Network Working Group                                        S. Poretsky
Internet-Draft                                      Allot Communications
Intended status: Informational                                 B. Imhoff
Expires: April 29, 2010                                 Juniper Networks
                                                           K. Michielsen
                                                           Cisco Systems
                                                        October 26, 2009


Terminology for Benchmarking Link-State IGP Data Plane Route Convergence
               draft-ietf-bmwg-igp-dataplane-conv-term-19

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   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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Abstract

   This document describes the terminology for benchmarking Interior
   Gateway Protocol (IGP) Route Convergence.  The terminology is to be
   used for benchmarking IGP convergence time through externally
   observable (black box) data plane measurements.  The terminology can
   be applied to any link-state IGP, such as ISIS and OSPF.


Table of Contents

   1.  Introduction and Scope . . . . . . . . . . . . . . . . . . . .  4
   2.  Existing Definitions . . . . . . . . . . . . . . . . . . . . .  4
   3.  Term Definitions . . . . . . . . . . . . . . . . . . . . . . .  4
     3.1.  Convergence Types  . . . . . . . . . . . . . . . . . . . .  5
       3.1.1.  Route Convergence  . . . . . . . . . . . . . . . . . .  5
       3.1.2.  Full Convergence . . . . . . . . . . . . . . . . . . .  5
       3.1.3.  Network Convergence  . . . . . . . . . . . . . . . . .  6
     3.2.  Instants . . . . . . . . . . . . . . . . . . . . . . . . .  6
       3.2.1.  Traffic Start Instant  . . . . . . . . . . . . . . . .  6
       3.2.2.  Convergence Event Instant  . . . . . . . . . . . . . .  7
       3.2.3.  Convergence Recovery Instant . . . . . . . . . . . . .  7
       3.2.4.  First Route Convergence Instant  . . . . . . . . . . .  8
     3.3.  Transitions  . . . . . . . . . . . . . . . . . . . . . . .  9
       3.3.1.  Convergence Event Transition . . . . . . . . . . . . .  9
       3.3.2.  Convergence Recovery Transition  . . . . . . . . . . .  9
     3.4.  Interfaces . . . . . . . . . . . . . . . . . . . . . . . . 10
       3.4.1.  Local Interface  . . . . . . . . . . . . . . . . . . . 10
       3.4.2.  Remote Interface . . . . . . . . . . . . . . . . . . . 10
       3.4.3.  Preferred Egress Interface . . . . . . . . . . . . . . 11
       3.4.4.  Next-Best Egress Interface . . . . . . . . . . . . . . 11
     3.5.  Benchmarking Methods . . . . . . . . . . . . . . . . . . . 11
       3.5.1.  Rate-Derived Method  . . . . . . . . . . . . . . . . . 11
       3.5.2.  Loss-Derived Method  . . . . . . . . . . . . . . . . . 13
       3.5.3.  Route-Specific Loss-Derived Method . . . . . . . . . . 14
     3.6.  Benchmarks . . . . . . . . . . . . . . . . . . . . . . . . 15
       3.6.1.  Full Convergence Time  . . . . . . . . . . . . . . . . 15
       3.6.2.  First Route Convergence Time . . . . . . . . . . . . . 16
       3.6.3.  Route-Specific Convergence Time  . . . . . . . . . . . 17
       3.6.4.  Loss-Derived Convergence Time  . . . . . . . . . . . . 18



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       3.6.5.  Route Loss of Connectivity Period  . . . . . . . . . . 19
       3.6.6.  Loss-Derived Loss of Connectivity Period . . . . . . . 20
     3.7.  Measurement Terms  . . . . . . . . . . . . . . . . . . . . 21
       3.7.1.  Convergence Event  . . . . . . . . . . . . . . . . . . 21
       3.7.2.  Packet Loss  . . . . . . . . . . . . . . . . . . . . . 22
       3.7.3.  Convergence Packet Loss  . . . . . . . . . . . . . . . 22
       3.7.4.  Connectivity Packet Loss . . . . . . . . . . . . . . . 23
       3.7.5.  Packet Sampling Interval . . . . . . . . . . . . . . . 23
       3.7.6.  Sustained Convergence Validation Time  . . . . . . . . 24
     3.8.  Miscellaneous Terms  . . . . . . . . . . . . . . . . . . . 24
       3.8.1.  Stale Forwarding . . . . . . . . . . . . . . . . . . . 24
       3.8.2.  Nested Convergence Event . . . . . . . . . . . . . . . 25
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . . 25
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 26
   6.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 26
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 26
     7.1.  Normative References . . . . . . . . . . . . . . . . . . . 26
     7.2.  Informative References . . . . . . . . . . . . . . . . . . 27
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 27
































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1.  Introduction and Scope

   This draft describes the terminology for benchmarking Link-State
   Interior Gateway Protocol (IGP) Convergence.  The motivation and
   applicability for this benchmarking is provided in [Po09a].  The
   methodology to be used for this benchmarking is described in [Po09m].
   The purpose of this document is to introduce new terms required to
   complete execution of the IGP Route Methodology [Po09m].

