Network Working Group                                     Vishwas Manral
Internet Draft                                          Netplane Systems
                                                              Russ White
                                                           Cisco Systems
                                                             Aman Shaikh
Expiration Date: July 2004                      University of California
File Name: draft-bmwg-ospfconv-term-07.txt                  January 2004

               OSPF Benchmarking Terminology and Concepts

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

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3. Motivation

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

4. Common Definitions

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

   o    White Box (Internal) Measurements

         -    Definition

              White Box measurements are measurements reported and col-
              lected on the Device Under Test (DUT) itself.

         -    Discussion

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

              Note: White box measurements can be influenced by the
              vendor's implementation of the various timers and process-
              ing 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 of comparison in
              benchmarks.  This has been a guiding principal of Bench-
              marking Methodology Working Group.

      o    Black Box (External) Measurements

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         -    Definition

              Black Box measurements infer the performance of the DUT
              through observation of its communications with other dev-

         -    Discussion

              One example of a black box measurement is when a down-
              stream device receives complete routing information from
              the DUT, it can be inferred that the DUT has transmitted
              all the routing information available. External measure-
              ments of internal operations may suffer in that they
              include not just the protocol action times, but also pro-
              pagation 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 combina-
              tion with internal operations) between two or more DUTs.
              Multi-device measurements may be internal or external.

5. Terms Defined Elsewhere

   Terms in this section are defined elsewhere, and included only to
   include a discussion of those terms in reference to [BENCHMARK].

      o    Point-to-Point links

         -    Definition

              See [OSPF], Section 1.2.

         -    Discussion

              A point-to-point link can take lesser 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

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              can be either numbered or unnumbered. However in the con-
              text of [BENCHMARK] and [OSPF], the two can be regarded
              the same.

      o    Broadcast Link

         -    Definition

              See [OSPF], Section 1.2.

         -    Discussion

              The adjacency formation time on a broadcast link can be
              more 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.

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

      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 give
              routes to the forwarding engine.

              Some implementations may force two intervals, the SPF hold
              time and the SPF delay, between successive SPF calcula-
              tions. 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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         o    Measurement Units

              The SPF time is generally measured in milliseconds.

      o    Hello Interval

         -    Definition

              See [OSPF], Section 7.1.

         -    Discussion

              The hello interval should be the same for all routers on a

              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
              timing out causes an OSPF process to notice an adjacency
              failure. Further discussion on 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
              RouterDeadInterval field. The router dead interval should
              be some multiple of the HelloInterval (say 4 times the
              hello interval), and must be the same for all routers
              attached to a common network.

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6. Concepts

6.1. The Meaning of Single Router Control Plane Convergence

   A network is termed to be converged when all of the devices within
   the network have a loop free path to each possible destination. Since
   we are not testing network convergence, but performance for a partic-
   ular device within a network, however, this definition needs to be
   narrowed somewhat 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 to react to the change in 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 the same place, and the process of
   a single individual meeting in 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, nor the amount of time between the data plane
   receiving that information and being able to actually forward

6.2. Measuring Convergence

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

      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 calculate a new Shortest Path Tree (SPT).

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

6.3. Types of Network Events

   A network event is an event which causes a change in the network

      o    Link or Neighbor Device Up

           The time needed for an OSPF implementation to recoginize a
           new link coming up on the device, build any necessarily adja-
           cencies, synchronize its database, and perform all other
           needed actions to converge.

      o    Initialization

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

      o    Adjacency Down

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

      o    Link Down

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

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7. Acknowedgements

   The authors would like to thank Howard Berkowitz (,
   Kevin Dubray, (, Scott Poretsky
   (, and Randy Bush ( for their dis-
   cussion, ideas, and support.

8. Normative References

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

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

9. Informative References

     Choudhury, Gagan L., Editor, "Prioritized Treatment of Specific
     OSPF Packets and Congestion Avoidance", draft-ietf-ospf-
     scalability-06.txt, August 2003.

10. Authors' Addresses

      Vishwas Manral,
      Netplane Systems,
      189 Prashasan Nagar,
      Road number 72,
      Jubilee Hills,

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

      Aman Shaikh
      University of California
      School of Engineering

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      1156 High Street
      Santa Cruz, CA  95064

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