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RFC 4062 - OSPF Benchmarking Terminology and Concepts


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Network Working Group                                          V. Manral
Request for Comments: 4062                                  SiNett Corp.
Category: Informational                                         R. White
                                                           Cisco Systems
                                                               A. Shaikh
                                                    AT&T Labs (Research)
                                                              April 2005

               OSPF Benchmarking Terminology and Concepts

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).

Abstract

   This document explains the terminology and concepts used in OSPF
   benchmarking.  Although some of these terms may be defined elsewhere
   (and we will refer the reader to those definitions in some cases) we
   include discussions concerning these terms, as they relate
   specifically to the tasks involved in benchmarking the OSPF protocol.

1.  Introduction

   This document is a companion to [BENCHMARK], which describes basic
   Open Shortest Path First [OSPF] testing methods.  This document
   explains terminology and concepts used in OSPF Testing Framework
   Documents, such as [BENCHMARK].

2.  Specification of Requirements

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].
   [RFC2119] key words in this document are used to ensure
   methodological control, which is very important in the specification
   of benchmarks.  This document does not specify a network-related
   protocol.

3.  Common Definitions

   Definitions in this section are well-known industry and benchmarking
   terms that may be defined elsewhere.

   o    White Box (Internal) Measurements

        -    Definition

             White box measurements are those reported and collected on
             the Device Under Test (DUT) itself.

        -    Discussion

             These measurements rely on output and event recording,
             along with the clocking and time stamping available on the
             DUT itself.  Taking measurements on the DUT may impact the
             actual outcome of the test, since it can increase processor
             loading, memory utilization, and timing factors.  Some
             devices may not have the required output readily available
             for taking internal measurements.

             Note: White box measurements can be influenced by the
             vendor's implementation of various timers and processing
             models.  Whenever possible, internal measurements should be
             compared to external measurements to verify and validate
             them.

             Because of the potential for variations in collection and
             presentation methods across different DUTs, white box
             measurements MUST NOT be used as a basis for comparison in
             benchmarks.  This has been a guiding principle of the
             Benchmarking Methodology Working Group.

   o    Black Box (External) Measurements

        -    Definition

             Black box measurements infer the performance of the DUT
             through observation of its communications with other
             devices.

        -    Discussion

             One example of a black box measurement is when a downstream
             device receives complete routing information from the DUT,
             it can be inferred that the DUT has transmitted all the
             routing information available.  External measurements of

             internal operations may suffer in that they include not
             just the protocol action times, but also propagation
             delays, queuing delays, and other such factors.

             For the purposes of [BENCHMARK], external techniques are
             more readily applicable.

   o    Multi-device Measurements

        -    Measurements assessing communications (usually in
             combination with internal operations) between two or more
             DUTs.  Multi-device measurements may be internal or
             external.

4.  Terms Defined Elsewhere

   Terms in this section are defined elsewhere and are included only as
   they apply to [BENCHMARK].

   o    Point-to-Point Links

        -    Definition

             See [OSPF], Section 1.2.

        -    Discussion

             A point-to-point link can take less time to converge than a
             broadcast link of the same speed because it does not have
             the overhead of DR election.  Point-to-point links can be
             either numbered or unnumbered.  However, in the context of
             [BENCHMARK] and [OSPF], the two can be regarded as the
             same.

   o    Broadcast Link

        -    Definition

             See [OSPF], Section 1.2.

        -    Discussion

             The adjacency formation time on a broadcast link can be
             greater than that on a point-to-point link of the same
             speed because DR election has to take place.  All routers
             on a broadcast network form adjacency with the DR and BDR.

             Asynchronous flooding also takes place through the DR.  In
             the context of convergence, it may take more time for an
             LSA to be flooded from one DR-other router to another
             because the LSA first has to be processed at the DR.

   o    Shortest Path First Execution Time

        -    Definition

             The time taken by a router to complete the SPF process, as
             described in [OSPF].

        -    Discussion

             This does not include the time taken by the router to
             install routes in the forwarding engine.

             Some implementations may force two intervals, the SPF hold
             time and the SPF delay, between successive SPF
             calculations.  If an SPF hold time exists, it should be
             subtracted from the total SPF execution time.  If an SPF
             delay exists, it should be noted in the test results.

        -    Measurement Units

             The SPF time is generally measured in milliseconds.

   o Hello Interval

        -    Definition

             See [OSPF], Section 7.1.

        -    Discussion

             The hello interval must be the same for all routers on a
             network.