   IGP convergence time is measured on the data plane at the Tester by
   observing packet loss through the DUT.  The methodology and
   terminology to be used for benchmarking IGP Convergence can be
   applied to IPv4 and IPv6 traffic and link-state IGPs such as ISIS
   [Ca90][Ho08], OSPF [Mo98][Co08], and others.


2.  Existing Definitions

   This document uses existing terminology defined in other BMWG work.
   Examples include, but are not limited to:

            Frame Loss Rate         [Ref.[Br91], section 3.6]
            Throughput              [Ref.[Br91], section 3.17]
            Offered Load            [Ref.[Ma98], section 3.5.2]
            Forwarding Rate         [Ref.[Ma98], section 3.6.1]
            Device Under Test (DUT) [Ref.[Ma98], section 3.1.1]
            System Under Test (SUT) [Ref.[Ma98], section 3.1.2]
            Out-of-order Packet     [Ref.[Po06], section 3.3.2]
            Duplicate Packet        [Ref.[Po06], section 3.3.3]
            Packet Reordering       [Ref.[Mo06], section 3.3]
            Stream                  [Ref.[Po06], section 3.3.2]
            Forwarding Delay        [Ref.[Po06], section 3.2.4]
            Loss Period             [Ref.[Ko02], section 4]

   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 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.  Term Definitions







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3.1.  Convergence Types

3.1.1.  Route Convergence

   Definition:

   The process of updating all components of the router, including the
   Routing Information Base (RIB) and Forwarding Information Base (FIB),
   along with software and hardware tables, with the most recent route
   change(s) such that forwarding for a route entry is successful on the
   Next-Best Egress Interface.

   Discussion:

   Route Convergence MUST occur after a Convergence Event.  Route
   Convergence can be observed externally by the rerouting of data
   traffic for a destination matching a route entry to the Next-best
   Egress Interface.  Completion of Route Convergence may or may not be
   sustained over time.

   Measurement Units: N/A

   Issues: None

   See Also:

   Network Convergence, Full Convergence, Convergence Event

3.1.2.  Full Convergence

   Definition:

   Route Convergence for all routes in the FIB.

   Discussion:

   Full Convergence MUST occur after a Convergence Event.  Full
   Convergence can be observed externally by the rerouting of data
   traffic to destinations matching all route entries to the Next-best
   Egress Interface.  Completion of Full Convergence is externally
   observable from the data plane when the Forwarding Rate of the data
   plane traffic on the Next-Best Egress Interface equals the Offered
   Load.

   Completion of Full Convergence may or may not be sustained over time.

   Measurement Units: N/A




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   Issues: None

   See Also:

   Network Convergence, Route Convergence, Convergence Event, Full
   Convergence Time, Convergence Recovery Instant

3.1.3.  Network Convergence

   Definition:

   Full Convergence in all routers throughout the network.

   Discussion:

   Network Convergence includes all Route Convergence operations for all
   routers in the network following a Convergence Event.

   Completion of Network Convergence can be observed by recovery of the
   network Forwarding Rate to equal the Offered Load, with no Stale
   Forwarding, and no Blenders [Ca01][Ci03].

   Completion of Network Convergence may or may not be sustained over
   time.

   Measurement Units: N/A

   Issues: None

   See Also:

   Route Convergence, Full Convergence, Stale Forwarding

3.2.  Instants

3.2.1.  Traffic Start Instant

   Definition:

   The time instant the Tester sends out the first data packet to the
   DUT.

   Discussion:

   If using the Loss-Derived Method or the Route-Specific Loss-Derived
   Method to benchmark IGP convergence time, and the applied Convergence
   Event does not cause instantaneous traffic loss for all routes at the
   Convergence Event Instant then the Tester SHOULD collect a timestamp



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   on the Traffic Start Instant in order to measure the period of time
   between the Traffic Start Instant and Convergence Event Instant.

   Measurement Units:

   hh:mm:ss:nnn:uuu, where 'nnn' is milliseconds and 'uuu' is
   microseconds.

   Issues: None

   See Also:

   Convergence Event Instant, Route-Specific Convergence Time, Loss-
   Derived Convergence Time.

3.2.2.  Convergence Event Instant

   Definition:

   The time instant that a Convergence Event occurs.

   Discussion:

   If the Convergence Event causes instantaneous traffic loss on the
   Preferred Egress Interface, the Convergence Event Instant is
   observable from the data plane as the instant that the DUT begins to
   exhibit packet loss.

   The Tester SHOULD collect a timestamp on the Convergence Event
   Instant if it is not observable from the data plane.

   Measurement Units:

   hh:mm:ss:nnn:uuu, where 'nnn' is milliseconds and 'uuu' is
   microseconds.

