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Network Working Group                                          V. ManralRequest for Comments: 4063                                  SiNett Corp.Category: Informational                                         R. White                                                           Cisco Systems                                                               A. Shaikh                                                    AT&T Labs (Research)                                                              April 2005Considerations When Using Basic OSPF Convergence BenchmarksStatus 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 discusses the applicability of various tests for   measuring single router control plane convergence, specifically in   regard to the Open Shortest First (OSPF) protocol.  There are two   general sections in this document, the first discusses advantages and   limitations of specific OSPF convergence tests, and the second   discusses more general pitfalls to be considered when routing   protocol convergence is tested.1.  Introduction   There is a growing interest in testing single router control plane   convergence for routing protocols, and many people are looking at   testing methodologies that 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 one attempts 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 the apparent   performance that routing protocols provide.Manral, et al.               Informational                      [Page 1]

RFC 4063          Considerations in OSPF Benchmarking         April 2005   This document describes in detail 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: In this document, the word "convergence" refers to single   router control plane convergence [TERM].2.  Advantages of Such Measurement   o    To be able to compare the iterations of a protocol        implementation.  It is often useful to be able to compare the        performance of two iterations of a given implementation of a        protocol in order to determine where improvements have been made        and where further improvements can be made.   o    To understand, given a set of parameters (network conditions),        how a particular implementation on a particular device will        perform.  For instance, if you were trying to decide the        processing power (size of device) required in a certain location        within a network, you could emulate the conditions that will        exist at that point in the network and use the test described to        measure the performance of several different 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 equipment        is to be deployed rather than some generated topology in these        tests will yield results that are closer to the real performance        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 sometimes 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        sometimes be helpful for operators to know the delay required        for individual tasks in order to optimize the resource usage in        the network.  For example, if the processing time on a router isManral, et al.               Informational                      [Page 2]

RFC 4063          Considerations in OSPF Benchmarking         April 2005        found to be x seconds, determining the rate at which to flood        LSAs to that router would be helpful so as not to overload the        network.3.  Assumptions Made and Limitations of Such Measurements   o    The interactions of convergence and forwarding; testing is        restricted 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 an implementation        does not acknowledge duplicate LSAs immediately on receipt, the        testing methods presented in [BENCHMARK] 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 [BENCHMARK] would include the times that the SPF        process is not running, thus giving inaccurate measurements.        ([BENCHMARK] measures the total time taken for SPF to run, not        the amount of time that SPF actually spends on the device's        processor.)   o    Some implementations may be multithreaded or use a        multiprocess/multirouter model of OSPF.  If because of this any        of the assumptions made during measurement are violated in such        a model, measurements could be inaccurate.   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 that        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 that need to be taken into        consideration when comparing different vendors' products.  One        difficulty is aligning the resources available on one device to        the resources available on another.Manral, et al.               Informational                      [Page 3]

RFC 4063          Considerations in OSPF Benchmarking         April 20054.  Observations on the Tests Described in [BENCHMARK]   Some observations recorded while implementing the tests described in   [BENCHMARK] are noted in this section.4.1.  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 because the amount of   time between the first LSA that 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 being tested actually begins   running SPF on the network change information.  If the delay between   the two LSAs is too long, the device may finish SPF processing before   receiving the duplicate LSA.  It is important to closely investigate   any delays between the receipt of an LSA and the beginning of an SPF   calculation in the tested device; multiple tests with various delays   might be required to determine what delay needs to be used to measure   the SPF calculation time accurately.   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.4.2.  Noise in the Measurement Device   The device on which measurements are taken (not the device being   tested) 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 receipt of information about the   packet by 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 to remove        it from the results.  This applies to the DUT as well.   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 completely, but        at least reduces it.   o    Keep the measurement box as lightly loaded as possible.  This        applies to the DUT as well.Manral, et al.               Informational                      [Page 4]

RFC 4063          Considerations in OSPF Benchmarking         April 2005   o    Having an estimate of noise can also be useful.   The DUT also adds noise to the measurement.4.3.  Gaining an Understanding of the Implementation Improves      Measurements   Although the tester will (generally) not have access to internal   information 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.4.4.  Gaining an Understanding of the Tests Improves Measurements   One method that can be used to become familiar with the tests   described in [BENCHMARK] is to perform the tests on an OSPF   implementation for which all the internal details are available.   Although there is no assurance that any two implementations will be   similar, this will provide a better understanding of the tests   themselves.5.  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 primary        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 that would be acceptable under        different situations; within an area, for instance, types 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 characterizations are        important to note in any test results.Manral, et al.               Informational                      [Page 5]

