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Versions: (draft-ogawa-forces-ceha) 00 01 02 03 04 RFC 7121

Network Working Group                                           K. Ogawa
Internet-Draft                                           NTT Corporation
Intended status: Standards Track                              W. M. Wang
Expires: April 20, 2011                    Zhejiang Gongshang University
                                                           E. Haleplidis
                                                    University of Patras
                                                           J. Hadi Salim
                                                       Mojatatu Networks
                                                            Oct 17, 2010


                   ForCES Intra-NE High Availability
                       draft-ietf-forces-ceha-00

Abstract

   This document discusses CE High Availability within a ForCES NE.

Status of this Memo

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

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   This Internet-Draft will expire on April 20, 2011.

Copyright Notice

   Copyright (c) 2010 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
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   the Trust Legal Provisions and are provided without warranty as



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   described in the Simplified BSD License.


Table of Contents

   1.  Definitions  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     2.1.  Document Scope . . . . . . . . . . . . . . . . . . . . . .  5
     2.2.  Quantifying Problem Scope  . . . . . . . . . . . . . . . .  5
   3.  RFC5810 CE HA Framework  . . . . . . . . . . . . . . . . . . .  6
     3.1.  Current CE High Availability Support . . . . . . . . . . .  6
       3.1.1.  Cold Standby Interaction with ForCES Protocol  . . . .  7
       3.1.2.  Responsibilities for HA  . . . . . . . . . . . . . . .  9
   4.  CE HA Hot Standby  . . . . . . . . . . . . . . . . . . . . . . 10
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 11
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     7.1.  Normative References . . . . . . . . . . . . . . . . . . . 11
     7.2.  Informative References . . . . . . . . . . . . . . . . . . 11
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11































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1.  Definitions

   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 RFC 2119.

   The following definitions are taken from [RFC3654]and [RFC3746]:

   Logical Functional Block (LFB) -- A template that represents a fine-
   grained, logically separate aspects of FE processing.

   ForCES Protocol -- The protocol used at the Fp reference point in the
   ForCES Framework in [RFC3746].

   ForCES Protocol Layer (ForCES PL) -- A layer in the ForCES
   architecture that embodies the ForCES protocol and the state transfer
   mechanisms as defined in [RFC5810].

   ForCES Protocol Transport Mapping Layer (ForCES TML) -- A layer in
   ForCES protocol architecture that specifically addresses the protocol
   message transportation issues, such as how the protocol messages are
   mapped to different transport media (like SCTP, IP, TCP, UDP, ATM,
   Ethernet, etc), and how to achieve and implement reliability,
   security, etc.



























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2.  Introduction

   Figure 1 illustrates a ForCES NE controlled by a set of redundant CEs
   with CE1 being active and CE2 and CEn-1 being a backup.

                           -----------------------------------------
                           | ForCES Network Element                |
                           |                        +-----------+  |
                           |                        |  CEn-1    |  |
                           |                        |  (Backup) |  |
     --------------   Fc   | +------------+      +------------+ |  |
     | CE Manager |--------+-|     CE1    |------|    CE2     |-+  |
     --------------        | |  (Active)  |  Fr  |  (Backup)  |    |
           |               | +-------+--+-+      +---+---+----+    |
           | Fl            |         |  |    Fp      /   |         |
           |               |         |  +---------+ /    |         |
           |               |       Fp|            |/     |Fp       |
           |               |         |            |      |         |
           |               |         |      Fp   /+--+   |         |
           |               |         |  +-------+    |   |         |
           |               |         |  |            |   |         |
     --------------    Ff  | --------+--+--      ----+---+----+    |
     | FE Manager |--------+-|     FE1    |  Fi  |     FE2    |    |
     --------------        | |            |------|            |    |
                           | --------------      --------------    |
                           |   |  |  |  |          |  |  |  |      |
                           ----+--+--+--+----------+--+--+--+-------
                               |  |  |  |          |  |  |  |
                               |  |  |  |          |  |  |  |
                                 Fi/f                   Fi/f

          Fp: CE-FE interface
          Fi: FE-FE interface
          Fr: CE-CE interface
          Fc: Interface between the CE Manager and a CE
          Ff: Interface between the FE Manager and an FE
          Fl: Interface between the CE Manager and the FE Manager
          Fi/f: FE external interface

                       Figure 1: ForCES Architecture

   The ForCES architecture allows FEs to be aware of multiple CEs but
   enforces that only one CE be the master controller.  This is known in
   the industry as 1+N redundancy [refxxxx].  The master CE controls the
   FEs via the ForCES protocol operating in the Fp interface.  If the
   master CE becomes faulty, a backup CE takes over and NE operation
   continues.  By definition, the current documented setup is known as
   cold-standby [refxxxx].  The CE set is static and is passed to the FE



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   by the FE Manager (FEM) via the Ff interface and to each CE by the CE
   Manager (CEM) in the Fc interface during the pre-association phase.

