Benchmarking Methodology WG                                 Sarah Banks
Internet Draft                                           VSS Monitoring
Intended status: Informational                        Fernando Calabria
Expires: April 7, 2015                                            Cisco
                                                            Gery Czirjak
                                                           Ramdas Machat
                                                         October 8, 2014

                       ISSU Benchmarking Methodology


   Modern forwarding devices attempt to minimize any control and data
   plane disruptions while performing planned software changes, by
   implementing a technique commonly known as an In Service Software
   Upgrade (ISSU).

   This document specifies a set of common methodologies and procedures
   designed to characterize the overall behavior of a Device Under Test
   (DUT), subject to an ISSU event.

Status of this Memo

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Table of Contents

   1. Introduction...................................................3
   2. Conventions used in this document..............................4
   3. Generic ISSU Process, phased approach..........................5
      3.1. Software Download.........................................6
      3.2. Software Staging..........................................6
      3.3. Upgrade Run...............................................7
      3.4. Upgrade Acceptance........................................7
   4. Test Methodology...............................................8
      4.1. Test Topology.............................................8
      4.2. Load Model................................................9
   5. ISSU Test Methodology.........................................10
      5.1. Pre-ISSU recommended verifications.......................10

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      5.2. Software Staging.........................................10
      5.3. Upgrade Run..............................................11
      5.4. Post ISSU verifications..................................12
      5.5. ISSU under negative stimuli..............................13
   6. ISSU Abort and Rollback.......................................14
   7. Final Report - Data Presentation - Analysis...................14
      7.1. Data collection considerations...........................16
   8. Security Considerations.......................................16
   9. IANA Considerations...........................................17
   10. Conclusions..................................................17
   11. References...................................................17
      11.1. Normative References....................................17
      11.2. Informative References..................................17
   12. Acknowledgments..............................................17

  1. Introduction

   As required by most Service Provider (SP) network operators, ISSU
   functionality has been implemented by modern forwarding devices to
   upgrade or downgrade from one software version to another with a goal
   of eliminating the downtime of the router and/or the outage of
   service. However, It is noted that while most operators expect that
   whiledesire such behavior as a elimination is the goal, minimal
   downtime and/or degradation of service is often expected.

   The ISSU operation may apply in terms of an atomic version change of
   the entire system software or it may be applied in a more modular
   sense such as for a patch or maintenance upgrade. The procedure
   described herein may be used to verify either approach, as may be
   supported by the vendor hardware and software.

   In support of this document, a set of expectations for an ISSU
   operation can be summarized as follows:

      - The software is successfully migrated, from one version to a
   successive version or vice versa.

      - There are no control plane interruptions throughout the process.
   That is, the upgrade/downgrade could be accomplished while the device
   remains "in service". It is noted however, that most service
   providers will still undertake such actions in a maintenance window
   (even in redundant environments) to minimize any risk.

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      - Interruptions to the forwarding plane are expected to be minimal
   to none.

      - The total time to accomplish the upgrade is minimized, again to
   reduce potential network outage exposure (e.g. an external failure
   event might impact the network as it operates with reduced

   This document provides a set of procedures to characterize a given
   forwarding device's ISSU behavior quantitatively, from the
   perspective of meeting the above expectations.

   Different hardware configurations may be expected to be benchmarked,
   but a typical configuration for a forwarding device that supports
   ISSU consists of at least one pair of Routing Processors (RP's) that
   operate in a redundant fashion, and single or multiple Forwarding
   Engines (Line Cards) that may or may not be redundant, as well as
   fabric cards or other components as applicable. However, this does
   not preclude the possibility that a device in question can perform
   ISSU functions through the operation of independent process
   components, which may be upgraded without impact to the overall
   operation of the device. As an example, perhaps the software module
   involved in SNMP functions can be upgraded without impacting other

   The concept of a multi-chassis deployment may also be characterized
   by the current set of proposed methodologies, but the implementation
   specific details (i.e. process placement and others) are beyond the
   scope of the current document.

   Since most modern forwarding devices, where ISSU would be applicable,
   do consist of redundant RP's and hardware-separated control plane and
   data plane functionality, this document will focus on methodologies
   which would be directly applicable to those platforms. It is
   anticipated that the concepts and approaches described herein may be
   readily extended to accommodate other device architectures as well.