   Issues: None

   See Also: Convergence Event

3.2.3.  Convergence Recovery Instant

   Definition:

   The time instant that Full Convergence has completed.

   Discussion:




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   The Full Convergence completed state MUST be maintained for an
   interval of duration equal to the Sustained Convergence Validation
   Time in order to validate the Convergence Recovery Instant.

   The Convergence Recovery Instant is observable from the data plane as
   the instant the DUT forwards traffic to all destinations over the
   Next-Best Egress Interface.

   When using the Rate-Derived Method, the Convergence Recovery Instant
   falls within the Packet Sampling Interval preceding the first
   interval where the observed Forwarding Rate on the Next-Best Egress
   Interface equals the Offered Load.

   Measurement Units:

   hh:mm:ss:nnn:uuu, where 'nnn' is milliseconds and 'uuu' is
   microseconds.

   Issues: None

   See Also:

   Sustained Convergence Validation Time, Full Convergence

3.2.4.  First Route Convergence Instant

   Definition:

   The time instant the first route entry completes Route Convergence
   following a Convergence Event

   Discussion:

   Any route may be the first to complete Route Convergence.  The First
   Route Convergence Instant is observable from the data plane as the
   instant that the first packet is received from the Next-Best Egress
   Interface.

   Measurement Units:

   hh:mm:ss:nnn:uuu, where 'nnn' is milliseconds and 'uuu' is
   microseconds.

   Issues: None

   See Also: Route Convergence





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3.3.  Transitions

3.3.1.  Convergence Event Transition

   Definition:

   A time interval following a Convergence Event in which Forwarding
   Rate on the Preferred Egress Interface gradually reduces to zero.

   Discussion:

   The Forwarding Rate during a Convergence Event Transition may not
   decrease linearly.

   The Forwarding Rate observed on all DUT egress interfaces may or may
   not decrease to zero.

   The Offered Load, the number of routes, and the Packet Sampling
   Interval influence the observations of the Convergence Event
   Transition using the Rate-Derived Method.  This is further discussed
   with the term "Rate-Derived Method".

   Measurement Units: seconds

   Issues: None

   See Also:

   Convergence Event, Rate-Derived Method

3.3.2.  Convergence Recovery Transition

   Definition:

   A time interval following the First Route Convergence Instant in
   which Forwarding Rate on the Next-Best Egress Interface gradually
   increases to equal the Offered Load.

   Discussion:

   The Forwarding Rate observed during a Convergence Recovery Transition
   may not increase linearly.

   The Offered Load, the number of routes, and the Packet Sampling
   Interval influence the observations of the Convergence Recovery
   Transition using the Rate-Derived Method.  This is further discussed
   with the term "Rate-Derived Method".




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   Measurement Units: seconds

   Issues: None

   See Also:

   Full Convergence,First Route Convergence Instant, Rate-Derived Method

3.4.  Interfaces

3.4.1.  Local Interface

   Definition:

   An interface on the DUT.

   Discussion:

   A failure of the Local Interface indicates that the failure occurred
   directly on the DUT.

   Measurement Units: N/A

   Issues: None

   See Also: Remote Interface

3.4.2.  Remote Interface

   Definition:

   An interface on a neighboring router that is not directly connected
   to any interface on the DUT.

   Discussion:

   A failure of a Remote Interface indicates that the failure occurred
   on a neighbor router's interface that is not directly connected to
   the DUT.

   Measurement Units: N/A

   Issues: None

   See Also: Local Interface






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3.4.3.  Preferred Egress Interface

   Definition:

   The outbound interface from the DUT for traffic routed to the
   preferred next-hop.

   Discussion:

   The Preferred Egress Interface is the egress interface prior to a
   Convergence Event.

   Measurement Units: N/A

   Issues: None

   See Also: Next-Best Egress Interface

3.4.4.  Next-Best Egress Interface

   Definition:

   The outbound interface from the DUT for traffic routed to the second-
   best next-hop.

   Discussion:

   The Next-Best Egress Interface becomes the egress interface after a
   Convergence Event.

   The Next-Best Egress Interface is of the same media type and link
   speed as the Preferred Egress Interface.

   Measurement Units: N/A

   Issues: None

   See Also: Preferred Egress Interface

3.5.  Benchmarking Methods

3.5.1.  Rate-Derived Method

   Definition:

   The method to calculate convergence time benchmarks from observing
   Forwarding Rate each Packet Sampling Interval.




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   Discussion:

   Figure 1 shows an example of the Forwarding Rate change in time
   during convergence as observed when using the Rate-Derived Method.

