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YANG Groupings for TCP Clients and TCP Servers
draft-ietf-netconf-tcp-client-server-22

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This is an older version of an Internet-Draft whose latest revision state is "Active".
Authors Kent Watsen , Michael Scharf
Last updated 2024-02-29 (Latest revision 2024-02-22)
Replaces draft-kwatsen-netconf-tcp-client-server
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draft-ietf-netconf-tcp-client-server-22
NETCONF Working Group                                          K. Watsen
Internet-Draft                                           Watsen Networks
Intended status: Standards Track                               M. Scharf
Expires: 25 August 2024                             Hochschule Esslingen
                                                        22 February 2024

             YANG Groupings for TCP Clients and TCP Servers
                draft-ietf-netconf-tcp-client-server-22

Abstract

   This document presents three YANG 1.1 modules to support the
   configuration of TCP clients and TCP servers.  The modules include
   basic parameters of a TCP connection relevant for client or server
   applications, as well as client configuration required for traversing
   proxies.  The modules can be used either standalone or in conjunction
   with configuration of other stack protocol layers.

Editorial Note (To be removed by RFC Editor)

   This draft contains placeholder values that need to be replaced with
   finalized values at the time of publication.  This note summarizes
   all of the substitutions that are needed.  No other RFC Editor
   instructions are specified elsewhere in this document.

   Artwork in this document contains shorthand references to drafts in
   progress.  Please apply the following replacements:

   *  AAAA --> the assigned RFC value for draft-ietf-netconf-crypto-
      types

   *  DDDD --> the assigned RFC value for this draft

   Artwork in this document contains placeholder values for the date of
   publication of this draft.  Please apply the following replacement:

   *  2024-02-22 --> the publication date of this draft

   The "Relation to other RFCs" section Section 1.1 contains the text
   "one or more YANG modules" and, later, "modules".  This text is
   sourced from a file in a context where it is unknown how many modules
   a draft defines.  The text is not wrong as is, but it may be improved
   by stating more directly how many modules are defined.

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   The "Relation to other RFCs" section Section 1.1 contains a self-
   reference to this draft, along with a corresponding reference in the
   Appendix.  Please replace the self-reference in this section with
   "This RFC" (or similar) and remove the self-reference in the
   "Normative/Informative References" section, whichever it is in.

   Tree-diagrams in this draft may use the '\' line-folding mode defined
   in RFC 8792.  However, nicer-to-the-eye is when the '\\' line-folding
   mode is used.  The AD suggested suggested putting a request here for
   the RFC Editor to help convert "ugly" '\' folded examples to use the
   '\\' folding mode.  "Help convert" may be interpreted as, identify
   what looks ugly and ask the authors to make the adjustment.

   The following Appendix section is to be removed prior to publication:

   *  Appendix A.  Change Log

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 25 August 2024.

