SDN Layers and Architecture Terminology
draft-haleplidis-sdnrg-layer-terminology-00
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|---|---|---|---|
| Authors | Evangelos Haleplidis , Spyros Denazis , Odysseas Koufopavlou , Kostas Pentikousis , Jamal Hadi Salim | ||
| Last updated | 2013-07-15 | ||
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draft-haleplidis-sdnrg-layer-terminology-00
SDNRG E. Haleplidis
Internet-Draft S. Denazis
Intended status: Informational O. Koufopavlou
Expires: January 16, 2014 University of Patras
K. Pentikousis
Huawei Technologies
J. Hadi Salim
Mojatatu Networks
July 15, 2013
SDN Layers and Architecture Terminology
draft-haleplidis-sdnrg-layer-terminology-00
Abstract
Software-Defined Networking introduces an abstraction layer and by
doing so separates the Forwarding from the Control layer. This
separation can allow faster innovation cycles at both layers as
experience has already shown. However, there is increasing confusion
as to what exactly SDN is, what is the layer stucture in an SDN
architecture and how do layers interface with each other. This
document aims to provide a concise reference for future discussions
in SDNRG.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 16, 2014.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Provisions Relating to IETF Documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. SDN Layers and Architecture . . . . . . . . . . . . . . . . . 5
2.1. Network Devices . . . . . . . . . . . . . . . . . . . . . 6
2.2. Control Plane . . . . . . . . . . . . . . . . . . . . . . 6
2.3. Management Plane . . . . . . . . . . . . . . . . . . . . . 7
2.4. Service Abstraction Layer . . . . . . . . . . . . . . . . 7
2.5. Application Plane . . . . . . . . . . . . . . . . . . . . 7
3. SDN Model View . . . . . . . . . . . . . . . . . . . . . . . . 8
3.1. ForCES . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.2. Openflow . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.3. NETCONF . . . . . . . . . . . . . . . . . . . . . . . . . 8
4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
7. Informative References . . . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
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1. Introduction
Software-Defined Networking introduces an abstraction layer between
the Forwarding and the Control layer in order to separate them. This
separation allows faster innovation for both layers as experience has
already shown. However, there is increasing confusion as to what
exactly SDN is, what layers comprise the SDN architecture and what
are the interfaces. This draft attempts to provide a concise
reference document for future discussions on SDN.
1.1. Requirements Language
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].
1.2. Terminology
This document introduces the following terms:
Software-Defined Networking (SDN) - A framework that supports the
separation of Control and Forwarding Planes via standardized
interfaces.
Network Device - A device that performs one or more network
operations related to packet manipulation and forwarding. A
network device can be physical or virtual.
Forwarding Plane (FP) - The network device part responsible for
forwarding traffic.
Operational Plane (OP) - The network device part responsible for
managing device operation.
Management Plane (MP) - Network funtionality responsible for
monitoring and maintaining network devices.
Control Plane (CP) - Part of the network that is assigned to
control one or more network devices. CP instructs network devices
how to treat and forward packets.
Application (App) - A piece of software that utilizes underlying
services to perform a function.
Service - A piece of software that performs one or more functions
and provides one or more APIs to applications or other services of
the same or different layers to provide said functions. Services
can be aggregated with other services to create a new service.
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Interface (Int) - A point of interaction between two parts. In
case these parts are not in the same physical location, the
interface is usually implemented as network protocol. In case
these parts are collocated in the same physical location the
interface can be a protocol or an open/proprietary software inter-
process communication API.
Device Abstraction Layer (DAL) - The device's abstraction layer
based on one or more models. If it is a physical device it may be
refered to as the Hardware Abstraction Layer (HAL). DAL provides
a uniform point of reference for the device.
Control Abstraction Layer (CAL) - The control plane's abstraction
layer. CAL provides access to the control plane southbound
interface.
Management Abstraction Layer (MAL) - The management plane's
abstraction layer. MAL provides access to the management plane
southbound interface.
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2. SDN Layers and Architecture
Figure 1 provides a detailed abstraction overview of the current SDN
architecture. Planes can be collocated with other planes or can be
physically separated, as we discuss below.
