SDNRG E. Haleplidis Internet-Draft S. Denazis Intended status: Informational University of Patras Expires: June 8, 2014 K. Pentikousis EICT J. Hadi Salim Mojatatu Networks D. Meyer Brocade O. Koufopavlou University of Patras December 5, 2013 SDN Layers and Architecture Terminology draft-haleplidis-sdnrg-layer-terminology-03 Abstract Software-Defined Networking (SDN) can in general be defined as a new approach for network programmability. Network programmability refers to the capacity to initialize, control, change, and manage network behavior dynamically via open interfaces as opposed to relying on closed-box solutions and propietary-defined interfaces. SDN emphasizes the role of software in running networks through the introduction of an abstraction for the data forwarding plane and, by doing so, separates it from the control plane. This separation allows faster innovation cycles at both planes as experience has already shown. However, there is increasing confusion as to what exactly SDN is, what is the layer structure in an SDN architecture and how do layers interface with each other. This document aims to answer these questions and provide a concise reference document for SDNRG, in particular, and the SDN community, in general, based on relevant peer-reviewed literature and documents in the RFC series. 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/. Haleplidis, et al. Expires June 8, 2014 [Page 1] Internet-Draft SDN Layers and Architecture Terminology December 2013 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 June 8, 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 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 . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 2. SDN Layers and Architecture . . . . . . . . . . . . . . . . . 5 2.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 6 2.2. Network Devices . . . . . . . . . . . . . . . . . . . . . 8 2.3. Control Plane . . . . . . . . . . . . . . . . . . . . . . 9 2.4. Management Plane . . . . . . . . . . . . . . . . . . . . 10 2.5. Service Abstraction Layer . . . . . . . . . . . . . . . . 11 2.6. Application Plane . . . . . . . . . . . . . . . . . . . . 11 3. SDN Model View . . . . . . . . . . . . . . . . . . . . . . . 12 3.1. ForCES . . . . . . . . . . . . . . . . . . . . . . . . . 12 3.2. NETCONF . . . . . . . . . . . . . . . . . . . . . . . . . 13 3.3. OpenFlow . . . . . . . . . . . . . . . . . . . . . . . . 14 3.4. I2RS . . . . . . . . . . . . . . . . . . . . . . . . . . 14 3.5. BFD . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 6. Security Considerations . . . . . . . . . . . . . . . . . . . 16 7. Informative References . . . . . . . . . . . . . . . . . . . 16 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18 1. Introduction Haleplidis, et al. Expires June 8, 2014 [Page 2] Internet-Draft SDN Layers and Architecture Terminology December 2013 Software-Defined Networking (SDN) is a relevant new term for the programmable networks paradigm [PNSurvey99][OF08]. In short, SDN refers to the ability to use software to program individual network devices dynamically and therefore control the behavior of the network as a whole [NV09]. A key element in SDN is the introduction of an abstraction between the (traditional) Forwarding and the Control planes in order to separate them and provide applications with the means necessary to programmatically control the network. The goal is to leverage on this separation, and the associated programmability, in order to reduce complexity and enable faster innovation at both planes [A4D05]. Current and earlier research in SDN often focuses on varying aspects of programmability, and we are frequently confronted with conflicting points of view regarding what exactly SDN is. For instance, we find that for various reasons (e.g. work focusing on one domain and therefore not necessarily applicable as-is to other domains), certain well-accepted definitions do not correlate well with each other. For example, both OpenFlow [OpenFlow] and NETCONF [RFC6241] have been characterized as SDN interfaces, but they refer to control and management respectively. This motivates us to consolidate the definitions of SDN in the literature and correlate them with earlier work in IETF and the research community. Of particular interest, for example, is to determine which layers comprise the SDN architecture and which interfaces and their corresponding attributes are best suitable to be used between them. As such, the aim of this document is not to standardize any particular layer or interface but rather to provide a concise reference document which reflects current approaches regarding the SDN layers