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Versions: (draft-litkowski-rtgwg-spf-uloop-pb-statement) 00 01 02 03 04

Routing Area Working Group                                  S. Litkowski
Internet-Draft                                   Orange Business Service
Intended status: Informational                               B. Decraene
Expires: November 24, 2017                                        Orange
                                                            M. Horneffer
                                                        Deutsche Telekom
                                                            May 23, 2017


   Link State protocols SPF trigger and delay algorithm impact on IGP
                              micro-loops
               draft-ietf-rtgwg-spf-uloop-pb-statement-04

Abstract

   A micro-loop is a packet forwarding loop that may occur transiently
   among two or more routers in a hop-by-hop packet forwarding paradigm.

   In this document, we are trying to analyze the impact of using
   different Link State IGP implementations in a single network in
   regards of micro-loops.  The analysis is focused on the SPF triggers
   and SPF delay algorithm.

Requirements Language

   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 [RFC2119].

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on November 24, 2017.






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Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Problem statement . . . . . . . . . . . . . . . . . . . . . .   3
   3.  SPF trigger strategies  . . . . . . . . . . . . . . . . . . .   5
   4.  SPF delay strategies  . . . . . . . . . . . . . . . . . . . .   5
     4.1.  Two steps SPF delay . . . . . . . . . . . . . . . . . . .   5
     4.2.  Exponential backoff . . . . . . . . . . . . . . . . . . .   6
   5.  Mixing strategies . . . . . . . . . . . . . . . . . . . . . .   7
   6.  Proposed work items . . . . . . . . . . . . . . . . . . . . .  11
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  13
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  13
     10.2.  Informative References . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   Link State IGP protocols are based on a topology database on which an
   SPF (Shortest Path First) algorithm like Dijkstra is implemented to
   find the optimal routing paths.

   Specifications like IS-IS ([RFC1195]) propose some optimizations of
   the route computation (See Appendix C.1) but not all the
   implementations are following those not mandatory optimizations.

   We will call "SPF trigger", the events that would lead to a new SPF
   computation based on the topology.

   Link State IGP protocols, like OSPF ([RFC2328]) and IS-IS
   ([RFC1195]), are using multiple timers to control the router behavior



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   in case of churn: SPF delay, PRC delay, LSP generation delay, LSP
   flooding delay, LSP retransmission interval...

   Some of those timers are standardized in protocol specification, some
   are not especially the SPF computation related timers.

   For non standardized timers, implementations are free to implement it
   in any way.  For some standardized timer, we can also see that rather
   than using static configurable values for such timer, implementations
   may offer dynamically adjusted timers to help controlling the churn.

   We will call "SPF delay", the timer that exists in most
   implementations that specifies the required delay before running SPF
   computation after a SPF trigger is received.

   A micro-loop is a packet forwarding loop that may occur transiently
   among two or more routers in a hop-by-hop packet forwarding paradigm.
   We can observe that these micro-loops are formed when two routers do
   not update their Forwarding Information Base (FIB) for a certain
   prefix at the same time.  The micro-loop phenomenon is described in
   [I-D.ietf-rtgwg-microloop-analysis].

   Some micro-loop mitigation techniques have been defined by IETF (e.g.
   [RFC6976], [I-D.ietf-rtgwg-uloop-delay]) but are not implemented due
   to complexity or are not providing a complete mitigation.

   In multi-vendor networks, using different implementations of a link
   state protocol may favor micro-loops creation during the convergence
   process due to discrepancies of timers.  Service Providers are
   already aware to use similar timers for all the network as a best
   practice, but sometimes it is not possible due to limitations of
   implementations.

   This document will present why it sounds important for service
   providers to have consistent implementations of Link State protocols
   across vendors.  We are particularly analyzing the impact of using
   different Link State IGP implementations in a single network in
   regards of micro-loops.  The analysis is focused on the SPF triggers
   and the SPF delay algorithm.

   This document is only stating the problem, and defining some work
   items but its not intended to provide a solution.

