YANG Model for Transmission Control Protocol (TCP) Configuration
draft-ietf-tcpm-yang-tcp-01

Document Type Active Internet-Draft (tcpm WG)
Authors Michael Scharf  , Vishal Murgai  , Mahesh Jethanandani 
Last updated 2021-01-03 (latest revision 2020-11-16)
Replaces draft-scharf-tcpm-yang-tcp
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TCPM                                                           M. Scharf
Internet-Draft                                      Hochschule Esslingen
Intended status: Standards Track                               V. Murgai
Expires: May 20, 2021                                            Samsung
                                                         M. Jethanandani
                                                          Kloud Services
                                                       November 16, 2020

    YANG Model for Transmission Control Protocol (TCP) Configuration
                      draft-ietf-tcpm-yang-tcp-01

Abstract

   This document specifies a YANG model for TCP on devices that are
   configured by network management protocols.  The YANG model defines a
   container for all TCP connections and groupings of some of the
   parameters that can be imported and used in TCP implementations or by
   other models that need to configure TCP parameters.  The model
   includes definitions from YANG Groupings for TCP Client and TCP
   Servers (I-D.ietf-netconf-tcp-client-server).  The model is NMDA (RFC
   8342) compliant.

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 May 20, 2021.

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

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   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
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Note to  RFC Editor . . . . . . . . . . . . . . . . . . .   3
   3.  Model Overview  . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Modeling Scope  . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  Model Design  . . . . . . . . . . . . . . . . . . . . . .   5
     3.3.  Tree Diagram  . . . . . . . . . . . . . . . . . . . . . .   6
   4.  TCP YANG Model  . . . . . . . . . . . . . . . . . . . . . . .   6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
     5.1.  The IETF XML Registry . . . . . . . . . . . . . . . . . .  13
     5.2.  The YANG Module Names Registry  . . . . . . . . . . . . .  13
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  14
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  15
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  16
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .  18
   Appendix B.  Changes compared to previous versions  . . . . . . .  18
   Appendix C.  Examples . . . . . . . . . . . . . . . . . . . . . .  19
     C.1.  Keepalive Configuration . . . . . . . . . . . . . . . . .  19
     C.2.  TCP-AO Configuration  . . . . . . . . . . . . . . . . . .  20
   Appendix D.  Complete Tree Diagram  . . . . . . . . . . . . . . .  21
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  22

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
   [RFC7950] 1.1 model for configuring TCP on network elements that
   support YANG data models, and is Network Management Datastore
   Architecture (NMDA) [RFC8342] compliant.  This module defines a
   container for TCP connection, and includes definitions from YANG
   Groupings for TCP Clients and TCP Servers
   [I-D.ietf-netconf-tcp-client-server].  The model has a narrow scope
   and focuses on fundamental TCP functions and basic statistics.  The
   model can be augmented or updated to address more advanced or
   implementation-specific TCP features in the future.

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   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 [RFC6241] or RESTCONF [RFC8040].  Moreover, many existing
   TCP/IP stacks do not use YANG data models.  Such TCP implementations
   often have other means to configure the parameters listed in this
   document, which are outside the scope of this document.

   This specification is orthogonal to the Management Information Base
   (MIB) for the Transmission Control Protocol (TCP) [RFC4022].  The
   basic statistics defined in this document follow the model of the TCP
   MIB.  An TCP Extended Statistics MIB [RFC4898] is also available, but
   this document does not cover such extended statistics.  It is
   possible also to translate a MIB into a YANG model, for instance
   using Translation of Structure of Management Information Version 2
   (SMIv2) MIB Modules to YANG Modules [RFC6643].  However, this
   approach is not used in this document, as such a translated model
   would not be up-to-date.

