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 draft-scharf-tcpm-yang-tcp-02 Abstract 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 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 https://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 8, 2020. Copyright Notice Copyright (c) 2019 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 Scharf & Murgai Expires January 8, 2020 [Page 1] Internet-Draft TCP Configuration July 2019 the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3 3. Model Overview . . . . . . . . . . . . . . . . . . . . . . . 3 3.1. Modeling Scope . . . . . . . . . . . . . . . . . . . . . 3 3.2. Basic TCP Configuration Parameters . . . . . . . . . . . 5 3.3. Model Design . . . . . . . . . . . . . . . . . . . . . . 6 3.4. Tree Diagram . . . . . . . . . . . . . . . . . . . . . . 7 4. TCP Configuration YANG Model . . . . . . . . . . . . . . . . 7 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 6. Security Considerations . . . . . . . . . . . . . . . . . . . 7 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 7.1. Normative References . . . . . . . . . . . . . . . . . . 8 7.2. Informative References . . . . . . . . . . . . . . . . . 9 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 10 Appendix B. Changes compared to previous versions . . . . . . . 10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 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 Scharf & Murgai Expires January 8, 2020 [Page 2] Internet-Draft TCP Configuration July 2019 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: o Application protocol models may include TCP parameters, for example in case of BGP [I-D.ietf-idr-bgp-model]. o TCP header attributes are modeled in other models, such as [I-D.ietf-netmod-acl-model]. o TCP-related configuration of a NAT is defined in [I-D.ietf-opsawg-nat-yang]. 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: o Global configuration: Many TCP implementations have configuration parameters that affect all TCP connections. Typical examples include the enabling or disabling optional protocol features. o Interface configuration: It can be useful to use different TCP parameters on different interfaces, e.g., different device ports or IP interfaces. In that case, TCP parameters can be part of the interface configuration. Typical examples are the Maximum Segment Size (MSS) or configuration related to hardware offloading. o Connection parameters: Many implementations have means to influence the behavior of each TCP connection, e.g., on the programming interface used by applications. A typical example are Scharf & Murgai Expires January 8, 2020 [Page 3] Internet-Draft TCP Configuration July 2019 socket options in the socket API, such as disabling the Nagle algorithm by TCP_NODELAY. In an application uses such an interface, it is possible that the configuration of the application or application protocol includes TCP-related parameters. An example is the YANG model for BGP configuration [I-D.ietf-idr-bgp-model]. o Policies: Setting of TCP parameters can also be part of system policies, templates, or profiles. An example would be the preferences defined in the TAPS interface [I-D.ietf-taps-interface]. 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: o Statistics: Counters for the number of active/passive opens, sent and received segments, errors, and possibly other detailed debugging information o TCP connection table: Access to status information for all TCP connections o TCP listener table: Tnformation about all TCP listening endpoints 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. Scharf & Murgai Expires January 8, 2020 [Page 4] Internet-Draft TCP Configuration July 2019 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: o Keepalives (see also [I-D.ietf-netconf-tcp-client-server]) * Idle-time (in seconds): integer * Probe-interval (in seconds): integer * Max-probes: integer o Maximum MSS (in byte): integer o FIN timeout (in seconds): integer o SACK (disable/enable): boolean o Timestamps (disable/enable): boolean o Path MTU Discovery (disable/enable): boolean o ECN * Enabling (disable/passive/active): enumeration 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: o Delayed ACK timeout (in ms) o Initial RTO value (in ms) o Maximum number of retransmissions o Window scaling o Maximum number of connections Scharf & Murgai Expires January 8, 2020 [Page 5] Internet-Draft TCP Configuration July 2019 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: o Window size: TCP stacks can either store window state variables (such as the congestion window) in segments or in bytes. o Buffer sizes: The memory management depends on the operating system. As the size of buffers can vary over several orders of magnitude, very different implementations exist. This typically influences TCP flow control. o Timers: Timer implementation is another area in which TCP stacks may differ. o Congestion control algorithms: Many congestion control algorithms have configuration parameters, but except for fundamental properties they often tie into the specific implementation. 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"; description "Enable support of Selective Acknowledgements (SACK)"; } } Scharf & Murgai Expires January 8, 2020 [Page 6] Internet-Draft TCP Configuration July 2019 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. Scharf & Murgai Expires January 8, 2020 [Page 7] Internet-Draft TCP Configuration July 2019 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", draft-ietf-netconf-tcp-client-server-02 (work in progress), 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., Ed., "YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)", RFC 6020, DOI 10.17487/RFC6020, October 2010, . [RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed., and A. Bierman, Ed., "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., Ed., "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, Ed., "YANG Tree Diagrams", BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018, . Scharf & Murgai Expires January 8, 2020 [Page 8] Internet-Draft TCP Configuration July 2019 [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", draft-ietf-idr-bgp- model-06 (work in progress), 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", draft-ietf-netmod-acl-model-21 (work in progress), 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)", draft-ietf-opsawg-nat-yang-17 (work in progress), 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", draft-ietf-taps-interface-03 (work in progress), 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, . Scharf & Murgai Expires January 8, 2020 [Page 9] Internet-Draft TCP Configuration July 2019 [RFC4022] Raghunarayan, R., Ed., "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 StandICT.eu 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 o Alignment with [I-D.ietf-netconf-tcp-client-server] o Removing backward-compatibility to the TCP MIB o Additional co-author Changes compared to draft-scharf-tcpm-yang-tcp-00 o Editorial improvements Authors' Addresses Michael Scharf Hochschule Esslingen - University of Applied Sciences Flandernstr. 101 Esslingen 73732 Germany Email: michael.scharf@hs-esslingen.de Scharf & Murgai Expires January 8, 2020 [Page 10] Internet-Draft TCP Configuration July 2019 Vishal Murgai Cisco Systems Inc Email: vmurgai@cisco.com Scharf & Murgai Expires January 8, 2020 [Page 11]