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Network Working Group
Request for Comments: 4061
Category: Informational
V. Manral
SiNett Corp.
R. White
Cisco Systems
A. Shaikh
AT&T Labs (Research)
April 2005

Benchmarking Basic OSPF Single Router Control Plane Convergence

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 © The Internet Society (2005).

Abstract

This document provides suggestions for measuring OSPF single router control plane convergence. Its initial emphasis is on the control plane of a single OSPF router. We do not address forwarding plane performance.

NOTE: In this document, the word "convergence" relates to single router control plane convergence only.

Table of Contents

   1.  Introduction....................................................2
   2.  Specification of Requirements...................................2
   3.  Overview and Scope..............................................3
   4.  Reference Topologies............................................4
   5.  Basic Performance Tests.........................................5
       5.1.  Time Required to Process an LSA...........................5
       5.2.  Flooding Time.............................................6
       5.3.  Shortest Path First Computation Time......................6
   6.  Basic Intra-area OSPF Tests.....................................8
       6.1.  Forming Adjacencies on Point-to-Point Links
             (Initialization)..........................................9
       6.2.  Forming Adjacencies on Point-to-Point Links...............9
       6.3.  Forming Adjacencies with Information Already in the
             Database.................................................10
       6.4.  Designated Router Election Time on a Broadcast Network...11
   
       6.5.  Initial Convergence Time on a Broadcast Network,
             Test 1...................................................11
       6.6.  Initial Convergence Time on a Broadcast Network,
             Test 2...................................................12
       6.7.  Link Down with Layer Two Detection.......................12
       6.8.  Link Down with Layer Three Detection.....................13
   7.  Security Considerations........................................13
   8.  Acknowledgements...............................................13
   9.  Normative References...........................................14
   10. Informative References.........................................14
   Authors' Addresses.................................................15
   Full Copyright Statement...........................................16

1. Introduction

There is a growing interest in routing protocol convergence testing, with many people looking at various tests to determine how long it takes for a network to converge after various conditions occur. The major problem with this sort of testing is that the framework of the tests has 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.

This document attempts to provide a framework for Open Shortest Path First [OSPF] performance testing, and to provide some tests for measuring some aspects of OSPF performance. The motivation of the document is to provide a set of tests that can provide the user comparable data from various vendors with which to evaluate the OSPF protocol performance on the devices.

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 [RFC2119]. RFC 2119 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. Overview and Scope

Although this document describes a specific set of tests aimed at characterizing the single router control plane convergence performance of OSPF processes in routers or other boxes that incorporate OSPF functionality, a key objective is to propose methodologies that produce directly comparable convergence-related measurements.

The following considerations are outside the scope of this document:

  • 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  Inter-area route generation, AS-external route generation, and
      simultaneous traffic on the control and data paths within the DUT.
      Although the tests outlined in this document measure SPF time,
      flooding times, and other aspects of OSPF convergence performance,
      this document does not provide tests for measuring external or
      summary route generation, route translation, or other OSPF inter-
      area and external routing performance.  These areas are expected
      to be dealt with in a later document.

The tests should be run more than once, since a single test run cannot be relied on to produce statistically sound results. The number of test runs and any variations between the tests should be recorded in the test results (see [TERM] for more information on what items should be recorded in the test results).

4. Reference Topologies

Several reference topologies that are used throughout the tests are described in the remaining sections of this document. All of the topologies have been collectively placed in one section to avoid repetition.

  • Reference Topology 1 (Emulated Topology)
                           (                   )
      DUT----Generator----(  emulated topology  )
                           (                   )

A simple back-to-back configuration. It's assumed that the link between the generator and the DUT is a point-to-point link, while the connections within the generator represent some emulated topology.

  • Reference Topology 2 (Generator and Collector)
                                        (                   )
      Collector-----DUT-----Generator--(  emulated topology  )
             \              /           (                   )
              \------------/

All routers are connected through point-to-point links. The cost of all links is assumed to be the same unless otherwise noted.

  • Reference Topology 3 (Broadcast Network)
      DUT     R1     R2
       |      |      |
      -+------+------+-----.....

Any number of routers could be included on the common broadcast network.

  • Reference Topology 4 (Parallel Links)
        /--(link 1)-----\           (                   )
      DUT               Generator--(  emulated topology  )
        \--(link 2)-----/           (                   )

In all cases the tests and topologies are designed to allow performance measurements to be taken all on a single device, whether this is the DUT or some other device in the network. This eliminates the need for synchronized clocks within the test networks.

5. Basic Performance Tests

These tests will measure aspects of the OSPF implementation as a process on the device under test, including

  • time required to process an LSA,
  • flooding time, and
  • Shortest Path First computation.

5.1. Time Required to Process an LSA

  • Using reference topology 1 (Emulated Topology), begin with all links up and a full adjacency established between the DUT and the generator.

