TCPM M. Scharf
Internet-Draft Hochschule Esslingen
Intended status: Standards Track V. Murgai
Expires: January 8, 2020 Cisco Systems Inc
July 7, 2019

YANG Groupings for Transmission Control Protocol (TCP) Configuration


This document specifies a YANG model for TCP on devices that are configured by network management protocols. The YANG model defines groupings for fundamental parameters that can be modified in many TCP implementations. The model extends a base model for TCP clients and servers [I-D.ietf-netconf-tcp-client-server].

Status of This Memo

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This Internet-Draft will expire on January 8, 2020.

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Table of Contents

1. Introduction

The Transmission Control Protocol (TCP) [RFC0793] is used by many applications in the Internet, including control and management protocols. Therefore, TCP is implemented on network elements that can be configured via network management protocols such as NETCONF [RFC6241] or RESTCONF [RFC8040]. This document specifies a YANG model [RFC6020][RFC7950] for configuring TCP on network elements that support YANG data models. This document extends a base model for TCP clients and servers [I-D.ietf-netconf-tcp-client-server]. The model focuses on fundamental and standard TCP functions that are widely implemented. The model can be augmented to address more advanced or implementation-specific TCP features. Operational state and statistics are outside the scope of this memo.

Many protocol stacks on Internet hosts use other methods to configure TCP, such as operating system configuration or policies. Many TCP/IP stacks cannot be configured by network management protocols such as NETCONF or RESTCONF and they do not use YANG data models. Yet, such TCP implementations often also have means to configure the parameters listed in this document. All parameters defined in this document are optional.

This specification is orthogonal to a Management Information Base (MIB) for the Transmission Control Protocol (TCP) that has been standardized [RFC4022]. A MIB providing extended statistics for TCP is also available [RFC4898], and there are also MIBs for UDP [RFC4113] and SCTP [RFC3873]. It is possible to translate a MIB into a YANG model, for instance using the translation described in [RFC6643]. However, this approach is not used in this document, as such a translated model would not be up-to-date.

There are also other related YANG models. Examples are:

2. Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

3. Model Overview

3.1. Modeling Scope

TCP is implemented on many different system architectures. As a result, there are may different and often implementation-specific ways to configure parameters of the TCP protocol engine. In addition, in many TCP/IP stacks configuration exists for different scopes:

There is no ground truth for setting certain TCP parameters, and traditionally different implementation have used different modeling approaches. For instance, one implementation may define a given configuration parameter globally, while another one uses per-interface settings, and both approaches work well for the corresponding use cases. Also, different systems may use different default values.

In addition to configuration of the TCP protocol engine, a TCP implementation typically also offers access to operational state and statistics. This includes amongst others:

This document focuses solely on modeling basic TCP configuration state. Operational state (see [RFC8342]) is outside the scope of this specification.

The YANG model defined in this document extends a base model for TCP clients and servers [I-D.ietf-netconf-tcp-client-server]. Similar to the base model, this specification only defines YANG groupings. This allows reuse of these groupings in different YANG data models. It is intended that these groupings will be used either standalone or for TCP-based protocols as part of a stack of protocol-specific configuration models.

3.2. Basic TCP Configuration Parameters

There are a number of basic system parameters that are configurable on many TCP implementations, even if not all TCP implementations may indeed have exactly all these settings. Also, the syntax, semantics and scope (e.g., global or interface-specific) can be different in different system architectures.

The following list of fundamental parameters considers both TCP implementations on hosts and on routers:

Some other parameters are also common but not ubiquitously supported, or modeled in very different ways. Therefore, the following attributes are not considered in this document:

TCP can be implemented in different ways and design choices by the protocol engine often affect configuration options. In a number of areas there are major differences between different software architectures. As a result, there are not many commonalities in the corresponding configuration parameters:

This document only models fundamental system parameters that are configurable on many TCP implementations, and for which the configuration is reasonably similar.

3.3. Model Design

[[Editor's node: This section requires further work.]]

This document extends the YANG model "ietf-tcp-common" defined in [I-D.ietf-netconf-tcp-client-server]. The exact modeling is TBD. The intention is to define YANG groupings for all parameters so that they can be used in different YANG models.

As an example, enabling the support of Selective Acknowledgements (SACK) can be modelled as follows:

  grouping tcp-sack-grouping {
    description "Support of Selective Acknowledgements (SACK)";

    leaf sack {
      type boolean;
      default "true";

        "Enable support of Selective Acknowledgements (SACK)";

A YANG model could then, for instance, import the YANG model "ietf-tcp-common" as well as the model defined in this document as follows:

  grouping example-tcp-config {
    description "Example TCP stack configuration";

    uses tcp-common-grouping;
    uses tcp-sack-grouping;

3.4. Tree Diagram

[[Editor's node: This section will be completed in follow-up versions of this document.]]