architecture. We expect that this document would be useful to upcoming work in SDNRG as well as future discussions within the SDN community as a whole. This document aims to address the potential work item in the SDNRG charter named "Survey of SDN approaches and Taxonomies", fostering better understanding of prominent SDN technologies in an technology- impartial and business-agnostic manner. As such we do not make any value statements nor discuss the applicability of any of the frameworks examined for any particular purpose. Instead, we document their characteristics and attributes and classify them thus providing a taxonomy. This document does not constitute a new IETF standard nor a new specification, and aims to receive rough consensus within SDNRG to be published in the IRTF Stream as per [RFC5743]. Haleplidis, et al. Expires June 8, 2014 [Page 3] Internet-Draft SDN Layers and Architecture Terminology December 2013 The remainder of this document is organized as follows. Section 1.1 explains the terminology used in this document. Figure 1 introduces a high-level overview of current SDN architecture abstractions. Finally, Section 3 discusses how the SDN Layer Architecture relates with prominent SDN-enabling technologies 1.1. Terminology This document uses the following terms: Software-Defined Networking (SDN) - A programmable networks approach 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. This reference model makes no distinction whether a network device is physical or virtual. Interface - A point of interaction between two entities. In case the entities are not in the same physical location, the interface is usually implemented as a network protocol. In case the entities are collocated in the same physical location the interface can be a protocol or an open/proprietary software inter- process communication API. Application (App) - A piece of software that utilizes underlying services to perform a function. Application operation can be parametrized, typically by passing certain arguments at call time, but it is meant to be a standalone piece of software and it does not offer any interfaces to other applications or services. 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 make use of said functions and returns one or more results. Services can be combined with other services, or called in a certain serialized manner, to create a new service. Forwarding Plane (FP) - The network device part responsible for forwarding traffic. Operational Plane (OP) - The network device part responsible for managing the overall device operation. Control Plane (CP) - Part of the network functionality that is assigned to control one or more network devices. CP instructs network devices with respect to how to treat and forward packets. Haleplidis, et al. Expires June 8, 2014 [Page 4] Internet-Draft SDN Layers and Architecture Terminology December 2013 The control plane interacts primarily with the forwarding plane and less with the operational plane. Management Plane (MP) - Part of the network functionality responsible for monitoring, configuring and maintaining one or more network devices. The management plane is mostly related with the operational plane and less with the forwarding plane. Device and resource Abstraction Layer (DAL) - The device's resource abstraction layer based on one or more models. If it is a physical device it may be referred to as the Hardware Abstraction Layer (HAL). DAL provides a uniform point of reference for the device's forwarding and operational resources. 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. 2. SDN Layers and Architecture Figure 1 provides a detailed high-level overview of the current SDN architecture abstractions. Note that planes can be collocated with other planes or can be physically separated, as we discuss below. SDN is based on the concept of separation between a controlled entity and a controller entity. The controller manipulates the controlled entity via an Interface. Interfaces, when local, are mostly API calls through some library or system call. However, such interfaces may be extended via some protocol definition (which may be local IPC or protocol that could also act remotely; the protocol may be defined as an open standard or in proprietary manner). o--------------------------------o | | | +-------------+ +----------+ | | | Application | | Service | | | +-------------+ +----------+ | | Application Plane | o---------------Y----------------o | *-----------------------------Y---------------------------------* | Service Abstraction Layer (SAL) | *------Y------------------------------------------------Y-------* | | Haleplidis, et al. Expires June 8, 