NETMOD D. Bogdanovic Internet-Draft Juniper Networks Intended status: Informational B. Claise Expires: September 24, 2015 C. Moberg Cisco Systmes, Inc. March 23, 2015 YANG model classification draft-bogdanovic-netmod-yang-model-classification-02 Abstract YANG became de facto standard language for data modeling in the industry. More and more groups uses YANG to create protocol and service models, both for configuration and operational models. Currently there is a lack of consistent terminology to categorize those models. A consistent terminology would help models categorization, assist in the analysis the YANG data modeling effort in the IETF and in the industry, and facilitate the YANG-related discussions between different groups. 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 September 24, 2015. Copyright Notice Copyright (c) 2015 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 Bogdanovic, et al. Expires September 24, 2015 [Page 1] Internet-Draft YANG model classification March 2015 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 2. First Dimension: Network YANG Data Model Layering . . . . . . 3 2.1. Network Service YANG Data Models . . . . . . . . . . . . 4 2.2. Network Element YANG Data models . . . . . . . . . . . . 5 3. Second Dimension: Model Type . . . . . . . . . . . . . . . . 5 3.1. Standard YANG model . . . . . . . . . . . . . . . . . . . 6 3.2. Standard Extension YANG Model . . . . . . . . . . . . . . 6 3.3. Proprietary Extension to Standard YANG Model . . . . . . 6 3.4. Vendor configuration model . . . . . . . . . . . . . . . 7 3.5. Proprietary YANG Model . . . . . . . . . . . . . . . . . 8 4. Typical Architecture . . . . . . . . . . . . . . . . . . . . 8 5. IETF, Other SDOs, and open source . . . . . . . . . . . . . . 9 6. Security Considerations . . . . . . . . . . . . . . . . . . . 10 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10 9. Change log [RFC Editor: Please remove] . . . . . . . . . . . 10 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 11 10.1. Normative References . . . . . . . . . . . . . . . . . . 11 10.2. Informative References . . . . . . . . . . . . . . . . . 11 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12 1. Introduction YANG [RFC6020] became de-facto standard language for data modeling in the industry. Not only at the IETF, but also in multiple Standard Development Organizations, different consortia, ad hoc groups, and OSP. Therefore, many YANG models are being developed and published. Today, there is no classification of models, there are no clear guidelines on how to layer models on each other, or how to classify existing or new models. With this document, the authors propose a new way to classify the YANG model, along with a taxonomy. Acknowledging that the YANG became the de-facto standard language for data modeling, the Internet Engineering Steering Group (IESG) has been encouraging the working groups to use the NETCONF [RFC6241] and YANG standards for configuration, especially in new charters [Writable-MIB-Module-IESG-Statement]. Bogdanovic, et al. Expires September 24, 2015 [Page 2] Internet-Draft YANG model classification March 2015 YANG Models can be classified according to two dimensions: based on the layer in the hierarchy of models, and based on the model type. Those two categories are covered in the next two sections. 2. First Dimension: Network YANG Data Model Layering When developing models, there are two approaches possible, top down and bottom up. Top down approach is driven by business requirements and bottom up is driven by technological ones. There are no hard requirements on how to create models, but it would be useful to have a classification and how to create models that can be easily reused, as with this time and energy will be saved in future development. We should stimulate both development styles, bottom up and top down, as each has its benefits and groups to which a certain style will be more appealing than the other. For layering purposes, we can classify data models into two layers: o Network Service YANG Model: an abstract view, in YANG, of a service deployed on one or multiple network elements. o Network Element YANG Model: describe the configuration parameters, in YANG, of a specific device technology or feature. Figure 1 displays example YANG models at different layers. By layering the models, it is easier to achieve reusability of existing lower layer models in higher level models and preventing duplication of same features modeled in different layers. When developing models per layers, it allows creating very focused groups in specific areas. As an example, creating protocol data definitions network equipment YANG data models should involve people that have intimate experience of implemention details. On the other hand, network service models are best developed by people experienced in network operations. Same network service, can be implemented and modeled using different Network Element YANG models. Bogdanovic, et al. Expires September 24, 