RE: RE: dyn part draft

Internet Draft                                              T. Anderson 
GSMP Working Group                                           Intel Labs 
Expiration Date: April 2003                                  J. Buerkle 
                                                        Nortel Networks 
 
                                                           October 2002 
    
      Requirements for the Dynamic Partitioning of Switching Elements 
                                      
                  <draft-ietf-gsmp-dyn-part-reqs-03.txt> 
    
    
Status of this Memo 
    
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   all provisions of Section 10 of RFC2026.   
    
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Conventions used in this document 
    
   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]. 
 
 
Abstract 
 
   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 
   party. 
    
    
Definitions 
    
   In this document, the following definitions will be used. 
    
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   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. 
    
   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 partition’s resources without requiring a restart of 
   that partition.  Instances of repartitioning in which connections to 
   controllers are disconnected before resources can be reallocated 
   therefore fall into this category.  
    
   Dynamic Partitioning - In dynamic partitioning, an active 
   partition’s 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 an explicit, 
   resources-reassigned error code in the response to a subsequent 
   request by the controller for an unavailable resource. 
    
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   Implicit Reactive Notification - This is similar to an Explicit 
   Reactive Notification except that the protocol does not contain any 
   explicit resources-reassigned error codes.  In this case, all that 
   the SE can do is to indicate that some general, unknown error or 
   generic resource error (i.e., some resource error problem has 
   occurred but the exact cause is not specified) has occurred when the 
   controller attempts to use unavailable resources.  In such cases, 
   the controller may attempt to determine whether a resource shortfall 
   caused the error by using whatever messages are available through 
   the control protocol to query available resources. 
    
 
Introduction 
    
   This document identifies the logical entities involved in the 
   partitioning of switching elements.  Furthermore, this document 
   provides a set of requirements for the behavior of these logical 
   entities as well as the protocols used by these logical entities to 
   communicate with one another.  A primary goal of the requirements 
   specified herein is to allow the resources allocated to a partition 
   to be increased or decreased while the partition is currently active 
   (i.e., it has an active connection with a controller).  This 
   document is primarily intended to facilitate the partitioning of 
   GSMP switches.  However, while we believe that the logical entities 
   and requirements specified here are necessary for the partitioning 
   of non-GSMP switches and (longest prefix match) forwarders (e.g., 
   routers), we do not believe that these requirements are necessarily 
   sufficient for the partitioning of those devices. 
    
   Three 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).  Conversely, a single logical 
   controller could consist of processes running on multiple physical 
   processors collaborating to provide proper control.  Likewise, there 
   may be multiple partition managers running on a single management 
   workstation.  A switching element may consist of one or more whole 
   or fractional physical elements.  For example, a SE may be a single 
   whole physical switch (e.g., blade in a chassis), multiple whole 
   physical switches (e.g., two blades in a chassis made to appear as a 
   single logical entity), a single fraction of a physical switch 
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   (which would enable nested partitions), or multiple fractions of 
   either the same or different physical switches (e.g., ports 1-3 on 
   blade 1 and ports 2-4 on blade 2).  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 [RFC3292], 
   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. 
 
   ------------------             ------------------- 
   |                | *         * |                 | 
   |    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 [RFC3292] and MEGACO [RFC3015].  These 
   protocols allow a many-to-many relationship between controller and 
   partition. 
    
   Interaction C is one by which a PM and a controller could 
   communicate to alter the nature of an active partition.  There is a 
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   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   
          partition. 
      - The controller’s response to a PM request. 
    
   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 for the affected partitions 
   must be severed.  (This severing must always occur even if the 
   resources to be reapportioned are not currently in use.)  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 those partitions.  Thus, static 
   repartitioning results in a period of downtime and a period in which 
   the controllers are reestablishing state for affected partitions.  
   Partitions of a SE that are not affected by a static resource 
   reallocation need not be transitioned to the down state nor would 
   controllers have to reestablish state with unaffected partitions. 
    
   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 
       resources?   
     - What should happen when the PM would like to decrease the 
       resources allocated to a partition but those resources are in 
       use? 
    
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Requirements 
    
   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, there MUST be a mechanism by which a PM can partition 
     of all resources discoverable through GSMP (e.g., label tables).  
     Resources used by GSMP indirectly (e.g., CPU), resources used by 
     non-GSMP switches, or resources (e.g., forwarding table entries) 
     used by forwarding-based network elements MAY be supported. 
   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 PM’s request.  (Requirement #8 addresses the 
     potential starvation issues raised by this requirement.) 
   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.  This 
     requirement allows permanent starvation as a result of requirement 
     #4 to be avoided. 
   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 
     partition. 
   14.  A controller MAY ask the PM for further resources or a 
     reduction in existing resources. 
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   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). 
   17.  There MUST be a mechanism by which a PM can query a SE to 
     determine the resources of that SE, the partitions currently 
     configured on that SE and the resources allocated to each 
     partition. 
    
Security Considerations 
    
   Only authorized PMs MUST be allowed to dynamically repartition a SE.  
   Therefore, SEs MUST use a secure process by which an authorized 
   entity may instruct the SE as to which PM should control it.  This 
   instruction MAY specify the PM explicitly or MAY specify the use of 
   a (discovery) protocol to dynamically locate the PM.  Similarly, 
   only the PM (or an authorized agent of the PM) that is 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 
 
   No intellectual property rights are being claimed with respect to 
   this document. 
    
Acknowledgements 
    
   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. 
    
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   [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 
   JF2-60 
   2111 NE 25th Avenue 
   Hillsboro, OR 97124 USA 
   Phone: +1 503 712 1760 
   Email: [email protected] 
    
   Joachim Buerkle 
   Nortel Networks Germany GmbH & Co. KG 
   Hahnstrasse 37-39 
   60528 Frankfurt 
   Phone:  ++49 (0)69 6697 3281 
   Email: [email protected]  
    
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