Copyright Notice

   Copyright (c) 2024 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 Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.1.  Relation to other RFCs  . . . . . . . . . . . . . . . . .   4
     1.2.  Specification Language  . . . . . . . . . . . . . . . . .   6
     1.3.  Adherence to the NMDA . . . . . . . . . . . . . . . . . .   6
   2.  The "ietf-tcp-common" Module  . . . . . . . . . . . . . . . .   6
     2.1.  Data Model Overview . . . . . . . . . . . . . . . . . . .   6
     2.2.  Example Usage . . . . . . . . . . . . . . . . . . . . . .   8
     2.3.  YANG Module . . . . . . . . . . . . . . . . . . . . . . .   9
   3.  The "ietf-tcp-client" Module  . . . . . . . . . . . . . . . .  12
     3.1.  Data Model Overview . . . . . . . . . . . . . . . . . . .  12
     3.2.  Example Usage . . . . . . . . . . . . . . . . . . . . . .  15
     3.3.  YANG Module . . . . . . . . . . . . . . . . . . . . . . .  16
   4.  The "ietf-tcp-server" Module  . . . . . . . . . . . . . . . .  24
     4.1.  Data Model Overview . . . . . . . . . . . . . . . . . . .  24
     4.2.  Example Usage . . . . . . . . . . . . . . . . . . . . . .  25
     4.3.  YANG Module . . . . . . . . . . . . . . . . . . . . . . .  25
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  28
     5.1.  Considerations for the "ietf-tcp-common" YANG Module  . .  28
     5.2.  Considerations for the "ietf-tcp-client" YANG Module  . .  29
     5.3.  Considerations for the "ietf-tcp-server" YANG Module  . .  30
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  31
     6.1.  The "IETF XML" Registry . . . . . . . . . . . . . . . . .  31
     6.2.  The "YANG Module Names" Registry  . . . . . . . . . . . .  32
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  32
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  32
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  33
   Appendix A.  Change Log . . . . . . . . . . . . . . . . . . . . .  35
     A.1.  00 to 01  . . . . . . . . . . . . . . . . . . . . . . . .  35
     A.2.  01 to 02  . . . . . . . . . . . . . . . . . . . . . . . .  35
     A.3.  02 to 03  . . . . . . . . . . . . . . . . . . . . . . . .  36
     A.4.  03 to 04  . . . . . . . . . . . . . . . . . . . . . . . .  36
     A.5.  04 to 05  . . . . . . . . . . . . . . . . . . . . . . . .  36
     A.6.  05 to 06  . . . . . . . . . . . . . . . . . . . . . . . .  36
     A.7.  06 to 07  . . . . . . . . . . . . . . . . . . . . . . . .  36
     A.8.  07 to 08  . . . . . . . . . . . . . . . . . . . . . . . .  36
     A.9.  08 to 09  . . . . . . . . . . . . . . . . . . . . . . . .  36
     A.10. 09 to 10  . . . . . . . . . . . . . . . . . . . . . . . .  37
     A.11. 10 to 11  . . . . . . . . . . . . . . . . . . . . . . . .  37
     A.12. 11 to 12  . . . . . . . . . . . . . . . . . . . . . . . .  37
     A.13. 12 to 13  . . . . . . . . . . . . . . . . . . . . . . . .  37
     A.14. 13 to 14  . . . . . . . . . . . . . . . . . . . . . . . .  37
     A.15. 14 to 15  . . . . . . . . . . . . . . . . . . . . . . . .  37
     A.16. 15 to 16  . . . . . . . . . . . . . . . . . . . . . . . .  38
     A.17. 16 to 17  . . . . . . . . . . . . . . . . . . . . . . . .  38
     A.18. 18 to 19  . . . . . . . . . . . . . . . . . . . . . . . .  38
     A.19. 18 to 19  . . . . . . . . . . . . . . . . . . . . . . . .  38

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     A.20. 19 to 20  . . . . . . . . . . . . . . . . . . . . . . . .  38
     A.21. 20 to 22  . . . . . . . . . . . . . . . . . . . . . . . .  38
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  39
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  39

1.  Introduction

   This document defines three YANG 1.1 [RFC7950] modules to support the
   configuration of TCP clients and TCP servers (TCP is defined in
   [RFC9293]), either as standalone or in conjunction with configuration
   of other stack protocol layers.

   The modules focus on three different types of base TCP parameters
   that matter for TCP-based applications: First, the modules cover
   fundamental configuration of a TCP client or TCP server application,
   such as addresses and port numbers.  Second, a reusable grouping
   enables modification of application-specific parameters for a TCP
   connections, such as use of TCP keep-alives.  And third, client
   configuration for traversing proxies is included as well.  In each
   case, the modules have a very narrow scope and focus on a minimum set
   of required parameters.

1.1.  Relation to other RFCs

   This document presents one or more YANG modules [RFC7950] that are
   part of a collection of RFCs that work together to, ultimately,
   support the configuration of both the clients and servers of both the
   NETCONF [RFC6241] and RESTCONF [RFC8040] protocols.

   The dependency relationship between the primary YANG groupings
   defined in the various RFCs is presented in the below diagram.  In
   some cases, a draft may define secondary groupings that introduce
   dependencies not illustrated in the diagram.  The labels in the
   diagram are a shorthand name for the defining RFC.  The citation
   reference for shorthand name is provided below the diagram.

   Please note that the arrows in the diagram point from referencer to
   referenced.  For example, the "crypto-types" RFC does not have any
   dependencies, whilst the "keystore" RFC depends on the "crypto-types"
   RFC.