           ^         Traffic                      Convergence
      Fwd  |         Start                        Recovery
      Rate |         Instant                      Instant
           | Offered  ^                             ^
           | Load --> ----------\                   /-----------
           |                     \                 /<--- Convergence
           |                      \     Packet    /      Recovery
           |       Convergence --->\     Loss    /       Transition
           |       Event            \           /
           |       Transition        \---------/ <-- Max Packet Loss
           |
           +--------------------------------------------------------->
                           ^                   ^                 time
                      Convergence         First Route
                      Event Instant       Convergence Instant

                 Figure 1: Rate-Derived Convergence Graph

   The Offered Load SHOULD consist of a single Stream [Po06].  If
   sending multiple Streams, the measured traffic rate statistics for
   all Streams MUST be added together.

   The destination addresses for the Offered Load MUST be distributed
   such that all routes or a statistically representative subset of all
   routes are matched and each of these routes is offered an equal share
   of the Offered Load.  It is RECOMMENDED to send traffic to all
   routes, but a statistically representative subset of all routes can
   be used if required.

   At least one packet per route for all routes matched in the Offered
   Load MUST be offered to the DUT within each Packet Sampling Interval.

   The Offered Load, the number of routes, and the Packet Sampling
   Interval influence the observations for the Rate-Derived Method.  It
   may be difficult to identify the different convergence time instants
   in the Rate-Derived Convergence Graph.  For example, it is possible
   that a Convergence Event causes the Forwarding Rate to drop to zero,
   while this may not be observed in the Forwarding Rate measurements if
   the Packet Sampling Interval is too large.

   Metrics measured at the Packet Sampling Interval MUST include
   Forwarding Rate and packet loss.




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   Rate-Derived Method is a RECOMMENDED method to measure convergence
   time benchmarks.

   To measure convergence time benchmarks for Convergence Events that do
   not cause instantaneous traffic loss for all routes at the
   Convergence Event Instant, the Tester SHOULD collect a timestamp of
   the Convergence Event Instant and the Tester SHOULD observe
   Forwarding Rate separately on the Next-Best Egress Interface.

   Since the Rate-Derived Method does not distinguish between individual
   traffic destinations, it SHOULD NOT be used for any route specific
   measurements.  Therefor Rate-Derived Method SHOULD NOT be used to
   benchmark Route Loss of Connectivity Period.

   Measurement Units: N/A

   Issues: None

   See Also:

   Packet Sampling Interval, Convergence Event, Convergence Event
   Instant, Full Convergence

3.5.2.  Loss-Derived Method

   Definition:

   The method to calculate the Loss-Derived Convergence Time and Loss-
   Derived Loss of Connectivity Period benchmarks from the amount of
   packet loss.

   Discussion:

   The Offered Load SHOULD consist of a single Stream [Po06].  If
   sending multiple Streams, the measured traffic rate statistics for
   all Streams MUST be added together.

   The destination addresses for the Offered Load MUST be distributed
   such that all routes or a statistically representative subset of all
   routes are matched and each of these routes is offered an equal share
   of the Offered Load.  It is RECOMMENDED to send traffic to all
   routes, but a statistically representative subset of all routes can
   be used if required.

   Loss-Derived Method SHOULD always be combined with Rate-Derived
   Method in order to observe Full Convergence completion.  The total
   amount of Convergence Packet Loss is collected after Full Convergence
   completion.



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   To measure convergence time and loss of connectivity benchmarks, the
   Tester SHOULD in general observe packet loss on all DUT egress
   interfaces (Connectivity Packet Loss).

   To measure convergence time benchmarks for Convergence Events that do
   not cause instantaneous traffic loss for all routes at the
   Convergence Event Instant, the Tester SHOULD collect timestamps of
   the Start Traffic Instant and of the Convergence Event Instant, and
   the Tester SHOULD observe packet loss separately on the Next-Best
   Egress Interface (Convergence Packet Loss).

   Since Loss-Derived Method does not distinguish between traffic
   destinations and the packet loss statistics are only collected after
   Full Convergence completion, this method can only be used to measure
   average values over all routes.  For these reasons Loss-Derived
   Method can only be used to benchmark Loss-Derived Convergence Time
   and Loss-Derived Loss of Connectivity Period.

   Note that the Loss-Derived Method measures an average over all
   routes, including the routes that may not be impacted by the
   Convergence Event, such as routes via non-impacted members of ECMP or
   parallel links.

   Measurement Units: seconds

   Issues: None

   See Also:

   Loss-Derived Convergence Time, Loss-Derived Loss of Connectivity
   Period, Convergence Packet Loss

3.5.3.  Route-Specific Loss-Derived Method

   Definition:

   The method to calculate the Route-Specific Convergence Time benchmark
   from the amount of packet loss during convergence for a specific
   route entry.

   Discussion:

   To benchmark Route-Specific Convergence Time, the Tester provides an
   Offered Load that consists of multiple Streams [Po06].  Each Stream
   has a single destination address matching a different route entry,
   for all routes or a statistically representative subset of all
   routes.  Convergence Packet Loss is measured for each Stream
   separately.