Note: The generator does not have direct knowledge of the state of the adjacency on the DUT. The fact that the adjacency may be in Full state on the generator does not mean that the DUT is ready. It may still (and is likely to) be requesting LSAs from the generator. This process, involving processing of requested LSAs, will affect the results of the test. The generator should either wait until it sees the DUT's router-LSA listing the adjacency with the generator or introduce a configurable delay before starting the test.

  • Send an LSA that is already in the DUT (a duplicate LSA), note the time difference between when the LSA is sent and when the ack is received. This measures the time taken to propagate the LSA and the ack, as well as the processing time of the duplicate LSA. This is dupLSAprocTime.
  • Send a new LSA from the generator to the DUT, followed immediately by a duplicate LSA (LSA that already resides in the database of DUT, but not the same as the one just sent).
  • The DUT will acknowledge this second LSA immediately; note the time of this acknowledgement. This is newLSAprocTime.

The amount of time required for an OSPF implementation to process the new LSA can be computed by subtracting dupLSAprocTime from newLSAprocTime.

Note: The duplicate LSA cannot be the same as the one just sent because of the MinLSInterval restriction [OSPF]. This test is taken from [BLACKBOX].

Note: This time may or may not include the time required to perform flooding-related operations, depending on when the implementation sends the ack: before it floods the LSA further, or after it does, or anywhere in between. In other words, this measurement may not mean the same thing in all implementations.

5.2. Flooding Time

  • Using reference topology 2 (Generator and Collector), enable OSPF on all links and allow the devices to build full adjacencies. Configure the collector so that it will block all flooding toward the DUT (but so that it continues receiving advertisements from the DUT).
  • Inject a new set of LSAs from the generator toward the collector and the DUT.
  • On the collector, note the time the flooding is complete across the link to the generator. Also note the time the flooding is complete across the link from the DUT.

The time from when the last LSA is received on the collector from the generator to when the last LSA is received on the collector from the DUT should be measured during this test. This time is important in link state protocols, since the loop-free nature of the network is reliant on the speed at which revised topology information is flooded.

Depending on the number of LSAs flooded, the sizes of the LSAs, the number of LSUs, and the rate of flooding, these numbers could vary by some amount. The settings and variances of these numbers should be reported with the test results.

5.3. Shortest Path First Computation Time

  • Use reference topology 1 (Emulated Topology), beginning with the DUT and the generator fully adjacent.
  • The default SPF timer on the DUT should be set to 0 so that any new LSA that arrives immediately results in the SPF calculation [BLACKBOX].
  • The generator should inject a set of LSAs toward the DUT; the DUT should be allowed to converge and install all best paths in the local routing table, etc.
  • Send an LSA that is already in the DUT (a duplicate LSA), note the time difference between when the LSA is sent and when the ack is received. This measures the time taken to propagate the LSA and the ack, as well as the processing time of the duplicate LSA. This is dupLSAprocTime.
  • Change the link cost between the generator and the emulated network it is advertising, and transmit the new LSA to the DUT.
  • Immediately inject another LSA that is a duplicate of some other LSA the generator has previously injected (preferably a stub network someplace within the emulated network).

Note: The generator should make sure that outbound LSA packing is not performed for the duplicate LSAs and that they are always sent in a separate Link-state Update packet. Otherwise, if the LSA carrying the topology change and the duplicate LSA are in the same packet, the SPF starts after the duplicate LSA is acked.

  • Measure the time between transmitting the second (duplicate) LSA and the acknowledgement for that LSA; this is the totalSPFtime. The total time required to run SPF can be computed by subtracting dupLSAprocTime from totalSPFtime.

The accuracy of this test is crucially dependent on the amount of time between the transmissions of the first and second LSAs. If too much time elapsed, the test is meaningless because the SPF run will complete before the second (duplicate) LSA is received. If the time elapsed is less, then both LSAs will be handled before the SPF run is scheduled and started, and thus the measurement would only be for the handling of the duplicate LSA.

This test is also specified in [BLACKBOX].

Note: This test may not be accurate on systems that implement OSPF as a multithreaded process, where the flooding takes place in a separate process (or on a different processor) than shortest path first computations.

It is also possible to measure the SPF time using white box tests (using output supplied by the OSPF software implementer), such as the following:

  • Using reference topology 1 (Emulated Topology), establish a full adjacency between the generator and the DUT.
  • Inject a set of LSAs from the generator toward the DUT. Allow the DUT to stabilize and install all best paths in the routing table, etc.
  • Change the link cost between the DUT and the generator (or the link between the generator and the emulated network it is advertising), such that a full SPF is required to run, although only one piece of information is changed.
  • Measure the amount of time required for the DUT to compute a new shortest path tree as a result of the topology changes injected by the generator. These measurements should be taken using available show and debug information on the DUT.