2.  Problem statement







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                                      A ---- B
                                      |      |
                                   10 |      | 10
                                      |      |
                                      C ---- D
                                      |  2   |
                                      Px     Px


          Figure 1 - Network topology suffering from micro-loops

   In Figure 1, A uses primarily the AC link to reach C.  When the AC
   link fails, the IGP convergence occurs.  If A converges before B, A
   will forward the traffic to C through B, but as B as not converged
   yet, B will loop back traffic to A, leading to a micro-loop.

   The micro-loop appears due to the asynchronous convergence of nodes
   in a network when an event occurs.

   Multiple factors (and combination of these factors) may increase the
   probability for a micro-loop to appear:

   o  the delay of failure notification: the more B is advised of the
      failure later than A, the more a micro-loop may have a chance to
      appear.

   o  the SPF delay: most of the implementations supports a delay for
      the SPF computation to try to catch as many events as possible.
      If A uses an SPF delay timer of x msec and B uses an SPF delay
      timer of y msec and x < y, B would start converging after A
      leading to a potential micro-loop.

   o  the SPF computation time: mostly a matter of CPU power and
      optimizations like incremental SPF.  If A computes its SPF faster
      than B, there is a chance for a micro-loop to appear.  CPUs are
      today faster enough to consider SPF computation time as
      negligeable (order of msec in a large network).

   o  the RIB and FIB prefix insertion speed or ordering: highly
      implementation dependant.

   This document will focus on analysis SPF delay (and associated
   triggers).








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3.  SPF trigger strategies

   Depending of the change advertised in LSP/LSA, the topology may be
   affected or not.  An implementation may avoid running the SPF
   computation (and may only run IP reachability computation instead) if
   the advertised change is not affecting topology.

   Different strategies exists to trigger the SPF computation:

   1.  An implementation may always run a full SPF whatever the change
       to process.

   2.  An implementation may run a full SPF only when required: e.g. if
       a link fails, a local node will run an SPF for its local LSP
       update.  If the LSP from the neighbor (describing the same
       failure) is received after SPF has started, the local node can
       decide that a new full SPF is not required as the topology has
       not change.

   3.  If the topology does not change, an implementation may only
       recompute the IP reachability.

   As pointed in Section 1, SPF optimizations are not mandatory in
   specifications, leading to multiple strategies to be implemented.

4.  SPF delay strategies

   Implementations of link state routing protocols use different
   strategies to delay the SPF computation.  We usually see the
   following:

   1.  Two steps delay.

   2.  Exponential backoff delay.

   Those behavior will be explained in the next sections.

4.1.  Two steps SPF delay

   The SPF delay is managed by four parameters:

   o  Rapid delay: amount of time to wait before running SPF.

   o  Rapid runs: amount of consecutive SPF runs that can use the rapid
      delay.  When the amount is exceeded the delay moves to the slow
      delay value .

   o  Slow delay: amount of time to wait before running SPF.



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   o  Wait time: amount of time to wait without events before going back
      to the rapid delay.

   Example: Rapid delay = 50msec, Rapid runs = 3, Slow delay = 1sec,
   Wait time = 2sec


   SPF delay time
       ^
       |
       |
   SD- |             x xx x
       |
       |
       |
   RD- |   x  x   x                    x
       |
       +---------------------------------> Events
           |  |   |  | || |            |
                           < wait time >

                   Figure 2 - Two steps delay algorithm

4.2.  Exponential backoff

   The algorithm has two modes: the fast mode and the backoff mode.  In
   the fast mode, the SPF delay is usually delayed by a very small
   amount of time (fast reaction).  When an SPF computation has run in
   the fast mode, the algorithm automatically moves to the backoff mode
   (a single SPF run is authorized in the fast mode).  In the backoff
   mode, the SPF delay is increasing exponentially at each run.  When
   the network becomes stable, the algorithm moves back to the fast
   mode.  The SPF delay is managed by four parameters:

   o  First delay: amount of time to wait before running SPF.  This
      delay is used only when SPF is in fast mode.

   o  Incremental delay: amount of time to wait before running SPF.
      This delay is used only when SPF is in backoff mode and increments
      exponentially at each SPF run.

   o  Maximum delay: maximum amount of time to wait before running SPF.

   o  Wait time: amount of time to wait without events before going back
      to the fast mode.

