General Switch Management Protocol (GSMP) Applicability
Protocol for controlling switches and managing label-based forwarding in MPLS networks.
Doria, A. and K. Sundell, "General Switch Management Protocol (GSMP) Applicability", RFC 3294, DOI 10.17487/RFC3294, June 2002, <https://www.rfc-editor.org/info/rfc3294>.
@misc{rfc3294,
series = {Request for Comments},
number = 3294,
howpublished = {RFC 3294},
publisher = {RFC Editor},
doi = {10.17487/RFC3294},
url = {https://www.rfc-editor.org/info/rfc3294},
author = {A. Doria and K. Sundell},
title = {{General Switch Management Protocol (GSMP) Applicability}},
pagetotal = 9,
year = 2002,
month = jun,
} RFC text
Contents
Network Working Group A. Doria
Request for Comments: 3294 Lulea University of Technology
Category: Informational K. Sundell
Nortel Networks
June 2002
General Switch Management Protocol (GSMP) Applicability
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 (2002). All Rights Reserved.
Abstract
This memo provides an overview of the GSMP (General Switch Management
Protocol) and includes information relating to its deployment in a IP
network in an MPLS environment. It does not discuss deployment in an
ATM (Asynchronous Transfer Mode) network or in a raw ethernet
configuration.
1. Overview
The General Switch Management Protocol (GSMP) has been available to
the IETF community for several years now as informational RFCs. Both
GSMPv1.1 (released in March 1996 as RFC 1987 [2]) and GSMPv2.0
(released in August 1998 as RFC 2297 [3]) are available. Several
vendors have implemented GSMPv1.1.
In V1.1 and V2 GSMP was intended only for use with ATM switches.
During the course of the last two years, the GSMP working group has
decided to expand the purview of GSMP to the point where it can be
used to control a number of different kinds of switch and can thus
live up to what its name indicates; a general switch management
protocol. To do this, commands and arguments needed to be
generalised and sections needed to be added, discussing the manner in
which the generalised protocol could be applied to specific kinds of
switches and port types. In short, the protocol has gone through
major changes in the last 24 months.
GSMP provides an interface that can be used to separate the data
forwarder from the routing and other control plane protocols such as
LDP. As such it allows service providers to move away from
monolithic systems that bundle the control plane and the data plane
into a single tightly coupled system - usually in a single chassis.
Separating the control components from the forwarding components and
using GSMP for switch management, enables service providers to create
multi-service systems composed of various vendors equipment. It also
allows for a more dynamic means of adding services to their networks.
The IETF GSMP working group was established in the routing area
because GSMP was being seen as an optional part of the MPLS solution.
In a MPLS system, it is possible to run the routing protocols and
label distribution protocols on one system while passing data across
a generic switch, e.g., an ATM switch. GSMP provides the switch
resource management mechanism needed in such a scenario.
GSMP has also been selected by the Multiservice Switching Forum (MSF)
as its protocol of choice for the Switch Control Interface identified
in their architecture. The MSF is an industry forum which, among its
activities establishes their member's requirements and then works
with the appropriate standards bodies to foster their goals. In the
case of GSMP, the MSF presented the IETF GSMP Working Group with a
set of requirements for GSMP. The working group has made a
determined effort to comply with those requirements in its
specifications.
2. GSMP V3 Document Set
The current version of GSMP is documented in 3 documents:
- GSMP: General Switch Management protocol V3 [5]
- GSMP-ENCAPS: General Switch Management Protocol (GSMP) Packet
Encapsulations for Asynchronous Transfer Mode (ATM), Ethernet and
Transmission Control Protocol (TCP) [4]
- GSMP-MIB: Definitions of Managed Objects for the General Switch
Management Protocol [1]
3. General Description
The General Switch Management Protocol V3 (GSMPv3) [5], is a general
purpose protocol to control a label switch. GSMP allows a
controller to establish and release connections across the switch;
add and delete leaves on a multicast connection; reserve
resources; manage switch ports; request configuration information;
and request statistics. It also allows the switch to inform the
controller of asynchronous events such as a link going down. The
GSMPv3 protocol is asymmetric, the controller being the master and
the switch being the slave.
A physical switch can be partitioned into many virtual switches.