Several caveats MUST be mentioned when a white box method of measuring SPF time is used. For instance, such white box tests are only applicable when testing various versions or variations within a single implementation of the OSPF protocol. Further, the same set of commands MUST be used in each iteration of such a test to ensure consistent results.

There is an interesting relationship between the SPF times reported by white box (internal) testing and black box (external) testing; each of these two types of tests may be used as a "sanity check" on the other by comparing results.

See [CONSIDERATIONS] for further discussion.

6. Basic Intra-area OSPF Tests

These tests measure the performance of an OSPF implementation for basic intra-area tasks, including: 

   o  Forming Adjacencies on Point-to-Point Link (Initialization)
  • Forming Adjacencies on Point-to-Point Links
  • Link Up with Information Already in the Database
  • Initial convergence Time on a Designated Router Electing (Broadcast) Network
  • Link Down with Layer 2 Detection
  • Link Down with Layer 3 Detection
  • Designated Router Election Time on A Broadcast Network

6.1. Forming Adjacencies on Point-to-Point Link (Initialization)

This test measures the time required to form an OSPF adjacency from the time a layer two (data link) connection is formed between two devices running OSPF.

  • Use reference topology 1 (Emulated Topology), beginning with the link between the generator and DUT disabled on the DUT. OSPF should be configured and operating on both devices.
  • Inject a set of LSAs from the generator toward the DUT.
  • Bring the link up at the DUT, noting the time when the link carrier is established on the generator.
  • Note the time when the acknowledgement for the last LSA transmitted from the DUT is received on the generator.

The time between the carrier establishment and the acknowledgement for the last LSA transmitted by the generator should be taken as the total amount of time required for the OSPF process on the DUT to react to a link up event with the set of LSAs injected, including the time required for the operating system to notify the OSPF process about the link up, etc. The acknowledgement for the last LSA transmitted is used instead of the last acknowledgement received in order to prevent timing skews due to retransmitted acknowledgements or LSAs.

6.2. Forming Adjacencies on Point-to-Point Links

This test measures the time required to form an adjacency from the time the first communication occurs between two devices running OSPF.

  • Using reference topology 1 (Emulated Topology), configure the DUT and the generator so that traffic can be passed along the link between them.
  • Configure the generator so that OSPF is running on the point-to- point link toward the DUT, and inject a set of LSAs.
  • Configure the DUT so that OSPF is initialized, but not running on the point-to-point link between the DUT and the generator.
  • Enable OSPF on the interface between the DUT and the generator on the DUT.
  • Note the time of the first hello received from the DUT on the generator.
  • Note the time of the acknowledgement from the DUT for the last LSA transmitted on the generator.

The time between the first hello received and the acknowledgement for the last LSA transmitted by the generator should be taken as the total amount of time required for the OSPF process on the DUT to build a FULL neighbor adjacency with the set of LSAs injected. The acknowledgement for the last LSA transmitted is used instead of the last acknowledgement received in order to prevent timing skews due to retransmitted acknowledgements or LSAs.

6.3. Forming Adjacencies with Information Already in the Database

  • Using reference topology 2 (Generator and Collector), configure all three devices to run OSPF.
  • Configure the DUT so that the link between the DUT and the generator is disabled.
  • Inject a set of LSAs into the network from the generator; the DUT should receive these LSAs through normal flooding from the collector.
  • Enable the link between the DUT and the generator.
  • Note the time of the first hello received from the DUT on the generator.
  • Note the time of the last DBD (Database Description) received on the generator.
  • Note the time of the acknowledgement from the DUT for the last LSA transmitted on the generator.

The time between the hello received by the generator from the DUT and the acknowledgement for the last LSA transmitted by the generator should be taken as the total amount of time required for the OSPF process on the DUT to build a FULL neighbor adjacency with the set of LSAs injected. In this test, the DUT is already aware of the entire network topology, so the time required should only include the processing of DBDs exchanged when in EXCHANGE state, the time to build a new router LSA containing the new connection information, and the time required to flood and acknowledge this new router LSA.

The acknowledgement for the last LSA transmitted is used instead of the last acknowledgement received in order to prevent timing skews due to retransmitted acknowledgements or LSAs.

6.4. Designated Router Election Time on a Broadcast Network

  • Using reference topology 3 (Broadcast Network), configure R1 to be the designated router on the link, and the DUT to be the backup designated router.
  • Enable OSPF on the common broadcast link on all the routers in the test bed.
  • Disable the broadcast link on R1.
  • Note the time of the last hello received from R1 on R2.
  • Note the time of the first network LSA generated by the DUT as received on R2.

The time between the last hello received on R2 and the first network LSA generated by the DUT should be taken as the amount of time required for the DUT to complete a designated router election computation. Note that this test includes the dead interval timer at the DUT, so this time may be factored out, or the hello and dead intervals may be reduced to lessen these timers' impact on the overall test times. All changed timers, the number of routers connected to the link, and other variable factors should be noted in the test results.