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                                  crypto-types
                                    ^      ^
                                   /        \
                                  /          \
                         truststore         keystore
                          ^     ^             ^  ^
                          |     +---------+   |  |
                          |               |   |  |
                          |      +------------+  |
   tcp-client-server      |     /         |      |
      ^    ^        ssh-client-server     |      |
      |    |           ^            tls-client-server
      |    |           |              ^     ^        http-client-server
      |    |           |              |     |                 ^
      |    |           |        +-----+     +---------+       |
      |    |           |        |                     |       |
      |    +-----------|--------|--------------+      |       |
      |                |        |              |      |       |
      +-----------+    |        |              |      |       |
                  |    |        |              |      |       |
                  |    |        |              |      |       |
               netconf-client-server       restconf-client-server

   +======================+===========================================+
   |Label in Diagram      | Originating RFC                           |
   +======================+===========================================+
   |crypto-types          | [I-D.ietf-netconf-crypto-types]           |
   +----------------------+-------------------------------------------+
   |truststore            | [I-D.ietf-netconf-trust-anchors]          |
   +----------------------+-------------------------------------------+
   |keystore              | [I-D.ietf-netconf-keystore]               |
   +----------------------+-------------------------------------------+
   |tcp-client-server     | [I-D.ietf-netconf-tcp-client-server]      |
   +----------------------+-------------------------------------------+
   |ssh-client-server     | [I-D.ietf-netconf-ssh-client-server]      |
   +----------------------+-------------------------------------------+
   |tls-client-server     | [I-D.ietf-netconf-tls-client-server]      |
   +----------------------+-------------------------------------------+
   |http-client-server    | [I-D.ietf-netconf-http-client-server]     |
   +----------------------+-------------------------------------------+
   |netconf-client-server | [I-D.ietf-netconf-netconf-client-server]  |
   +----------------------+-------------------------------------------+
   |restconf-client-server| [I-D.ietf-netconf-restconf-client-server] |
   +----------------------+-------------------------------------------+

                 Table 1: Label in Diagram to RFC Mapping

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1.2.  Specification 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.

1.3.  Adherence to the NMDA

   This document is compliant with the Network Management Datastore
   Architecture (NMDA) [RFC8342].  It does not define any protocol
   accessible nodes that are "config false".

2.  The "ietf-tcp-common" Module

   This section defines a YANG 1.1 module called "ietf-tcp-common".  A
   high-level overview of the module is provided in Section 2.1.
   Examples illustrating the module's use are provided in Examples
   (Section 2.2).  The YANG module itself is defined in Section 2.3.

2.1.  Data Model Overview

   This section provides an overview of the "ietf-tcp-common" module in
   terms of its features and groupings.

2.1.1.  Model Scope

   This document presents a common "grouping" statement for basic TCP
   connection parameters that matter to applications.  It is "common" in
   that this grouping is used by both the "ietf-tcp-client" and "ietf-
   tcp-server" modules.  In some TCP stacks, such parameters can also
   directly be set by an application using system calls, such as the
   sockets API.  The base YANG model in this document focuses on
   modeling TCP keep-alives.  This base model can be extended as needed.

2.1.2.  Features

   The following diagram lists all the "feature" statements defined in
   the "ietf-tcp-common" module:

   Features:
     +-- keepalives-supported

   The diagram above uses syntax that is similar to but not defined in
   [RFC8340].

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2.1.3.  Groupings

   The "ietf-tcp-common" module defines the following "grouping"
   statement:

   *  tcp-common-grouping

   This grouping is presented in the following subsection.

2.1.3.1.  The "tcp-common-grouping" Grouping

   The following tree diagram [RFC8340] illustrates the "tcp-common-
   grouping" grouping:

     grouping tcp-common-grouping:
       +-- keepalives! {keepalives-supported}?
          +-- idle-time?        uint16
          +-- max-probes?       uint16
          +-- probe-interval?   uint16

   Comments:

   *  The "keepalives" node is a "presence" container so that the
      mandatory descendant nodes do not imply that keepalives must be
      configured.

