Internet Draft                                              T. Anderson
Expiration: January 2003                                     Intel Labs
File: draft-ietf-gsmp-dyn-part-reqs-02.txt                   J. Buerkle
                                                        Nortel Networks

                                                              July 2002

      Requirements for the Dynamic Partitioning of Switching Elements

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.  Internet-Drafts are
   working documents of the Internet Engineering Task Force (IETF), its
   areas, and its working groups.  Note that other groups may also
   distribute working documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six
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Conventions used in this document

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


   This document identifies a set of requirements for the mechanisms
   used to dynamically reallocate the resources of a switching element
   (e.g., an ATM switch) to its partitions.  These requirements are
   particularly critical in the case of an operator creating a switch
   partition and then leasing control of that partition to a third


   In this document, the following definitions will be used.

   Switching Element - A device that switches packets (e.g., an ATM
   switch or MPLS LSR) and whose resources can be divided into
   partitions, each of which can be independently controlled by a
   different controller.

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   Partition - A partition is a set of switching element (SE)
   resources.  Partitions are also referred to as virtual SEs.

   Active Partition - An active partition is a partition in which the
   resources are in use; either under the direct control of a separate
   controller or under internal policy based control.

   Controller - The entity responsible for controlling the operations
   of an active partition.

   Static Partitioning - In static partitioning, no changes can be made
   to any active partitionÆs resources without requiring a restart of
   that partition.  Instances of repartitioning in which connections to
   controllers are disconnected before resources are reallocated
   therefore fall into this category.

   Dynamic Partitioning - In dynamic partitioning, an active
   partitionÆs resources can be reapportioned without requiring a
   restart of the partition.

   Frozen Partition - A frozen partition is an active partition that is
   in the process of being shutdown.  A frozen partition's unused
   resources are relinquished, but all current connections are allowed
   to remain until removed by the controller.  As connections close the
   resources are returned to the SE.

   Deterministic Partitioning - In deterministic partitioning, each
   active partition is given an allotted quantity of each resource.
   The usage of resources in one active partition does not influence
   the resources available to another active partition.  All
   discussions in these requirements presuppose the use of
   deterministic partitioning.

   Statistical Partitioning - In statistical partitioning, some or all
   resources are pooled among the active partitions, and allocations
   may be based on percentages or on some other metric.  Discussion of
   statistical partitions is outside the scope of these requirements.

   Proactive Notification - A proactive notification is a message sent
   from a SE to its controller at the time an event occurs.
   Specifically, if a SE asynchronously sends the controller a message
   when it is dynamically partitioned, we say that the SE has
   proactively notified its controller of the resource reapportionment.

   Explicit Reactive Notification - In explicit reactive notification,
   the SE does not asynchronously send a message when dynamic
   partitioning occurs.  Instead, the SE includes a "resource changed"
   error code in the response to a subsequent request by the

   Implicit Reactive Notification - This is similar to an Explicit
   Reactive Notification except that the protocol does not contain an
   explicit "resource changed" error.  In this case, all that the SE
   can do is to indicate that some unspecified error has occurred when
   the controller attempts to use non-allocated resources.
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   Several logical entities are involved in the partitioning and
   control of a SE.  First, a switching element (for the purposes of
   this draft) is a device that "switches" packets, whose resources can
   be partitioned and whose partitions can each be controlled by a
   single controller. (This partitioning also implies the ability to
   enforce this division of resources between competing partitions).
   Second, the partition manager (PM) is a management entity that
   specifies the number of virtual SEs into which the SE should be
   partitioned and the resources to be allocated to each virtual SE.
   Lastly, a controller directs the use of the resources of one or more
   partitions to provide a set of services.

   In the rest of this draft, we will deal exclusively with logical
   entities although it is worth noting here that there are many
   possible mappings of logical entities to physical entities.  For
   example, there may be multiple logical controllers running on a
   single physical processor (and for convenience we may refer to this
   processor as a physical controller).  Likewise, there may be
   multiple partition managers running on a single management
   workstation.  A switching element may consist of multiple physical
   elements (e.g., some number of blades in a chassis) or fractional
   physical elements (i.e., nested partitioning).  Finally, any
   combination of these logical entities could theoretically be
   collocated on the same physical resources.