2014 [Page 5] Internet-Draft SDN Layers and Architecture Terminology December 2013 | Service Interface | | | o------Y------------------o o---------------------Y------o | | 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-------------* | | | | | | | o------------|------------o o------------|---------------o | | | CP | MP | Southbound | Southbound | Interface | Interface | | *------------Y---------------------------------Y----------------* | Device and resource Abstraction Layer (DAL) | *------------Y---------------------------------Y----------------* | | | | | o-------Y----------o +-----+ o--------Y----------o | | | Forwarding Plane | | App | | Operational Plane | | | o------------------o +-----+ o-------------------o | | Network Device | +---------------------------------------------------------------+ Figure 1: SDN Layer Architecture 2.1. Overview This document follows a network device centric approach: Control refers to the device's packet handling while Management refers to the device's operation. The reader should keep in mind throughout this document that we make no distinction between "physical" and "virtual" network devices, as we do not delve into implementation or performance aspects. In other words, a network device can be implemented fully in hardware, fully in software, or any hybrid combination in between. Similarly, network device software can run on "bare metal" or on a virtualized substrate. Finally, we do not distinguish on whether a device is implemented as an overlay or as a part/component of some other device. SDN spans multiple planes as illustrated in Figure 1. Starting from the bottom part of the figure and moving towards the upper part, we identify the following planes: Haleplidis, et al. Expires June 8, 2014 [Page 6] Internet-Draft SDN Layers and Architecture Terminology December 2013 o Forwarding Plane - Responsible for handling packets in the datapath. Actions of the forwarding plane include, but are not limited to, forwarding, dropping and changing packets. The forwarding plane is usually the termination point for control plane services and applications. The forwarding plane can contain forwarding resources such as classifiers. o Operational Plane - Responsible for managing the operational state of the Network Device, e.g. active/inactive, number of ports, port status, etc. The Operational Plane is usually the termination point for management plane services and applications. The operational plane relates to (operational aspects of) Network Device resources such as ports, memory, and so on. o Control Plane - Responsible for taking decisions on how packets should be forwarded by one or more Network Devices and pushing such decisions down to the Network Devices to be executed. The control plane usually focuses mostly on the forwarding plane and less on the operational plane of the device. The control plane may be interested in operational plane information which could include, for example, the current state of a particular port or its capabilities. The control plane job is to fine tune the forwarding plane. o Management Plane - Responsible for monitoring, configuring and maintaining network devices, e.g. taking decisions regarding the state of a Network Device. The management plane usually focuses mostly on the operational plane on the device and less on the forwarding plane. The management plane may be used to configure the forwarding plane, but it does so infrequently and in a more wholesale approach than the control plane. For instance, the management plane may set up all or part of the forwarding rules at once, although such action would be expected to be used sparingly. o Application Plane - The plane where applications and services reside. Note that applications may be implemented in a modular fashion and therefore can often span multiple planes in Figure 1. All planes mentioned above are connected via Interfaces (as indicated with "Y" in Figure 1. An Interface may take multiple roles depending on whether the connected planes reside on the same (physical or virtual) device. If the respective planes are designed so that they do not have to reside in the same device, then the Interface can only take the form of a protocol. If the planes are co-located on the same device, then the Interface could either be an open/proprietary protocol, an open/proprietary software inter-process communication API, or operating system kernel system calls. Haleplidis, et al. Expires June 8, 2014 [Page 7] Internet-Draft SDN Layers and Architecture Terminology December 2013 Applications, i.e. software programs that perform specific computations that consume services without providing access