   *  The "idle-time", "max-probes", and "probe-interval" nodes have the
      common meanings.  Please see the YANG module in Section 2.3 for
      details.

2.1.4.  Protocol-accessible Nodes

   The "ietf-tcp-common" module defines only "grouping" statements that
   are used by other modules to instantiate protocol-accessible nodes.
   Thus this module, when implemented, does not itself define any
   protocol-accessible nodes.

2.1.5.  Guidelines for Configuring TCP Keep-Alives

   Network stacks may include "keep-alives" in their TCP
   implementations, although this practice is not universally accepted.
   If keep-alives are included, [RFC9293] mandates that the application
   MUST be able to turn them on or off for each TCP connection, and that
   they MUST default to off.

   Keep-alive mechanisms exist in many protocols.  Depending on the
   protocol stack, TCP keep-alives may only be one out of several
   alternatives.  Which mechanism(s) to use depends on the use case and

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   application requirements.  If keep-alives are needed by an
   application, it is RECOMMENDED that the liveness check happens only
   at the protocol layers that are meaningful to the application.

   A TCP keep-alive mechanism SHOULD only be invoked in server
   applications that might otherwise hang indefinitely and consume
   resources unnecessarily if a client crashes or aborts a connection
   during a network failure [RFC9293].  TCP keep-alives may consume
   significant resources both in the network and in endpoints (e.g.,
   battery power).  In addition, frequent keep-alives risk network
   congestion.  The higher the frequency of keep-alives, the higher the
   overhead.

   Given the cost of keep-alives, parameters have to be configured
   carefully:

   *  The default idle interval (leaf "idle-time") is two hours, i.e.,
      7200 seconds [RFC9293].  A lower value MAY be configured, but idle
      intervals SHOULD NOT be smaller than 15 seconds.  Longer idle
      intervals SHOULD be used when possible.

   *  The maximum number of sequential keep-alive probes that can fail
      (leaf "max-probes") trades off responsiveness and robustness
      against packet loss.  ACK segments that contain no data are not
      reliably transmitted by TCP.  Consequently, if a keep-alive
      mechanism is implemented it MUST NOT interpret failure to respond
      to any specific probe as a dead connection [RFC9293].  Typically,
      a single-digit number should suffice.

   *  TCP implementations may include a parameter for the number of
      seconds between TCP keep-alive probes (leaf "probe-interval").  In
      order to avoid congestion, the time interval between probes MUST
      NOT be smaller than one second.  Significantly longer intervals
      SHOULD be used.  It is important to note that keep-alive probes
      (or replies) can get dropped due to network congestion.  Sending
      further probe messages into a congested path after a short
      interval, without backing off timers, could cause harm and result
      in a congestion collapse.  Therefore it is essential to pick a
      large, conservative value for this interval.

2.2.  Example Usage

   This section presents an example showing the "tcp-common-grouping"
   populated with some data.

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   <!-- The outermost element below doesn't exist in the data model. -->
   <!--  It simulates if the "grouping" were a "container" instead.  -->

   <tcp-common xmlns="urn:ietf:params:xml:ns:yang:ietf-tcp-common">
     <keepalives>
       <idle-time>7200</idle-time>
       <max-probes>9</max-probes>
       <probe-interval>75</probe-interval>
     </keepalives>
   </tcp-common>

2.3.  YANG Module

   The ietf-tcp-common YANG module references [RFC6991] and [RFC9293].

   <CODE BEGINS> file "ietf-tcp-common@2024-02-22.yang"

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

     organization
       "IETF NETCONF (Network Configuration) Working Group and the
        IETF TCP Maintenance and Minor Extensions (TCPM) Working Group";

     contact
       "WG Web:   https://datatracker.ietf.org/wg/netconf
                  https://datatracker.ietf.org/wg/tcpm
        WG List:  NETCONF WG list <mailto:netconf@ietf.org>
                  TCPM WG list <mailto:tcpm@ietf.org>
        Authors:  Kent Watsen <mailto:kent+ietf@watsen.net>
                  Michael Scharf
                  <mailto:michael.scharf@hs-esslingen.de>";

     description
       "This module define a reusable 'grouping' that is common
        to both TCP-clients and TCP-servers.  This grouping statement
        is used by both the 'ietf-tcp-client' and 'ietf-tcp-server'
        modules.