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   Route-Specific Loss-Derived Method SHOULD always be combined with
   Rate-Derived Method in order to observe Full Convergence completion.
   The total amount of Convergence Packet Loss for each Stream is
   collected after Full Convergence completion.

   Route-Specific Loss-Derived Method is a RECOMMENDED method to measure
   convergence time benchmarks.

   To measure convergence time and loss of connectivity benchmarks, the
   Tester SHOULD in general observe packet loss on all DUT egress
   interfaces (Connectivity Packet Loss).

   To measure convergence time benchmarks for Convergence Events that do
   not cause instantaneous traffic loss for all routes at the
   Convergence Event Instant, the Tester SHOULD collect timestamps of
   the Start Traffic Instant and of the Convergence Event Instant, and
   the Tester SHOULD observe packet loss separately on the Next-Best
   Egress Interface (Convergence Packet Loss).

   Since Route-Specific Loss-Derived Method uses traffic streams to
   individual routes, it measures packet loss as it would be experienced
   by a network user.  For this reason Route-Specific Loss-Derived
   Method is RECOMMENDED to measure Route-Specific Convergence Time
   benchmarks and Route Loss of Connectivity Period benchmarks.

   Measurement Units: seconds

   Issues: None

   See Also:

   Route-Specific Convergence Time, Route Loss of Connectivity Period,
   Convergence Packet Loss

3.6.  Benchmarks

3.6.1.  Full Convergence Time

   Definition:

   The time duration of the period between the Convergence Event Instant
   and the Convergence Recovery Instant as observed using the Rate-
   Derived Method.

   Discussion:

   Using the Rate-Derived Method, Full Convergence Time can be
   calculated as the time difference between the Convergence Event



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   Instant and the Convergence Recovery Instant, as shown in Equation 1.

        Full Convergence Time =
            Convergence Recovery Instant - Convergence Event Instant

                                Equation 1

   The Convergence Event Instant can be derived from the Forwarding Rate
   observation or from a timestamp collected by the Tester.

   For the testcases described in [Po09m], it is expected that Full
   Convergence Time equals the maximum Route-Specific Convergence Time
   when benchmarking all routes in FIB using the Route-Specific Loss-
   Derived Method.

   It is not possible to measure Full Convergence Time using the Loss-
   Derived Method.

   Measurement Units: seconds

   Issues: None

   See Also:

   Full Convergence, Rate-Derived Method, Route-Specific Loss-Derived
   Method

3.6.2.  First Route Convergence Time

   Definition:

   The duration of the period between the Convergence Event Instant and
   the First Route Convergence Instant as observed using the Rate-
   Derived Method.

   Discussion:

   Using the Rate-Derived Method, First Route Convergence Time can be
   calculated as the time difference between the Convergence Event
   Instant and the First Route Convergence Instant, as shown with
   Equation 2.

      First Route Convergence Time =
          First Route Convergence Instant - Convergence Event Instant

                                Equation 2

   The Convergence Event Instant can be derived from the Forwarding Rate



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   observation or from a timestamp collected by the Tester.

   For the testcases described in [Po09m], it is expected that First
   Route Convergence Time equals the minimum Route-Specific Convergence
   Time when benchmarking all routes in FIB using the Route-Specific
   Loss-Derived Method.

   It is not possible to measure First Route Convergence Time using the
   Loss-Derived Method.

   Measurement Units: seconds

   Issues: None

   See Also:

   Rate-Derived Method, Route-Specific Loss-Derived Method, First Route
   Convergence Instant

3.6.3.  Route-Specific Convergence Time

   Definition:

   The amount of time it takes for Route Convergence to be completed for
   a specific route, as calculated from the amount of packet loss during
   convergence for a single route entry.

   Discussion:

   Route-Specific Convergence Time can only be measured using the Route-
   Specific Loss-Derived Method.

   If the applied Convergence Event causes instantaneous traffic loss
   for all routes at the Convergence Event Instant, Connectivity Packet
   Loss should be observed.  Connectivity Packet Loss is the combined
   packet loss observed on Preferred Egress Interface and Next-Best
   Egress Interface.  When benchmarking Route-Specific Convergence Time,
   Connectivity Packet Loss is measured and Equation 3 is applied for
   each measured route.  The calculation is equal to Equation 7 in
   Section 3.6.5.

   Route-Specific Convergence Time =
      Connectivity Packet Loss for specific route/Offered Load per route

                                Equation 3

   If the applied Convergence Event does not cause instantaneous traffic
   loss for all routes at the Convergence Event Instant, then the Tester



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   SHOULD collect timestamps of the Traffic Start Instant and of the
   Convergence Event Instant, and the Tester SHOULD observe Convergence
   Packet Loss separately on the Next-Best Egress Interface.  When
   benchmarking Route-Specific Convergence Time, Convergence Packet Loss
   is measured and Equation 4 is applied for each measured route.