  2. Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC-2119 [RFC2119].

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   In this document, these words will appear with that interpretation
   only when in ALL CAPS. Lower case uses of these words are not to be
   interpreted as carrying RFC-2119 significance.

   In this document, the characters ">>" preceding an indented line(s)
   indicates a compliance requirement statement using the key words
   listed above. This convention aids reviewers in quickly identifying
   or finding the explicit compliance requirements of this RFC.

  3. Generic ISSU Process, phased approach

   ISSU may be viewed as the behavior of a device when exposed to a
   planned change in its software functionality. This may mean changes
   to the core operating system, separate processes or daemons or even
   of firmware logic in programmable hardware devices (e.g. CPLD/FPGA).
   The goal of an ISSU implementation is to permit such actions with
   minimal or no disruption to the primary operation of the device in

   ISSU may be user initiated through direct interaction with the device
   or activated through some automated process on a management system or
   even on the device itself. For the purposes of this document, we will
   focus on the model where the ISSU action is initiated by direct user

   The ISSU process can be viewed as a series of different phases or
   activities, as defined below. For each of these phases, the test
   operator MUST record the outcome as well as any relevant observations
   (defined further in the present document). Note that, a given vendor
   implementation may or may not permit the abortion of the in-progress
   ISSU at particular stages. There may also be certain restrictions as
   to ISSU availability given certain functional configurations (for
   example, ISSU in the presence of Bidirectional Failure Detection
   (BFD) [RFC 5880] may not be supported. It is incumbent upon the test
   operator to ensure that the DUT is appropriately configured to
   provide the appropriate test environment as needed. As with any
   properly orchestrated test effort, the test plan document should
   reflect these and other relevant details and SHOULD be written with
   close attention to the expected production-operating environment. The
   combined analysis of the results of each phase will characterize the
   overall ISSU process with the main goal of being able to identify and
   quantify any disruption in service (from the data and control plane
   perspective) allowing operators to plan their maintenance activities
   with greater precision.

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   The generic ISSU process can be viewed as a series of the following

3.1. Software Download

   In this first phase, the requested software package may be downloaded
   to the router and is typically stored onto a device. The downloading
   of software may be performed automatically by the device as part of
   the upgrade process, or it may be initiated separately. Such
   separation allows an administrator to download the new code inside or
   outside of a maintenance window; it is anticipated that downloading
   new code and saving it to disk on the router will not impact
   operations. In the case where the software can be downloaded outside
   of the actual upgrade process, the administrator SHOULD do so;
   downloading software can skew timing results based on factors that
   are often not comparative in nature. Internal compatibility
   verification may be performed by the software running on the DUT, to
   verify the checksum of the files downloaded as well as any other
   pertinent checks. Depending upon vendor implementation, these
   mechanisms may extend to include verification that the downloaded
   module(s) meet a set of identified pre-requisites such as hardware or
   firmware compatibility or minimum software requirements. Where such
   mechanisms are made available by the product, they should be
   verified, by the tester, with the perspective of avoiding operational
   issues in production. Verification should include both positive
   verification (ensuring that an ISSU action should be permitted) as
   well as negative tests (creation of scenarios where the verification
   mechanisms would report exceptions).

3.2. Software Staging

   In this second phase, the requested software package is loaded into
   the pertinent components of a given forwarding device (typically the
   RP in standby state).  Internal compatibility verification may be
   performed by the software running on the DUT, as part of the upgrade
   process itself, to verify the checksum of the files downloaded as
   well as any other pertinent checks. Depending upon vendor
   implementation, these mechanisms may extend to include verification
   that the downloaded module(s) meet a set of identified pre-requisites
   such as hardware or firmware compatibility or minimum software
   requirements. Where such mechanisms are made available by the
   product, they should be verified, by the tester, with the perspective
   of avoiding operational issues in production. In this case, the

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   execution of these checks is within scope of the upgrade time, and
   SHOULD be included in the testing results. Once the new software is
   downloaded to the pertinent components of the DUT, the upgrade begins
   and the DUT begins to prepare itself for upgrade. Depending on the
   vendor implementation, it is expected that redundant hardware pieces
   within the DUT are upgraded, including the backup or secondary RP.