to other applications, can be implemented natively inside a plane or can span multiple planes. Services, i.e. software programs that provide APIs to other applications or services, can also be natively implemented in specific planes. Services that span multiple planes belong to the application plane as well. While not shown in Figure 1, services, applications or even planes, can be placed in a recursive manner thus providing overlay semantics to the model. Additionally, this document considers four abstraction layers: The Device and resource Abstraction Layer (DAL) abstracts the device's forwarding and operational plane resources to the control and management plane, respectively. Variations of DAL may abstract both planes or either of the two. The Control Abstraction Layer (CAL) abstracts the CP southbound interface and the DAL from the applications and services of the Control Plane. The Management Abstraction Layer (MAL) abstracts the MP southbound interface and the DAL from the applications and services of the Management Plane. The Service Abstraction Layer (SAL) provides service abstractions for use by applications and other services. 2.2. Network Devices A Network Device is an entity that receives packets on its ports and performs one or more network functions on them. For example, the network device could forward a received packet, drop it, alter the packet header (or payload) and forward the packet, and so on. NDs can be implemented in hardware or software and can be either a physical or virtual network element. As mentioned above, this document makes no distinction between these. Each network device 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 packets. The Forwarding Plane provides switching, routing transformation and filtering functions. Resources of the forwarding plane include but are not limited to filters, meters, markers and classifiers. Haleplidis, et al. Expires June 8, 2014 [Page 8] Internet-Draft SDN Layers and Architecture Terminology December 2013 The Operational Plane is responsible for operational state of the ND, for example, with respect to status of network ports and interfaces. Resources of the operational plane include but are not limited to memory, CPU, ports, interfaces and queues. The Forwarding and the Operational Planes can be exposed via a Device and resource Abstraction Layer (DAL), which may be comprised of one or more abstraction models. Examples of Forwarding Plane abstraction models are the ForCES model [RFC5812] and the OpenFlow switch model [OpenFlow]. Examples of the Operational Plane abstraction model include the ForCES model [RFC5812], the YANG model [RFC6020] and SNMP MIBs [RFC3418]. Examples of Network Devices include switches and routers. Additional examples include network elements that may operate at a layer above IP, such as firewalls, load balancers and video transcoders. Note that applications can also reside in a network device. Examples of such applications include event monitoring, and handling (offloading) topology discovery or ARP [RFC0826] in the device itself instead of forwarding such traffic to the control plane. 2.3. Control Plane The Control plane is usually distributed and is responsible mainly for the configuration of the Forwarding Plane using a Control Plane Southbound Interface (CPSI) with DAL as a point of reference. The Control Plane is responsible for instructing the Forwarding Plane about how to handle network packets. Control Plane functionalities usually include: o Topology discovery and maintenance o Packet route selection and instantiation o Path failover mechanisms The CPSI is usually defined with the following characteristics: o As a time-critical interface which requires low latency and sometimes high bandwidth in order to perform many operations in short order. o Oriented towards wire efficiency and device representation instead of human readability Haleplidis, et al. Expires June 8, 2014 [Page 9] Internet-Draft SDN Layers and Architecture Terminology December 2013 Examples include fast and high frequency of flow or table updates, high throughput and robustness for packet handling and events. 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 [OpenFlow]. 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 examples include a virtual private LAN service, service tunnels, topology services, etc. 2.4. Management Plane The Management Plane is usually centralized and aims to ensure that the network, which consists of network devices, is running optimally by communicating with the network devices's Operational Plane using a Management Plane Southbound Interface (MPSI) with DAL as a point of reference. Management plane functionalities are typically initiated, based on an overall network view, and traditionally have been human-centric. However, lately algorithms are replacing most human intervention. Management plane functionalities [FCAPS] [RFC3535] usually include: o Fault and Monitoring management o Configuration management Normally MSPI, in contrast to the CPSI, is not a time-critical interface and does not share the CPSI requirements. MSPI is [RFC3535] typically closer to human interaction than the control plane and therefore the MSPI usually has the following characteristics: o It is oriented more towards usability, with optimal wire performance being a secondary concern. o Messages tend to be less frequent than in the CPSI Haleplidis, et al. Expires June 8, 2014 [Page 10] Internet-Draft SDN Layers and Architecture Terminology December 2013 As an example of usability versus performance, we refer to the consensus of the 2002 IAB Workshop [RFC3535], as mentioned in [RFC6632], where textual configuration files should be able to contain international characters. Human-readable strings should utilize UTF-8, and protocol elements should be in case-insensitive ASCII which require more processing capabilities to parse. The MPSI can range from a protocol, to an API or even interprocess communication. If the Management Plane is not embedded in the network device, the MSPI 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 and fault detection and recovery applications. Management Plane Services provide access to other services or applications above the Management Plane. 2.5. Service Abstraction Layer The Service Abstraction Layer (SAL) provides access from services of the control, management and application planes to services and applications of the application plane. We note that the term (as well as the acronym) is overloaded, as it is often used in several contexts ranging from system design to service-oriented architectures. We emphasize that this term relates to Figure 1 and we map it accordingly in Section 3 to prominent SDN approaches. Service Interfaces can take many forms pertaining to their specific requirements. Examples of service interfaces include but are not limited to, RESTful APIs, open or proprietary protocols such as NETCONF, inter-process communications, CORBA interfaces, etc. 2.6. Application Plane Applications and services that use services from the control and/or management plane form the Application Plane. Additionally, services residing in the Application Plane may provide services to other services and applications that reside in the application plane via the service interface. Haleplidis, et al. Expires June 8, 2014 [Page 11] Internet-Draft SDN Layers and Architecture Terminology December 2013 Examples of applications include network topology discovery, network provisioning, path reservation, etc. 3. SDN Model View We advocate that the SDN southbound interface should encompass both CSPI and MSPI. The SDN northbound interface is implemented in the Service Abstraction Layer of Figure 1. 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 The Forwarding and Control Element Separation (ForCES [RFC5810]) is an IETF framework consisting of a model and two protocols. ForCES separates the Forwarding from the Control Plane via an open interface, namely the ForCES protocol which operates on entities of the forwarding plane that have been modeled using the ForCES model. The ForCES model is based on the fact that a network element is composed of numerous logically separate entities that cooperate to provide a given functionality -such as routing or IP switching- and yet appear as a normal integrated network element to external entities and secondly with a protocol to transport information. ForCES models the Forwarding Plane using Logical Functional Blocks (LFBs) which are connected in a graph, composing the Forwarding Element (FE). LFBs are described in an XML language, based on an XML schema. LFB definitions include: o Base and custom-defined datatypes o Metadata definitions o Input and Output ports o Operational parameters, or components o Capabilities o Event definitions Haleplidis, et al. Expires June 8, 2014 [Page 12] Internet-Draft SDN Layers and Architecture Terminology December 2013 The ForCES model can be used to define LFBs from fine- to coarse- grained as needed. The ForCES protocol is agnostic to the model and can be used to monitor, configure and control any ForCES-modeled element. The protocol has very simple commands: Set, Get and Del. ForCES is a protocol designed for high throughput and fast updates. ForCES [RFC5810] can be mapped to the framework illustrated in Figure 1 as follows: o The ForCES model can be used to describe DAL, both for the Operational and the Forwarding Plane, using LFBs. o The ForCES protocol can then be both the CPSI and the MPSI. ForCES is inherently specified for the CPSI and satisfies its requirements, however it can also be utilized for the MPSI. o CAL and MAL must be able to utilize the ForCES protocol. 3.2. NETCONF The Network Configuration Protocol (NETCONF [RFC6241]), is an IETF- standardized network management protocol [RFC6632]. NETCONF provides mechanisms to install, manipulate, and delete the configuration of network devices. NETCONF protocol operations are realized as remote procedure calls (RPCs). The NETCONF protocol uses an Extensible Markup Language (XML) based data encoding for the configuration data as well as the protocol messages. Additionally, the YANG data modeling language has been developed for specifying NETCONF data models and protocol operations. YANG is a data modeling language used to model configuration and state data manipulated by NETCONF, NETCONF remote procedure calls, and NETCONF notifications. YANG models the hierarchical organization of data as a tree, in which each node has either a value or a set of child nodes. Additionally, YANG structures data models into modules and submodules allowing reusability and augmentation. YANG models can describe constraints to be enforced on the data. Additionally YANG has a set of base datatype and allows custom defined datatypes as well. Haleplidis, et al. Expires June 8, 2014 [Page 13] Internet-Draft SDN Layers and Architecture Terminology December 2013 YANG allows the definition of NETCONF RPCs allowing the protocol to have an extensible number of commands. For RPC definition, the operations names, input parameters, and output parameters are defined using YANG data definition statements. NETCONF can be mapped to the framework illustrated in Figure 1 as follows: o The YANG model [RFC6020] is suitable for specifying DAL for the operational plane and NETCONF [RFC6241] for the MPSI. o Technically, the YANG model [RFC6020] can be used to specify DAL for the Forwarding plane as well, but NETCONF [RFC6241] being a management protocol not designed for fast updates is likely not suitable for the requirements of CPSI. 3.3. OpenFlow OpenFlow is a framework developed by Standford, currently run by the Open Networking Foundation, initially to provide a way for researchers to run experimental protocols in the network. OpenFlow provides a protocol with which a controller may manage a static model of an OpenFlow switch. An OpenFlow Switch consists of one or more flow tables which perform packet lookups and forwarding, a group table and an OpenFlow channel to an external controller. The switch communicates with the controller which manages the switch via the OpenFlow protocol. OpenFlow can be mapped to the framework illustrated in Figure 1 as follows: o The Openflow switch specifications [OpenFlow] covers DAL for the Forwarding Plane and provides the specification for 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. OF-CONFIG overlaps with the OpenFlow DAL, but with NETCONF [RFC6241] as the transport protocol it shares the limitations described in the previous section. o CAL must be able to utilize the OpenFlow protocol. o MAL must be able to utilize the NETCONF protocol. 3.4. I2RS Haleplidis, et al. Expires June 8, 2014 [Page 14] Internet-Draft SDN Layers and Architecture Terminology December 2013 I2RS, although still work in progress at the IETF, can be mapped to the framework illustrated in Figure 1 as follows: o The I2RS architecture [I-D.ietf-i2rs-architecture] is concerned with the Control and Application Planes and uses whatever CPSI and DAL are available, whether that is ForCES, OpenFlow or another Interface. o The I2RS agent is a Control Plane Service. All services or applications on top of that belong to either the Control or the Application plane. o Currently the I2RS working group if developing an Information Model [I-D.ietf-i2rs-rib-info-model] in regards to the Service Abstraction Layer for the I2RS agent. 3.5. BFD Bidirectional Forwarding Detection (BFD) [RFC5880], is an IETF network protocol designed for detecting communication failures between two forwarding elements which are directly connected. It is intended to be implemented in some component of the forwarding engine of a system, in cases where the forwarding and control engines are separated. BFD provides low-overhead detection of faults even on physical media that do not support failure detection of any kind, such as Ethernet, virtual circuits, tunnels and MPLS Label Switched Paths. BFD could be mapped to the framework illustrated in Figure 1 either as: 1. A control plane service or application that would use the CPSI towards the forwarding plane to send/receive BFD packets. 