             Decreasing the hello interval can allow the router dead
             interval (below) to be reduced, thus reducing convergence
             times in those situations where the router dead interval's
             timing out causes an OSPF process to notice an adjacency
             failure.  Further discussion of small hello intervals is
             given in [OSPF-SCALING].

   o    Router Dead Interval

        -    Definition

             See [OSPF], Section 7.1.

        -    Discussion

             This is advertised in the router's Hello Packets in the
             Router-DeadInterval field.  The router dead interval should
             be some multiple of the HelloInterval (perhaps 4 times the
             hello interval) and must be the same for all routers
             attached to a common network.

5.  Concepts

5.1.  The Meaning of Single Router Control Plane Convergence

   A network is termed as converged when all the devices within the
   network have a loop-free path to each possible destination.  However,
   because we are not testing network convergence but testing
   performance for a particular device within a network, this definition
   needs to be streamlined to fit within a single device view.

   In this case, convergence will mean the point in time when the DUT
   has performed all actions needed in order to react to the change in
   the topology represented by the test condition.  For instance, an
   OSPF device must flood any new information it has received, rebuild
   its shortest path first (SPF) tree, and install any new paths or
   destinations in the local routing information base (RIB, or routing
   table).

   Note that the word "convergence" has two distinct meanings: the
   process of a group of individuals meeting at the same place, and the
   process of an individual coming to the same place as an existing
   group.  This work focuses on the second meaning of the word, so we
   consider the time required for a single device to adapt to a network
   change to be Single Router Convergence.

   This concept does not include the time required for the control plane
   of the device to transfer the information required to forward packets
   to the data plane.  It also does not include the amount of time
   between when the data plane receives that information and when it is
   able to forward traffic.

5.2.  Measuring Convergence

   Obviously, there are several elements to convergence, even under the
   definition given above for a single device, including (but not
   limited to) the following:

   o    The time it takes for the DUT to pass the information about a
        network event on to its neighbors.

   o    The time it takes for the DUT to process information about a
        network event and to calculate a new Shortest Path Tree (SPT).

   o    The time it takes for the DUT to make changes in its local RIB
        reflecting the new shortest path tree.

5.3.  Types of Network Events

   A network event is an event that causes a change in the network
   topology.

   o    Link or Neighbor Device Up

        The time needed for an OSPF implementation to recognize a new
        link coming up on the device, to build any necessary
        adjacencies, to synchronize its database, and to perform all
        other actions necessary to converge.

   o    Initialization

        The time needed for an OSPF implementation to be initialized, to
        recognize any links across which OSPF must run, to build any
        needed adjacencies, to synchronize its database, and to perform
        other actions necessary to converge.

   o    Adjacency Down

        The time needed for an OSPF implementation to recognize a link
        down/adjacency loss based on hello timers alone, to propagate
        any information as necessary to its remaining adjacencies, and
        to perform other actions necessary to converge.

   o    Link Down

        The time needed for an OSPF implementation to recognize a link
        down based on layer 2-provided information, to propagate any
        information as needed to its remaining adjacencies, and to
        perform other actions necessary to converge.

6.  Security Considerations

   This document does not modify the underlying security considerations
   in [OSPF].

7.  Acknowledgements

   The authors would like to thank Howard Berkowitz (hcb@clark.net),
   Kevin Dubray (kdubray@juniper.net), Scott Poretsky
   (sporetsky@avici.com), and Randy Bush (randy@psg.com) for their
   discussion, ideas, and support.

8.  Normative References

   [BENCHMARK]    Manral, V., White, R., and A. Shaikh, "Benchmarking
                  Basic OSPF Single Router Control Plane Convergence",
                  RFC 4061, April 2005.

   [OSPF]         Moy, J., "OSPF Version 2", STD 54, RFC 2328, April
                  1998.

   [RFC2119]      Bradner, S., "Key words for use in RFCs to Indicate
                  Requirement Levels", BCP 14, RFC 2119, March 1997.

9.  Informative References

   [OSPF-SCALING] Choudhury, Gagan L., Editor, "Prioritized Treatment of
                  Specific OSPF Packets and Congestion Avoidance", Work
                  in Progress, August 2003.

Authors' Addresses

   Vishwas Manral,
   SiNett Corp,
   Ground Floor,
   Embassy Icon Annexe,
   2/1, Infantry Road,
   Bangalore, India

   EMail: vishwas@sinett.com

   Russ White
   Cisco Systems, Inc.
   7025 Kit Creek Rd.
   Research Triangle Park, NC 27709

   EMail: riw@cisco.com

   Aman Shaikh
   AT&T Labs (Research)
   180 Park Av, PO Box 971
   Florham Park, NJ 07932

   EMail: ashaikh@research.att.com

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