3.3. Upgrade Run

   In this phase, a switchover of RPs may take place, where one RP is
   now upgraded with the new version of software. More importantly, the
   "Upgrade Run" phase is where the internal changes made to information
   and state stored on the router, on disk and in memory, are either
   migrated to the "new" version of code, or transformed/rebuilt to meet
   the standards of the new version of code, and pushed onto the
   appropriate pieces of hardware. It is within this phase that any
   outage(s) on the control or forwarding plane MAY be expected to be

   This is the critical phase of the ISSU, where the control plane
   should not be impacted and any interruptions to the forwarding plane
   should be minimal to none.

   For some implementations, the above two steps may be concatenated
   into one monolithic operation. In such case, the calculation of the
   respective ISSU time intervals may need to be adapted accordingly. If
   any control or data plane interruptions occur, it is expected to be
   observed and recorded within this stage.

3.4. Upgrade Acceptance

   In this phase, the new version of software MUST be running in all the
   physical nodes of the logical forwarding device. (RP's and LC's as
   applicable). At this point, configuration control is returned to the
   operator and normal device operation i.e. outside of ISSU-oriented
   operation, is resumed.

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  4. Test Methodology

   As stated by
   (when it becomes an RFC) The Test Topology Setup must be part of an
   ITE (Isolated Test Environment)

   The reporting of results MUST take into account the repeatability
   considerations from Section 4 of [RFC2544].  It is RECOMMENDED to
   perform multiple trials and report average results. The results are
   reported in a simple statement including the measured frame loss and
   ISSU impact times.

4.1. Test Topology

   The hardware configuration of the DUT (Device Under test) MUST be
   identical to the one expected to be or currently deployed in
   production in order for the benchmark to have relevance. This would
   include the number of RP's, hardware version, memory and initial
   software release, any common chassis components, such as fabric
   hardware in the case of a fabric-switching platform and the specific
   LC's (version, memory, interfaces type, rate etc.)

   For the Control and Data plane, differing configuration approaches
   MAY be utilized. The recommended approach relies on "mimicking" the
   existing production data and control plane information, in order to
   emulate all the necessary Layer1 through Layer3 and, if appropriate,
   upper layer characteristics of the network, as well as end to end
   traffic/communication pairs. In other words, design a representative
   load model of the production environment and deploy a collapsed
   topology utilizing test tools and/or external devices, where the DUT
   will be tested. Note that, the negative impact of ISSU operations is
   likely to impact scaled, dynamic topologies to a greater extent than
   simpler, static environments. As such, this methodology is advised
   for most test scenarios.

   The second, more simplistic approach is to deploy an ITE "Isolated
   Testing Environment" as described in some of the existing standards
   for benchmarking methodologies (e.g. RFC2544/RFC6815) in which end-
   points are "directly" connected to the DUT. In this manner control
   plane information is kept to a minimum (only connected interfaces)
   and only a basic data plane of sources and destinations is applied.
   If this methodology is selected, care must be taken to understand
   that the systemic behavior of the ITE may not be identical to that
   experienced by a device in a production network role. That is,
   control plane validation may be minimal to none if this methodology

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   is employed. It may be possible to perform some degree of data plane
   validation with this approach.

4.2. Load Model

   In consideration of the defined test topology, a load model must be
   developed to exercise the DUT while the ISSU event is introduced.
   This applied load should be defined in such a manner as to provide a
   granular, repeatable verification of the ISSU impact on transit
   traffic. Sufficient traffic load (rate) should be applied to permit
   timing extrapolations at a minimum granularity of 100 milliseconds
   e.g. 100Mbps for a 10Gbps interface. The use of steady traffic
   streams rather than bursty loads is preferred to simplify analysis.
   The traffic should be patterned to provide a broad range of source
   and destination pairs, which resolve to a variety of FIB (forwarding
   information base) prefix lengths. If the production network
   environment includes multicast traffic or VPN's (L2, L3 or IPSec) it
   is critical to include these in the model.

   For mixed protocol environments (e.g. IPv4 and IPv6), frames SHOULD
   be distributed between the different protocols.  The distribution
   SHOULD approximate the network conditions of deployment.  In all
   cases, the details of the mixed protocol distribution MUST be
   included in the reporting.