   Route-Specific Convergence Time =
       Convergence Packet Loss for specific route/Offered Load per route
       - (Convergence Event Instant - Traffic Start Instant)

                                Equation 4

   The Convergence Event Instant and Traffic Start Instant SHOULD be
   collected by the Tester.

   The Route-Specific Convergence Time benchmarks enable minimum,
   maximum, average, and median convergence time measurements to be
   reported by comparing the results for the different route entries.
   It also enables benchmarking of convergence time when configuring a
   priority value for route entry(ies).  Since multiple Route-Specific
   Convergence Times can be measured it is possible to have an array of
   results.  The format for reporting Route-Specific Convergence Time is
   provided in [Po09m].

   Measurement Units: seconds

   Issues: None

   See Also:

   Convergence Event, Convergence Packet Loss, Connectivity Packet Loss,
   Route Convergence

3.6.4.  Loss-Derived Convergence Time

   Definition:

   The average Route Convergence time for all routes in FIB, as
   calculated from the amount of packet loss during convergence.

   Discussion:

   Loss-Derived Convergence Time is measured using the Loss-Derived
   Method.

   If the applied Convergence Event causes instantaneous traffic loss
   for all routes at the Convergence Event Instant, Connectivity Packet
   Loss should be observed.  Connectivity Packet Loss is the combined



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   packet loss observed on Preferred Egress Interface and Next-Best
   Egress Interface.  When benchmarking Loss-Derived Convergence Time,
   Connectivity Packet Loss is measured and Equation 5 is applied.

                 Loss-Derived Convergence Time =
                     Connectivity Packet Loss/Offered Load

                                Equation 5

   If the applied Convergence Event does not cause instantaneous traffic
   loss for all routes at the Convergence Event Instant, then the Tester
   SHOULD collect timestamps of the Start Traffic Instant and of the
   Convergence Event Instant and the Tester SHOULD observe Convergence
   Packet Loss separately on the Next-Best Egress Interface.  When
   benchmarking Loss-Derived Convergence Time, Convergence Packet Loss
   is measured and Equation 6 is applied.

         Loss-Derived Convergence Time =
             Convergence Packet Loss/Offered Load
             - (Convergence Event Instant - Traffic Start Instant)

                                Equation 6

   The Convergence Event Instant and Traffic Start Instant SHOULD be
   collected by the Tester.

   Measurement Units: seconds

   Issues: None

   See Also:

   Convergence Packet Loss, Connectivity Packet Loss, Route Convergence

3.6.5.  Route Loss of Connectivity Period

   Definition:

   The time duration of traffic loss for a specific route entry
   following a Convergence Event until Full Convergence completion, as
   observed using the Route-Specific Loss-Derived Method.

   Discussion:

   In general the Route Loss of Connectivity Period is not equal to the
   Route-Specific Convergence Time.  If the DUT continues to forward
   traffic to the Preferred Egress Interface after the Convergence Event
   is applied then the Route Loss of Connectivity Period will be smaller



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   than the Route-Specific Convergence Time.  This is also specifically
   the case after reversing a failure event.

   The Route Loss of Connectivity Period may be equal to the Route-
   Specific Convergence Time if, as a characteristic of the Convergence
   Event, traffic for all routes starts dropping instantaneously on the
   Convergence Event Instant.  See discussion in [Po09m].

   For the testcases described in [Po09m] the Route Loss of Connectivity
   Period is expected to be a single Loss Period [Ko02].

   When benchmarking Route Loss of Connectivity Period, Connectivity
   Packet Loss is measured for each route and Equation 7 is applied for
   each measured route entry.  The calculation is equal to Equation 3 in
   Section 3.6.3.

   Route Loss of Connectivity Period =
      Connectivity Packet Loss for specific route/Offered Load per route

                                Equation 7

   Route Loss of Connectivity Period SHOULD be measured using Route-
   Specific Loss-Derived Method.

   Measurement Units: seconds

   Issues: None

   See Also:

   Route-Specific Convergence Time, Route-Specific Loss-Derived Method,
   Connectivity Packet Loss

3.6.6.  Loss-Derived Loss of Connectivity Period

   Definition:

   The average time duration of traffic loss for all routes following a
   Convergence Event until Full Convergence completion, as observed
   using the Loss-Derived Method.

   Discussion:

   In general the Loss-Derived Loss of Connectivity Period is not equal
   to the Loss-Derived Convergence Time.  If the DUT continues to
   forward traffic to the Preferred Egress Interface after the
   Convergence Event is applied then the Loss-Derived Loss of
   Connectivity Period will be smaller than the Loss-Derived Convergence



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   Time.  This is also specifically the case after reversing a failure
   event.

   The Loss-Derived Loss of Connectivity Period may be equal to the
   Loss-Derived Convergence Time if, as a characteristic of the
   Convergence Event, traffic for all routes starts dropping
   instantaneously on the Convergence Event Instant.  See discussion in
   [Po09m].