   From an FE perspective, the knobs of control for a CE set are defined
   by the FEPO LFB in [RFC5810], Appendix B.  Section 3.1 of this
   document details these knobs further.

2.1.  Document Scope

   By current definition, the Fr interface is out of scope for the
   ForCES architecture.  However, it is expected that organizations
   implementing a set of CEs will need to have the CEs communicate to
   each other via the Fr interface in order to achieve the
   synchronization necessary for controlling the FEs.

   The problem scope addressed by this document falls into 2 areas:

   1.  To describe with more clarity (than [RFC5810]) how current cold-
       standby approach operates within the NE cluster.

   2.  To describe how to evolve the cold-standby setup to a hot-standby
       redundancy setup so as to improve the failover time and NE
       availability.

2.2.  Quantifying Problem Scope

   The NE recovery and availability is dependent on several time-
   sensitive metrics:

   1.  How fast the CE plane failure is detected the FE.

   2.  How fast a backup CE becomes operational.

   3.  How fast the FEs associate with the new master CE.

   4.  How fast the FEs recover their state and become operational.

   The design goals of the current [RFC5810] choices to meet the above
   goals are driven by desire for simplicity.

   To quantify the above criteria with the current prescribed ForCES CE
   setup in [RFC5810]:

   1.  How fast the CE side detects a CE failure is left undefined.  To
       illustrate an extreme scenario, we could have a human operator
       acting as the monitoring entity to detect faulty CEs.  How fast
       such detection happens could be in the range of seconds to days.
       A more active monitor on the Fr interface could improve this



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       detection.

   2.  How fast the backup CE becomes operational is also currently out
       of scope.  In the current setup, a backup CE need not be
       operational at all (for example, to save power) and therefore it
       is feasible for a monitoring entity to boot up a backup CE after
       it detects the failure of the master CE.  In this document
       Section 4 we suggest that at least one backup CE be online so as
       to improve this metric.

   3.  How fast an FE associates with new master CE is also currently
       undefined.  The cost of an FE connecting and associating adds to
       the recovery overhead.  As mentioned above we suggest having at
       least one backup CE online.  In Section 4 we propose to zero out
       the connection and association cost on failover by having each FE
       associate with all online backup CEs after associating to the
       active CE.  Note that if an FE pre-associates with backup CEs,
       then the system will be technically operating in hot-standby
       mode.

   4.  And last: How fast an FE recovers its state depends on how much
       NE state exists.  By ForCES current definition, the new master CE
       assumes zero state on the FE and starts from scratch to update
       the FE.  So the larger the state, the longer the recovery.


3.  RFC5810 CE HA Framework

   To achieve CE High Availabilty, FEs and CEs MUST inter-operate per
   [RFC5810] definition which is repeated for contextual reasons in
   Section 3.1.  It should be noted that in this default setup, which
   MUST be implemented by CEs and FEs needing HA, the Fr plane is out of
   scope (and if available is proprietary to an implementation).

3.1.  Current CE High Availability Support

   As mentioned earlier, although there can be multiple redundant CEs,
   only one CE actively controls FEs in a ForCES NE.  In practice there
   may be only one backup CE.  At any moment in time only one master CE
   can control the FEs.  In addition, the FE connects and associates to
   only the master CE.  The FE and the CE PL are aware of the primary
   and one or more secondary CEs.  This information (primary, secondary
   CEs) is configured on the FE and the CE PLs during pre-association by
   the FEM and the CEM respectively.

   Figure 2 below illustrates the Forces message sequences that the FE
   uses to recover the connection in current defined cold-standby
   scheme.



