[Docs] [txt|pdf|xml|html] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: (draft-litkowski-rtgwg-spf-uloop-pb-statement) 00 01 02 03 04 05 06 07

Routing Area Working Group                                  S. Litkowski
Internet-Draft                                   Orange Business Service
Intended status: Informational                               B. Decraene
Expires: November 24, 2018                                        Orange
                                                            M. Horneffer
                                                        Deutsche Telekom
                                                            May 23, 2018


   Link State protocols SPF trigger and delay algorithm impact on IGP
                              micro-loops
               draft-ietf-rtgwg-spf-uloop-pb-statement-07

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, with
   respect to micro-loops.  The analysis is focused on the 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
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   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, 2018.






Litkowski, et al.       Expires November 24, 2018               [Page 1]


Internet-Draft                spf-microloop                     May 2018


Copyright Notice

   Copyright (c) 2018 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
   (https://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 . . . . . . . . . . . . . . . . . . . . . .   4
   3.  SPF trigger strategies  . . . . . . . . . . . . . . . . . . .   5
   4.  SPF delay strategies  . . . . . . . . . . . . . . . . . . . .   5
     4.1.  Two steps SPF delay . . . . . . . . . . . . . . . . . . .   6
     4.2.  Exponential backoff . . . . . . . . . . . . . . . . . . .   6
   5.  Mixing strategies . . . . . . . . . . . . . . . . . . . . . .   7
   6.  Benefits of standardized SPF delay behavior . . . . . . . . .  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
   the SPF (Shortest Path First) algorithm is run to find a consistent
   set of non-looping routing paths.

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

   We will call "SPF triggers", 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



Litkowski, et al.       Expires November 24, 2018               [Page 2]


Internet-Draft                spf-microloop                     May 2018


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

   Some of those timers (values and behavior) are standardized in
   protocol specifications, while some are not.  The SPF computation
   related timers have generally remained unspecified.

   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].

   Two micro-loop mitigation techniques have been defined by IETF.
   [RFC6976] has not been widely implemented, presumably due to the
   complexity of the technique.  [I-D.ietf-rtgwg-uloop-delay]) has been
   implemented.  However, it does not prevent all micro-loops that can
   occur for a given topology and failure scenario.

   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 (values and behavior) 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 delay
   algorithm.

   [I-D.ietf-rtgwg-backoff-algo] defines a solution that satisfies this
   problem statement and this document captures the reasoning of the
   provided solution.





Litkowski, et al.       Expires November 24, 2018               [Page 3]


Internet-Draft                spf-microloop                     May 2018


2.  Problem statement

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


          Figure 1 - Network topology suffering from micro-loops

   In Figure 1, S uses primarily the SD link to reach the prefixes
   behind D (Px).  When the SD link fails, the IGP convergence occurs.
   If S converges before E, S will forward the traffic to Px through E,
   but as E has not converged yet, E will loop back traffic to S,
   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 (or a combination of these factors) may increase the
   probability for a micro-loop to appear:

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

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

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

   o  the SPF computation order: an SPF trigger can be common to
      multiple IGP areas or levels (e.g., IS-IS Level1/Level2) or for
      multiple address families with multi-topologies.  There is no
      specified order for SPF computation today and it is implementation
      dependent.  In such scenarios, if the order of SPF computation
      done in S and E for each area/level/topology/SPF-algorithm is
      different, there is a possibility for a micro-loop to appear.



Litkowski, et al.       Expires November 24, 2018               [Page 4]


Internet-Draft                spf-microloop                     May 2018


   o  the RIB and FIB prefix insertion speed or ordering.  This is
      highly dependent on the implementation.

   This document will focus on analysis of the SPF delay behavior and
   associated triggers.

3.  SPF trigger strategies

   Depending on the change advertised in LSPDU or 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 does not affect the topology.

   Different strategies exists to trigger the SPF computation:

   1.  An implementation may always run a full SPF for any type of
       change.

   2.  An implementation may run a full SPF only when required.  For
       example, 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 noted in Section 1, SPF optimizations are not mandatory in
   specifications.  This has led to the implementation of different
   strategies.

4.  SPF delay strategies

   Implementations of link state routing protocols use different
   strategies to delay the SPF computation.  The two most common SPF
   delay behaviors are the following:

   1.  Two phase SPF delay.

   2.  Exponential backoff delay.

   Those behavior will be explained in the next sections.