        Copyright (c) 2023 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 Revised
        BSD License set forth in Section 4.c of the IETF Trust's

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        Legal Provisions Relating to IETF Documents
        (https://trustee.ietf.org/license-info).

        This version of this YANG module is part of RFC DDDD
        (https://www.rfc-editor.org/info/rfcDDDD); 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 2024-02-22 {
       description
         "Initial version";
       reference
         "RFC DDDD: YANG Groupings for TCP Clients and TCP Servers";
     }

     // Features

     feature keepalives-supported {
       description
         "Indicates that keepalives are supported.";
     }

     // Groupings

     grouping tcp-common-grouping {
       description
         "A reusable grouping for configuring TCP parameters common
          to TCP connections as well as the operating system as a
          whole.";
       container keepalives {
         if-feature "keepalives-supported";
         presence
           "Indicates that keepalives are enabled, aligning to
            the requirement in Section 3.8.4 RFC 9293 that
            keepalives are off by default.";
         description
           "Configures the keep-alive policy, to proactively test the
            aliveness of the TCP peer.  An unresponsive TCP peer is
            dropped after approximately (idle-time + max-probes *
            probe-interval) seconds.  Further guidance can be found
            in Section 2.1.5 of RFC DDDD.";
         reference

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           "RFC 9293: Transmission Control Protocol (TCP)";
         leaf idle-time {
           type uint16 {
             range "1..max";
           }
           units "seconds";
           default 7200;
           description
             "Sets the amount of time after which if no data has been
              received from the TCP peer, a TCP-level probe message
              will be sent to test the aliveness of the TCP peer.
              Two hours (7200 seconds) is safe value, per RFC 9293
              Section 3.8.4.";
           reference
             "RFC 9293: Transmission Control Protocol (TCP)";

         }
         leaf max-probes {
           type uint16 {
             range "1..max";
           }
           default 9;
           description
             "Sets the maximum number of sequential keep-alive probes
              that can fail to obtain a response from the TCP peer
              before assuming the TCP peer is no longer alive.";
         }
         leaf probe-interval {
           type uint16 {
             range "1..max";
           }
           units "seconds";
           default 75;
           description
             "Sets the time interval between failed probes. The interval
              SHOULD be significantly longer than one second in order to
              avoid harm on a congested link.";
         }
       } // container keepalives
     } // grouping tcp-common-grouping

   }

   <CODE ENDS>

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3.  The "ietf-tcp-client" Module

   This section defines a YANG 1.1 module called "ietf-tcp-client".  A
   high-level overview of the module is provided in Section 3.1.
   Examples illustrating the module's use are provided in Examples
   (Section 3.2).  The YANG module itself is defined in Section 3.3.

3.1.  Data Model Overview

   This section provides an overview of the "ietf-tcp-client" module in
   terms of its features and groupings.

3.1.1.  Features

   The following diagram lists all the "feature" statements defined in
   the "ietf-tcp-client" module:

   Features:
     +-- local-binding-supported
     +-- tcp-client-keepalives
     +-- proxy-connect
         +-- socks4-supported {proxy-connect}?
         +-- socks4a-supported {proxy-connect}?
         +-- socks5-supported {proxy-connect}?
             +-- socks5-gss-api {socks5-supported}?
             +-- socks5-username-password {socks5-supported}?

   Comments:

   *  The "local-binding-supported" feature indicates that the server
      supports configuring local bindings (i.e., the local address and
      local port) for TCP clients."

   *  The "tcp-client-keepalives" feature indicates that per socket TCP
      keepalive parameters are configurable for TCP clients on the
      server implementing this feature.

   *  The "proxy-connect" feature indicates the TCP-client supports
      connecting through TCP proxies.

   *  The "socks4-supported" feature indicates the TCP-client supports
      Socks4-based proxies.

   *  The "socks4a-supported" feature indicates the TCP-client supports
      Socks4a-based proxies.  The difference between Socks4 and Socks4a
      is that Socks4a enables the "remote-address" to be specified using
      a hostname, in addition to an IP address.

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   *  The "socks5-supported" feature indicates the TCP-client supports
      Socks5-based proxies.

