RFC 8960 | MPLS Base YANG Data Model | December 2020 |
Saad, et al. | Standards Track | [Page] |
- Stream:
- Internet Engineering Task Force (IETF)
- RFC:
- 8960
- Category:
- Standards Track
- Published:
- ISSN:
- 2070-1721
RFC 8960
A YANG Data Model for MPLS Base
Abstract
This document contains a specification of the MPLS base YANG data model. The MPLS base YANG data model serves as a base framework for configuring and managing an MPLS switching subsystem on an MPLS-enabled router. It is expected that other MPLS YANG data models (e.g., MPLS Label Switched Path (LSP) static, LDP, or RSVP-TE YANG data models) will augment the MPLS base YANG data model.¶
Status of This Memo
This is an Internet Standards Track document.¶
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841.¶
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at https://www.rfc-editor.org/info/rfc8960.¶
Copyright Notice
Copyright (c) 2020 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 (https://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.¶
1. Introduction
A core routing YANG data model is defined in [RFC8349]; it provides a basis for the development of routing data models for specific Address Families (AFs). Specifically, [RFC8349] defines a model for a generic Routing Information Base (RIB) that is AF agnostic. [RFC8349] also defines two instances of RIBs based on the generic RIB model for IPv4 and IPv6 AFs.¶
The MPLS base model defined in this document augments the generic RIB model defined in [RFC8349] with additional data that enables MPLS forwarding for one or more specific destination prefixes present in one or more AF RIBs, as described in the MPLS architecture document [RFC3031].¶
The MPLS base model also defines a new instance of the generic RIB YANG data model as defined in [RFC8349] to store native MPLS routes. The native MPLS RIB instance stores one or more routes that are not associated with other AF instance RIBs (such as IPv4 or IPv6 instance RIBs) but are enabled for MPLS forwarding. Examples of such native MPLS routes are routes programmed by RSVP on one or more transit MPLS routers along the path of a Label Switched Path (LSP). Other examples are MPLS routes that cross-connect to specific Layer 2 adjacencies, such as Layer 2 Attachment Circuits (ACs); or Layer 3 adjacencies, such as Segment Routing (SR) Adjacency Segments (Adj-SIDs) as described in [RFC8402].¶
The MPLS base YANG data model serves as a basis for future development of MPLS YANG data models covering MPLS features and subsystems that are more sophisticated. The main purpose is to provide essential building blocks for other YANG data models involving different control-plane protocols and MPLS functions.¶
To this end, it is expected that the MPLS base data model will be augmented by a number of other YANG modules developed by the IETF (e.g., by the TEAS and MPLS Working Groups).¶
The YANG module defined in this document conforms to the Network Management Datastore Architecture (NMDA) [RFC8342].¶
1.1. Terminology
The terminology for describing YANG data models is found in [RFC7950].¶
2. MPLS Base Model
This document describes the "ietf-mpls" YANG module, which provides base components of the MPLS data model. It is expected that other MPLS YANG modules will augment the "ietf-mpls" YANG module for other MPLS extensions to provision LSPs (e.g., MPLS static, MPLS LDP, or MPLS RSVP-TE LSPs).¶
2.1. Model Overview
This document models MPLS-labeled routes as an augmentation of the generic routing RIB data model as defined in [RFC8349]. For example, IP prefix routes (e.g., routes stored in IPv4 or IPv6 RIBs) are augmented to carry additional data to enable them for MPLS forwarding.¶
This document also defines a new instance of the generic RIB model defined in [RFC8349] to store one or more native MPLS routes (described further in Section 2.3) by extending the identity "address-family" defined in [RFC8349] with a new "mpls" identity; see Section 3 of [RFC8349].¶
2.2. Model Organization
The "ietf-mpls" YANG module defines the following identities:¶
- mpls:
- Identity that extends the "address-family" identity of RIB instances, as defined in [RFC8349], to represent the native MPLS RIB instance.¶
- label-block-alloc-mode:
- A base YANG identity for one or more supported label-block allocation modes.¶
The "ietf-mpls" YANG module contains the following high-level types and groupings:¶
- mpls-operations-type:
- An enumeration type that represents support for possible MPLS operation types (impose-and-forward, pop-and-forward, pop-impose-and-forward, and pop-and-lookup).¶
- nhlfe-role:
- An enumeration type that represents the role of the Next Hop Label Forwarding Entry (NHLFE).¶
- nhlfe-single-contents:
- A YANG grouping that describes a single NHLFE and its associated parameters as described in the MPLS architecture document [RFC3031]. This grouping is specific to the case when a single next hop is associated with the route.¶
The NHLFE is used when forwarding a labeled packet. It contains the following information:¶
- The packet's next hop. For "nhlfe-single-contents", only a single next hop is expected, while for "nhlfe-multiple-contents", multiple next hops are possible.¶
-
The operation to perform on the packet's label stack. This can be one of the following operations:¶
- a.