Litkowski, et al.       Expires November 24, 2018               [Page 5]


Internet-Draft                spf-microloop                     May 2018


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, after the
      initial SPF trigger event.

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

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

   o  Wait time: amount of time to wait without receiving SPF trigger
      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 phase 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:





Litkowski, et al.       Expires November 24, 2018               [Page 6]


Internet-Draft                spf-microloop                     May 2018


   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

   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

   In Figure 1, 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 a Full SPF for any change, and uses the




Litkowski, et al.       Expires November 24, 2018               [Page 7]


Internet-Draft                spf-microloop                     May 2018


   exponential backoff strategy for SPF delay (start=150ms, inc=150ms,
   max=1s)

   We also consider the following sequence of events:

   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 |



Litkowski, et al.       Expires November 24, 2018               [Page 8]


Internet-Draft                spf-microloop                     May 2018


   |        |                    |      300ms)      |      300ms)      |
   |        |                    |                  |                  |
   |        |                    |                  |                  |
   |        |                    |                  |                  |
   |        |                    |                  |                  |
   | 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   |
   +--------+--------------------+------------------+------------------+

   Table 1 - Route computation when S and E use the different behaviors
                        and multiple events appear

   In the Table 1, 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 node S and node E,
   leading to the creation of micro-loops.

   The same issue can also appear with only a single type of event as
   shown below:

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



Litkowski, et al.       Expires November 24, 2018               [Page 9]


Internet-Draft                spf-microloop                     May 2018


   |        |                    |      150ms)      |      150ms)      |
   |        |                    |                  |                  |
   |        |                    |                  |                  |
   | 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)      |
   |        |                    |                  |                  |



Litkowski, et al.       Expires November 24, 2018              [Page 10]


Internet-Draft                spf-microloop                     May 2018


   |        |                    |                  |                  |
   |        |                    |                  |                  |
   |        |                    |                  |                  |
   | 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   |                  |
   |        |                    |                  |                  |
   |        |                    |                  |                  |
   +--------+--------------------+------------------+------------------+

   Table 2 - Route computation upon multiple link down events when S and
                       E use the different behaviors

6.  Benefits of standardized SPF delay behavior

   Using the same event sequence as in Table 1, we may expect fewer and/
   or shorter micro-loops using a standardized SPF delay.

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



Litkowski, et al.       Expires November 24, 2018              [Page 11]


Internet-Draft                spf-microloop                     May 2018


   |        |                    |                  |                  |
   |        |                    |                  |                  |
   | 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   |
   +--------+--------------------+------------------+------------------+

    Table 3 - Route computation when S and E use the same standardized
                                 behavior

   As displayed above, there could be some other parameters like router
   computation power, flooding timers that may also influence micro-
   loops.  In all the examples in this document comparing the SPF timer
   behavior of router S and router E, we have made router E a bit slower
   than router S.  This can lead to micro-loops even when both S and E
   use a common standardized SPF behavior.  However, we expect that by
   aligning implementations of the SPF delay, service providers may
   reduce the number and the duration of micro-loops.




Litkowski, et al.       Expires November 24, 2018              [Page 12]


Internet-Draft                spf-microloop                     May 2018


7.  Security Considerations

   This document does not introduce any security consideration.

8.  Acknowledgements

   Authors would like to thank Mike Shand and Chris Bowers for their
   useful comments.

9.  IANA Considerations

   This document has no action for IANA.

10.  References

10.1.  Normative References

   [I-D.ietf-rtgwg-backoff-algo]
              Decraene, B., Litkowski, S., Gredler, H., Lindem, A.,
              Francois, P., and C. Bowers, "SPF Back-off Delay algorithm
              for link state IGPs", draft-ietf-rtgwg-backoff-algo-10
              (work in progress), March 2018.

   [RFC1195]  Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
              dual environments", RFC 1195, DOI 10.17487/RFC1195,
              December 1990, <https://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,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC2328]  Moy, J., "OSPF Version 2", STD 54, RFC 2328,
              DOI 10.17487/RFC2328, April 1998,
              <https://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-09 (work
              in progress), November 2017.



Litkowski, et al.       Expires November 24, 2018              [Page 13]


Internet-Draft                spf-microloop                     May 2018


   [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, <https://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



























Litkowski, et al.       Expires November 24, 2018              [Page 14]


Html markup produced by rfcmarkup 1.127, available from https://tools.ietf.org/tools/rfcmarkup/