Network Working Group                                     Vishwas Manral
Internet Draft                                          Netplane Systems
                                                              Russ White
                                                           Cisco Systems
                                                             Aman Shaikh
Expiration Date: June 2003                      University of California
File Name: draft-ietf-bmwg-ospfconv-applicability-01.txt    January 2003

         Benchmarking Applicability for Basic OSPF Convergence

1. 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
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2. Abstract

   This draft describes the applicability of [2] and similar work which
   may be done in the future. Refer to [3] for terminology used in this
   draft and [2]. The draft defines the advantages as well as
   limitations of using the method defined in [2], besides describing
   the pitfalls to avoid during measurement.

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3. Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [1].

4. Motivation

   There is a growing interest in testing SR-Convergence for routing
   protocols, with many people looking at testing methodologies which
   can provide information on how long it takes for a network to
   converge after various network events occur. It is important to
   consider the framework within which any given convergence test is
   executed when attempting to apply the results of the testing, since
   the framework can have a major impact on the results. For instance,
   determining when a network is converged, what parts of the router's
   operation are considered within the testing, and other such things
   will have a major impact on what apparent performance routing
   protocols provide.

   This document describes in detail the various benefits and pitfalls
   of tests described in [2]. It also explains how such measurements can
   be useful for providers and the research community.

5. Advantages of Such Measurement

      o    To be able to compare the iterations of a protocol implemen-
           tation. It is often useful to be able to compare the perfor-
           mance of two iterations of a given implementation of a proto-
           col to determine where improvements have been made and where
           further improvements can be made.

      o    To understand, given a set parameters (network conditions),
           how a particular implementation on a particular device is
           going to perform. For instance, if you were trying to decide
           the processing power (size of device) required in a certain
           location within a network, you can emulate the conditions
           which are going to exist at that point in the network and use
           the test described to measure the perfomance of several dif-
           ferent routers. The results of these tests can provide one
           possible data point for an intelligent decision.

           If the device being tested is to be deployed in a running
           network, using routes taken from the network where the equip-
           ment is to be deployed rather than some generated topology in

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           these tests will give results which are closer to the real
           preformance of the device. Care should be taken to emulate or
           take routes from the actual location in the network where the
           device will be (or would be) deployed. For instance, one set
           of routes may be taken from an abr, one set from an area 0
           only router, various sets from stub area, another set from
           various normal areas, etc.

      o    To measure the performance of an OSPF implementation in a
           wide variety of scenarios.

      o    To be used as parameters in OSPF simulations by researchers.
           It may some times be required for certain kinds of research
           to measure the individual delays of each parameter within an
           OSPF implementation. These delays can be measured using the
           methods defined in [2].

      o    To help optimize certain configurable parameters. It may some
           times be helpful for operators to know the delay required for
           individual tasks so as to optimize the resource usage in the
           network i.e. if it is found that the processing time is x
           seconds on an router, it would be helpful to determine the
           rate at which to flood LSA's to that router so as to not
           overload the network.

6. Assumptions Made and Limitations of such measurements

 o    The interactions of SR-Convergence and forwarding; testing is res-
      tricted to events occurring within the control plane. Forwarding
      performance is the primary focus in [4] and it is expected to be
      dealt with in work that ensues from [5].

 o    Duplicate LSAs are Acknowledged Immediately. A few tests rely on
      the property that duplicate LSA Acknowledgements are not delayed
      but are done immediately. However if some implementation does not
      acknowledge duplicate LSAs immediately on receipt, the testing
      methods presented in [2] could give inaccurate measurements.

 o    It is assumed that SPF is non-preemptive. If SPF is implemented so
      that it can (and will be) preempted, the SPF measurements taken in
      [2] would include the times that the SPF process is not running
      ([2] measures the total time taken for SPF to run, not the amount
      of time that SPF actually spends on the device's processor), thus
      giving inaccurate measurements.

 o    Some implementations may be multithreaded or use a

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      multiprocess/multirouter model of OSPF. If because of this any of
      the assumptions taken in measurement are violated in such a model,
      it could lead to inaccurate measurements.

 o    The measurements resulting from the tests in [2] may not provide
      the information required to deploy a device in a large scale net-
      work. The tests described focus on individual components of an
      OSPF implementation's performance, and it may be difficult to com-
      bine the measurements in a way which accurately depicts a device's
      performance in a large scale network. Further research is required
      in this area.

7. Observations on the Tests Described in [2]

   Some observations taken while implementing the tests described in [2]
   are noted in this section.

7.1. Measuring the SPF Processing Time Externally

   The most difficult test to perform is the external measurement of the
   time required to perform an SPF calculation, since the amount of time
   between the first LSA which indicates a topology change and the
   duplicate LSA is critical. If the duplicate LSA is sent too quickly,
   it may be received before the device under test actually begins run-
   ning SPF on the network change information. If the delay between the
   two LSAs is too long, the device under test may finish SPF processing
   before receiving the duplicate LSA. It is important to closely inves-
   tigate any delays between the receipt of an LSA and the beginning of
   an SPF calculation in the device under test; multiple tests with
   various delays might be required to determine what delay needs to be
   used to accurately measure the SPF calculation time.

7.2. Noise in the Measurement Device

   The device on which measurements are taken (not the device under
   test) also adds noise to the test results, primarily in the form of
   delay in packet processing and measurement output. The largest source
   of noise is generally the delay between the receipt of packets by the
   measuring device and the information about the packet reaching the
   device's output, where the event can be measured. The following steps
   may be taken to reduce this sampling noise:

    o    Take lot of samples Do we need to explain that further. As Russ
         had previously pointed out.

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    o    Try to take time-stamp for a packet as early as possible.
         Depending on the operating system being used on the box, one
         can instrument the kernel to take the time-stamp when the
         interrupt is processed. This does not eliminate the noise com-
         pletely, but at least reduces it.

    o    Keep the measurement box as lightly loaded as possible.

    o    Having an estimate of noise can also be useful.

         The DUT also adds noise to the measurement. Points (a) and (c)
         apply to the DUT as well.

7.3. Gaining an Understanding of the Implementation Improves Measure-

   While the tester will (generally) not have access to internal infor-
   mation about the OSPF implementation being tested using [2], the more
   thorough the tester's knowledge of the implementation is, the more
   accurate the results of the tests will be. For instance, in some
   implementations, the installation of routes in local routing tables
   may occur while the SPF is being calculated, dramatically impacting
   the time required to calculate the SPF.

7.4. Gaining an Understanding of the Tests Improves Measurements

   One method which can be used to become familiar with the tests
   described in [2] is to perform the tests on an OSPF implementation
   for which all the internal details are available, such as GateD.
   While there is no assurance that any two implementations will be
   similar, this will provide a better understanding of the tests them-

8. Acknowledgements

    Thanks to Howard Berkowitz, ( and the rest of the BGP
   benchmarking team for their support and to Kevin
   Dubray( who realized the need of this draft.

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9. References

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

 [2]  Manral, V., "Benchmarking Methodology for Basic OSPF Convergence",
      draft-ietf-bmwg-ospfconv-intraarea, January 2003

 [3]  Manral, V., "OSPF Convergence Testing Terminiology and Concepts",
      draft-ietf-bmwg-ospfconv-term, January 2003

 [4]  Bradner, S., McQuaid, J., "Benchmarking Methodology for Network
      Interconnect Devices", RFC2544, March 1999.

 [5]  Trotter, G., "Terminology for Forwarding Information Base (FIB)
      based Router Performance", RFC3222, October 2001.

10. Authors' Addresses
      Vishwas Manral
      Netplane Systems
      189 Prashasan Nagar
      Road number 72
      Jubilee Hills
      Hyderabad, India

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

      Aman Shaikh
      University of California
      School of Engineering
      1156 High Street
      Santa Cruz, CA  95064

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