   Example: First delay = 50msec, Incremental delay = 50msec, Maximum
   delay = 1sec, Wait time = 2sec



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   SPF delay time
       ^
   MD- |               xx x
       |
       |
       |
       |
       |
       |             x
       |
       |
       |
       |          x
       |
   FD- |   x  x                        x
   ID  |
       +---------------------------------> Events
           |  |   |  | || |            |
                           < wait time >
          FM->BM -------------------->FM

                  Figure 3 - Exponential delay algorithm

5.  Mixing strategies


                              S ---- E
                              |      |
                           10 |      | 10
                              |      |
                              D ---- A
                              |  2
                              Px


                                 Figure 4

   In Figure 4, we consider a flow of packet from S to D.  We consider
   that S is using optimized SPF triggering (Full SPF is triggered only
   when necessary), and two steps SPF delay (rapid=150ms,rapid-runs=3,
   slow=1s).  As implementation of S is optimized, Partial Reachability
   Computation (PRC) is available.  We consider the same timers as SPF
   for delaying PRC.  We consider that E is using a SPF trigger strategy
   that always compute Full SPF and exponential backoff strategy for SPF
   delay (start=150ms, inc=150ms, max=1s)






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   We also consider the following sequence of events (note : the time
   scale does not intend to represent a real router time scale where
   jitters are introduced to all timers) :

   o  t0=0 ms: a prefix is declared down in the network.  We consider
      this event to happen at time=0.

   o  200ms: the prefix is declared as up.

   o  400ms: a prefix is declared down in the network.

   o  1000ms: S-D link fails.

   +--------+--------------------+------------------+------------------+
   |  Time  |   Network Event    | Router S events  | Router E events  |
   +--------+--------------------+------------------+------------------+
   |  t0=0  |    Prefix DOWN     |                  |                  |
   |  10ms  |                    | Schedule PRC (in | Schedule SPF (in |
   |        |                    |      150ms)      |      150ms)      |
   |        |                    |                  |                  |
   |        |                    |                  |                  |
   | 160ms  |                    |    PRC starts    |    SPF starts    |
   | 161ms  |                    |     PRC ends     |                  |
   | 162ms  |                    |  RIB/FIB starts  |                  |
   | 163ms  |                    |                  |     SPF ends     |
   | 164ms  |                    |                  |  RIB/FIB starts  |
   | 175ms  |                    |   RIB/FIB ends   |                  |
   | 178ms  |                    |                  |   RIB/FIB ends   |
   |        |                    |                  |                  |
   | 200ms  |     Prefix UP      |                  |                  |
   | 212ms  |                    | Schedule PRC (in |                  |
   |        |                    |      150ms)      |                  |
   | 214ms  |                    |                  | Schedule SPF (in |
   |        |                    |                  |      150ms)      |
   |        |                    |                  |                  |
   |        |                    |                  |                  |
   | 370ms  |                    |    PRC starts    |                  |
   | 372ms  |                    |     PRC ends     |                  |
   | 373ms  |                    |                  |    SPF starts    |
   | 373ms  |                    |  RIB/FIB starts  |                  |
   | 375ms  |                    |                  |     SPF ends     |
   | 376ms  |                    |                  |  RIB/FIB starts  |
   | 383ms  |                    |   RIB/FIB ends   |                  |
   | 385ms  |                    |                  |   RIB/FIB ends   |
   |        |                    |                  |                  |
   | 400ms  |    Prefix DOWN     |                  |                  |
   | 410ms  |                    | Schedule PRC (in | Schedule SPF (in |
   |        |                    |      300ms)      |      300ms)      |