   There are other existing TCP-related YANG models, which are
   orthogonal to this specification.  Examples are:

   o  TCP header attributes are modeled in other models, such as YANG
      Data Model for Network Access Control Lists (ACLs) [RFC8519] and
      Distributed Denial-of-Service Open Thread Signaling (DOTS) Data
      Channel Specification [RFC8783].

   o  TCP-related configuration of a NAT (e.g., NAT44, NAT64,
      Destination NAT, ...) is defined in A YANG Module for Network
      Address Translation (NAT) and Network Prefix Translation (NPT)
      [RFC8512] and A YANG Data Model for Dual-Stack Lite (DS-Lite)
      [RFC8513].

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.

2.1.  Note to RFC Editor

   This document uses several placeholder values throughout the
   document.  Please replace them as follows and remove this note before
   publication.

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   RFC XXXX, where XXXX is the number assigned to this document at the
   time of publication.

   2020-11-16 with the actual date of the publication of this document.

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 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
      socket options in the socket API, such as disabling the Nagle
      algorithm by TCP_NODELAY.  If 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 BGP YANG Model for Service Provider
      Networks [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 An Abstract Application Layer Interface to
      Transport Services [I-D.ietf-taps-interface].

   As a result, there is no ground truth for setting certain TCP
   parameters, and traditionally different TCP 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, TCP can be implemented in different

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   ways and design choices by the protocol engine often affect
   configuration options.

   Nonetheless, a number of TCP stack parameters require configuration
   by YANG models.  This document therefore defines a minimal YANG model
   with fundamental parameters directly following from TCP standards.

   An important use case is the TCP configuration on network elements
   such as routers, which often use YANG data models.  The model
   therefore specifies TCP parameters that are important on such TCP
   stacks.

   A typical example is the support of TCP-AO [RFC5925].  TCP-AO is
   increasingly supported on routers to secure routing protocols such as
   BGP.  In that case, TCP-AO configuration is required on routers.  The
   model includes the required TCP parameters for TCP-AO configuration.
   The key chain for TCP-AO can be modeled by the YANG Data Model for
   Key Chains [RFC8177].

   Given an installed base, the model also allows enabling of the legacy
   TCP MD5 [RFC2385] signature option.  As the TCP MD5 signature option
   is obsoleted by TCP-AO, it is strongly RECOMMENDED to use TCP-AO.

   Similar to the TCP MIB [RFC4022], this document also specifies basic
   statistics and a TCP connection table.

   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

   This allows implementations of TCP MIB [RFC4022] to migrate to the
   YANG model defined in this memo.

3.2.  Model Design

   The YANG model defined in this document includes definitions from the
   YANG Groupings for TCP Clients and TCP Servers
   [I-D.ietf-netconf-tcp-client-server].  Similar to that model, this
   specification 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.  An
   example could be the BGP YANG Model for Service Provider Networks
   [I-D.ietf-idr-bgp-model].

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3.3.  Tree Diagram

   This section provides a abridged tree diagram for the YANG module
   defined in this document.  Annotations used in the diagram are
   defined in YANG Tree Diagrams [RFC8340].

   module: ietf-tcp
     +--rw tcp!
        +--rw connections
        |     ...
        +--rw server {server}?
        |     ...
        +--rw client {client}?
        |     ...
        +--ro statistics {statistics}?
              ...

4.  TCP YANG Model

  <CODE BEGINS> file "ietf-tcp@2020-11-16.yang"

  module ietf-tcp {
    yang-version "1.1";
    namespace "urn:ietf:params:xml:ns:yang:ietf-tcp";
    prefix "tcp";

    import ietf-yang-types {
      prefix "yang";
      reference
        "RFC 6991: Common YANG Data Types.";
    }
    import ietf-tcp-client {
      prefix "tcpc";
    }
    import ietf-tcp-server {
      prefix "tcps";
    }
    import ietf-tcp-common {
      prefix "tcpcmn";
    }
    import ietf-inet-types {
      prefix "inet";
    }

    organization
      "IETF TCPM Working Group";

    contact

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      "WG Web:   <http://tools.ietf.org/wg/tcpm>
       WG List:  <tcpm@ietf.org>

       Authors: Michael Scharf (michael.scharf at hs-esslingen dot de)
                Vishal Murgai (vmurgai at gmail dot com)
                Mahesh Jethanandani (mjethanandani at gmail dot com)";

    description
      "This module focuses on fundamental and standard TCP functions
       that widely implemented. The model can be augmented to address
       more advanced or implementation specific TCP features.