- Replace the label at the top of the label stack with one or more specified new labels.¶
- b.
- Pop the label stack.¶
- c.
- Replace the label at the top of the label stack with a specified new label, and then push one or more specified new labels onto the label stack.¶
- d.
- Push one or more labels onto an unlabeled packet.¶
The NHLFE may also contain:¶
- The data-link encapsulation to use when transmitting the packet.¶
- The way to encode the label stack when transmitting the packet.¶
- Any other information needed in order to properly dispose of the packet.¶
- nhlfe-multiple-contents:
- A YANG grouping that describes a set of NHLFEs and their associated parameters as described in the MPLS architecture document [RFC3031]. This grouping is used when multiple next hops are associated with the route.¶
- interfaces-mpls:
- A YANG grouping that describes the list of MPLS-enabled interfaces on a device.¶
- label-blocks:
- A YANG grouping that describes the list of assigned MPLS label blocks and their properties.¶
- rib-mpls-properties:
- A YANG grouping for the augmentation of the generic RIB with MPLS label forwarding data as defined in [RFC3031].¶
- rib-active-route-mpls-input:
- A YANG grouping for the augmentation to the "active-route" RPC that is specific to the MPLS RIB instance.¶
2.3. Model Design
The MPLS routing model is based on the core routing data model defined in [RFC8349]. Figure 2 shows the extensions introduced by the MPLS base model on defined RIBs.¶
As shown in Figure 2, the MPLS base YANG data model augments defined instances of AF RIBs with additional data that enables MPLS forwarding for destination prefixes stored in such RIBs. For example, an IPv4 prefix stored in RIB(v4) is augmented to carry an MPLS local label and one or more per-next-hop remote labels to enable MPLS forwarding for such a prefix.¶
The MPLS base model also creates a separate instance of the generic RIB model defined in [RFC8349] to store one or more MPLS native routes that are enabled for MPLS forwarding but are not stored in one or more other AF RIBs.¶
Some examples of such native MPLS routes are:¶
- Routes programmed by RSVP on Label Switching Routers (LSRs) along the path of an LSP,¶
- Routes that cross-connect an MPLS local label to a Layer 2 or Layer 3 Virtual Routing and Forwarding (VRF) entity,¶
- Routes that cross-connect an MPLS local label to a specific Layer 2 adjacency or interface, such as Layer 2 Attachment Circuits (ACs), or¶
- Routes that cross-connect an MPLS local label to a Layer 3 adjacency or interface, such as MPLS Segment Routing (SR) Adjacency Segments (Adj-SIDs) or SR MPLS Binding SIDs as defined in [RFC8402].¶
2.4. Model Tree Diagram
The MPLS base tree diagram, which follows the notation defined in [RFC8340], is shown in Figure 3.¶
2.5. MPLS Base YANG Module
This section describes the "ietf-mpls" YANG module, which provides base components of the MPLS data model. Other YANG modules may import and augment the MPLS base module to add feature-specific data.¶
The "ietf-mpls" YANG module imports the following YANG modules:¶
- "ietf-routing" as defined in [RFC8349]¶
- "ietf-routing-types" as defined in [RFC8294]¶
- "ietf-yang-types" as defined in [RFC6991]¶
- "ietf-interfaces" as defined in [RFC8343]¶
This YANG module also references the following RFCs in defining the types, YANG groupings, and other features of the YANG module: [RFC3031], [RFC3032], [RFC4090], [RFC5714], and [RFC7424].¶
3. IANA Considerations
This document registers the following URI in the "ns" subregistry of the "IETF XML Registry" [RFC3688].¶
- URI:
- urn:ietf:params:xml:ns:yang:ietf-mpls¶
- Registrant Contact:
- The MPLS WG of the IETF.¶
- XML:
- N/A; the requested URI is an XML namespace.¶
