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Network Working Group                                             Q. Xie
Internet-Draft                                                  Motorola
Expires: May 9, 2005                                          L. Yarroll
                                                     TimeSys Corporation
                                                       November 08, 2004


                    RSERPOOL Redundancy-model Policy
               draft-xie-rserpool-redundancy-model-03.txt

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Copyright Notice

   Copyright (C) The Internet Society (2004).  All Rights Reserved.

Abstract

   This document defines RSERPOOL Redundancy-model Member Selection
   Policy parameter and the related procedures.  This policy is designed
   to be flexible and capable of supporting a wide range of advanced
   redundancy models found in some high availability systems.  The
   design uses the extensibility in RSERPOOL pool load sharing policy.






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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1   Definitions  . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Conventions  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Redundancy-model Member Selection Policy Parameter . . . . . .  3
   4.  Member Selection Procedures under Redundancy-model Policy  . .  5
   5.  Examples for Implementing Various Redundancy Models  . . . . .  6
     5.1   2N Redundancy with Active/Standby Protection . . . . . . .  6
     5.2   N+M Redundancy with Active/Standby Protection  . . . . . .  6
     5.3   N-way Redundancy with Active/Standby Protection  . . . . .  7
     5.4   N-way Redundancy with Active/Active Protection . . . . . .  7
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  7
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . .  7
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  7
   9.  Normative References . . . . . . . . . . . . . . . . . . . . .  7
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . .  8
       Intellectual Property and Copyright Statements . . . . . . . .  9

































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1.  Introduction

   The pool member selection policy in RSERPOOL design [2][3] is both
   flexible and extensible.  By observing the pool's member selection
   policy a pool user (PU) can accomplish a wide range of different load
   distribution schemes and communications strategies across the pool
   elements (PE) in the pool.

   Some most basic load distribution schemes, such as the round-robin
   and least used policies, are already defined in ASAP [1].  In this
   document, we define another member selection policy -
   Redundancy-model policy - in order to support a variety of more
   advanced redundancy models used in some high availability systems.

1.1  Definitions

   This document uses the following terms:

   Pool (or server pool): See [3];

   Pool element (PE): See [3];

   Pool user (PU): See [3];

   ENRP handlespace (or handlespace): See [3];

   ENRP handlespace server (or ENRP server): See [3];


2.  Conventions

   The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
   SHOULD NOT, RECOMMENDED, NOT RECOMMENDED, MAY, and OPTIONAL, when
   they appear in this document, are to be interpreted as described in
   [5].

3.  Redundancy-model Member Selection Policy Parameter

   This defines a new Member Selection Policy TLV structure that SHOULD
   be used to indicate the role of a PE in a high availability
   redundancy model.  This definition follows the member selection
   policy extension rules described in Section 3.6? of [6]









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       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |        Type = 0x6             |      Length = variable        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Policy=0x5   |  (reserved)   |    HA Role    | Service State |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :            Backup PE Identifier Parameter (optional)          :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Type, Length, and Policy fields are defined in Section 3.6? in
   [6], with the addition of the following new Policy value:

         Value     Policy
         -----     ---------
         0x5       HA Redundancy-model support

   Other fields are defined as follows:



      High Availability (HA) role: 8 bits (unsigned integer)

         Indicating the role of the corresponding PE in the HA
         redundancy model.  The following HA roles are currently
         defined:

         Value     HA state
         -----     ---------
         0x1       No role
         0x2       Standby
         0x3       Active
         0x4       Dual role
         other values are reserved by IETF and MUST NOT be used.

      Service State: 8 bit (unsigned integer)

         Indicating the current service state elected by the
         corresponding PE.  The following service states are currently
         defined:

         Value     Service state
         -----     -------------
         0x1       In service
         0x2       Stopping
         other values are reserved by IETF and MUST NOT be used.





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      Backup PE Identifier Parameter:

         This TLV is used in some redundancy models to indicate the
         designate backup of this PE.  The format of PE Identifier
         Parameter is defined in [6]

   More detailed description of the HA states and Service states is
   given in the following sections.

4.  Member Selection Procedures under Redundancy-model Policy

   When sending to a pool of Redundancy-model policy, a PU MUST use the
   following rules to select the recipient of the message:

   1.  When sending a new message for the first time to the pool, the PU
       SHOULD select a PE whose HA role is either "Active" or "Dual
       role" and service state is "In service." If more than one PEs in
       the pool meets these criteria, the PU SHOULD select one of them
       as the recipient of this message in a round-robin fashion.

   2.  When the PU is re-sending a message which was previously sent to
       a PE (PE_A) in the pool but failed because PE_A is found
       unreachable (i.e., a fail-over case), the PU SHOULD select a
       qualified backup PE as the message recipient, by following the
       steps below:

       A.  First check if PE_A has a designated backup PE, whose
           presence and PE Id are indicated by the presence of the
           "Backup PE Identifier Parameter" in the Member Selection
           Policy TLV of PE_A.

       B.  If no backup is designated by PE_A, the PU SHOULD select a PE
           whose HA role is either "Standby" or "Dual role", and service
           state is "In service." If no such PE can be found in the
           pool, the PU SHOULD abort re-sending the message and notify
           the application about the failure.  If multiple PEs exist in
           the pool that meet these criteria, the PU SHOULD select one
           of them in a round-robin fashion.