   *  The "socks5-gss-api" feature indicates that the server, when
      acting as a TCP-client, supports authenticating to a SOCKS Version
      5 proxy server using GSSAPI credentials.

   *  The "socks5-username-password" feature indicates that the server,
      when acting as a TCP-client, supports authenticating to a SOCKS
      Version 5 proxy server using 'username' and 'password'
      credentials."

   The diagram above uses syntax that is similar to but not defined in
   [RFC8340].

3.1.2.  Groupings

   The "ietf-tcp-client" module defines the following "grouping"
   statement:

   *  tcp-client-grouping

   This grouping is presented in the following subsection.

3.1.2.1.  The "tcp-client-grouping" Grouping

   The following tree diagram [RFC8340] illustrates the "tcp-client-
   grouping" grouping:

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     grouping tcp-client-grouping:
       +-- remote-address                inet:host
       +-- remote-port?                  inet:port-number
       +-- local-address?                inet:ip-address
       |       {local-binding-supported}?
       +-- local-port?                   inet:port-number
       |       {local-binding-supported}?
       +-- proxy-server! {proxy-connect}?
       |  +-- (proxy-type)
       |     +--:(socks4) {socks4-supported}?
       |     |  +-- socks4-parameters
       |     |     +-- remote-address    inet:ip-address
       |     |     +-- remote-port?      inet:port-number
       |     +--:(socks4a) {socks4a-supported}?
       |     |  +-- socks4a-parameters
       |     |     +-- remote-address    inet:host
       |     |     +-- remote-port?      inet:port-number
       |     +--:(socks5) {socks5-supported}?
       |        +-- socks5-parameters
       |           +-- remote-address               inet:host
       |           +-- remote-port?                 inet:port-number
       |           +-- authentication-parameters!
       |              +-- (auth-type)
       |                 +--:(gss-api) {socks5-gss-api}?
       |                 |  +-- gss-api
       |                 +--:(username-password)
       |                          {socks5-username-password}?
       |                    +-- username-password
       |                       +-- username                string
       |                       +---u ct:password-grouping
       +---u tcpcmn:tcp-common-grouping

   Comments:

   *  The "remote-address" node, which is mandatory, may be configured
      as an IPv4 address, an IPv6 address, or a hostname.

   *  The "remote-port" node is not mandatory, but its default value is
      the invalid value '0', thus forcing the consuming data model to
      refine it in order to provide it an appropriate default value.

   *  The "local-address" node, which is enabled by the "local-binding-
      supported" feature (Section 2.1.2), may be configured as an IPv4
      address, an IPv6 address, or a wildcard value.

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   *  The "local-port" node, which is enabled by the "local-binding-
      supported" feature (Section 2.1.2), is not mandatory.  Its default
      value is '0', indicating that the operating system can pick an
      arbitrary port number.

   *  The "proxy-server" node is enabled by a "feature" statement and,
      for servers that enable it, is a "presence" container so that the
      descendant "mandatory true" choice node does not imply that the
      proxy-server node must be configured.  The proxy-server node uses
      a "choice" statement to allow one of several types of proxies to
      be configured.  The choices presented in this document include
      Socks4, Socks4a, and Socks5, each enabled by a YANG feature (see
      Section 3.1.1).  Other proxy types may be added by future work.

   *  This grouping uses the "password-grouping" grouping discussed in
      [I-D.ietf-netconf-crypto-types].

   *  This grouping uses the "tcp-common-grouping" grouping discussed in
      Section 2.1.3.1.

3.1.3.  Protocol-accessible Nodes

   The "ietf-tcp-client" module defines only "grouping" statements that
   are used by other modules to instantiate protocol-accessible nodes.
   Thus this module, when implemented, does not itself define any
   protocol-accessible nodes.