   However, for many reasons, the physical realm often reflects this
   logical division of functionality.  To facilitate this division,
   several protocols, such as MEGACO [RFC3015] and GSMP [GSMPv3], exist
   that allow control functionality to be physically separated from
   switching functionality.  Recently, some regulatory environments
   have mandated multi-provider access to a single physical
   infrastructure.  To satisfy these regulations, a common use of
   partitioning will be for the owner of the SE to partition the SE
   into several virtual SEs and then to lease these to third parties.
   In this case, the PM will likely be physically separate from all of
   the controllers.  For locality (and therefore ease) of management,
   SEs will be remotely configurable and thus the PM will be physically
   separated from the SE.  The following illustration depicts this
   arrangement.  The dashed lines indicate interactions between the
   entities and are labeled with the cardinality of the relationship
   between the entities.

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   ------------------             -------------------
   |                | *         * |                 |
   |    Partition   |-------------|   Controller    |
   |     Manager    |      C      |                 |
   ------------------             -------------------
                 1 \                / *
                    \              /
                     \ A        B /
                      \          /
                     * \        / *
                   |  --------/---   |
                   |  |Partition |   |
                   |  |          |   |
                   |  ------------   |
                   |Switching element|

   Interaction A is one in which the PM partitions the SE and allocates
   resources to the partitions it creates.  There is a one-to-many
   relationship between PMs and SEs.  In order to support dynamic
   partitioning, this document will place certain requirements on
   proposed (or new) solutions in this space.

   Interaction B is one in which the controller configures and manages
   an active partition.  Current protocols implementing this
   interaction include GSMP [GSMPv3] and MEGACO [RFC3015].  These
   protocols allow a many-to-many relationship between controller and

   Interaction C is one by which a PM and a controller could
   communicate to alter the nature of an active partition.  There is a
   many-to-many relationship between PMs and controllers.  For example,
   there are multiple PMs per controller in the case where a controller
   is managing two partitions from different SEs and there are multiple
   controllers per PM in the case where a SE has two partitions each
   managed by a different controller.  Possible types of interactions
   between PM and controller include:
      - A controller could request that the resources of one of its
        active partitions be altered; either increased or decreased.
      - The PM could respond to a controller request for altered
        resource levels.
      - The PM could request that a controller release resources
        currently allocated to one of its active partitions. This could
        involve the following types of request:
        - A request to relinquish allocated but currently unused
          resources.  That is to put a freeze on additional use of the
          specified resources.
        - A request to relinquish used resources.
        - A request to relinquish an active partition.  That is
          a request that a controller release control of an active
      - The controllerÆs response to a PM request.
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   As far as the authors know, no proposed standard solutions currently
   exist for interactions of type C.

Dynamic Partitioning

   Static repartitioning of a SE can be a costly and inefficient
   process.  First, before static repartitioning can take place, all
   existing connections with controllers must be severed.  When this
   happens, the SE will typically release all the state configured by
   the controller.  Then, the virtual SE must be placed in the "down"
   state while the repartitioning takes place.  Once the repartitioning
   is completed, the partitions are placed in the "up" state and the
   controllers are allowed to reconnect to the partitions.  Then, the
   controllers can reestablish state in the active partition.  Thus,
   static repartitioning results in a period of downtime and a period
   in which the controllers are reestablishing state.  This is the case
   even if resources that are not currently in use in one partition,
   either an active or an inactive partition, are intended for a fully
   loaded active partition.

   Therefore, dynamic partitioning is to be preferred to static
   partitioning since it avoids the downtime and loss of state
   associated with static partitioning.  However, a different set of
   potential problems exists for dynamic partitioning.  Some questions
   to be answered include the following:
     - How is the controller notified of an increase or decrease in
     - What should happen when the PM would like to decrease the
       resources allocated to a partition but those resources are in


   This document does not attempt to answer the preceding questions but
   instead defines a set of requirements that any solution to these
   problems MUST satisfy.