Note: If R1 sends a "goodbye hello", typically a hello with its neighbor list empty, in the process of shutting down its interface, using the time when this hello is received instead of the time when the last one was would provide a more accurate measurement.

6.5. Initial Convergence Time on a Broadcast Network, Test 1

  • Using reference topology 3 (Broadcast Network), begin with the DUT connected to the network with OSPF enabled. OSPF should be enabled on R1, but the broadcast link should be disabled.
  • Enable the broadcast link between R1 and the DUT. Note the time of the first hello received by R1.
  • Note the time when the first network LSA is flooded by the DUT at R1.
  • The difference between the first hello and the first network LSA is the time required by the DUT to converge on this new topology.

This test assumes that the DUT will be the designated router on the broadcast link. A similar test could be designed to test the convergence time when the DUT is not the designated router.

This test maybe performed with a varying number of devices attached to the broadcast network, and with varying sets of LSAs being advertised to the DUT from the routers attached to the broadcast network. Variations in the LSA sets and other factors should be noted in the test results.

The time required to elect a designated router, as measured in Section 6.4, above, may be subtracted from the results of this test to provide just the convergence time across a broadcast network.

Note that although all the other tests in this document include route calculation time in the convergence time, as described in [TERM], this test may not include route calculation time in the resulting measured convergence time, because initial route calculation may occur after the first network LSA is flooded.

6.6. Initial Convergence Time on a Broadcast Network, Test 2

  • Using reference topology 3 (Broadcast Network), begin with the DUT connected to the network with OSPF enabled. OSPF should be enabled on R1, but the broadcast link should be disabled.
  • Enable the broadcast link between R1 and the DUT. Note the time of the first hello transmitted by the DUT with a designated router listed.
  • Note the time when the first network LSA is flooded by the DUT at R1.
  • The time difference between the first hello with a designated router lists and the first network LSA is the period required by the DUT to converge on this new topology.

6.7. Link Down with Layer 2 Detection

  • Using reference topology 4 (Parallel Links), begin with OSPF in the Full state between the generator and the DUT. Both links should be point-to-point links with the ability to notify the operating system immediately upon link failure.
  • Disable link 1; this should be done in such a way that the keepalive timers at the data link layer will have no impact on the DUT recognizing the link failure (the operating system in the DUT should recognize this link failure immediately). Disconnecting the cable on the generator end would be one possibility; shutting the link down would be another.
  • Note the time of the link failure on the generator.
  • At the generator, note the time of the receipt of the new router LSA from the DUT notifying the generator of the link 2 failure.

The difference in the time between the initial link failure and the receipt of the LSA on the generator across link 2 should be taken as the time required for an OSPF implementation to recognize and process a link failure, including the time required to generate and flood an LSA describing the link down event to an adjacent neighbor.

6.8. Link Down with Layer 3 Detection

  • Using reference topology 4 (Parallel Links), begin with OSPF in the Full state between the generator and the DUT.
  • Disable OSPF processing on link 1 from the generator. This should be done in such a way that it does not affect link status; the DUT MUST note the failure of the adjacency through the dead interval.
  • At the generator, note the time of the receipt of the new router LSA from the DUT notifying the generator of the link 2 failure.

The difference in the time between the initial link failure and the receipt of the LSA on the generator across link 2 should be taken as the time required for an OSPF implementation to recognize and process an adjacency failure.

7. Security Considerations

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

8. Acknowledgements

   Thanks to Howard Berkowitz (hcb@clark.net) for his encouragement and
   support.  Thanks also to Alex Zinin (zinin@psg.net), Gurpreet Singh
   (Gurpreet.Singh@SpirentCom.com), and Yasuhiro Ohara
   (yasu@sfc.wide.ad.jp) for their comments.

9. Normative References

   [OSPF]           Moy, J., "OSPF Version 2", STD 54, RFC 2328, April
                    1998.
   
   [TERM]           Manral, V., White, R., and A. Shaikh, "OSPF
                    Benchmarking Terminology and Concepts", RFC 4062,
                    April 2005.
   
   [CONSIDERATIONS] Manral, V., White, R., and A. Shaikh,
                    "Considerations When Using Basic OSPF Convergence
                    Benchmarks", RFC 4063, April 2005.
   
   [RFC2119]        Bradner, S., "Key words for use in RFCs to Indicate
                    Requirement Levels", BCP 14, RFC 2119, March 1997.

10. 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.
   
   [BLACKBOX]       Shaikh, A. and Greenberg, A., "Experience in Black-
                    box OSPF measurement", Proc. ACM SIGCOMM Internet
                    Measurement Workshop (IMW), November 2001

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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