3.2.  Example Usage

   This section presents two examples showing the "tcp-client-grouping"
   populated with some data.  This example shows a TCP-client configured
   to not connect via a proxy:

   <!-- The outermost element below doesn't exist in the data model. -->
   <!--  It simulates if the "grouping" were a "container" instead.  -->

   <tcp-client xmlns="urn:ietf:params:xml:ns:yang:ietf-tcp-client">
     <remote-address>www.example.com</remote-address>
     <remote-port>8443</remote-port>
     <local-address>192.0.2.2</local-address>
     <local-port>12345</local-port>
     <keepalives>
       <idle-time>7200</idle-time>
       <max-probes>9</max-probes>
       <probe-interval>75</probe-interval>
     </keepalives>
   </tcp-client>

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   This example shows a TCP-client configured to connect via a proxy:

   <!-- The outermost element below doesn't exist in the data model. -->
   <!--  It simulates if the "grouping" were a "container" instead.  -->

   <tcp-client xmlns="urn:ietf:params:xml:ns:yang:ietf-tcp-client">
     <remote-address>www.example.com</remote-address>
     <remote-port>8443</remote-port>
     <local-address>192.0.2.2</local-address>
     <local-port>12345</local-port>
     <proxy-server>
       <socks5-parameters>
         <remote-address>proxy.example.com</remote-address>
         <remote-port>1080</remote-port>
         <authentication-parameters>
           <username-password>
             <username>foobar</username>
             <cleartext-password>secret</cleartext-password>
           </username-password>
         </authentication-parameters>
       </socks5-parameters>
     </proxy-server>
     <keepalives>
       <idle-time>7200</idle-time>
       <max-probes>9</max-probes>
       <probe-interval>75</probe-interval>
     </keepalives>
   </tcp-client>

3.3.  YANG Module

   The ietf-tcp-client YANG module references [SOCKS_4A], [RFC1928],
   [RFC1929], [RFC2743], [RFC6991], [RFC9293], and
   [I-D.ietf-netconf-crypto-types].

   <CODE BEGINS> file "ietf-tcp-client@2024-02-22.yang"

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

     import ietf-inet-types {
       prefix inet;
       reference
         "RFC 6991: Common YANG Data Types";
     }

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     import ietf-crypto-types {
       prefix ct;
       reference
         "RFC AAAA: YANG Data Types and Groupings for Cryptography";
     }

     import ietf-tcp-common {
       prefix tcpcmn;
       reference
         "RFC DDDD: YANG Groupings for TCP Clients and TCP Servers";
     }

     organization
       "IETF NETCONF (Network Configuration) Working Group and the
        IETF TCP Maintenance and Minor Extensions (TCPM) Working Group";

     contact
       "WG Web:   https://datatracker.ietf.org/wg/netconf
                  https://datatracker.ietf.org/wg/tcpm
        WG List:  NETCONF WG list <mailto:netconf@ietf.org>
                  TCPM WG list <mailto:tcpm@ietf.org>
        Authors:  Kent Watsen <mailto:kent+ietf@watsen.net>
                  Michael Scharf
                  <mailto:michael.scharf@hs-esslingen.de>";

     description
       "This module defines reusable groupings for TCP clients that
        can be used as a basis for specific TCP client instances.

        Copyright (c) 2024 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 Revised
        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 DDDD
        (https://www.rfc-editor.org/info/rfcDDDD); 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

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        capitals, as shown here.";

     revision 2024-02-22 {
       description
         "Initial version";
       reference
         "RFC DDDD: YANG Groupings for TCP Clients and TCP Servers";
     }

     // Features

     feature local-binding-supported {
       description
         "Indicates that the server supports configuring local
          bindings (i.e., the local address and local port) for
          TCP clients.";
     }

     feature tcp-client-keepalives {
       description
         "Per socket TCP keepalive parameters are configurable for
          TCP clients on the server implementing this feature.";
       reference
         "RFC 9293: Transmission Control Protocol (TCP)";
     }

     feature proxy-connect {
       description
         "Indicates the TCP-client supports connecting through
          TCP proxies.";
     }

     feature socks4-supported {
       if-feature proxy-connect;
       description
         "Indicates the TCP-client supports Socks4-based proxies.";
       reference
         "SOCKS Proceedings:
            1992 Usenix Security Symposium.";
     }

     feature socks4a-supported {
       if-feature proxy-connect;
       description
         "Indicates the TCP-client supports Socks4a-based proxies.";
       reference
         "OpenSSH message:
            SOCKS 4A: A Simple Extension to SOCKS 4 Protocol

