Network Working Group
   Expires in: April 2005
                                                   Scott Poretsky
                                                   Quarry Technologies

                                                   October 2004

                 Considerations for Benchmarking
                IGP Data Plane Route Convergence


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   This document is an Internet-Draft and is in full conformance with
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   This draft provides considerations for IGP Route Convergence
   benchmarking methodology [1] and IGP Route Convergence benchmarking
   terminology [2].  The methodology and terminology is to be used
   for benchmarking route convergence and can be applied to any
   link-state IGP such as ISIS [3] and OSPF [4].  The data plane is
   measured to obtain the convergence benchmarking metrics described
   in [1].

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INTERNET-DRAFT          Benchmarking Applicability for          October 2004
                       IGP Data Plane Route Convergence

   Table of Contents
     1. Introduction ...............................................2
     2. Existing definitions .......................................2
     3. Factors for IGP Route Convergence Time......................2
     4. Network Events that Cause Route Convergence.................3
     5. Use of Data Plane for IGP Route Convergence Benchmarking....3
     6. Security Considerations.....................................4
     7. Acknowledgements............................................4
     8. References..................................................4
     9. Author's Address............................................5

   1. Introduction
   IGP Convergence is a critical performance parameter.  Customers
   of Service Providers use packet loss due to IGP Convergence as a
   key metric of their network service quality.  Service Providers
   use IGP Convergence time as a key metric of router design and
   architecture.  Fast network convergence can be optimally achieved
   through deployment of fast converging routers.  The fundamental
   basis by which network users and operators benchmark convergence
   is packet loss, which is an externally observable event having
   direct impact on their application performance.

   IGP Route Convergence is a Direct Measure of Quality (DMOQ) when
   benchmarking the data plane.  For this reason it is important to
   develop a standard router benchmarking methodology and terminology
   for measuring IGP convergence that uses the data plane as described
   in [1] and [2].  This document describes all of the factors that
   influence a convergence measurement and how a purely black box test
   can be designed to account for all of these factors.  This enables
   accurate benchmarking and evaluation for route convergence time.

   2.  Existing definitions

   For the sake of clarity and continuity this RFC adopts the template
   for definitions set out in Section 2 of RFC 1242.  Definitions are
   indexed and grouped together in sections for ease of reference.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   this document are to be interpreted as described in RFC 2119.

   3. Factors for IGP Route Convergence Time

   There are four major categories of factors contributing to the
   measured Router IGP Convergence Time.   As discussed in [5], [6],
   [7], [8] and [9], these categories are Event Detection, SPF
   Processing, IGP Advertisement, and FIB Update.  These have numerous
   components that influence the convergence time.  These are listed
   as follow:

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                       IGP Data Plane Route Convergence

        -Event Detection-
        SONET failure indication time
        PPP failure indication time
        IGP Hello Dead Interval

        -SPF Processing-
        SPF Delay Time
        SPF Hold time
        SPF Execution time

        -IGP Advertisement-
        LSA/LSP Flood Packet Pacing
        LSA/LSP Retransmission Packet Pacing
        LSA/LSP Generation time

        -FIB Update-
        Tree Build time
        Hardware Update time

   The contribution of each of these factors listed above will vary
   with each router vendors' architecture and IGP implementation.
   It is therefore necessary to design a convergence test that
   considers all of these components, not just one or a few of these
   components.  The additional benefit of designing a test for all
   components is that it enables black-box testing in which knowledge
   of the routers' internal implementations is not required.  It is
   then possible to make valid use of the convergence benchmarking
   metrics when comparing routers from different vendors.

   4. Network Events that Cause Convergence
   There are different types of network events that can cause IGP
   convergence.  These network events are administrative link
   removal, unplanned link failure, line card failure, and route
   changes such as withdrawal, flap, next-hop change, and cost change.
   When benchmarking a router it is important to measure the
   convergence time for local and remote occurrence of these network
   events.  The convergence time measured will vary whether the network
   event occurred locally or remotely due to varying combinations of
   factors listed in the previous sections.  This behavior makes it
   possible to design purely black-box tests that isolate
   measurements for each of the components of convergence time.

   5. Use of Data Plane for IGP Route Convergence Benchmarking
   Customers of service providers use packet loss as the metric to
   calculate convergence time.  Packet loss is an externally observable
   event having direct impact on customers' application performance.
   For this reason it is important to develop a standard router
   benchmarking methodology and terminology that is a Direct Measure
   of Quality (DMOQ) for measuring IGP convergence.  Such a
   methodology uses the data plane as described in [1] and [2].

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                       IGP Data Plane Route Convergence

   An additional benefit of using packet loss for calculation of
   IGP Route Convergence time is that it enables black-box tests to
   be designed.  Data traffic can be offered to the
   device under test (DUT), an emulated network event can be forced
   to occur, and packet loss can be externally measured to calculate
   the convergence time.  Knowledge of the DUT architecture and IGP
   implementation is not required. There is no need to rely on the
   DUT to produce the test results.  There is no need to build
   intrusive test harnesses for the DUT.

   Use of data traffic and measurement of packet loss on the data
   plane also enables Route Convergence methodology test cases that
   consider the time for the Route Controller to update the FIB on
   the forwarding engine of the hardware.  A router is not fully
   converged until all components are updated and traffic is
   rerouted to the correct egress interface.  As long as there is
   packet loss, routes have not converged.  It is possible to send
   diverse traffic flows to destinations matching every route in the
   FIB so that the time it takes for the router to converge an entire
   route table can be benchmarked.

   6. Security Considerations

        Documents of this type do not directly effect the security of
        the Internet or of corporate networks as long as benchmarking
        is not performed on devices or systems connected to operating

   7. Acknowledgements
        Thanks to Curtis Villamizar for sharing so much of his
        knowledge and experience through the years. Also, special
        thanks to the many Network Engineers and Network Architects
        at the Service Providers who are always eager to discuss
        Route Convergence.

   8. References
      [1]   Poretsky, S., "Benchmarking Methodology for IGP Data Plane
            Route Convergence", draft-ietf-bmwg-igp-dataplane-conv-meth-04,
            work in progress, October 2004.

      [2]   Poretsky, S., "Benchmarking Terminology for IGP Data Plane
            Route Convergence", draft-ietf-bmwg-igp-dataplane-conv-term-04,
            work in progress, October 2004.

      [3]   Callon, R., "Use of OSI IS-IS for Routing in TCP/IP and Dual
            Environments", RFC 1195, December 1990.

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

      [5]   Villamizar, C., "Convergence and Restoration Techniques for
            ISP Interior Routing", NANOG 25, October 2002.

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                       IGP Data Plane Route Convergence

      [6]   Katz, D., "Why are we Scared of SPF?  IGP Scaling and
            Stability", NANOG 25, October 2002.

      [7]   Filsfils, C., "Deploying Tight-SLA Services on an Internet
            Backbone: ISIS Fast Convergence and Differentiated Services
            Design (tutorial)", NANOG 25, October 2002.

      [8]   Alaettinoglu, C. and Casner, S., "ISIS Routing on the Qwest
            Backbone: a Recipe for Subsecond ISIS Convergence", NANOG 24,
            October 2002.

      [9]   Alaettinoglu, C., Jacobson, V., and Yu, H., "Towards
            Millisecond IGP Convergence", NANOG 20, October 2000.

   9. Author's Address

        Scott Poretsky
        Quarry Technologies
        8 New England Executive Park
        Burlington, MA 01803

        Phone: + 1 781 395 5090

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