nexthop Technologies
   825 Victors Way
   Ann Arbor, MI  48108

   Phone: +1 734 222-1610

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


   Marianne Lepp


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Full Copyright Statement

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