This section provides a tree diagram [RFC8340] for the YANG module defined in this document.

4. TCP Configuration YANG Model

[[Editor's node: This section is TBD.]]

5. IANA Considerations

[[Editor's node: This section will be completed in follow-up versions of this document.]]

6. 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.

7. References

7.1. Normative References

[I-D.ietf-netconf-tcp-client-server] Watsen, K. and M. Scharf, "YANG Groupings for TCP Clients and TCP Servers", Internet-Draft draft-ietf-netconf-tcp-client-server-02, July 2019.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7, RFC 793, DOI 10.17487/RFC0793, September 1981.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[RFC6020] Bjorklund, M., "YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)", RFC 6020, DOI 10.17487/RFC6020, October 2010.
[RFC6241] Enns, R., Bjorklund, M., Schoenwaelder, J. and A. Bierman, "Network Configuration Protocol (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011.
[RFC6242] Wasserman, M., "Using the NETCONF Protocol over Secure Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011.
[RFC7950] Bjorklund, M., "The YANG 1.1 Data Modeling Language", RFC 7950, DOI 10.17487/RFC7950, August 2016.
[RFC8040] Bierman, A., Bjorklund, M. and K. Watsen, "RESTCONF Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017.
[RFC8340] Bjorklund, M. and L. Berger, "YANG Tree Diagrams", BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018.
[RFC8341] Bierman, A. and M. Bjorklund, "Network Configuration Access Control Model", STD 91, RFC 8341, DOI 10.17487/RFC8341, March 2018.
[RFC8342] Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K. and R. Wilton, "Network Management Datastore Architecture (NMDA)", RFC 8342, DOI 10.17487/RFC8342, March 2018.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018.

7.2. Informative References

[I-D.ietf-idr-bgp-model] Jethanandani, M., Patel, K. and S. Hares, "BGP YANG Model for Service Provider Networks", Internet-Draft draft-ietf-idr-bgp-model-06, June 2019.
[I-D.ietf-netmod-acl-model] Jethanandani, M., Agarwal, S., Huang, L. and D. Blair, "Network Access Control List (ACL) YANG Data Model", Internet-Draft draft-ietf-netmod-acl-model-21, November 2018.
[I-D.ietf-opsawg-nat-yang] Boucadair, M., Sivakumar, S., Jacquenet, C., Vinapamula, S. and Q. Wu, "A YANG Module for Network Address Translation (NAT) and Network Prefix Translation (NPT)", Internet-Draft draft-ietf-opsawg-nat-yang-17, September 2018.
[I-D.ietf-taps-interface] Trammell, B., Welzl, M., Enghardt, T., Fairhurst, G., Kuehlewind, M., Perkins, C., Tiesel, P. and C. Wood, "An Abstract Application Layer Interface to Transport Services", Internet-Draft draft-ietf-taps-interface-03, March 2019.
[RFC3873] Pastor, J. and M. Belinchon, "Stream Control Transmission Protocol (SCTP) Management Information Base (MIB)", RFC 3873, DOI 10.17487/RFC3873, September 2004.
[RFC4022] Raghunarayan, R., "Management Information Base for the Transmission Control Protocol (TCP)", RFC 4022, DOI 10.17487/RFC4022, March 2005.
[RFC4113] Fenner, B. and J. Flick, "Management Information Base for the User Datagram Protocol (UDP)", RFC 4113, DOI 10.17487/RFC4113, June 2005.
[RFC4898] Mathis, M., Heffner, J. and R. Raghunarayan, "TCP Extended Statistics MIB", RFC 4898, DOI 10.17487/RFC4898, May 2007.
[RFC6643] Schoenwaelder, J., "Translation of Structure of Management Information Version 2 (SMIv2) MIB Modules to YANG Modules", RFC 6643, DOI 10.17487/RFC6643, July 2012.

Appendix A. Acknowledgements

Michael Scharf is supported by the project, which is funded by the European Commission under the Horizon 2020 Programme.

Appendix B. Changes compared to previous versions

Changes compared to draft-scharf-tcpm-yang-tcp-01

Changes compared to draft-scharf-tcpm-yang-tcp-00

Authors' Addresses

Michael Scharf Hochschule Esslingen - University of Applied Sciences Flandernstr. 101 Esslingen, 73732 Germany EMail:
Vishal Murgai Cisco Systems Inc EMail: