RFC 3532
Requirements for the Dynamic Partitioning of Switching Elements
Pages: 11
Informational
Informational
Network Working Group T. Anderson Request for Comments: 3532 Intel Labs Category: Informational J. Buerkle Nortel Networks May 2003 Requirements for the Dynamic Partitioning of Switching Elements Status of this Memo This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (2003). All Rights Reserved.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.Table of Contents
1. Definitions ................................................ 2 2. Introduction ............................................... 3 3. Dynamic Partitioning ....................................... 6 4. Requirements ............................................... 7 5. Security Considerations .................................... 9 6. Intellectual Property Considerations ....................... 9 7. Acknowledgements ........................................... 9 8. Normative References ....................................... 10 9. Informative References ..................................... 10 10. Authors' Addresses ......................................... 10 11. Full Copyright Statement ................................... 11
1. Definitions
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. 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.
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.
2. 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
document) 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 document, 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 (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 co-located 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 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.
3. 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?
4. 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 all resources discoverable through GSMP (e.g., label tables). Partitioning of 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.
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.
5. 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.
6. Intellectual Property Considerations
The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on the
IETF's procedures with respect to rights in standards-track and
standards-related documentation can be found in RFC 2026. Copies of
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proprietary rights by implementors or users of this specification can
be obtained from the IETF Secretariat.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive
Director.
7. Acknowledgements
The authors would like to acknowledge the contributions of Avri Doria
and Jonathan Sadler to this document.
8. Normative References
[RFC2119] Bradner, S. "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3292] Doria, A., Hellstrand, F., Sundell, K. and T. Worster, "General Switch Management Protocol (GSMP) V3", RFC 3292, June 2002.9. Informative References
[RFC3015] Cuervo, F., Greene, N., Rayhan, A., Huitema, C., Rosem, B. and J. Segers, "Megaco Protocol 1.0," RFC 3015, November 2000.10. Authors' Addresses
Todd A. Anderson Intel Labs JF2-60 2111 NE 25th Avenue Hillsboro, OR 97124 USA Phone: +1 503 712 1760 EMail: todd.a.anderson@intel.com Joachim Buerkle Nortel Networks Germany GmbH & Co. KG Hahnstrasse 37-39 60528 Frankfurt Phone: ++49 (0)69 6697 3281 EMail: joachim.buerkle@nortelnetworks.com
11. Full Copyright Statement
Copyright (C) The Internet Society (2003). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society.