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   |        |                    |                  |                  |
   |        |                    |                  |                  |
   |        |                    |                  |                  |
   |        |                    |                  |                  |
   | 710ms  |                    |    PRC starts    |    SPF starts    |
   | 711ms  |                    |     PRC ends     |                  |
   | 712ms  |                    |  RIB/FIB starts  |                  |
   | 713ms  |                    |                  |     SPF ends     |
   | 714ms  |                    |                  |  RIB/FIB starts  |
   | 716ms  |                    |   RIB/FIB ends   |   RIB/FIB ends   |
   |        |                    |                  |                  |
   | 1000ms |   S-D link DOWN    |                  |                  |
   | 1010ms |                    | Schedule SPF (in | Schedule SPF (in |
   |        |                    |      150ms)      |      600ms)      |
   |        |                    |                  |                  |
   |        |                    |                  |                  |
   | 1160ms |                    |    SPF starts    |                  |
   | 1161ms |                    |     SPF ends     |                  |
   | 1162ms |   Micro-loop may   |  RIB/FIB starts  |                  |
   |        |  start from here   |                  |                  |
   | 1175ms |                    |   RIB/FIB ends   |                  |
   |        |                    |                  |                  |
   |        |                    |                  |                  |
   |        |                    |                  |                  |
   |        |                    |                  |                  |
   | 1612ms |                    |                  |    SPF starts    |
   | 1615ms |                    |                  |     SPF ends     |
   | 1616ms |                    |                  |  RIB/FIB starts  |
   | 1626ms |  Micro-loop ends   |                  |   RIB/FIB ends   |
   +--------+--------------------+------------------+------------------+

                    Route computation event time scale

   In the table above, we can see that due to discrepancies in the SPF
   management, after multiple events (of a different type), the values
   of the SPF delay are completely misaligned between nodes leading to
   long micro-loops creation.

   The same issue can also appear with only single type of events as
   displayed below:

   +--------+--------------------+------------------+------------------+
   |  Time  |   Network Event    | Router S events  | Router E events  |
   +--------+--------------------+------------------+------------------+
   |  t0=0  |     Link DOWN      |                  |                  |
   |  10ms  |                    | Schedule SPF (in | Schedule SPF (in |
   |        |                    |      150ms)      |      150ms)      |
   |        |                    |                  |                  |



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   |        |                    |                  |                  |
   | 160ms  |                    |    SPF starts    |    SPF starts    |
   | 161ms  |                    |     SPF ends     |                  |
   | 162ms  |                    |  RIB/FIB starts  |                  |
   | 163ms  |                    |                  |     SPF ends     |
   | 164ms  |                    |                  |  RIB/FIB starts  |
   | 175ms  |                    |   RIB/FIB ends   |                  |
   | 178ms  |                    |                  |   RIB/FIB ends   |
   |        |                    |                  |                  |
   | 200ms  |     Link DOWN      |                  |                  |
   | 212ms  |                    | Schedule SPF (in |                  |
   |        |                    |      150ms)      |                  |
   | 214ms  |                    |                  | Schedule SPF (in |
   |        |                    |                  |      150ms)      |
   |        |                    |                  |                  |
   |        |                    |                  |                  |
   | 370ms  |                    |    SPF starts    |                  |
   | 372ms  |                    |     SPF ends     |                  |
   | 373ms  |                    |                  |    SPF starts    |
   | 373ms  |                    |  RIB/FIB starts  |                  |
   | 375ms  |                    |                  |     SPF ends     |
   | 376ms  |                    |                  |  RIB/FIB starts  |
   | 383ms  |                    |   RIB/FIB ends   |                  |
   | 385ms  |                    |                  |   RIB/FIB ends   |
   |        |                    |                  |                  |
   | 400ms  |     Link DOWN      |                  |                  |
   | 410ms  |                    | Schedule SPF (in | Schedule SPF (in |
   |        |                    |      150ms)      |      300ms)      |
   |        |                    |                  |                  |
   |        |                    |                  |                  |
   | 560ms  |                    |    SPF starts    |                  |
   | 561ms  |                    |     SPF ends     |                  |
   | 562ms  |   Micro-loop may   |  RIB/FIB starts  |                  |
   |        |  start from here   |                  |                  |
   | 568ms  |                    |   RIB/FIB ends   |                  |
   |        |                    |                  |                  |
   |        |                    |                  |                  |
   | 710ms  |                    |                  |    SPF starts    |
   | 713ms  |                    |                  |     SPF ends     |
   | 714ms  |                    |                  |  RIB/FIB starts  |
   | 716ms  |  Micro-loop ends   |                  |   RIB/FIB ends   |
   |        |                    |                  |                  |
   | 1000ms |     Link DOWN      |                  |                  |
   | 1010ms |                    | Schedule SPF (in | Schedule SPF (in |
   |        |                    |       1s)        |      600ms)      |
   |        |                    |                  |                  |
   |        |                    |                  |                  |
   |        |                    |                  |                  |