This document registers the following YANG module in the "YANG Module Names" registry [RFC6020].¶
4. Security Considerations
The YANG module specified in this document defines a schema for data that is designed to be accessed via network management protocols such as NETCONF [RFC6241] or RESTCONF [RFC8040]. The lowest NETCONF layer is the secure transport layer, and the mandatory-to-implement secure transport is Secure Shell (SSH) [RFC6242]. The lowest RESTCONF layer is HTTPS, and the mandatory-to-implement secure transport is TLS [RFC8446].¶
The Network Configuration Access Control Model (NACM) [RFC8341] provides the means to restrict access for particular NETCONF or RESTCONF users to a preconfigured subset of all available NETCONF or RESTCONF protocol operations and content.¶
There are a number of data nodes defined in this YANG module that are writable/creatable/deletable (i.e., config true, which is the default). These data nodes may be considered sensitive or vulnerable in some network environments. Write operations (e.g., edit-config) to these data nodes without proper protection can have a negative effect on network operations. These are the subtrees and data nodes and their sensitivity/vulnerability:¶
- "/rt:routing/mpls:mpls/mpls:label-blocks":
- There are data nodes under this path that are writable, such as "start-label" and "end-label". Write operations to those data nodes may result in disruption to existing traffic.¶
Some of the readable data nodes in this YANG module may be considered sensitive or vulnerable in some network environments. It is thus important to control read access (e.g., via get, get-config, or notification) to these data nodes. These are the subtrees and data nodes and their sensitivity/vulnerability:¶
- "/rt:routing/rt:ribs/rt:rib/rt:routes/rt:route/rt:next-hop/rt:next-hop-options/rt:next-hop-list/rt:next-hop-list/rt:next-hop" and "/rt:routing/rt:ribs/rt:rib/rt:active-route/rt:output/rt:route/rt:next-hop/rt:next-hop-options/rt:simple-next-hop":
- These two paths are augmented by additional MPLS leafs defined in this model. Access to this information may disclose the next-hop information for the prefix route and/or other information.¶
Some of the RPC operations in this YANG module may be considered sensitive or vulnerable in some network environments. It is thus important to control access to these operations. These are the operations and their sensitivity/vulnerability:¶
- "/rt:routing/rt:ribs/rt:rib/rt:active-route/rt:input" and "/rt:routing/rt:ribs/rt:rib/rt:active-route/rt:output/rt:route":
- These two paths are augmented by additional MPLS data nodes that are defined in this model. Access to those paths may disclose information about per-prefix routes and/or other information; such disclosure may be used for further attacks.¶
The security considerations spelled out in [RFC3031] and [RFC3032] apply for this document as well.¶
5. References
5.1. Normative References
- [RFC3032]
- Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack Encoding", RFC 3032, DOI 10.17487/RFC3032, , <https://www.rfc-editor.org/info/rfc3032>.
- [RFC3688]
- Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, DOI 10.17487/RFC3688, , <https://www.rfc-editor.org/info/rfc3688>.
- [RFC6020]
- Bjorklund, M., Ed., "YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)", RFC 6020, DOI 10.17487/RFC6020, , <https://www.rfc-editor.org/info/rfc6020>.
- [RFC6241]
- Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed., and A. Bierman, Ed., "Network Configuration Protocol (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, , <https://www.rfc-editor.org/info/rfc6241>.
- [RFC6242]
- Wasserman, M., "Using the NETCONF Protocol over Secure Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, , <https://www.rfc-editor.org/info/rfc6242>.