       C.  If a backup (PE_B) is designated by PE_A and exists in the
           pool and its service state is "In service", the PU SHOULD
           select PE_B as the recipient of the message being re-sent,
           regardless of the HA state of PE_B.

       D.  If a backup (PE_B) is designated by PE_A but does not exist
           in the pool (i.e., the PE Id in the "Backup PE Identifier
           Parameter" in PE_A dose not match any PE in the pool), the PU
           SHOULD abort re-sending the message and notify the



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           application about the failure.

       E.  If a backup (PE_B) is designated by PE_A and exists in the
           pool but its service state is NOT "In service", the PU SHOULD
           attempt to find a qualified backup for PE_B, by recursively
           invoking the above steps.

       In the case where the failed PE does not have a designated backup
       and the sending PU has succeeded in finding a qualified backup PE
       for the failed PE using the above procedures, the PU MAY keep a
       record of its finding and use the same backup for all subsequent
       fail-over events that may occur on the same failed PE.


5.  Examples for Implementing Various Redundancy Models

5.1  2N Redundancy with Active/Standby Protection

   In this redundancy model there are two PEs registered in the pool;
   one has its HA role set to Active and the other's set to Standby.
   The active PE is providing the service while the standby PE is
   prepared to take over the active role should the active PE fail.

   In this redundancy model, the active PE does not have to have a
   designated backup, i.e., it does not need to include a "Backup PE
   Identifier Parameter" in its selection policy TLV when registering.

5.2  N+M Redundancy with Active/Standby Protection

   This redundancy model allows flexible active-standby relationships to
   be defined between the PEs in a pool.  A pool with the N+M redundancy
   model consists of N PEs registered with their HA role set to Active
   (active PEs) and M PEs registered with their HA role set to Standby
   (standby PEs).

   Normally, the value of M is less than or equal to N, which means that
   a single PE can act as a standby for several active PEs at a time.  A
   common use of the N+M redundancy model is N+1 redundancy.  This is a
   special case of the N+M redundancy model.  In the pool using N+1
   redundancy, a single PE acts as a standby for all active PEs.

   In operation, the active PEs are provided the service while the
   standby PEs are prepared to become backup to any of the active PEs,
   should one or more of them fails.

   In this redundancy model, the active PEs do not have to have a
   designated backup, i.e., they do not need to include a "Backup PE
   Identifier Parameter" in their selection policy TLV when registering.



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5.3  N-way Redundancy with Active/Standby Protection

   In this redundancy model, there are N (an even number) PEs in the
   pool.  The PEs are paired to form N/2 active/standby pairs.  In each
   pair, the active PE is providing the service while the standby PE is
   prepared to take over the active role should the active PE fail.
   Load is distributed across the N/2 active PEs.

   To implement such a pool, at registration each active PE needs to set
   its HA role to Active and indicate its designated backup by including
   a "Backup PE Identifier Parameter" in its selection policy TLV that
   contains the PE id of the backup.  The standby PEs simply register
   with their HA role set to Standby and omit the "Backup PE Identifier
   Parameter."

5.4  N-way Redundancy with Active/Active Protection

   In this redundancy model there are one or more PEs in the pool, and
   are registered with their HA role set to Dual role.  All PEs in the
   pool are actively providing service and are prepared to backup others
   at the same time.

   Note, this redundancy model can also be implemented (in some cases
   more efficiently) by using other active/active member selection
   policies such as the Round Robin and Weighted Round Robin policies
   (see Section 4.5.2? [1]).

6.  IANA Considerations

   A new RSERPOOL Member Selection Policy type (HA Redundancy-model
   support: 0x5) will need to be registered with IANA.  Additionally,
   the IETF reserved values specified in this document will need to be
   managed by IANA.

7.  Security Considerations

   TBD

8.  Acknowledgements

   The authors wish to thank Randy Presuhn and others for their review
   and comments.

9  Normative References

   [1]  Stewart, R., Xie, Q., Stillman, M. and M. Tuexen, "Aggregate
        Server Access Protocol (ASAP)", draft-ietf-rserpool-asap-10
        (work in progress), October 2004.



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   [2]  Tuexen, M., Xie, Q., Stewart, R., Shore, M., Ong, L., Loughney,
        J. and M. Stillman, "Requirements for Reliable Server Pooling",
        RFC 3237, January 2002.

   [3]  Tuexen, M., Xie, Q., Stewart, R., Shore, M. and J. Loughney,
        "Architecture for Reliable Server Pooling",
        draft-ietf-rserpool-arch-08 (work in progress), October 2004.

   [4]  Bradner, S., "The Internet Standards Process -- Revision 3", BCP
        9, RFC 2026, October 1996.

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

   [6]  Stewart, R., Xie, Q., Stillman, M. and M. Tuexen, "Aggregate
        Server Access Protocol (ASAP) and Endpoint Name Resolution
        (ENRP) common parameters document",
        draft-ietf-rserpool-common-param-07 (work in progress), October
        2004.


Authors' Addresses

   Qiaobing Xie
   Motorola, Inc.
   1501 W. Shure Drive, 2-F9
   Arlington Heights, IL  60004
   US

   Phone: +1-847-632-3028
   EMail: qxie1@email.mot.com


   La Monte H.P. Yarroll
   TimeSys Corporation
   925 Liberty Avenue
   Pittsburgh, PA  15122
   USA

   Phone: +1-412-325-6391
   EMail: piggy@acm.org










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Acknowledgment

   Funding for the RFC Editor function is currently provided by the
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