   The feature, protocol timing and other relevant configurations
   should be matched to the expected production environment. Deviations
   from the production templates may be deemed necessary by the test
   operator (for example, certain features may not support ISSU or the
   test bed may not be able to accommodate such). However, the impact
   of any such divergence should be clearly understood and the
   differences MUST be recorded in the results documentation.

   It is recommended that an NMS system be deployed, preferably similar
   to that utilized in production. This will allow for monitoring of
   the DUT while it is being tested both in terms of supporting the
   system resource impact analysis as well as from the perspective of
   detecting interference with non-transit (management) traffic as a
   result of the ISSU operation. Additionally, a DUT management session
   other than snmp-based, typical of usage in production, should be
   established to the DUT and monitored for any disruption.

   It is suggested that the actual test exercise be managed utilizing
   direct console access to the DUT, if at all possible to avoid the

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   possibility that a network interruption impairs execution of the
   test exercise.

   All in all, the load model should attempt to simulate the production
   network environment to the greatest extent possible in order to
   maximize the applicability of the results generated.

  5. ISSU Test Methodology

   As previously described, for the purposes of this test document, the
   ISSU process is divided into three main phases. The following
   methodology assumes that a suitable test topology has been
   constructed per section 4. A description of the methodology to be
   applied for each of the above phases follows:

5.1. Pre-ISSU recommended verifications

     Verify that enough hardware and software resources are available to
     complete the Load operation (enough disk space).

     Verify that the redundancy states between RPs and other nodes are
     as expected (e.g. redundancy on, RP's synchronized).

     Verify that the device, if running NSR capable routing protocols,
     is in a "ready" state; that is, that the sync between RPs is
     complete and the system is ready for failover, if necessary.

     Gather a configuration snapshot of the device and all of its
     applicable components.

     Verify that the node is operating in a "steady" state (that is, no
     critical or maintenance function is being currently performed).

     Note any other operational characteristics that the tester may deem
     applicable to the specific implementation deployed.

5.2. Software Staging

     Establish all relevant protocol adjacencies and stabilize routing
     within the test topology. In particular, ensure that the scaled

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     levels of the dynamic protocols are dimensioned as specified by the
     test topology plan.

     Clear relevant logs and interface counters to simplify analysis. If
     possible, set logging timestamps to a highly granular mode. If the
     topology includes management systems, ensure that the appropriate
     polling levels have been applied, sessions established and that the
     responses are per expectation.

     Apply the traffic loads as specified in the load model previously
     developed for this exercise.

     Document an operational baseline for the test bed with relevant
     data supporting the above steps (include all relevant load
     characteristics of interest in the topology e.g. routing load,
     traffic volumes, memory and CPU utilization)

     Note the start time (T0) and begin the code change process
     utilizing the appropriate mechanisms as expected to be used in
     production (e.g. active download with TFTP/FTP/SCP/etc. or direct
     install from local or external storage facility). In order to
     ensure that ISSU process timings are not skewed by the lack of a
     network wide synchronization source, the use of a network NTP
     source is encouraged.

     Take note of any logging information and command line interface
     (CLI) prompts as needed (this detail will be vendor-specific).
     Respond to any DUT prompts in a timely manner.

     Monitor the DUT for the reload of secondary RP to the new software
     level. Once the secondary has stabilized on the new code, note the
     completion time. The duration of these steps will be logged as

     Review system logs for any anomalies, check that relevant dynamic
     protocols have remained stable and note traffic loss if any. Verify
     that deployed management systems have not identified any unexpected

5.3. Upgrade Run

     The following assumes that the software load step and upgrade step
     are discretely controllable. If not, maintain the afore-mentioned
     timer and monitor for completion of the ISSU as described below.

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     Note the start time and initiate the actual upgrade procedure.
     Monitor the operation of the secondary route processor while it
     initializes with the new software and assumes mastership of the

     At this point, pay particular attention to any indications of
     control plane disruption, traffic impact or other anomalous
     behavior. Once the DUT has converged upon the new code and returned
     to normal operation note the completion time and log the duration
     of this step as T2.