   1. There MUST be a mechanism by which a PM can create virtual SEs on
     the SE and allocate SE resources to those virtual SEs.
   2. SEs MUST ensure that controllers do not use more resources than
     those currently allocated to each virtual SE.  Therefore, each
     control protocol MUST provide either an explicit reactive
     notification or an implicit reactive notification to indicate
     resource exhaustion.
   3. Furthermore, this mechanism MUST support the partitioning of all
     resources discoverable through GSMP (e.g., label tables).  Other
     resources used by GSMP indirectly (e.g., CPU) or resources (e.g.,
     forwarding table entries) used by other types of SEs MAY be
   4. If a PM instructs a SE to release resources allocated to an active
     partition and if any of those resources are currently in use, the
     SE MUST deny the PMÆs request.
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   5. Subsequent to a resource reallocation failure, the PM SHOULD make
     use of one or both of the capabilities described in requirements 6
     and 7.
   6. A PM SHOULD be able to tell a SE to make an active partition into
     a frozen partition.
   7. A PM SHOULD be able to contact the controller to ask it to reduce
     its resource utilization.
   8. The PM MUST be able to exercise "power on/off" type control of the
     virtual SEs that it has created.  When the virtual power to an
     active partition is turned off, the partition becomes inactive and
     any controllers associated with that partition are disconnected.
     This capability allows a PM to resort to static partitioning when
     a controller is uncooperative about releasing resources.
   9. During dynamic repartitioning, a SE MUST maintain all existing
     state associated with the partitions being modified.
   10.  Control protocols SHOULD NOT include any mechanism by which a
     SE can ask its controller to reduce its resource usage.
   11.  Control protocols MAY contain proactive resource notification
     messages by which a SE could instantaneously inform the controller
     of an increase or decrease in resources.  (We do not specifically
     require control protocols to contain proactive notifications
     because all control protocols must already have explicit or
     implicit reactive notifications as mentioned in requirement #2).
   12.  A PM MAY directly inform a controller of a change in virtual SE
     resources rather than rely on the implicit resource exhaustion
     mechanism of the control protocol.
   13.  SEs MAY inform the PM of resource exhaustion on a particular
   14.  A controller MAY ask the PM for further resources or a
     reduction in existing resources.
   15.  To support the automation of interaction between the PM and
     attached controllers, the PM MUST be able to determine from the SE
     the addresses of the controllers that are currently attached to a
     virtual SE.  Additionally, the SE MAY allow the PM to determine
     which control protocol (and version thereof) is currently managing
     each active partition.
   16.  A SE MAY support the ability to have one virtual SE provide a
     service to another virtual SE within the same physical SE.  For
     example, a SE may be configured to provide a virtual link between
     two virtual SEs.  Furthermore:
     a. There MUST be a mechanism by which the SE can inform the PM
        which of these partition-to-partition services are provided by
        the SE.
     b. There MUST be a mechanism by which the PM can configure the
        available partition-to-partition services.
     c. If the configuration of a partition-to-partition service
        results in a virtual port being added/removed from a virtual
        SE, the SE MUST notify all controllers attached to that virtual
        SE (assuming that the corresponding control protocol supports
        such notifications).

Security Considerations

   Only authorized PMs MUST be allowed to dynamically repartition a SE.
   Similarly, only the PM (or an authorized agent of the PM) that is
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   authorized to partition a SE MUST be allowed to contact controllers
   to request that they decrease their resources or inform them that
   their resources have been increased.  Likewise, the PM MUST verify
   and authenticate that any requests for additional/fewer resources
   for a virtual SE have come from a controller authorized to control
   the specified virtual SE.

Intellectual Property Considerations

   The IETF is being notified of intellectual property rights claimed
   in regard to some or all of the specification contained in this
   document.  For more information, consult the online list of claimed


   The authors would like to acknowledge the contributions of Avri
   Doria and Jonathan Sadler to this draft.

Normative References

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

   [RFC3292] A. Doria, et. al., "General Switch Management Protocol
             (GSMP) V3", RFC3292, June 2002.

Informative References

   [RFC3015]  F. Cuervo, et. al., "Megaco Protocol 1.0," RFC3015,
              November 2000.

Author Information

   Todd A. Anderson
   Intel Labs
   2111 NE 25th Avenue
   Hillsboro, OR 97124 USA
   Phone: +1 503 712 1760

   Joachim Buerkle
   Nortel Networks Germany GmbH & Co. KG
   Hahnstrasse 37-39
   60528 Frankfurt
   Phone:  ++49 (0)69 6697 3281

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