- [RFC6991]
- Schoenwaelder, J., Ed., "Common YANG Data Types", RFC 6991, DOI 10.17487/RFC6991, , <https://www.rfc-editor.org/info/rfc6991>.
- [RFC7950]
- Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language", RFC 7950, DOI 10.17487/RFC7950, , <https://www.rfc-editor.org/info/rfc7950>.
- [RFC8040]
- Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF Protocol", RFC 8040, DOI 10.17487/RFC8040, , <https://www.rfc-editor.org/info/rfc8040>.
- [RFC8294]
- Liu, X., Qu, Y., Lindem, A., Hopps, C., and L. Berger, "Common YANG Data Types for the Routing Area", RFC 8294, DOI 10.17487/RFC8294, , <https://www.rfc-editor.org/info/rfc8294>.
- [RFC8340]
- Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams", BCP 215, RFC 8340, DOI 10.17487/RFC8340, , <https://www.rfc-editor.org/info/rfc8340>.
- [RFC8341]
- Bierman, A. and M. Bjorklund, "Network Configuration Access Control Model", STD 91, RFC 8341, DOI 10.17487/RFC8341, , <https://www.rfc-editor.org/info/rfc8341>.
- [RFC8342]
- Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K., and R. Wilton, "Network Management Datastore Architecture (NMDA)", RFC 8342, DOI 10.17487/RFC8342, , <https://www.rfc-editor.org/info/rfc8342>.
- [RFC8343]
- Bjorklund, M., "A YANG Data Model for Interface Management", RFC 8343, DOI 10.17487/RFC8343, , <https://www.rfc-editor.org/info/rfc8343>.
- [RFC8349]
- Lhotka, L., Lindem, A., and Y. Qu, "A YANG Data Model for Routing Management (NMDA Version)", RFC 8349, DOI 10.17487/RFC8349, , <https://www.rfc-editor.org/info/rfc8349>.
- [RFC8402]
- Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., Decraene, B., Litkowski, S., and R. Shakir, "Segment Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, , <https://www.rfc-editor.org/info/rfc8402>.
- [RFC8446]
- Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, , <https://www.rfc-editor.org/info/rfc8446>.
5.2. Informative References
- [RFC3031]
- Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol Label Switching Architecture", RFC 3031, DOI 10.17487/RFC3031, , <https://www.rfc-editor.org/info/rfc3031>.
- [RFC4090]
- Pan, P., Ed., Swallow, G., Ed., and A. Atlas, Ed., "Fast Reroute Extensions to RSVP-TE for LSP Tunnels", RFC 4090, DOI 10.17487/RFC4090, , <https://www.rfc-editor.org/info/rfc4090>.
- [RFC5714]
- Shand, M. and S. Bryant, "IP Fast Reroute Framework", RFC 5714, DOI 10.17487/RFC5714, , <https://www.rfc-editor.org/info/rfc5714>.
- [RFC7424]
- Krishnan, R., Yong, L., Ghanwani, A., So, N., and B. Khasnabish, "Mechanisms for Optimizing Link Aggregation Group (LAG) and Equal-Cost Multipath (ECMP) Component Link Utilization in Networks", RFC 7424, DOI 10.17487/RFC7424, , <https://www.rfc-editor.org/info/rfc7424>.
- [RFC7951]
- Lhotka, L., "JSON Encoding of Data Modeled with YANG", RFC 7951, DOI 10.17487/RFC7951, , <https://www.rfc-editor.org/info/rfc7951>.
Appendix A. Data Tree Instance Example
A simple network setup is shown in Figure 5. R1 runs the IS-IS routing protocol and learns about the reachability of two IPv4 prefixes (P1: 198.51.100.1/32 and P2: 198.51.100.2/32) and two IPv6 prefixes (P3: 2001:db8:0:10::1/128 and P4: 2001:db8:0:10::2/128). We also assume that R1 learns about local and remote MPLS label bindings for each prefix using IS-IS (e.g., using Segment Routing (SR) extensions).¶
The instance data tree could then be illustrated as shown in Figure 6, using JSON format [RFC7951]:¶
Acknowledgments
The authors would like to thank Xia Chen for her contributions to the early draft revisions of this document.¶