GSMPv3 does not provide support for defining switch partitions.
GSMPv3 treats a virtual switch as if it were a physical switch.
GSMPv3 may be transported in three ways:
- GSMPv3 operation across an IP network is specified.
- GSMPv3 operation across an ATM virtual channel is specified.
- GSMPv3 operation across an Ethernet link is specified.
Other encapsulations are possible, but have not been defined.
Encapsulations are defined in [4].
A label switch is a frame or cell switch that supports connection
oriented switching using the exact match forwarding algorithm
based on labels attached to incoming cells or frames.
A label switch may support multiple label types. However, each
switch port can support only one label type. The label type
supported by a given port is indicated in a port configuration
message. Connections may be established between ports supporting
different label types using the adaptation methods. GSMPv3
supports TLV labels similar to those defined in MPLS. Examples of
labels which are defined include ATM, Frame Relay, DS1, DS3, E1,
E3, MPLS Generic Labels and MPLS FECs.
A connection across a switch is formed by connecting an incoming
labelled channel to one or more outgoing labelled channels.
Connections are generally referenced by the input port on which
they arrive and the label values of their incoming labelled
channel. In some messages, connections are referenced by the
output port.
GSMPv3 supports point-to-point and point-to-multipoint connections.
A multipoint-to-point connection is specified by establishing
multiple point-to-point connections, each of which specifies the
same output label. A multipoint-to-multipoint connection is
specified by establishing multiple point-to-multipoint connections
each of which specifies a different input label with the same
output labels.
In general a connection is established with a certain quality of
service (QoS). GSMPv3 includes a default QoS Configuration and
additionally allows the negotiation of alternative, optional QoS
configurations. The default QoS Configuration includes three QoS
Models: a default service model, a simple priority model and a QoS
profile model. GSMPv3 also supports the reservation of resources
when the labels are not yet known. This ability can be used in
support of MPLS.
GSMP contains an adjacency protocol. The adjacency protocol is used
to synchronise states across the link, to negotiate which version
of the GSMP protocol to use, to discover the identity of the
entity at the other end of a link, and to detect when it changes.
3.1 Switch Partitioning
In GSMPv3 switch partitioning is static and occurs prior to running
the protocol. The partitions of a physical switch are isolated from
each other by the implementation and the controller assumes that the
resources allocated to a partition are at all times available to that
partition and only that partition. A partition appears to its
controller as a physical label switch. The resources allocated to a
partition appear to the controller as if they were the actual
physical resources of a physical switch. For example if the
bandwidth of a port is divided among several partitions, each
partition would appear to the controller to have its own independent
port with its fixed set of resources.
GSMPv3 controls a partitioned switch through the use of a partition
identifier that is carried in every GSMPv3 message. Each partition
has a one-to-one control relationship with its own logical controller
entity (which in the remainder of the document is referred to simply
as a controller) and GSMPv3 independently maintains adjacency between
each controller-partition pair.
3.2 Switch and controller interactions
Multiple switches may be controlled by a single controller using
multiple instantiations of the protocol over separate control
connections.
Alternatively, multiple controllers can control a single switch.
Each controller would establish a control connection to the switch
using the adjacency protocol. The adjacency mechanism maintains a
state table indicating the control connections that are being
maintained by the same partition. The switch provides information to
the controller group about the number and identity of the attached
controllers. It does nothing, however, to co-ordinate the activities
of the controllers, and will execute all commands as they are
received. It is the controller group's responsibility to co-ordinate
its use of the switch. This mechanism is most commonly used for
controller redundancy and load sharing. Definition of the mechanism
by which controllers use to co-ordinate their control is not within
GSMPv3's scope.
3.3 Service support
All GSMPv3 switches support the default QoS Configuration. A GSMPv3
switch may additionally support one or more alternative QoS
Configurations. GSMP includes a negotiation mechanism that allows a
controller to select from the QoS configurations that a switch
supports.
The default QoS Configuration includes three models:
The Service Model is based on service definitions found external
to GSMP such as in CR-LDP, Integrated Services or ATM Service
Categories. Each connection is assigned a specific service
that defines the handling of the connection by the switch.
Additionally, traffic parameters and traffic controls may be
assigned to the connection depending on the assigned service.