       Copyright (c) 2020 IETF Trust and the persons identified as
       authors of the code.  All rights reserved.

       Redistribution and use in source and binary forms, with or
       without modification, is permitted pursuant to, and subject to
       the license terms contained in, the Simplified BSD License set
       forth in Section 4.c of the IETF Trust's Legal Provisions
       Relating to IETF Documents
       (https://trustee.ietf.org/license-info).

       This version of this YANG module is part of RFC XXXX
       (https://www.rfc-editor.org/info/rfcXXXX); see the RFC itself
       for full legal notices.

       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 (RFC 2119) (RFC 8174) when, and only when,
       they appear in all capitals, as shown here.";

    revision "2020-11-16" {
      description
        "Initial Version";
      reference
        "RFC XXXX, TCP Configuration.";
    }

    // Features
    feature server {
      description
        "TCP Server configuration supported.";
    }

    feature client {
      description
        "TCP Client configuration supported.";

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    }

    feature statistics {
      description
        "This implementation supports statistics reporting.";
    }

    // TCP-AO Groupings

    grouping ao {
      leaf enable-ao {
        type boolean;
        default "false";
        description
          "Enable support of TCP-Authentication Option (TCP-AO).";
      }

      leaf send-id {
        type uint8 {
          range "0..255";
        }
        must "../enable-ao = 'true'";
        description
          "The SendID is inserted as the KeyID of the TCP-AO option
           of outgoing segments.";
        reference
          "RFC 5925: The TCP Authentication Option.";
      }

      leaf recv-id {
        type uint8 {
          range "0..255";
        }
        must "../enable-ao = 'true'";
        description
          "The RecvID is matched against the TCP-AO KeyID of incoming
           segments.";
        reference
          "RFC 5925: The TCP Authentication Option.";
      }

      leaf include-tcp-options {
        type boolean;
        must "../enable-ao = 'true'";
        default true;
        description
          "Include TCP options in MAC calculation.";
      }

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      leaf accept-key-mismatch {
        type boolean;
        must "../enable-ao = 'true'";
        description
          "Accept TCP segments with a Master Key Tuple (MKT) that is not
           configured.";
      }
      description
        "Authentication Option (AO) for TCP.";
      reference
        "RFC 5925: The TCP Authentication Option.";
    }

    // MD5 grouping

    grouping md5 {
      description
        "Grouping for use in authenticating TCP sessions using MD5.";
      reference
        "RFC 2385: Protection of BGP Sessions via the TCP MD5
         Signature.";

      leaf enable-md5 {
        type boolean;
        default "false";
        description
          "Enable support of MD5 to authenticate a TCP session.";
      }
    }

    // TCP configuration

    container tcp {
      presence "The container for TCP configuration.";

      description
        "TCP container.";

      container connections {
        list connection {
          key "local-address remote-address local-port remote-port";

          leaf local-address {
            type inet:ip-address;
            description
              "Local address that forms the connection identifier.";
          }

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          leaf remote-address {
            type inet:ip-address;
            description
              "Remote address that forms the connection identifier.";
          }

          leaf local-port {
            type inet:port-number;
            description
              "Local TCP port that forms the connection identifier.";
          }

          leaf remote-port {
            type inet:port-number;
            description
              "Remote TCP port that forms the connection identifier.";
          }

          container common {
            uses tcpcmn:tcp-common-grouping;

            choice authentication {
              case ao {
                uses ao;
                description
                  "Use TCP-AO to secure the connection.";
              }

              case md5 {
                uses md5;
                description
                  "Use TCP-MD5 to secure the connection.";
              }
              description
                "Choice of how to secure the TCP connection.";
            }
            description
              "Common definitions of TCP configuration. This includes
               parameters such as how to secure the connection,
               that can be part of either the client or server.";
          }
          description
            "Connection related parameters.";
        }
        description
          "A container of all TCP connections.";
      }

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      container server {
        if-feature server;
        uses tcps:tcp-server-grouping;
        description
          "Definitions of TCP server configuration.";
      }

      container client {
        if-feature client;
        uses tcpc:tcp-client-grouping;
        description
          "Definitions of TCP client configuration.";
      }

      container statistics {
        if-feature statistics;
        config false;

        leaf active-opens {
          type yang:counter32;
          description
            "The number of times that TCP connections have made a direct
             transition to the SYN-SENT state from the CLOSED state.";
        }

        leaf passive-opens {
          type yang:counter32;
          description
            "The number of times TCP connections have made a direct
             transition to the SYN-RCVD state from the LISTEN state.";
        }

        leaf attempt-fails {
          type yang:counter32;
          description
            "The number of times that TCP connections have made a direct
             transition to the CLOSED state from either the SYN-SENT
             state or the SYN-RCVD state, plus the number of times that
             TCP connections have made a direct transition to the
             LISTEN state from the SYN-RCVD state.";
        }

        leaf establish-resets {
          type yang:counter32;
          description
            "The number of times that TCP connections have made a direct
             transition to the CLOSED state from either the ESTABLISHED
             state or the CLOSE-WAIT state.";

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        }

        leaf currently-established {
          type yang:gauge32;
          description
            "The number of TCP connections for which the current state
             is either ESTABLISHED or CLOSE-WAIT.";
        }

        leaf in-segments {
          type yang:counter64;
          description
            "The total number of segments received, including those
             received in error.  This count includes segments received
             on currently established connections.";
        }

        leaf out-segments {
          type yang:counter64;
          description
            "The total number of segments sent, including those on
             current connections but excluding those containing only
             retransmitted octets.";
        }

        leaf retransmitted-segments {
          type yang:counter32;
          description
            "The total number of segments retransmitted; that is, the
             number of TCP segments transmitted containing one or more
             previously transmitted octets.";
        }

        leaf in-errors {
          type yang:counter32;
          description
            "The total number of segments received in error (e.g., bad
             TCP checksums).";
        }

        leaf out-resets {
          type yang:counter32;
          description
            "The number of TCP segments sent containing the RST flag.";
        }

        action reset {
          description

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            "Reset statistics action command.";
          input {
            leaf reset-at {
              type yang:date-and-time;
              description
                "Time when the reset action needs to be
                 executed.";
            }
          }
          output {
            leaf reset-finished-at {
              type yang:date-and-time;
              description
                "Time when the reset action command completed.";
            }
          }
        }
        description
          "Statistics across all connections.";
      }
    }
  }

  <CODE ENDS>

5.  IANA Considerations

5.1.  The IETF XML Registry

   This document registers two URIs in the "ns" subregistry of the IETF
   XML Registry [RFC3688].  Following the format in IETF XML Registry
   [RFC3688], the following registrations are requested:

      URI: urn:ietf:params:xml:ns:yang:ietf-tcp
      Registrant Contact: The TCPM WG of the IETF.
      XML: N/A, the requested URI is an XML namespace.

5.2.  The YANG Module Names Registry

   This document registers a YANG modules in the YANG Module Names
   registry YANG - A Data Modeling Language [RFC6020].  Following the
   format in YANG - A Data Modeling Language [RFC6020], the following
   registrations are requested:

      name:         ietf-tcp
      namespace:    urn:ietf:params:xml:ns:yang:ietf-tcp
      prefix:       tcp
      reference:    RFC XXXX

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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) described in Using the NETCONF
   protocol over 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:

   o  Server configuration.  Unrestricted access to all the nodes under
      server configuration, e.g. local-address or keepalive idle-timer,
      can cause connections to the server to fail or to timeout
      prematurely.

   o  Client configuration.  Similar to server configuration,
      unrestricted access to the nodes under client configuration can
      cause connections from the client to fail, or connections to the
      server to be redirected, and in case of keepalive, cause
      connections to timeout prematurely etc.