2015 [Page 3] Internet-Draft YANG model classification March 2015 +-----------------------+ | | | OSS/BSS | | | +-----------------------+ Network Service YANG data models ------------------------------- +------------+ +-------------+ +-------------+ | | | | | | | - VPWS | | - VPLS | | L3VPN | | - L2VPN | | - L2VPN | | | | | | | | | +------------+ +-------------+ +-------------+ Network Element YANG data models --------------------------------- +------------+ +------------+ +--------------+ +-----------+ | | | | | | | | | MPLS | | BGP | | Interface | | Routing | | | | | | | | | +------------+ +------------+ +--------------+ +-----------+ Fig. 1 YANG Model layers 2.1. Network Service YANG Data Models Network Service YANG models are created by network operators to contain the characteristics of a service, as discussed with their customers. That is, it does not provide details for configuring network elements or protocols. A separate process is responsible for mapping this Network Service Model onto the Network Element YANG Models, depending on how the network operator chooses to realize the service. For example, http://datatracker.ietf.org/doc/draft-l3vpn-service- yang/ provides an abstracted view of the Layer 3 IP VPN service configuration components. It will be up to an orchestrator to take this as an input and use specific configurations models on the network element layer to configure the different network elements to deliver the service. Network Service YANG models can be developed in multiple ways. Building them monolithic from vendor models or by combining one or more service components into an end to end service data model. It specifies complete service that is provided by the network operator. Bogdanovic, et al. Expires September 24, 2015 [Page 4] Internet-Draft YANG model classification March 2015 Building monolithic network service model has an advantage of doing it fast, but at the expense of flexibility of updating the service later or changing equipment vendors. Such an end to end service can be VPLS/VPWS, L2VPN, IPsec, etc. If we take into example VPLS L2VPN service, it can be built as a single network service model or it can be built from several service components. VPWS L2VPN service can be built on top of MPLS or IP network core. When building such a network service model, network variations have to be taken into the account and by creating service components modle, such as MPLS, BGP service component models, it is easier to build a network service model, such as VPWS L2VPN. 2.2. Network Element YANG Data models This is base model for all higher models. It fully describes a protocol or technology, such as OSPF [I-D.ietf-ospf-yang], ISIS [I-D.ietf-isis-yang-isis-cfg] or feature, such as the access control list [I-D.ietf-netmod-acl-model]. 3. Second Dimension: Model Type At very high level, models can be divided into proprietary and standard. Each vendor, consortium, open source project can publish their models and those are considered proprietary models. When an SDO, such as IETF or IEEE, publishes an accepted model document, then this is a standard model. There are use cases where a consortium has published work which de facto became standard, such as Linux kernel, but for the clarity in this document, authors are making a separation between models based on the above description. Standard YANG Model: YANG model defined by an Standard Development organization (SDO), e.g. IETF, IEEE. Standard Extension YANG Model: YANG Model that describes a standard extension, example route filter, to standard filter YANG model. Proprietary Extension to Standard YANG Model: As the Standard YANG Models contains a subset of all the Vendor Configuration Models, proprietary extensions must complement the Standard YANG Models to represent a Vendor Configuration Model. Proprietary YANG Model: A non Standard YANG Model. Vendor Configuration Model: It describes all configurable capabilities of the device and what device vendor exposes for configuration. The vendor configuration model can be CLI or YANG- based. Bogdanovic, et al. Expires September 24, 2015 [Page 5] Internet-Draft YANG model classification March 2015 As mentioned earlier in this document, there are two ways of designing models, top down and bottom up with one restriction. Everything is dependent on the vendor data model. That model describes all the possibilities and if model developers prefers, they can use vendor model only to design service components, network service and business service. Using vendor model provides all capabilities today, but it comes with restrictions of portability between vendors and to certain extent devices. On the other hand, only standard models and standard extensions can be used, but this might result in less feature rich or less efficient services. Service model developer has a choice to reuse service components or write a model completely based on vendor data model. 