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
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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.
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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
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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.
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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 [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:
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- 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?
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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.
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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).
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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
claims of rights made available for publication and any assurances of
licenses to be made available, or the result of an attempt made to
obtain a general license or permission for the use of such
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.
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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:
[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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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
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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
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English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
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Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
Anderson, et al. Informational [Page 11]