   For the testcases described in [Po09m] each route's Route Loss of
   Connectivity Period is expected to be a single Loss Period [Ko02].

   When benchmarking Loss-Derived Loss of Connectivity Period,
   Connectivity Packet Loss is measured for all routes and Equation 8 is
   applied.  The calculation is equal to Equation 5 in Section 3.6.4.

          Loss-Derived Loss of Connectivity Period =
             Connectivity Packet Loss for all routes/Offered Load

                                Equation 8

   Loss-Derived Loss of Connectivity Period SHOULD be measured using
   Loss-Derived Method.

   Measurement Units: seconds

   Issues: None

   See Also:

   Loss-Derived Convergence Time, Loss-Derived Method, Connectivity
   Packet Loss

3.7.  Measurement Terms

3.7.1.  Convergence Event

   Definition:

   The occurrence of a planned or unplanned event in the network that
   will result in a change in the egress interface of the Device Under
   Test (DUT) for routed packets.

   Discussion:

   Convergence Events include but are not limited to link loss, routing
   protocol session loss, router failure, configuration change, and
   better next-hop learned via a routing protocol.



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   Measurement Units: N/A

   Issues: None

   See Also: Convergence Event Instant

3.7.2.   Packet Loss

   Definition:

   The number of packets that should have been forwarded by a DUT under
   a constant Offered Load that were not forwarded due to lack of
   resources.

   Discussion:

   Packet Loss is a modified version of the term "Frame Loss Rate" as
   defined in [Br91].  The term "Frame Loss" is intended for Ethernet
   Frames while "Packet Loss" is intended for IP packets.

   Measurement units: Number of offered packets that are not forwarded.

   Issues: None

   See Also: Convergence Packet Loss

3.7.3.  Convergence Packet Loss

   Definition:

   The number of packets lost due to a Convergence Event until Full
   Convergence completes, as observed on the Next-Best Egress Interface.

   Discussion:

   Convergence Packet Loss is observed on the Next-Best Egress
   Interface.  It only needs to be observed for Convergence Events that
   do not cause instantaneous traffic loss at Convergence Event Instant.

   Convergence Packet Loss includes packets that were lost and packets
   that were delayed due to buffering.  The magnitude of an acceptable
   Forwarding Delay is a parameter of the methodology.  If a maximum
   acceptable Forwarding Delay threshold is applied it MUST be reported.

   Measurement Units: number of packets

   Issues: None




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   See Also:

   Packet Loss, Full Convergence, Convergence Event, Connectivity Packet
   Loss

3.7.4.  Connectivity Packet Loss

   Definition:

   The number of packets lost due to a Convergence Event until Full
   Convergence completes.

   Discussion:

   Connectivity Packet Loss is observed on all DUT egress interfaces.

   Convergence Packet Loss includes packets that were lost and packets
   that were delayed due to buffering.  The magnitude of an acceptable
   Forwarding Delay is a parameter of the methodology.  If a maximum
   acceptable Forwarding Delay threshold is applied it MUST be reported.

   Measurement Units: number of packets

   Issues: None

   See Also:

   Packet Loss, Route Loss of Connectivity Period, Convergence Event,
   Convergence Packet Loss

3.7.5.  Packet Sampling Interval

   Definition:

   The interval at which the Tester (test equipment) polls to make
   measurements for arriving packets.

   Discussion:

   At least one packet per route for all routes matched in the Offered
   Load MUST be offered to the DUT within the Packet Sampling Interval.
   Metrics measured at the Packet Sampling Interval MUST include
   Forwarding Rate and received packets.

   Packet Sampling Interval can influence the convergence graph as
   observed with the Rate-Derived Method.  This is particularly true
   when implementations complete Full Convergence in less time than the
   Packet Sampling Interval.  The Convergence Event Instant and First



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   Route Convergence Instant may not be easily identifiable and the
   Rate-Derived Method may produce a larger than actual convergence
   time.

   The recommended value for configuration of the Packet Sampling
   Interval when using the Rate-Derived Method is provided in [Po09m].
   For the other benchmark methods the value of the Packet Sampling
   Interval does not contribute to the measurement accuracy.

   Measurement Units: seconds

   Issues: None

   See Also: Rate-Derived Method

3.7.6.  Sustained Convergence Validation Time

   Definition:

   The amount of time for which the completion of Full Convergence is
   maintained without additional packet loss.

   Discussion:

   The purpose of the Sustained Convergence Validation Time is to
   produce convergence benchmarks protected against fluctuation in
   Forwarding Rate after the completion of Full Convergence is observed.
   The RECOMMENDED Sustained Convergence Validation Time to be used is 5
   seconds.  The BMWG selected 5 seconds based upon RFC 2544 [Br99]
   which recommends waiting 2 seconds for residual frames to arrive
   (this is the Forwarding Delay threshold for the last packet sent) and
   5 seconds for DUT restabilization.