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   |        |                    |                  |                  |
   | 1612ms |                    |                  |    SPF starts    |
   | 1615ms |                    |                  |     SPF ends     |
   | 1616ms |   Micro-loop may   |                  |  RIB/FIB starts  |
   |        |  start from here   |                  |                  |
   | 1626ms |                    |                  |   RIB/FIB ends   |
   |        |                    |                  |                  |
   |        |                    |                  |                  |
   |        |                    |                  |                  |
   |        |                    |                  |                  |
   | 2012ms |                    |    SPF starts    |                  |
   | 2014ms |                    |     SPF ends     |                  |
   | 2015ms |                    |  RIB/FIB starts  |                  |
   | 2025ms |  Micro-loop ends   |   RIB/FIB ends   |                  |
   |        |                    |                  |                  |
   |        |                    |                  |                  |
   +--------+--------------------+------------------+------------------+

                    Route computation event time scale

6.  Proposed work items

   In order to enhance the current Link State IGP behavior, authors
   would encourage working on standardization of some behaviours.

   Authors are proposing the following work items :

   o  Standardize SPF trigger strategy.

   o  Standardize computation timer scope: single timer for all
      computation operations, separated timers ...

   o  Standardize "slowdown" timer algorithm including its association
      to a particular timer: authors of this document does not presume
      that the same algorithm must be used for all timers.

   Using the same event sequence as in figure 2, we may expect fewer
   and/or shorter micro-loops using standardized implementations.

   +--------+--------------------+------------------+------------------+
   |  Time  |   Network Event    | Router S events  | Router E events  |
   +--------+--------------------+------------------+------------------+
   |  t0=0  |    Prefix DOWN     |                  |                  |
   |  10ms  |                    | Schedule PRC (in | Schedule SPF (in |
   |        |                    |      150ms)      |      150ms)      |
   |        |                    |                  |                  |
   |        |                    |                  |                  |
   | 160ms  |                    |    PRC starts    |    PRC starts    |