     Review the syslog data in the DUT and neighboring devices for any
     behavior, which would be disruptive in a production environment
     (linecard reloads, control plane flaps etc.). Examine the traffic
     generators for any indication of traffic loss over this interval.
     If the Test Set reported any traffic loss, note the number of
     frames lost as "TP_frames". If the test set also provides outage
     duration, note this as TP_time (alternatively this may be
     calculated as TP/offered pps (packets per second) load).

     Verify the DUT status observations as per any NMS systems managing
     the DUT and its neighboring devices. Document the observed CPU and
     memory statistics both during the ISSU upgrade event and after and
     ensure that memory and CPU have returned to an expected (previously
     baselined) level.

5.4. Post ISSU verifications

     The following describes a set of post-ISSU verification tasks that
     are not directly part of the ISSU process, but are recommended for
     execution in order to validate a successful upgrade:

     . Configuration delta analysis

          o Examine the post-ISSU configurations to determine if any
          changes have occurred either through process error or due to
          differences in the implementation of the upgraded code.

     . Exhaustive control plane analysis

          o Review the details of the RIB and FIB to assess whether any
          unexpected changes have been introduced in the forwarding

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     . Verify that both RPs are up and that the redundancy mechanism for
     the control plane is enabled and fully synchronized.

     . Verify that no control plane (protocol) events or flaps were

     . Verify that no L1 and or L2 interface flaps were observed.

     . Document the hitless operation or presence of an outage based
     upon the counter values provided by the Test Set.

5.5. ISSU under negative stimuli

     As an OPTIONAL Test Case, the operator may want to perform an ISSU
     test while the DUT is under stress by introducing route churn to
     any or all of the involved phases of the ISSU process.

     One approach relies on the operator to gather statistical
     information from the production environment and determine a
     specific number of routes to flap every 'fixed' or 'variable'
     interval. Alternatively, the operator may wish to simply pre-select
     a fixed number of prefixes to flap. As an example, an operator may
     decide to flap 1% of all the BGP routes every minute and restore
     them 1 minute afterwards. The tester may wish to apply this
     negative stimulus throughout the entire ISSU process or most
     importantly, during the run phase.

     It is important to ensure that these routes, which are introduced
     solely for stress proposes, MUST not overlap the ones (per the Load
     Model) specifically leveraged to calculate the TP (recorded
     outage). Furthermore, there SHOULD NOT be 'operator induced'
     control plane - protocol adjacency flaps for the duration of the
     test process as it may adversely affect the characterization of the
     entire test exercise. For example, triggering IGP adjacency events
     may force re-computation of underlying routing tables with
     attendant impact to the perceived ISSU timings. While not
     recommended, if such trigger events are desired by the test
     operator, care should be taken to avoid the introduction of
     unexpected anomalies within the test harness.

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  6. ISSU Abort and Rollback

   Where a vendor provides such support, the ISSU process could be
   aborted for any reason by the operator. However, the end results and
   behavior may depend on the specific phase where the process was
   aborted. While this is implementation dependent, as a general
   recommendation, if the process is aborted during the "Software
   Download" or "Software Staging" phases, no impact to service or
   device functionality should be observed. In contrast, if the process
   is aborted during the "Upgrade Run" or "Upgrade Accept" phases, the
   system may reload and revert back to the previous software release
   and as such, this operation may be service affecting.

   Where vendor support is available, the abort/rollback functionality
   should be verified and the impact, if any, quantified generally
   following the procedures provided above.

  7. Final Report - Data Presentation - Analysis

   All ISSU impact results are summarized in a simple statement
   describing the "ISSU Disruption Impact" including the measured frame
   loss and impact time, where impact time is defined as the time frame
   determined per the TP reported outage. These are considered to be
   the primary data points of interest.
   However, the entire ISSU operational impact should also be
   considered in support of planning for maintenance and as such,
   additional reporting points are included.