2. Or, better, as it was intended for, i.e. as an application that runs on the device itself and uses the forwarding plane to send/ receive BFD packets and update the operational plane resources accordingly. 4. Acknowledgements The authors would like to acknowledge David Meyer, Salvatore Loreto and Sudhir Modali for the initial discussion on the SDNRG mailing list as well as their draft-specific comments that helped put this document in a better shape. Haleplidis, et al. Expires June 8, 2014 [Page 15] Internet-Draft SDN Layers and Architecture Terminology December 2013 Additionally the authors would like to acknowledge Russ White, Linda Dunbar, Robert Raszuk, Pedro Martinez-Julia, Lee Young, Yaakov Stein, Shivleela Arlimatti, Gurkan Deniz, Scott Brim, Carlos Pignataro, Ramki Krishnan, Bless Roland, Tim Copley, Francisco Javier Ros Munoz, Sriganesh Kini, Alan Clark, Erik Nordmark for their critical comments and discussions at the IETF 88 meeting (and the SDNRG mailing list), which we took into consideration while revising this document. 5. IANA Considerations This memo makes no requests to IANA. 6. Security Considerations TBD 7. Informative References [A4D05] Greenberg, Albert, et al., "A clean slate 4D approach to network control and management", ACM SIGCOMM Computer Communication Review 35.5 (2005): 41-54 , 2005. [FCAPS] International Telecommunication Union, "X.700: Management Framework For Open Systems Interconnection (OSI) For CCITT Applications", September 1992, . [I-D.ietf-i2rs-architecture] Atlas, A., Halpern, J., Hares, S., Ward, D., and T. Nadeau, "An Architecture for the Interface to the Routing System", draft-ietf-i2rs-architecture-00 (work in progress), August 2013. [I-D.ietf-i2rs-rib-info-model] Bahadur, N., Folkes, R., Kini, S., and J. Medved, "Routing Information Base Info Model", draft-ietf-i2rs-rib-info- model-01 (work in progress), October 2013. [I-D.pfaff-ovsdb-proto] Pfaff, B. and B. Davie, "The Open vSwitch Database Management Protocol", draft-pfaff-ovsdb-proto-04 (work in progress), October 2013. [NV09] Chowdhury, NM Mosharaf Kabir, and Raouf Boutaba, "Network virtualization: state of the art and research challenges", Communications Magazine, IEEE 47.7 (2009): 20-26 , 2009. [OF-CONFIG] Haleplidis, et al. Expires June 8, 2014 [Page 16] Internet-Draft SDN Layers and Architecture Terminology December 2013 Open Networking Foundation, "OpenFlow Management and Configuration Protocol 1.1.1", March 2013, . [OF08] McKeown, Nick, et al., "OpenFlow: enabling innovation in campus networks", ACM SIGCOMM Computer Communication Review 38.2 (2008): 69-74 , 2008. [OpenFlow] Open Networking Foundation, "The OpenFlow 1.4 Specification.", October 2013, . [PNSurvey99] Campbell, Andrew T., et al, "A survey of programmable networks", ACM SIGCOMM Computer Communication Review 29.2 (1999): 7-23 , September 1992. [RFC0826] Plummer, D., "Ethernet Address Resolution Protocol: Or converting network protocol addresses to 48.bit Ethernet address for transmission on Ethernet hardware", STD 37, RFC 826, November 1982. [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. [RFC3535] Schoenwaelder, J., "Overview of the 2002 IAB Network Management Workshop", RFC 3535, May 2003. [RFC5743] Falk, A., "Definition of an Internet Research Task Force (IRTF) Document Stream", RFC 5743, December 2009. [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. Haleplidis, et al. Expires June 8, 2014 [Page 17] Internet-Draft SDN Layers and Architecture Terminology December 2013 [RFC5812] Halpern, J. and J. Hadi Salim, "Forwarding and Control Element Separation (ForCES) Forwarding Element Model", RFC 5812, March 2010. [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection (BFD)", RFC 5880, June 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. [RFC6632] Ersue, M. and B. Claise, "An Overview of the IETF Network Management Standards", RFC 6632, June 2012. 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 Kostas Pentikousis EICT GmbH Torgauer Strasse 12-15 10829 Berlin Germany Email: k.pentikousis@eict.de Haleplidis, et al. Expires June 8, 2014 [Page 18] Internet-Draft SDN Layers and Architecture Terminology December 2013 Jamal Hadi Salim Mojatatu Networks Suite 400, 303 Moodie Dr. Ottawa, Ontario K2H 9R4 Canada Email: hadi@mojatatu.com David Meyer Brocade Email: dmm@1-4-5.net Odysseas Koufopavlou University of Patras Department of Electrical and Computer Engineering Patras 26500 Greece Email: odysseas@ece.upatras.gr Haleplidis, et al. Expires June 8, 2014 [Page 19]