   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:

   o  Unrestricted access to connection information of the client or
      server can be used by a malicious user to launch an attack, e.g.
      MITM.

   o  Similarly, unrestricted access to statistics of the client or
      server can be used by a malicious user to exploit any
      vulnerabilities of the system.

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   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:

   o  The YANG module allows for the statistics to be cleared by
      executing the reset action.  This action should be restricted to
      users with the right permission.

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-08
              (work in progress), August 2020.

   [RFC0793]  Postel, J., "Transmission Control Protocol", STD 7,
              RFC 793, DOI 10.17487/RFC0793, September 1981,
              <https://www.rfc-editor.org/info/rfc793>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC2385]  Heffernan, A., "Protection of BGP Sessions via the TCP MD5
              Signature Option", RFC 2385, DOI 10.17487/RFC2385, August
              1998, <https://www.rfc-editor.org/info/rfc2385>.

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              DOI 10.17487/RFC3688, January 2004,
              <https://www.rfc-editor.org/info/rfc3688>.

   [RFC5925]  Touch, J., Mankin, A., and R. Bonica, "The TCP
              Authentication Option", RFC 5925, DOI 10.17487/RFC5925,
              June 2010, <https://www.rfc-editor.org/info/rfc5925>.

   [RFC6020]  Bjorklund, M., Ed., "YANG - A Data Modeling Language for
              the Network Configuration Protocol (NETCONF)", RFC 6020,
              DOI 10.17487/RFC6020, October 2010,
              <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, June 2011,
              <https://www.rfc-editor.org/info/rfc6241>.

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   [RFC6242]  Wasserman, M., "Using the NETCONF Protocol over Secure
              Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,
              <https://www.rfc-editor.org/info/rfc6242>.

   [RFC7950]  Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
              RFC 7950, DOI 10.17487/RFC7950, August 2016,
              <https://www.rfc-editor.org/info/rfc7950>.

   [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
              <https://www.rfc-editor.org/info/rfc8040>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8177]  Lindem, A., Ed., Qu, Y., Yeung, D., Chen, I., and J.
              Zhang, "YANG Data Model for Key Chains", RFC 8177,
              DOI 10.17487/RFC8177, June 2017,
              <https://www.rfc-editor.org/info/rfc8177>.

   [RFC8340]  Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
              BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,
              <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, March 2018,
              <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, March 2018,
              <https://www.rfc-editor.org/info/rfc8342>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.

7.2.  Informative References

   [I-D.ietf-idr-bgp-model]
              Jethanandani, M., Patel, K., Hares, S., and J. Haas, "BGP
              YANG Model for Service Provider Networks", draft-ietf-idr-
              bgp-model-09 (work in progress), June 2020.

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   [I-D.ietf-taps-interface]
              Trammell, B., Welzl, M., Enghardt, T., Fairhurst, G.,
              Kuehlewind, M., Perkins, C., Tiesel, P., Wood, C., and T.
              Pauly, "An Abstract Application Layer Interface to
              Transport Services", draft-ietf-taps-interface-10 (work in
              progress), November 2020.

   [I-D.touch-tcpm-ao-test-vectors]
              Touch, J. and J. Kuusisaari, "TCP-AO Test Vectors", draft-
              touch-tcpm-ao-test-vectors-01 (work in progress), August
              2020.

   [RFC4022]  Raghunarayan, R., Ed., "Management Information Base for
              the Transmission Control Protocol (TCP)", RFC 4022,
              DOI 10.17487/RFC4022, March 2005,
              <https://www.rfc-editor.org/info/rfc4022>.

   [RFC4898]  Mathis, M., Heffner, J., and R. Raghunarayan, "TCP
              Extended Statistics MIB", RFC 4898, DOI 10.17487/RFC4898,
              May 2007, <https://www.rfc-editor.org/info/rfc4898>.