        Software download/secondary update        T1
        Upgrade/Run                               T2
        ISSU Traffic Disruption (Frame Loss)      TP_frames
        ISSU Traffic Impact Time (milliseconds)   TP Time

        ISSU Housekeeping Interval               T3
       (Time for both RP's up on new code
         and fully synced - Redundancy restored)

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        Total ISSU Maintenance Window            T4 (sum of T1+T2+T3)

   The results reporting MUST provide the following information:

       . DUT hardware and software detail
       . Test Topology definition and diagram (especially as related
       to the ISSU operation)
       . Load Model description including protocol mixes and any
       divergence from the production environment
       . Time Results as per above
       . Anomalies Observed during ISSU
       . Anomalies Observed in post-ISSU analysis

   It is RECOMMENDED that the following parameters be reported in these

          Parameter                Units or Examples

          Traffic Load             Frames per second and bits per

          Disruption (average)     Frames

          Impact Time (average)    Milliseconds

          Number of trials         Integer count

          Protocols                IPv4, IPv6, MPLS, etc.

          Frame Size               Octets

          Port Media               Ethernet, Gigabit Ethernet (GbE),
                                   Packet over SONET (POS), etc.

          Port Speed               10 Gbps, 1 Gbps, 100 Mbps, etc.

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          Interface Encap.         Ethernet, Ethernet VLAN,
                                   PPP, High-Level Data Link Control

    Number of Prefixes
    flapped (ON Interval)
    (Optional)                 # of prefixes  / Time (minutes)

    Number of Prefixes
    flapped (OFF Interval)      # of prefixes  / Time (minutes)

   Document any configuration deltas, which are observed after the ISSU
   upgrade has taken effect. Note differences, which are driven by
   changes in the patch or release level as well as items, which are
   aberrant changes due to software faults. In either of these cases,
   any unexpected behavioral changes should be analyzed and a
   determination made as to the impact of the change (be it functional
   variances or operational impacts to existing scripts or management

7.1. Data collection considerations

   When a DUT is undergoing an ISSU operation, it's worth noting that
   the DUT's data collection and reporting of data, such as counters,
   interface statistics, log messages, etc., might not be accurate. As
   such, one SHOULD NOT rely on the DUTs data collection methods, but
   rather, SHOULD use the test tools and equipment to collect data used
   for reporting in Section 7. Care and consideration should be paid in
   testing or adding new test cases, such that the desired data can be
   collected from the test tools themselves, or other external
   equipment, outside of the DUT itself.

  8. Security Considerations

   None at this time.

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  9. IANA Considerations

   None at this time.

  10. Conclusions

   None at this time.

  11. References

11.1. Normative References

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

   [2]   Crocker, D. and Overell, P.(Editors), "Augmented BNF for Syntax
         Specifications: ABNF", RFC 2234, Internet Mail Consortium and
         Demon Internet Ltd., November 1997.

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2234] Crocker, D. and Overell, P.(Editors), "Augmented BNF for
             Syntax Specifications: ABNF", RFC 2234, Internet Mail
             Consortium and Demon Internet Ltd., November 1997.

11.2. Informative References

   [3]   Faber, T., Touch, J. and W. Yue, "The TIME-WAIT state in TCP
         and Its Effect on Busy Servers", Proc. Infocom 1999 pp. 1573-

   [Fab1999] Faber, T., Touch, J. and W. Yue, "The TIME-WAIT state in
             TCP and Its Effect on Busy Servers", Proc. Infocom 1999 pp.

    [RFC2234]Crocker, D. and Overell, P.(Editors), "Augmented BNF for
             Syntax Specifications: ABNF", RFC 2234, Internet Mail
             Consortium and Demon Internet Ltd., November 1997.

  12. Acknowledgments

   The authors wish to thanks Vibin Thomas for his valued review and

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   Copyright (c) 2014 IETF Trust and the persons identified as authors
   of the code. All rights reserved.

   Redistribution and use in source and binary forms, with or without
   modification, are permitted provided that the following conditions
   are met:

   o  Redistributions of source code must retain the above copyright
      notice, this list of conditions and the following disclaimer.

   o  Redistributions in binary form must reproduce the above copyright
      notice, this list of conditions and the following disclaimer in
      the documentation and/or other materials provided with the

   o  Neither the name of Internet Society, IETF or IETF Trust, nor the
      names of specific contributors, may be used to endorse or promote
      products derived from this software without specific prior written


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Internet-Draft     <Benchmarking Software Upgrade>         October 2014

   Authors' Addresses

   Sarah Banks
   VSS Monitoring

   Fernando Calabria
   Cisco Systems

   Gery Czirjak
   Juniper Networks

   Ramdas Machat
   Juniper Networks

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