+--------------------------------+
| |
| +-------------+ +----------+ |
| | Application | | Service | |
| +-------------+ +----------+ |
| Application Plane |
+---------------Y----------------+
|
+-----------------------------Y---------------------------------+
| Service Abstraction Layer (SAL) |
+------Y------------------------------------------------Y-------+
| |
| Service Interface |
| |
+------Y------------------+ +---------------------Y------+
| | Control Plane | | Management Plane | |
| +----Y----+ +-----+ | | +-----+ +----Y----+ |
| | Service | | App | | | | App | | Service | |
| +----Y----+ +--Y--+ | | +--Y--+ +----Y----+ |
| | | | | | | |
| +----Y-----------Y----+ | | +---Y---------------Y----+ |
| | Control Abstraction | | | | Management Abstraction | |
| | Layer (CAL) | | | | Layer (MAL) | |
| +----------Y----------+ | | +----------Y-------------+ |
| | | | | |
+------------|------------+ +------------|---------------+
| |
| Control Plane | Management Plane
| Southbound Interface | Southbound Interface
| |
+------------Y---------------------------------Y----------------+
| Device Abstraction Layer (DAL) |
+------------Y---------------------------------Y----------------+
| | | |
| +-------Y----------+ +-----+ +---------Y---------+ |
| | Forwarding Plane | | App | | Operational Plane | |
| +------------------+ +-----+ +-------------------+ |
| Network Device |
+---------------------------------------------------------------+
Figure 1: SDN Layer Architecture
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2.1. Network Devices
A Network Device, implemented in hardware or in software, physical or
virtual, has both a Forwarding Plane and an Operational Plane. The
Forwarding Plane, commonly referred to as the data path, is
responsible for handling and forwarding of packets. The Operational
Plane represents the operational state of the device, for example,
with respect to network ports and interfaces.
The Forwarding and the Operational Planes can be exposed using a
Device Abstraction Layer (DAL), which may comprise one or more
abstraction models. Examples of Forwarding Plane abstraction models
are the ForCES model [RFC5812] and the OpenFlow switch model
[OpenFlow1.3.1]. Examples of the Operational Plane abstraction model
include the ForCES model [RFC5812], the YANG model [RFC6020] and SNMP
MIBs [RFC3418].
Applications can also reside in the network device. Examples of such
applications are event monitoring, and offloading topology discovery
or ARP in the device itself instead of forwarding such traffic to the
control plane.
2.2. Control Plane
The Control Plane communicates with the Forwarding Plane of devices
using a Control Plane Southbound Interface (CPSI) with DAL as a point
of reference and is responsible for instructing the Forwarding Plane
on how to handle network packets. CPSI can be implemented using a
protocol, an API or even interprocess communication. If the Control
Plane and the Network Device are not collocated, then this interface
is certainly a protocol. Examples of CPSIs are ForCES [RFC5810] and
the Openflow protocol [OpenFlow1.3.1].
The Control Abstraction Layer (CAL) provides access to control
applications and services to various CPSIs. The Control Plane may
support more than one CPSIs.
Control applications can use CAL to control a network device without
providing any service to upper layers. Examples include applications
that perform control functions, such as OSPF, BGP, etc.
Control Plane Services provide access to other Services or
Application above the control plane. Examples include a virtual
private LAN service, service tunnels, etc.
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2.3. Management Plane
The Management Plane communicates with the network device Operational
Plane using a Management Plane Southbound Interface (MPSI) with DAL
as a point of reference. This interface can range from a protocol,
to an API or even interprocess communication. If the Management
Plane is not embedded in the network device, this interface is
certainly a protocol. Examples of MPSIs are ForCES [RFC5810],
NETCONF [RFC6241], OVSDB [I-D.pfaff-ovsdb-proto] and SNMP [RFC3411].
The Management Abstraction Layer (MAL) provides access to management
applications and services to various MPSIs. The Management Plane may
support more than one MPSI.
Management Applications can use MAL to manage the network device
without providing any service to upper layers. Examples of
management applications include network monitoring applications.
Management Plane Services provide access to other services or
application above the Management Plane.
2.4. Service Abstraction Layer
The Service Abstraction Layer (SAL) provides access from services of
the control, management and applciation plane to services and
applications of the application plane. Examples of service
interfaces are REST APIs.
2.5. Application Plane
Applications and services that use services from the control and/or
management plane form the Application Plane.
Addditionally, services residing in the Application Plane may provide
services to other services and applications that reside in the
application plane via the service interface.