   Measurement Units: seconds

   Issues: None

   See Also:

   Full Convergence, Convergence Recovery Instant

3.8.  Miscellaneous Terms

3.8.1.  Stale Forwarding

   Definition:

   Forwarding of traffic to route entries that no longer exist or to



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   route entries with next-hops that are no longer preferred.

   Discussion:

   Stale Forwarding can be caused by a Convergence Event and can
   manifest as a "black-hole" or microloop that produces packet loss, or
   out-of-order packets, or delayed packets.  Stale Forwarding can exist
   until Network Convergence is completed.

   Measurement Units: N/A

   Issues: None

   See Also: Network Convergence

3.8.2.  Nested Convergence Event

   Definition:

   The occurrence of a Convergence Event while the route table is
   converging from a prior Convergence Event.

   Discussion:

   The Convergence Events for a Nested Convergence Event MUST occur with
   different neighbors.  A possible observation from a Nested
   Convergence Event will be the withdrawal of routes from one neighbor
   while the routes of another neighbor are being installed.

   Measurement Units: N/A

   Issues: None

   See Also: Convergence Event


4.  Security Considerations

   Benchmarking activities as described in this memo are limited to
   technology characterization using controlled stimuli in a laboratory
   environment, with dedicated address space and the constraints
   specified in the sections above.

   The benchmarking network topology will be an independent test setup
   and MUST NOT be connected to devices that may forward the test
   traffic into a production network, or misroute traffic to the test
   management network.




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   Further, benchmarking is performed on a "black-box" basis, relying
   solely on measurements observable external to the DUT/SUT.

   Special capabilities SHOULD NOT exist in the DUT/SUT specifically for
   benchmarking purposes.  Any implications for network security arising
   from the DUT/SUT SHOULD be identical in the lab and in production
   networks.


5.  IANA Considerations

   This document requires no IANA considerations.


6.  Acknowledgements

   Thanks to Sue Hares, Al Morton, Kevin Dubray, Ron Bonica, David Ward,
   Peter De Vriendt and the BMWG for their contributions to this work.


7.  References

7.1.  Normative References

   [Br91]   Bradner, S., "Benchmarking terminology for network
            interconnection devices", RFC 1242, July 1991.

   [Br97]   Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.

   [Br99]   Bradner, S. and J. McQuaid, "Benchmarking Methodology for
            Network Interconnect Devices", RFC 2544, March 1999.

   [Ca90]   Callon, R., "Use of OSI IS-IS for routing in TCP/IP and dual
            environments", RFC 1195, December 1990.

   [Co08]   Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF for
            IPv6", RFC 5340, July 2008.

   [Ho08]   Hopps, C., "Routing IPv6 with IS-IS", RFC 5308,
            October 2008.

   [Ko02]   Koodli, R. and R. Ravikanth, "One-way Loss Pattern Sample
            Metrics", RFC 3357, August 2002.

   [Ma98]   Mandeville, R., "Benchmarking Terminology for LAN Switching
            Devices", RFC 2285, February 1998.




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   [Mo06]   Morton, A., Ciavattone, L., Ramachandran, G., Shalunov, S.,
            and J. Perser, "Packet Reordering Metrics", RFC 4737,
            November 2006.

   [Mo98]   Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.

   [Po06]   Poretsky, S., Perser, J., Erramilli, S., and S. Khurana,
            "Terminology for Benchmarking Network-layer Traffic Control
            Mechanisms", RFC 4689, October 2006.

   [Po09a]  Poretsky, S., "Considerations for Benchmarking Link-State
            IGP Data Plane Route Convergence",
            draft-ietf-bmwg-igp-dataplane-conv-app-17 (work in
            progress), March 2009.

   [Po09m]  Poretsky, S. and B. Imhoff, "Benchmarking Methodology for
            Link-State IGP Data Plane Route Convergence",
            draft-ietf-bmwg-igp-dataplane-conv-meth-18 (work in
            progress), July 2009.

7.2.  Informative References

   [Ca01]   Casner, S., Alaettinoglu, C., and C. Kuan, "A Fine-Grained
            View of High Performance Networking", NANOG 22, June 2001.

   [Ci03]   Ciavattone, L., Morton, A., and G. Ramachandran,
            "Standardized Active Measurements on a Tier 1 IP Backbone",
            IEEE Communications Magazine p90-97, May 2003.


Authors' Addresses

   Scott Poretsky
   Allot Communications
   67 South Bedford Street, Suite 400
   Burlington, MA  01803
   USA

   Phone: + 1 508 309 2179
   Email: sporetsky@allot.com











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   Brent Imhoff
   Juniper Networks
   1194 North Mathilda Ave
   Sunnyvale, CA  94089
   USA

   Phone: + 1 314 378 2571
   Email: bimhoff@planetspork.com


   Kris Michielsen
   Cisco Systems
   6A De Kleetlaan
   Diegem, BRABANT  1831
   Belgium

   Email: kmichiel@cisco.com


































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