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. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference 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 Haleplidis, et al. Expires January 16, 2014 [Page 1] Internet-Draft SDN Layers and Architecture Terminology July 2013 Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. 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 Haleplidis, et al. Expires January 16, 2014 [Page 2] Internet-Draft SDN Layers and Architecture Terminology July 2013 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. Haleplidis, et al. Expires January 16, 2014 [Page 3] Internet-Draft SDN Layers and Architecture Terminology July 2013 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. Haleplidis, et al. Expires January 16, 2014 [Page 4] Internet-Draft SDN Layers and Architecture Terminology July 2013 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 Haleplidis, et al. Expires January 16, 2014 [Page 5] Internet-Draft SDN Layers and Architecture Terminology July 2013 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. Haleplidis, et al. Expires January 16, 2014 [Page 6] Internet-Draft SDN Layers and Architecture Terminology July 2013 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. Haleplidis, et al. Expires January 16, 2014 [Page 7] Internet-Draft SDN Layers and Architecture Terminology July 2013 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. Haleplidis, et al. Expires January 16, 2014 [Page 8] Internet-Draft SDN Layers and Architecture Terminology July 2013 4. Acknowledgements TBD Haleplidis, et al. Expires January 16, 2014 [Page 9] Internet-Draft SDN Layers and Architecture Terminology July 2013 5. IANA Considerations This memo makes no requests to IANA. Haleplidis, et al. Expires January 16, 2014 [Page 10] Internet-Draft SDN Layers and Architecture Terminology July 2013 6. Security Considerations TBD Haleplidis, et al. Expires January 16, 2014 [Page 11] Internet-Draft SDN Layers and Architecture Terminology July 2013 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", . [OpenFlow1.3.1] Open Networking Foundation, "The OpenFlow 1.3 Specification.", . [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. Haleplidis, et al. Expires January 16, 2014 [Page 12] Internet-Draft SDN Layers and Architecture Terminology July 2013 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 Haleplidis, et al. Expires January 16, 2014 [Page 13]