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         FE                   CE Primary        CE Secondary
         |                       |                    |
         |  Asso Estb,Caps exchg |                    |
       1 |<--------------------->|                    |
         |                       |                    |
         |       state update    |                    |
       2 |<--------------------->|                    |
         |                       |                    |
         |                       |                    |
         |                   FAILURE                  |
         |                                            |
         |         Asso Estb,Caps exchange            |
       3 |<------------------------------------------>|
         |                                            |
         |              Event Report (pri CE down)    |
       4 |------------------------------------------->|
         |                                            |
         |         state update from scratch          |
       5 |<------------------------------------------>|


                  Figure 2: CE Failover for Cold Standby

3.1.1.  Cold Standby Interaction with ForCES Protocol

   High Availability parameterization in an FE is driven by configuring
   the FE Protocol Object (FEPO) LFB.

   The FEPO CEID component identifies the current master CE and the
   component table BackupCEs identifies the backup CEs.  The FEPO FE
   Heartbeat Interval, CE Heartbeat Dead Interval, and CE Heartbeat
   policy help in detecting connectivity problems between an FE and CE.
   The CE Failover policy defines how the FE should react on a detected
   failure.

   Figure 3 illustrates the defined state machine that facilitates
   connection recovery.

   The FE connects to the CE specified on FEPO CEID component.  If it
   fails to connect to the defined CE, it moves it to the bottom of
   table BackupCEs and sets its CEID component to be the first CE
   retrieved from table BackupCEs.  The FE then attempts to associate
   with the CE designated as the new primary CE.  The FE continues
   through this procedure until it successfully connects to one of the
   CEs.






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       (CE issues Teardown ||    +-----------------+
          Lost association) &&   | Pre-Association |
         CE failover policy = 0  | (Association    |
             +------------>-->-->|   in            +<----+
             |                   | progress)       |     |
             |     CE Issues     +--------+--------+     |
             |     Association        |                  | CEFTI
             |       Response         V                  | timer
             |     ___________________+                  | expires
             |     |                                     |
             |     V                                     ^
           +-+-----------+                          +-------+-----+
           |             |                          |  Not        |
           |             |  (CE issues Teardown ||  |  Associated |
           |             |    Lost association) &&  |             |
           | Associated  |  CE Failover Policy = 1  | (May        |
           |             |                          | Continue    |
           |             |---------->------->------>|  Forwarding)|
           |             |                          |             |
           +-------------+                          +-------------+
                ^                                         V
                |                                         |
                |            CE Issues                    |
                |            Association                  |
                |            Setup                        |
                +_________________________________________+


                 Figure 3: FE State Machine considering HA

   When communication fails between the FE and CE (which can be caused
   by either the CE or link failure but not FE related), either the TML
   on the FE will trigger the FE PL regarding this failure or it will be
   detected using the HB messages between FEs and CEs.  The
   communication failure, regardless of how it is detected, MUST be
   considered as a loss of association between the CE and corresponding
   FE.

   If the FE's FEPO CE Failover Policy is configured to mode 0 (the
   default), it will immediately transition to the pre-association
   phase.  This means that if association is again established, all FE
   state will need to be re-established.

   If the FE's FEPO CE Failover Policy is configured to mode 1, it
   indicates that the FE is capable of HA restart recovery.  In such a
   case, the FE transitions to the not associated state and the CEFTI
   timer[RFC 5810] is started.  The FE MAY continue to forward packets
   during this state.  It MAY also recycle through any configured backup



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   CEs in a round-robin fashion.  It first adds its primary CE to the
   bottom of table BackupCEs and sets its CEID component to be the first
   secondary retrieved from table BackupCEs.  The FE then attempts to
   associate with the CE designated as the new primary CE.  If it fails
   to re-associate with any CE and the CEFTI expires, the FE then
   transitions to the pre-association state.

   If the FE, while in the not associated state, manages to reconnect to
   a new primary CE before CEFTI expires it transitions to the
   Associated state.  Once re-associated, the FE tries to recover any
   state that may have been lost during the not associated state.  How
   the FE achieves to re-synchronize its state is out of scope for the
   current ForCES architecture.

   An explicit message (a Config message setting Primary CE component in
   ForCES Protocol object) from the primary CE, can also be used to
   change the Primary CE for an FE during normal protocol operation.  In
   this case, the FE transitions to the Not Associated State and
   attempts to Associate with the new CE.

3.1.2.  Responsibilities for HA

   XXX: we may remove this section (not much value to overall
   discussion)

   TML Level:

   1.  The TML controls logical connection availability and failover.

   2.  The TML also controls peer HA management.

   At this level, control of all lower layers, for example transport
   level (such as IP addresses, MAC addresses etc) and associated links
   going down are the role of the TML.