In the Simple Abstract Model a connection is assigned a priority
when it is established. It may be assumed that for connections
that share the same output port, a cell or frame on a
connection with a higher priority is much more likely to exit
the switch before a cell or frame on a connection with a lower
priority if they are both in the switch at the same time.
The QoS Profile Model provides a simple mechanism that allows QoS
semantics defined externally to GSMP to be assigned to
connections. Each profile is an opaque indicator that has been
predefined in the controller and in the switch.
4. Summary of Message Set
The following table gives a summary of the messages defined in this
version of the specification. It also makes a recommendation of the
minimal set of messages that should be supported in an MPLS
environment. These messages will be labelled as "Required", though
the service provided by the other messages are essential for the
operation of carrier quality controller/switch operations. GSMPv1.1
or GSMPv2 commands that are no longer support are marked as
"Obsolete" and should no longer be used.
4.1 Messages Table
Message Name Message Number Status
Connection Management Messages
Add Branch........................16 Required
ATM Specific - VPC............26
Delete Tree.......................18
Verify Tree.......................19 Obsoleted
Delete All Input..................20
Delete All Output.................21
Delete Branches...................17 Required
Move Output Branch................22
ATM Specific - VPC............27
Move Input Branch.................23
ATM Specific - VPC............28
Port Management Messages
Port Management...................32 Required
Label Range.......................33
State and Statistics Messages
Connection Activity...............48
Port Statistics...................49 Required
Connection Statistics.............50
QoS Class Statistics..............51 Reserved
Report Connection State...........52
Configuration Messages
Switch Configuration..............64 Required
Port Configuration................65 Required
All Ports Configuration...........66 Required
Service Configuration.............67
Reservation Messages
Reservation Request...............70 Required
Delete Reservation................71 Required
Delete All Reservations...........72
Event Messages
Port Up...........................80
Port Down.........................81
Invalid Label.....................82
New Port..........................83
Dead Port.........................84
Abstract and Resource Model Extension Messages
Reserved.Message Range.........200-249
Adjacency Protocol.................10 Required
5. Security Considerations
The security of GSMP's TCP/IP control channel has been addressed in
[4]. For all uses of GSMP over an IP network, it is REQUIRED that
GSMP be run over TCP/IP using the security considerations discussed
in [4].
References
[1] Sjostrand, H., Buerkle, J. and B. Srinivasan, "Definitions of
Managed Objects for the General Switch Management Protocol
(GSMP)", RFC 3295, June 2002.
[2] Newman, P., Edwards, W., Hinden, R., Hoffman, E., Ching Liaw, F.,
Lyon, T. and Minshall, G., "Ipsilon's General Switch Management
Protocol Specification Version 1.1", RFC 1987, August 1996.
[3] Newman, P., Edwards, W., Hinden, R., Hoffman, E., Ching Liaw, F.,
Lyon, T. and G. Minshall, "Ipsilon's General Switch Management
Protocol Specification Version 2.0", RFC 2297, March 1998.
[4] Worster, T., Doria, A. and J. Buerkle, "General Switch Management
Protocol (GSMP) Packet Encapsulations for Asynchronous Transfer
Mode (ATM), Ethernet and Transmission Control Protocol (TCP)",
RFC 3293, June 2002.
[5] Doria, A., Sundell, K., Hellstrand, F. and T. Worster, "General
Switch Management Protocol (GSMP) V3", RFC 3292, June 2002.
Authors' Addresses
Avri Doria
Div. of Computer Communications
Lulea University of Technology
S-971 87 Lulea
Sweden
Phone: +1 401 663 5024
EMail: avri@acm.org
Kenneth Sundell
Nortel Networks AB
S:t Eriksgatan 115 A
P.O. Box 6701
SE-113 85 Stockholm Sweden
EMail: sundell@nortelnetworks.com
Full Copyright Statement
Copyright (C) The Internet Society (2002). 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.
AI ELI5
On this page
§1Overview and Purpose
The General Switch Management Protocol (GSMP) has evolved from a protocol designed for ATM switches to a general-purpose protocol for controlling label switches in IP and MPLS networks. GSMP v3 separates the data forwarding plane from the control plane: a controller sends commands to a switch to establish connections, manage ports, reserve resources, and request statistics. The switch responds with acknowledgments and can also send asynchronous event notifications, such as link state changes.