   [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,
              <https://www.rfc-editor.org/info/rfc6643>.

   [RFC8512]  Boucadair, M., Ed., Sivakumar, S., Jacquenet, C.,
              Vinapamula, S., and Q. Wu, "A YANG Module for Network
              Address Translation (NAT) and Network Prefix Translation
              (NPT)", RFC 8512, DOI 10.17487/RFC8512, January 2019,
              <https://www.rfc-editor.org/info/rfc8512>.

   [RFC8513]  Boucadair, M., Jacquenet, C., and S. Sivakumar, "A YANG
              Data Model for Dual-Stack Lite (DS-Lite)", RFC 8513,
              DOI 10.17487/RFC8513, January 2019,
              <https://www.rfc-editor.org/info/rfc8513>.

   [RFC8519]  Jethanandani, M., Agarwal, S., Huang, L., and D. Blair,
              "YANG Data Model for Network Access Control Lists (ACLs)",
              RFC 8519, DOI 10.17487/RFC8519, March 2019,
              <https://www.rfc-editor.org/info/rfc8519>.

   [RFC8783]  Boucadair, M., Ed. and T. Reddy.K, Ed., "Distributed
              Denial-of-Service Open Threat Signaling (DOTS) Data
              Channel Specification", RFC 8783, DOI 10.17487/RFC8783,
              May 2020, <https://www.rfc-editor.org/info/rfc8783>.

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Appendix A.  Acknowledgements

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

   The following persons have contributed to this document by reviews:
   Mohamed Boucadair

Appendix B.  Changes compared to previous versions

   Changes compared to draft-scharf-tcpm-yang-tcp-04

   o  Removed congestion control

   o  Removed global stack parameters

   Changes compared to draft-scharf-tcpm-yang-tcp-03

   o  Updated TCP-AO grouping

   o  Added congestion control

   Changes compared to draft-scharf-tcpm-yang-tcp-02

   o  Initial proposal of a YANG model including base configuration
      parameters, TCP-AO configuration, and a connection list

   o  Editorial bugfixes and outdated references reported by Mohamed
      Boucadair

   o  Additional co-author Mahesh Jethanandani

   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 Vishal Murgai

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

   o  Editorial improvements

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Appendix C.  Examples

C.1.  Keepalive Configuration

   This particular example demonstrates how both a particular connection
   can be configured for keepalives.

   [note: '\' line wrapping for formatting only]

   <?xml version="1.0" encoding="UTF-8"?>
   <!--
    This example shows how TCP keepalive can be configured for
    a given connection. An idle connection is dropped after
    idle-time + (max-probes * probe-interval).
   -->
   <config xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <tcp
         xmlns="urn:ietf:params:xml:ns:yang:ietf-tcp">
       <connections>
         <connection>
           <local-address>192.168.1.1</local-address>
           <remote-address>192.168.1.2</remote-address>
           <local-port>1025</local-port>
           <remote-port>80</remote-port>
           <common>
             <keepalives>
               <idle-time>5</idle-time>
               <max-probes>5</max-probes>
               <probe-interval>10</probe-interval>
             </keepalives>
           </common>
         </connection>
       </connections>
       <!--
        It is not clear why a server and client configuration is
        needed here even as they under a feature statement and
        therefore are required only if the feature is declared.
        Adding it so that yanglint allows this validation to run.
       -->
       <server>
         <local-address>192.168.1.1</local-address>
       </server>
       <client>
         <remote-address>192.168.1.2</remote-address>
       </client>
     </tcp>
   </config>

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C.2.  TCP-AO Configuration

   The following example demonstrates how to model a TCP-AO [RFC5925]
   configuration for the example in TCP-AO Test Vectors
   [I-D.touch-tcpm-ao-test-vectors], Section 5.1.1.