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   | 161ms  |                    |     PRC ends     |                  |
   | 162ms  |                    |  RIB/FIB starts  |     PRC ends     |
   | 163ms  |                    |                  |  RIB/FIB starts  |
   | 175ms  |                    |   RIB/FIB ends   |                  |
   | 176ms  |                    |                  |   RIB/FIB ends   |
   |        |                    |                  |                  |
   | 200ms  |     Prefix UP      |                  |                  |
   | 212ms  |                    | Schedule PRC (in |                  |
   |        |                    |      150ms)      |                  |
   | 213ms  |                    |                  | Schedule PRC (in |
   |        |                    |                  |      150ms)      |
   |        |                    |                  |                  |
   |        |                    |                  |                  |
   | 370ms  |                    |    PRC starts    |    PRC starts    |
   | 372ms  |                    |     PRC ends     |                  |
   | 373ms  |                    |  RIB/FIB starts  |     PRC ends     |
   | 374ms  |                    |                  |  RIB/FIB starts  |
   | 383ms  |                    |   RIB/FIB ends   |                  |
   | 384ms  |                    |                  |   RIB/FIB ends   |
   |        |                    |                  |                  |
   | 400ms  |    Prefix DOWN     |                  |                  |
   | 410ms  |                    | Schedule PRC (in | Schedule PRC (in |
   |        |                    |      300ms)      |      300ms)      |
   |        |                    |                  |                  |
   |        |                    |                  |                  |
   |        |                    |                  |                  |
   |        |                    |                  |                  |
   | 710ms  |                    |    PRC starts    |    PRC starts    |
   | 711ms  |                    |     PRC ends     |     PRC ends     |
   | 712ms  |                    |  RIB/FIB starts  |                  |
   | 713ms  |                    |                  |  RIB/FIB starts  |
   | 716ms  |                    |   RIB/FIB ends   |   RIB/FIB ends   |
   |        |                    |                  |                  |
   | 1000ms |   S-D link DOWN    |                  |                  |
   | 1010ms |                    | Schedule SPF (in | Schedule SPF (in |
   |        |                    |      150ms)      |      150ms)      |
   |        |                    |                  |                  |
   |        |                    |                  |                  |
   | 1160ms |                    |    SPF starts    |                  |
   | 1161ms |                    |     SPF ends     |    SPF starts    |
   | 1162ms |   Micro-loop may   |  RIB/FIB starts  |     SPF ends     |
   |        |  start from here   |                  |                  |
   | 1163ms |                    |                  |  RIB/FIB starts  |
   | 1175ms |                    |   RIB/FIB ends   |                  |
   | 1177ms |  Micro-loop ends   |                  |   RIB/FIB ends   |
   +--------+--------------------+------------------+------------------+

                    Route computation event time scale



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   As displayed above, there could be some other parameters like router
   computation power, flooding timers that may also influence micro-
   loops.  In Figure 4, we consider E to be a bit slower than S, leading
   to micro-loop creation.  Despite of this, we expect that by aligning
   implementations at least on SPF trigger and SPF delay, service
   provider may reduce the number and the duration of micro-loops.

7.  Security Considerations

   This document does not introduce any security consideration.

8.  Acknowledgements

   Authors would like to thank Mike Shand for his useful comments.

9.  IANA Considerations

   This document has no action for IANA.

10.  References

10.1.  Normative References

   [RFC1195]  Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
              dual environments", RFC 1195, DOI 10.17487/RFC1195,
              December 1990, <http://www.rfc-editor.org/info/rfc1195>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC2328]  Moy, J., "OSPF Version 2", STD 54, RFC 2328,
              DOI 10.17487/RFC2328, April 1998,
              <http://www.rfc-editor.org/info/rfc2328>.

10.2.  Informative References

   [I-D.ietf-rtgwg-microloop-analysis]
              Zinin, A., "Analysis and Minimization of Microloops in
              Link-state Routing Protocols", draft-ietf-rtgwg-microloop-
              analysis-01 (work in progress), October 2005.

   [I-D.ietf-rtgwg-uloop-delay]
              Litkowski, S., Decraene, B., Filsfils, C., and P.
              Francois, "Micro-loop prevention by introducing a local
              convergence delay", draft-ietf-rtgwg-uloop-delay-04 (work
              in progress), April 2017.



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Internet-Draft                spf-microloop                     May 2017


   [RFC6976]  Shand, M., Bryant, S., Previdi, S., Filsfils, C.,
              Francois, P., and O. Bonaventure, "Framework for Loop-Free
              Convergence Using the Ordered Forwarding Information Base
              (oFIB) Approach", RFC 6976, DOI 10.17487/RFC6976, July
              2013, <http://www.rfc-editor.org/info/rfc6976>.

Authors' Addresses

   Stephane Litkowski
   Orange Business Service

   Email: stephane.litkowski@orange.com


   Bruno Decraene
   Orange

   Email: bruno.decraene@orange.com


   Martin Horneffer
   Deutsche Telekom

   Email: martin.horneffer@telekom.de



























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