The protocol enables service providers to move away from monolithic systems that tightly couple control and forwarding. Instead, operators can deploy switches from one vendor controlled by routing software from another, allowing multi-vendor networks and greater operational flexibility. The Multiservice Switching Forum (MSF) selected GSMP as its protocol of choice for switch control interfaces.
Instead of having one big box that does everything, you can have simple switches controlled by separate software. That lets you mix and match equipment from different companies.
- Control planeRouting protocols, label distribution, service policies
- GSMPProtocol for switch control and configuration
- Data planeLabel switch, port management, packet forwarding
§2Switch Architecture and Label Types
A label switch is a frame or cell switch that uses exact-match forwarding on labels attached to incoming frames or cells. GSMP treats each switch (or virtual partition of a physical switch) as a collection of ports, where each port supports one label type. Label types supported include ATM VCs, Frame Relay DLCIs, DS1/DS3 circuits, MPLS generic labels, and MPLS Forwarding Equivalence Classes (FECs).
Connections are formed by connecting incoming labeled channels on an input port to one or more outgoing labeled channels on output ports. GSMP supports point-to-point connections (unicast), point-to-multipoint connections (one sender, multiple receivers), and approximations of multipoint-to-point and multipoint-to-multipoint. A single controller can manage multiple switches, and multiple controllers can manage a single switch for redundancy and load sharing, though coordination among controllers is the controllers' responsibility.
The switch has ports, each marked with a label. Connections link an input port label to output port labels, just like wires in a patch panel.
§3Connections and Quality of Service
When the controller establishes a connection, it specifies the input port and label, the output port(s) and label(s), and a quality-of-service (QoS) class. GSMP v3 includes a default QoS configuration with three service models. The Service Model assigns a service type (from external definitions like CR-LDP or IntServ) that determines how the switch handles the connection. The Simple Priority Model assigns a priority level, and the switch favors higher-priority traffic when cells or frames share an output port. The QoS Profile Model allows a predefined profile identifier that encodes QoS semantics known to both controller and switch.
GSMP also supports resource reservation before labels are known, useful for MPLS deployments where label assignment may be dynamic. The controller can reserve bandwidth on ports and request statistics such as connection activity, port statistics, and per-connection statistics.
When you make a connection, you say how important it is. The switch then makes sure important connections get through even when it is busy.
- Port Configuration
- Port Configuration Ack
- Add Connection (in-port, in-label, out-port, out-label, QoS)
- Connection Established Ack
§4Messages and Protocol Operation
GSMP v3 defines several message categories. Connection Management Messages add or delete branches on point-to-point or multipoint connections, move branches, and delete entire connection trees. Port Management Messages configure ports and label ranges. Configuration Messages report and set switch and service configurations. Reservation Messages reserve and release switch resources. State and Statistics Messages request connection states and statistics. Event Messages notify the controller of asynchronous events like port up, port down, or invalid label errors.
The protocol operates over IP networks (using TCP), ATM virtual channels, or Ethernet links. An Adjacency Protocol synchronizes state, negotiates protocol version, discovers the entity on the other end of the link, and detects when it changes. A partition identifier carried in every message allows a physical switch to be sliced into virtual switches, each with its own controller.
The controller and switch exchange messages: 'add this connection,' 'delete that port,' 'send me statistics,' 'your link just went down.'
§5Deployment in MPLS Networks
GSMP v3 is designed to work in MPLS networks where routing protocols and label distribution protocols (such as LDP or CR-LDP) run on a controller or control plane, while a separate label switch physically forwards packets. The controller uses GSMP to manage the switch, configure ports, and direct label distribution. This separation of concerns allows the switch to be a simpler, faster device.
In a typical deployment, a controller establishes BGP or other routing relationships and uses LDP to negotiate labels with other routers. When paths need to be set up, the controller uses GSMP to instruct the switch to create the forwarding rules. The switch can support multiple QoS configurations, and controllers can negotiate which QoS model the switch should use for a given connection or service.
The routing brain (controller) decides what connections to make. It tells the fast switch (data plane) exactly what to do via GSMP.