[note: '\' line wrapping for formatting only]

<?xml version="1.0" encoding="UTF-8"?>
<!--
 This example sets TCP-AO configuration parameters as
 demonstrated by examples in draft-touch-tcpm-ao-test-vectors.
-->
<config xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <key-chains
      xmlns="urn:ietf:params:xml:ns:yang:ietf-key-chain">
    <key-chain>
      <name>ao-config</name>
      <description>"An example for TCP-AO configuration."</descriptio\
n>
      <key>
        <key-id>61</key-id>
        <crypto-algorithm>hmac-sha-1-12</crypto-algorithm>
        <key-string>
          <hexadecimal-string>01:23:a5:93:b9:db:70:62:9b:be:2c:a6:77:cd:fd:e\
a:6f:e0:ac:ad</hexadecimal-string>
        </key-string>
      </key>
    </key-chain>
  </key-chains>
  <tcp
      xmlns="urn:ietf:params:xml:ns:yang:ietf-tcp">
    <!--
        The example in draft-touch-tcpm-ao-test-vectors uses
        IP addresses that are not valid for examples. Changing
        them here to valid addresses.
    -->
    <server>
      <local-address>192.168.1.1</local-address>
    </server>
    <client>
      <remote-address>192.168.1.2</remote-address>
    </client>
  </tcp>
</config>

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Appendix D.  Complete Tree Diagram

   Here is the complete tree diagram for the TCP YANG model.

   module: ietf-tcp
     +--rw tcp!
        +--rw connections
        |  +--rw connection*
        |          [local-address remote-address local-port remote-port]
        |     +--rw local-address     inet:ip-address
        |     +--rw remote-address    inet:ip-address
        |     +--rw local-port        inet:port-number
        |     +--rw remote-port       inet:port-number
        |     +--rw common
        |        +--rw keepalives!
        |        |  +--rw idle-time         uint16
        |        |  +--rw max-probes        uint16
        |        |  +--rw probe-interval    uint16
        |        +--rw (authentication)?
        |           +--:(ao)
        |           |  +--rw enable-ao?             boolean
        |           |  +--rw send-id?               uint8
        |           |  +--rw recv-id?               uint8
        |           |  +--rw include-tcp-options?   boolean
        |           |  +--rw accept-key-mismatch?   boolean
        |           +--:(md5)
        |              +--rw enable-md5?            boolean
        +--rw server {server}?
        |  +--rw local-address    inet:ip-address
        |  +--rw local-port?      inet:port-number
        |  +--rw keepalives!
        |     +--rw idle-time         uint16
        |     +--rw max-probes        uint16
        |     +--rw probe-interval    uint16
        +--rw client {client}?
        |  +--rw remote-address    inet:host
        |  +--rw remote-port?      inet:port-number
        |  +--rw local-address?    inet:ip-address
        |  +--rw local-port?       inet:port-number
        |  +--rw keepalives!
        |     +--rw idle-time         uint16
        |     +--rw max-probes        uint16
        |     +--rw probe-interval    uint16
        +--ro statistics {statistics}?
           +--ro active-opens?             yang:counter32
           +--ro passive-opens?            yang:counter32
           +--ro attempt-fails?            yang:counter32
           +--ro establish-resets?         yang:counter32

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           +--ro currently-established?    yang:gauge32
           +--ro in-segments?              yang:counter64
           +--ro out-segments?             yang:counter64
           +--ro retransmitted-segments?   yang:counter32
           +--ro in-errors?                yang:counter32
           +--ro out-resets?               yang:counter32
           +---x reset
              +---w input
              |  +---w reset-at?   yang:date-and-time
              +--ro output
                 +--ro reset-finished-at?   yang:date-and-time

Authors' Addresses

   Michael Scharf
   Hochschule Esslingen - University of Applied Sciences
   Flandernstr. 101
   Esslingen  73732
   Germany

   Email: michael.scharf@hs-esslingen.de

   Vishal Murgai
   Samsung

   Email: vmurgai@gmail.com

   Mahesh Jethanandani
   Kloud Services

   Email: mjethanandani@gmail.com

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