Network Working Group                                     Vishwas Manral
Internet Draft                                          Netplane Systems
                                                              Russ White
                                                           Cisco Systems
                                                             Aman Shaikh
Expiration Date: September 2003                 University of California
File Name: draft-ietf-bmwg-ospfconv-applicability-03.txt      March 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
   Task Force (IETF), its Areas, and its Working Groups. Note that other
   groups may also distribute working documents as Internet Drafts.

   Internet Drafts are draft documents valid for a maximum of six
   months.  Internet Drafts may be updated, replaced, or obsoleted by
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   Drafts as reference material or to cite them other than as a "working
   draft" or "work in progress".

   The list of current Internet-Drafts can be accessed at

   The list of Internet-Draft Shadow Directories can be accessed at

2. Abstract

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

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3. Motivation

   There is a growing interest in testing single router control plane
   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 [BENCHMARK]. It also explains how such
   measurements can be useful for providers and the research community.

   NOTE: The word convergence within this document refers to single
   router contorl plane convergence [TERM].

4. 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
           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

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           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 [BENCHMARK].

      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.

5. Assumptions Made and Limitations of such measurements

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

 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 [BENCHMARK] could give inaccurate measure-

 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
      [BENCHMARK] would include the times that the SPF process is not
      running ([BENCHMARK] 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
      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.

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

 o    The measurements described in [BENCHMARK] should be used with
      great care when comparing two different implementations of OSPF
      from two different vendors. For instance, there are many other
      factors than convergence speed which must be taken into considera-
      tion when comparing different vendor's products, and it's diffi-
      cult to align the resources available on one device to the
      resources available on another device.

6. Observations on the Tests Described in [BENCHMARK]

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

6.1. 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.

   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.

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6.2. 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    Increasing the number of samples taken will generally improve
         the tester's ability to determine what is noise, and remove it
         from the results.

    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.

6.3. 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 [BENCHMARK],
   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.

6.4. Gaining an Understanding of the Tests Improves Measurements

   One method which can be used to become familiar with the tests
   described in [BENCHMARK] is to perform the tests on an OSPF implemen-
   tation 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

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7. LSA and Destination mix

   In many OSPF benchmark tests, a generator injecting a number of LSAs
   is called for. There are several areas in which injected LSAs can be
   varied in testing:

      o    The number of destinations represented by the injected LSAs

           Each destination represents a single reachable IP network;
           these will be leaf nodes on the shortest path tree. The pri-
           mary impact to performance should be the time required to
           insert destinations in the local routing table and handling
           the memory required to store the data.

      o    The types of LSAs injected

           There are several types of LSAs which would be acceptable
           under different situations; within an area, for instance,
           type 1, 2, 3, 4, and 5 are likely to be received by a router.
           Within a not-so-stubby area, however, type 7 LSAs would
           replace the type 5 LSAs received. These sorts of characteri-
           zations are important to note in any test results.

      o    The Number of LSAs injected

           Within any injected set of information, the number of each
           type of LSA injected is also important. This will impact the
           shortest path algorithms ability to handle large numbers of
           nodes, large shortest path first trees, etc.

      o    The Order of LSA Injection

           The order in which LSAs are injected should not favor any
           given data structure used for storing the LSA database on the
           device under test. For instance, AS-External LSA's have AS
           wide flooding scope; any Type-5 LSA originated is immediately
           flooded to all neighbors. However the Type-4 LSA which
           announces the ASBR as a border router is originated in an
           area at SPF time (by ABR's on the edge of the area in which
           the ASBR is). If SPF isn't scheduled immediately on the ABRs
           originating the type 4 LSA, the type-4 LSA is sent after the

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           type-5 LSA's reach a router in the adjacent area. So routes
           to the external destinations aren't immediately added to the
           routers in the other areas. When the routers which already
           have the type 5's receive the type-4 LSA, all the external
           routes are added to the tree at the same time. This timing
           could produce different results than a router receiving a
           type 4 indicating the presence of a border router, followed
           by the type 5's originated by that border router.

           The ordering can be changed in various tests to provide
           insight on the efficiency of storage within the DUT. Any such
           changes in ordering should be noted in test results.

8. Tree Shape and the SPF Algorithm

   The complexity of Dijkstra's algo depends on the data structure used
   for storing vertices with their current minimum distances from the
   source. The simplest structure is a list of vertices currently reach-
   able from the source. Finding the minimum cost vertex then would take
   O(size of the list). There will be O(n) such operations if we assume
   that all the vertices are ultimately reachable from the source. More-
   over, after the vertex with min cost is found, the algo iterates thru
   all the edges of the vertex and updates cost of other vertices. With
   an adjacency list representation, this step when iterated over all
   the vertices, would take O(E) time. Thus, overall running time is:

   O(sum(i:1, n)(size(list at level i) + E).

   So, everything boils down to the size(list at level i).

   If the graph is linear:


           and source is a vertex on the end, then size(list at level i)

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           = 1 for all i. Moreover, E = n - 1. Therefore, running time
           is O(n).

           If graph is a balanced binary tree:

              /    \
             1      2
            / \    / \
           3   4  5   6

           size(list at level i) is a little complicated. First it
           increases by 1 at each level upto a certain number, and then
           goes down by 1. If we assumed that tree is a complete tree
           (like the one in the draft) with k levels (1 to k), then
           size(list) goes on like this: 1, 2, 3,

           Then the number of edges E is still n - 1. It then turns out
           that the run-time is O(n^2) for such a tree.

           If graph is a complete graph (fully-connected mesh), then
           size(list at level i) = n - i.  Number of edges E = O(n^2).
           Therefore, run-time is O(n^2).

           shortest path first algorithm to compute the best paths
           through the network need to be aware that the construction of
           the tree may impact the performance of the algorithm. Best
           practice would be to try and make any emulated network look
           as much like a real network as possible, especially in the
           area of the tree depth, the meshiness of the network, the
           number of stub links verses transit links, and the number of
           connections and nodes to process at each level within the
           original tree.

9. Topology Generation

   As the size of networks grows, it becomes more and more difficult to
   actually create a large scale network on which to test the properties
   of routing protocols and their implementations. In general, network
   emulators are used to provide emulated topologies which can be adver-
   tised to a device with varying conditions. Route generators either
   tend to be a specialized device, a piece of software which runs on a
   router, or a process that runs on another operating system, such as
   Linux or another variant of Unix.

   Some of the characteristics of this device should be:

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 o    The ability to connect to the several devices using both point-
      to-point and broadcast high speed media. Point-to-point links can
      be emulated with high speed Ethernet as long as there is no hub or
      other device in between the DUT and the route generator, and the
      link is configured as a point-to-point link within OSPF.

 o    The ability to create a set of LSAs which appear to be a logical,
      realistic topology. For instance, the generator should be able to
      mix the number of point-to-point and broadcast links within the
      emulated topology, and should be able to inject varying numbers of
      externally reachable destinations.

 o    The ability to withdraw and add routing information into and from
      the emulated topology to emulate links flapping.

 o    The ability to randomly order the LSAs representing the emulated
      topology as they are advertised.

 o    The ability to log or otherwise measure the time between packets
      transmitted and received.

 o    The ability to change the rate at which OSPF LSAs are transmitted.

 o    The generator and the collector should be fast enough so that they
      are not bottle necks. The devices should also have a degree of
      granularity of measurement atleast as small as desired from the
      test results.

10. 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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11. Normative References

      Manral, V., "Benchmarking Basic OSPF Single Router Control Plane
      Convergence", draft-bmwg-ospfconv-intraarea-05, March 2003

 [TERM]Manral, V., "OSPF Convergence Testing Terminiology and Concepts",
      draft-bmwg-ospfconv-term-04, March 2003

12. Informative References

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

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

13. 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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