3.1. Standard YANG model With YANG we have a common language, that enables different communities to express data models that are widely understandable without lot of additional explanation. This enables different groups, such as IETF, to standardize data models, defined as an IETF RFC, and vendors to support them, which will make it easier to for network operators to manage their network configuration programmatically. The Standard YANG Models can distinguished between the core YANG models, such as the YANG Data Model for Interface Management [RFC7223], and the technology specific YANG models, such as the Configuration Data Model for the IP Flow Information Export (IPFIX) and Packet Sampling (PSAMP) Protocols [RFC6728]. 3.2. Standard Extension YANG Model Standard Extension is the conditional portion of a Standard YANG Model, expressed with the feature, if-feature, augment YANG statements [RFC6020]. An example of such standard extension is policy based routing (PBR). PBR is found in many vendor implementations and have many common features, but not all vendors support PBR on all of their devices. 3.3. Proprietary Extension to Standard YANG Model Proprietary extension is a conditional portion of a Standard YANG Model, expressed with feature, if-feature, augment YANG statements [RFC6020]. Proprietary extensions are required as the Standard YANG model will not cover all the possible configuration parameters of the different vendors. Proprietary extension can be a feature depending on hardware platform capabilities and it is not available by other vendors. Such an example could be match condition for packet classification used for PBR. Bogdanovic, et al. Expires September 24, 2015 [Page 6] Internet-Draft YANG model classification March 2015 3.4. Vendor configuration model Base model for all other models is the vendor configuration model. It describes all configurable capabilities of the device and what device vendor exposes for configuration. The standard configuration model is a subset of vendor configuration model. The standard configuration model can be broken into base model and standard extension models, where the base is common data model and standard extensions are standard features that are not implemented by all vendors. Example of standard base model is Access Control List and routing filter is a standard extension on ACL. Or another example: encryption algorithm is standard feature, but the different types, like md5, hmac-md5, hmac-sha1, etc are standard extensions, as it is not that all vendors have all encryption algorithm types implemented. Although all vendors provide very similar functionality using standards, implementations are different. One of basic examples are dynamic routing protocols. We can see today two main types of routing protocol configuration. protocol centric - all the protocol related config is contained with the protocol itself. Especially in case of multiple instances of the routing protocol running in different routing- instances (routing-instance as described in core routing model [I-D.ietf-netmod-routing-cfg]), all the routing-instance protocol config is contained in the default routing instance. Router ospf 10 Default-metric 100 Address-family ipv4 vrf VRF1 Network x.x.x.x area 0 Address-family ipv4 vrf VRF2 Network x.x.x.x area 0 Address-family ipv4 Network x.x.x.x area 1 In term of YANG model, the routing protocol configuration will be defined within the default routing-instance and the routing- protocol config will contain multiple instances referring to other routing-instances. VRF centric - All the protocol related config for a routing- instance is contained within this routing-instance. Bogdanovic, et al. Expires September 24, 2015 [Page 7] Internet-Draft YANG model classification March 2015 Routing-instance VRF1 { Protocols isis { } } Routing-instance VRF2 { Protocols isis { } } In terms of YANG model, the routing protocol configuration for a routing-instance will be defined within the associated routing- instance. The bottom line message is that, even if YANG models are standardized, they will provide different CLI outcomes, simply because the CLI among vendors is not standardized. 3.5. Proprietary YANG Model While waiting for the Standard YANG Models to be published, the different vendors might offer Proprietary YANG Models. 4. Typical Architecture Bogdanovic, et al. Expires September 24, 2015 [Page 8] Internet-Draft YANG model classification March 2015 +--------------------------------------------------------+ | OSS/BSS | +--------------------------------------------------------+ +--------------------------------------------------------+ | Orchestrator | | +------------------------------------------------+ | | | network service model | | | | | | | +------------------------------------------------+ | +--------------------------------------------------------+ +--------------------------------------------------------+ | Network element | | | | | +-----------------------+ | +-------------------+ | | | Standard YANG model | | | Proprietary | | | | | | | YANG model | | | +-----------------------+ | | | | | | | | | | +-----------------------+ | | | | | | Proprietary Extension | | | | | | | To YANG Standard | | | | | | | Model | | | | | | +-----------------------+ | +-------------------+ | | | | | +-------------------------------------------------+ | | | Vendor Configuration Model | | | +-------------------------------------------------+ | +--------------------------------------------------------+ Fig. 2 Typical Architecture The OSS/BSS may contains business related models. Those models, which may or may not be written in YANG, are outside the scope of the IETF work 5. IETF, Other SDOs, and open source IETF, as a standard defining organization (SDO), is well positioned to standardize Network Element YANG models. With a wide range of expertise found within its working groups focused on those technology definitions. As IETF participants implement those protocols, they have deep expertise about the implementation and finding a common base standard configuration model between vendors should be a very viable goal. Bogdanovic, et al. Expires September 24, 2015 [Page 9] Internet-Draft YANG model classification March 2015 In some situation where the protocols are standardized by different SDOs, those SDOs should be responsible for its YANG data modeling effort. For example, the IETF has transferred the responsibility for some IEEE technology-related MIB modules to the IEEE 802.1 and 802.3 Working Group [RFC4663], [RFC7448]. Similarly, the IEEE should be responsible for similar YANG data modeling efforts. Developing Network Service YANG Models requires network operations expertise. When those operators participate in IETF work, the right working group can be formed, and those Service YANG Models can be developed within IETF. However, some other groups, like Metro Ethernet Forum or CableLabs, could be better positioned for service modeling related to their area of expertise. Today there are many open source projects and some of them are becoming de facto standards, like the Linux kernel. Many such open source projects, like Open Daylight, OpenStack, etc, are doing very good work and their work is being accepted and deployed in production environments. They bring a lot of very valuable experience to other groups. From IETF perspective, if there is such a work present, it can be used as a very good starting point for modeling within IETF. 6. Security Considerations At this stage, authors of the draft didn't look into security considerations. 7. IANA Considerations This document requests no action by IANA. 8. Acknowledgements Thanks to David Ball for his enlightenments on Metro Ethernet Forum service aspects. 9. Change log [RFC Editor: Please remove] version 1: restructure the document, add the two dimensions, add the interaction with the different SDOs and opensource projects, add the definitions. version 2: added definitions for config and service models clarified second dimension of model classification. fixed typos Bogdanovic, et al. Expires September 24, 2015 [Page 10] Internet-Draft YANG model classification March 2015 10. References 10.1. Normative References [RFC6020] Bjorklund, M., "YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)", RFC 6020, October 2010. 10.2. Informative References [I-D.ietf-isis-yang-isis-cfg] Litkowski, S., Yeung, D., Lindem, A., Zhang, J., and L. Lhotka, "YANG Data Model for ISIS protocol", draft-ietf- isis-yang-isis-cfg-01 (work in progress), October 2014. [I-D.ietf-netmod-acl-model] Bogdanovic, D., Sreenivasa, K., Huang, L., and D. Blair, "Network Access Control List (ACL) YANG Data Model", draft-ietf-netmod-acl-model-01 (work in progress), February 2015. [I-D.ietf-netmod-routing-cfg] Lhotka, L., "A YANG Data Model for Routing Management", draft-ietf-netmod-routing-cfg-16 (work in progress), October 2014. [I-D.ietf-ospf-yang] Yeung, D., Qu, Y., Zhang, J., Bogdanovic, D., and K. Sreenivasa, "Yang Data Model for OSPF Protocol", draft- ietf-ospf-yang-00 (work in progress), March 2015. [RFC4663] Harrington, D., "Transferring MIB Work from IETF Bridge MIB WG to IEEE 802.1 WG", RFC 4663, September 2006. [RFC6241] Enns, R., Bjorklund, M., Schoenwaelder, J., and A. Bierman, "Network Configuration Protocol (NETCONF)", RFC 6241, June 2011. [RFC6728] Muenz, G., Claise, B., and P. Aitken, "Configuration Data Model for the IP Flow Information Export (IPFIX) and Packet Sampling (PSAMP) Protocols", RFC 6728, October 2012. [RFC7223] Bjorklund, M., "A YANG Data Model for Interface Management", RFC 7223, May 2014. [RFC7448] Taylor, T. and D. Romascanu, "MIB Transfer from the IETF to the IEEE 802.3 WG", RFC 7448, February 2015. Bogdanovic, et al. Expires September 24, 2015 [Page 11] Internet-Draft YANG model classification March 2015 [Writable-MIB-Module-IESG-Statement] "Writable MIB Module IESG Statement", . Authors' Addresses Dean Bogdanovic Juniper Networks Email: deanb@juniper.net Benoit Claise Cisco Systmes, Inc. Email: bclaise@cisco.com Carl Moberg Cisco Systmes, Inc. Email: camoberg@cisco.com Bogdanovic, et al. Expires September 24, 2015 [Page 12]