   PL Level:
   All other functionality, including configuring the HA behavior during
   setup, the CE IDs used to identify primary and secondary CEs,
   protocol messages used to report CE failure (Event Report), Heartbeat
   messages used to detect association failure, messages to change the
   primary CE (Config), and other HA related operations described
   before, are the PL responsibility.

   To put the two together, if a path to a primary CE is down, the TML
   would take care of failing over to a backup path, if one is
   available.  If the CE is totally unreachable then the PL would be
   informed and it would take the appropriate actions described before.




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4.  CE HA Hot Standby

   In this section we make some small extensions to the existing scheme
   to enable it to achieve hot standby HA.  With these suggested changes
   we achieve some of the goals defined in Section 2.2, namely:

   o  How fast a backup CE becomes operational.

   o  How fast the FEs associate with the new master CE.

   As described in Section 3.1, the FEM configures the FE to make it
   aware of all the CEs in the NE.  The FEM also configures the FE to
   make it aware of which CE is the master and which are backup(s).  The
   FE's FEPO LFB CEID component identifies the current master CE and
   table BackupCEs identifies the backup CEs.  The FE only connects to
   the master CE and then proceeds to associate with it.  The master
   thereafter controls the FE and receives events from it.  This
   continues until there is communication failure between the FE and CE
   at which point the FE attempts to connect to a CE from the BackupCEs
   table until it succeeds to connect and associate with one listed CE.

   It is recommended that at least one backup CE should be online.
   Doing so will improve how fast the backup CE will take to be
   operational (as opposed to bringing up a backup CE when we detect a
   master CE fault).  If we assume that a CE implementation does state
   synchronization between CEs, then the cost of making the backup CE
   operational and ready to serve FEs; in such a case an associating FE
   could immediately become operational.

   If we assume the presence of at least one backup CE online, we can
   improve how fast the FEs associate with a new master CE by making two
   changes:

   The first change that needs to be made is to have the FE, soon after
   successfully connecting and associating with the master CE, to
   proceed and connect as well as associate with the rest of the CEs
   listed in the BackupCEs table.

   By virtue of having multiple CE connections, the FE switchover to a
   new master CE will be relatively much faster.  The overall effect is
   improving the NE recovery time in case of communication failure or
   faults of the master CE.

   XXX: below paragraph needs more text discussion ..

   The FE MUST respond to messages issued by only the master CE.  This
   simplifies the synchronization and avoids the concept of locking FE
   state.  The FE MUST drop any messages from backup CEs (XXX: Should we



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   log and increment some stat?).

   XXX: below paragraph needs text discussion ..

   Again for the sake of simplicity, asynchronous events and heartbeats
   are sent to all associated-to CEs.  Packet redirects continue to be
   sent only to the master CE.

   XXXX: We need to have an extra state for each CE (master, connected,
   associated, stats etc) on the FEPO - so probably another change to
   current FEPO components.


5.  IANA Considerations

   TBA


6.  Security Considerations

   TBA


7.  References

7.1.  Normative References

   [RFC5810]  Doria, A., Hadi Salim, J., Haas, R., Khosravi, H., Wang,
              W., Dong, L., Gopal, R., and J. Halpern, "Forwarding and
              Control Element Separation (ForCES) Protocol
              Specification", RFC 5810, March 2010.

7.2.  Informative References

   [RFC3654]  Khosravi, H. and T. Anderson, "Requirements for Separation
              of IP Control and Forwarding", RFC 3654, November 2003.

   [RFC3746]  Yang, L., Dantu, R., Anderson, T., and R. Gopal,
              "Forwarding and Control Element Separation (ForCES)
              Framework", RFC 3746, April 2004.

   [RFC5812]  Halpern, J. and J. Hadi Salim, "Forwarding and Control
              Element Separation (ForCES) Forwarding Element Model",
              RFC 5812, March 2010.







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Authors' Addresses

   Kentaro Ogawa
   NTT Corporation
   3-9-11 Midori-cho
   Musashino-shi, Tokyo  180-8585
   Japan

   Email: ogawa.kentaro@lab.ntt.co.jp


   Weiming Wang
   Zhejiang Gongshang University
   149 Jiaogong Road
   Hangzhou  310035
   P.R.China

   Phone: +86-571-88057712
   Email: wmwang@mail.zjgsu.edu.cn


   Evangelos Haleplidis
   University of Patras
   Patras
   Greece

   Email: ehalep@ece.upatras.gr


   Jamal Hadi Salim
   Mojatatu Networks
   Ottawa, Ontario
   Canada

   Email: hadi@mojatatu.com
















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