RFC 4063          Considerations in OSPF Benchmarking         April 2005   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 algorithm's 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        being tested.  For instance, AS-External LSAs 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 ABRs 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 type-5 LSA's reach a        router in the adjacent area.  Therefore, routes to the external        destinations aren't immediately added to the routers in the        other areas.  When the routers that already have the type 5s        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 5s originated by that        border router.        The ordering can be changed in various tests to provide insight        into the efficiency of storage within the DUT.  Any such changes        in ordering should be noted in test results.6.  Tree Shape and the SPF Algorithm   The complexity of Dijkstra's algorithm 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   reachable from the source.  In a simple list of vertices, finding the   minimum cost vertex would then 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.  Moreover, after the vertex   with minimum cost is found, the algorithm iterates through all the   edges of the vertex and updates the cost of other vertices.  With an   adjacency list representation, this step, when iterated over all the   vertices, would take O(E) time, with E being the number of edges in   the graph.  Thus, the overall running time is:   O(sum(i:1, n)(size(list at level i) + E).Manral, et al.               Informational                      [Page 6]

RFC 4063          Considerations in OSPF Benchmarking         April 2005   So everything boils down to the size(list at level i).   If the graph is linear,      root       |       1       |       2       |       3       |       4       |       5       |       6   and source is a vertex on the end, then size(list at level i) = 1 for   all i.  Moreover, E = n - 1.  Therefore, running time is O(n).   If the graph is a balanced binary tree,       root      /    \     1      2    / \    / \   3   4  5   6   size(list at level i) is a little complicated.  First, it increases   by 1 at each level up to a certain number, and then it goes down by   1.  If we assume that the tree is a complete tree (as shown above)   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 the 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).   Therefore, the performance of the shortest path first algorithm used   to compute the best paths through the network is dependent on the   construction of the tree.  The best practice would be to try to make   any emulated network look as much like a real network as possible,   especially in the area of the tree depth, the meshiness of theManral, et al.               Informational                      [Page 7]

RFC 4063          Considerations in OSPF Benchmarking         April 2005   network, the number of stub links versus transit links, and the   number of connections and nodes to process at each level within the   original tree.7.  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 that can be   advertised to a device with varying conditions.  Route generators   tend to be either 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 as follows:   o    The ability to connect to 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 between the DUT and the route generator, and the        link is configured as a point-to-point link within OSPF        [BROADCAST-P2P].   o    The ability to create a set of LSAs that 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 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 flapping links.   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 that they        are not bottlenecks.  The devices should also have a degree of        granularity of measurement at least as small as is desired from        the test results.Manral, et al.               Informational                      [Page 8]

RFC 4063          Considerations in OSPF Benchmarking         April 20058.  Security Considerations   This document does not modify the underlying security considerations   in [OSPF].9.  Acknowledgements   Thanks to Howard Berkowitz (hcb@clark.net) and the rest of the BGP   benchmarking team for their support and to Kevin Dubray   (kdubray@juniper.net), who realized the need for this document.10.  Normative References   [BENCHMARK]     Manral, V., White, R., and A. Shaikh, "Benchmarking                   Basic OSPF Single Router Control Plane Convergence",RFC 4061, April 2005.   [TERM]          Manral, V., White, R., and A. Shaikh, "OSPF                   Benchmarking Terminology and Concepts",RFC 4062,                   April 2005.   [OSPF]          Moy, J., "OSPF Version 2", STD 54,RFC 2328, April                   1998.11.  Informative References   [INTERCONNECT]  Bradner, S. and J. McQuaid, "Benchmarking Methodology                   for Network Interconnect Devices",RFC 2544, March                   1999.   [FIB-TERM]      Trotter, G., "Terminology for Forwarding Information                   Base (FIB) based Router Performance",RFC 3222,                   December 2001.   [BROADCAST-P2P] Shen, Naiming, et al., "Point-to-point operation over                   LAN in link-state routing protocols", Work in                   Progress, August, 2003.Manral, et al.               Informational                      [Page 9]

RFC 4063          Considerations in OSPF Benchmarking         April 2005Authors' 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.comManral, et al.               Informational                     [Page 10]

RFC 4063          Considerations in OSPF Benchmarking         April 2005Full Copyright Statement   Copyright (C) The Internet Society (2005).   This document is subject to the rights, licenses and restrictions   contained inBCP 78, and except as set forth therein, the authors   retain all their rights.   This document and the information contained herein are provided on an   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Intellectual Property   The IETF takes no position regarding the validity or scope of any   Intellectual Property Rights or other rights that might be claimed to   pertain to the implementation or use of the technology described in   this document or the extent to which any license under such rights   might or might not be available; nor does it represent that it has   made any independent effort to identify any such rights.  Information   on the procedures with respect to rights in RFC documents can be   found inBCP 78 andBCP 79.   Copies of IPR disclosures made to the IETF Secretariat and any   assurances of licenses to be made available, or the result of an   attempt made to obtain a general license or permission for the use of   such proprietary rights by implementers or users of this   specification can be obtained from the IETF on-line IPR repository athttp://www.ietf.org/ipr.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights that may cover technology that may be required to implement   this standard.  Please address the information to the IETF at ietf-   ipr@ietf.org.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Manral, et al.               Informational                     [Page 11]