Network Working Group
   Expires in: May 2008
   Intended Status: Informational

                                                   Scott Poretsky
                                                   Reef Point Systems

                                                   November 2007

                   Considerations for Benchmarking
             Link-State IGP Data Plane Route Convergence


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Copyright Notice
   Copyright (C) The IETF Trust (2007).

   This document discusses considerations for benchmarking Interior
   Gateway Protocol (IGP) Route Convergence for any link-state IGP, such
   as Intermediate System-Intermediate System (ISIS) and Open-Shorted
   Path first (OSPF).   A companion methodology document is to
   be used for benchmarking IGP convergence time through externally
   observable (black box) data plane measurements.  A companion
   terminology document is to be referenced to support the benchmarking.

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INTERNET-DRAFT        Considerations for Benchmarking  November 2007
                      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....4
     6. IANA Considerations.........................................4
     7. Security Considerations.....................................4
     8. Acknowledgements............................................5
     9. Normative References........................................5
     10. Author's Address...........................................6

1. Introduction
   Convergence Time is a critical performance parameter.  Customers
   of Service Providers use convergence packet loss [Po07t] due to
   Interior Gateway Protocol (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
   for any IGP such as Intermediate System - Intermediate System
   (ISIS) [Ca90] and Open-Shorted Path first (OSPF) [Mo98].  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 [Po07m] and [Po07t].  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

2.  Existing definitions
   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   this document are to be interpreted as described in BCP 14, RFC
   2119 [Br97].  RFC 2119 defines the use of these key words to help
   make the intent of standards track documents as clear as possible.
   While this document uses these keywords, this document is not a
   standards track document.

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 [Vi02],
   [Ka02], [Fi02], [Al02] and [Al00], these categories are Event
   Detection, Shortest Path First (SPF) Processing, IGP Advertisement,
   and Forwarding Information Base (FIB) Update.  These have numerous
   components that influence the convergence time, as listed below:

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                      IGP Data Plane Route Convergence

      -Event Detection-
        Physical Layer failure/recovery indication time
        Layer 2 failure/recovery 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

      -Increased Forwarding Delay due to Queueing

   The contribution of each of these factors listed above will vary
   with each router vendors' architecture and IGP implementation.
   Routers may have a centralized forwarding architecture, in which
   one route table is calculated and referenced for all arriving
   packets, or a distributed forwarding architecture, in which the
   central route table is calculated and distributed to the
   interfaces for local look-up as packets arrive.  The distributed
   route tables are typically maintained in hardware.

   It is therefore necessary to design a convergence test that
   considers all of these components contributing to convergence time
   and is independent of the Device Under Test (DUT) architecture,
   The benefit of designing a test for these considerations 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 as follow:
       * administrative link removal
       * unplanned link failure
       * line card failure
       * route changes such as withdrawal, flap, next-hop change,
         and cost change.
       * session loss due to loss of peer or adjancency
       * link recovery
       * link insertion

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INTERNET-DRAFT        Considerations for Benchmarking  November 2007
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   When benchmarking a router it is important to measure 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 [Po07m]
   using the terminology provided in [Po07t].

   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. IANA Considerations

   This document requires no IANA considerations.

7. 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 production networks.

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8. Acknowledgements
   Thanks to Curtis Villamizar for sharing so much of his knowledge
   and experience through the years. Thanks to Ron Bonica, Al Morton,
   David Ward, and the BMWG for their reviews and comments.

9. References
9.1 Normative References

      [Br97] Bradner, S., "Key words for use in RFCs to Indicate
          Requirement Levels", RFC 2119, March 1997

      [Ca90] Callon, R., "Use of OSI IS-IS for Routing in TCP/IP
          and Dual Environments", RFC 1195, December 1990.

      [Mo98] Moy, J., "OSPF Version 2", RFC 2328, IETF, April 1998.

      [Po07m] Poretsky, S., "Benchmarking Methodology for
          Link-State IGP Data Plane Route Convergence",
          draft-ietf-bmwg-igp-dataplane-conv-meth-14, work in
          progress, November 2007.

      [Po07t] Poretsky, S., "Benchmarking Terminology for
          Link-State IGP Data Plane Route Convergence",
          draft-ietf-bmwg-igp-dataplane-conv-term-14, work in
          progress, November 2007.

9.2 Informative References

      [Al00] Alaettinoglu, C., Jacobson, V., and Yu, H., "Towards
          Millisecond IGP Convergence", NANOG 20, March 2000.

      [Al02] Alaettinoglu, C. and Casner, S., "ISIS Routing on the
          Qwest Backbone: a Recipe for Subsecond ISIS Convergence",
          NANOG 24, March 2002.

      [Fi02] Filsfils, C., "Deploying Tight-SLA Services on an
          Internet   Backbone: ISIS Fast Convergence and
          Differentiated Services Design (tutorial)", NANOG 25,
          March 2002.

      [Ka02] Katz, D., "Why are we Scared of SPF?  IGP Scaling and
          Stability", NANOG 25, March 2002.

      [Vi02] Villamizar, C., "Convergence and Restoration Techniques
          for ISP Interior Routing", NANOG 25, March 2002.

Poretsky                                                     [Page 5]

INTERNET-DRAFT        Considerations for Benchmarking  November 2007
                      IGP Data Plane Route Convergence

10. Author's Address
      Scott Poretsky
      Reef Point Systems
      3 Federal Street
      Billerica, MA 01821 USA
      Phone: + 1 508 439 9008

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Poretsky                                                     [Page 6]