Examples of applications include network topology discovery, network
provisioning, path reservation, etc.
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3. SDN Model View
We advocate that the SDN southbound interface should encompass both
the CSPI and the MSPI.
The SDN northbound interface is implemented in the Service
Abstraction Layer.
The above model can be used to describe in a concise manner all
prominent SDN-enabling technologies, as we explain in the following
subsections.
3.1. ForCES
ForCES can be mapped on the above framework as follows:
o The ForCES model can be used to describe the DAL, both for the
Operational and the Forwarding Plane.
o The ForCES protocol can then be the CPSI and the MPSI.
o CAL and the MAL must be able to utilize the ForCES protocol
3.2. Openflow
Openflow can be mapped on the above framework as follows:
o The Openflow switch specifications [OpenFlow1.3.1] covers DAL for
the Forwarding Plane and provides the specifications for CAL and
CPSI.
o The OF-CONFIG protocol [OF-CONFIG] based on the YANG model
[RFC6020], provides DAL for the Operational Plane and specifies
NETCONF [RFC6241] as the MPSI.
o CAL must be able to utilize the Openflow protocol.
o MAL must be able to utilize the NETCONF protocol.
3.3. NETCONF
NETCONF can be mapped on the above framework as follows:
o The YANG model [RFC6020] is suitable for specifying DAL for the
Operational plane and NETCONF [RFC6241] for the MPSI.
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4. Acknowledgements
TBD
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5. IANA Considerations
This memo makes no requests to IANA.
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6. Security Considerations
TBD
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7. Informative References
[I-D.pfaff-ovsdb-proto]
Pfaff, B. and B. Davie, "The Open vSwitch Database
Management Protocol", draft-pfaff-ovsdb-proto-02 (work in
progress), March 2013.
[OF-CONFIG]
Open Networking Foundation, "OpenFlow Management and
Configuration Protocol 1.1", <https://
www.opennetworking.org/images/stories/downloads/
sdn-resources/onf-specifications/openflow-config/
of-config-1.1.pdf>.
[OpenFlow1.3.1]
Open Networking Foundation, "The OpenFlow 1.3
Specification.", <https://www.opennetworking.org/images/
stories/downloads/sdn-resources/onf-specifications/
openflow/openflow-spec-v1.3.1.pdf>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3411] Harrington, D., Presuhn, R., and B. Wijnen, "An
Architecture for Describing Simple Network Management
Protocol (SNMP) Management Frameworks", STD 62, RFC 3411,
December 2002.
[RFC3418] Presuhn, R., "Management Information Base (MIB) for the
Simple Network Management Protocol (SNMP)", STD 62,
RFC 3418, December 2002.
[RFC5810] Doria, A., Hadi Salim, J., Haas, R., Khosravi, H., Wang,
W., Dong, L., Gopal, R., and J. Halpern, "Forwarding and
Control Element Separation (ForCES) Protocol
Specification", RFC 5810, March 2010.
[RFC5812] Halpern, J. and J. Hadi Salim, "Forwarding and Control
Element Separation (ForCES) Forwarding Element Model",
RFC 5812, March 2010.
[RFC6020] Bjorklund, M., "YANG - A Data Modeling Language for the
Network Configuration Protocol (NETCONF)", RFC 6020,
October 2010.
[RFC6241] Enns, R., Bjorklund, M., Schoenwaelder, J., and A.
Bierman, "Network Configuration Protocol (NETCONF)",
RFC 6241, June 2011.
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Authors' Addresses
Evangelos Haleplidis
University of Patras
Department of Electrical and Computer Engineering
Patras, 26500
Greece
Email: ehalep@ece.upatras.gr
Spyros Denazis
University of Patras
Department of Electrical and Computer Engineering
Patras, 26500
Greece
Email: sdena@upatras.gr
Odysseas Koufopavlou
University of Patras
Department of Electrical and Computer Engineering
Patras, 26500
Greece
Email: odysseas@ece.upatras.gr
Kostas Pentikousis
Huawei Technologies
Carnotstrasse 4
10587 Berlin
Germany
Email: k.pentikousis@huawei.com
Jamal Hadi Salim
Mojatatu Networks
Suite 400, 303 Moodie Dr.
Ottawa, Ontario K2H 9R4
Canada
Email: hadi@mojatatu.com
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