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            https://www.openssh.com/txt/socks4a.protocol.";
     }

     feature socks5-supported {
       if-feature proxy-connect;
       description
         "Indicates the TCP-client supports Socks5-based proxies.";
       reference
         "RFC 1928:
            SOCKS Protocol Version 5";
     }

     feature socks5-gss-api {
       if-feature socks5-supported;
       description
         "Indicates that the server, when acting as a TCP-client,
          supports authenticating to a SOCKS Version 5 proxy server
          using GSSAPI credentials.";
       reference
         "RFC 1928: SOCKS Protocol Version 5";
     }

     feature socks5-username-password {
       if-feature socks5-supported;
       description
         "Indicates that the server, when acting as a TCP-client,
          supports authenticating to a SOCKS Version 5 proxy server
          using 'username' and 'password' credentials.";
       reference
         "RFC 1928: SOCKS Protocol Version 5";
     }

     // Groupings

     grouping tcp-client-grouping {
       description
         "A reusable grouping for configuring a TCP client.

          Note that this grouping uses fairly typical descendant
          node names such that a stack of 'uses' statements will
          have name conflicts.  It is intended that the consuming
          data model will resolve the issue (e.g., by wrapping
          the 'uses' statement in a container called
          'tcp-client-parameters').  This model purposely does
          not do this itself so as to provide maximum flexibility
          to consuming models.";

       leaf remote-address {

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         type inet:host;
         mandatory true;
         description
           "The IP address or hostname of the remote peer to
            establish a connection with.  If a domain name is
            configured, then the DNS resolution should happen on
            each connection attempt.  If the DNS resolution
            results in multiple IP addresses, the IP addresses
            are tried according to local preference order until
            a connection has been established or until all IP
            addresses have failed.";
       }
       leaf remote-port {
         type inet:port-number;
         default "0";
         description
           "The IP port number for the remote peer to establish a
            connection with.  An invalid default value is used
            so that importing modules may 'refine' it with the
            appropriate default port number value.";
       }
       leaf local-address {
         if-feature "local-binding-supported";
         type inet:ip-address;
         description
           "The local IP address/interface to bind to for when
            connecting to the remote peer.  INADDR_ANY ('0.0.0.0') or
            INADDR6_ANY ('0:0:0:0:0:0:0:0' a.k.a. '::') MAY be used to
            explicitly indicate the implicit default, that the server
            can bind to any IPv4 or IPv6 address.";
       }
       leaf local-port {
         if-feature "local-binding-supported";
         type inet:port-number;
         default "0";
         description
           "The local IP port number to bind to for when connecting
            to the remote peer.  The port number '0', which is the
            default value, indicates that any available local port
            number may be used.";
       }
       container proxy-server {
         if-feature "proxy-connect";
         presence
           "Indicates that a proxy connection has been configured.
            Present so that the mandatory descendant nodes do not
            imply that this node must be configured.";
         choice proxy-type {

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           mandatory true;
           description
             "Selects a proxy connection protocol.";
           case socks4 {
             if-feature socks4-supported;
             container socks4-parameters {
               leaf remote-address {
                 type inet:ip-address;
                 mandatory true;
                 description
                   "The IP address of the proxy server.";
               }
               leaf remote-port {
                 type inet:port-number;
                 default "1080";
                 description
                   "The IP port number for the proxy server.";
               }
               description
                 "Parameters for connecting to a TCP-based proxy
                  server using the SOCKS4 protocol.";
               reference
                 "SOCKS, Proceedings: 1992 Usenix Security Symposium.";
             }
           }
           case socks4a {
             if-feature socks4a-supported;
             container socks4a-parameters {
               leaf remote-address {
                 type inet:host;
                 mandatory true;
                 description
                   "The IP address or hostname of the proxy server.";
               }
               leaf remote-port {
                 type inet:port-number;
                 default "1080";
                 description
                   "The IP port number for the proxy server.";
               }
               description
                 "Parameters for connecting to a TCP-based proxy
                  server using the SOCKS4a protocol.";
               reference
                 "SOCKS Proceedings:
                    1992 Usenix Security Symposium.
                  OpenSSH message:
                    SOCKS 4A: A Simple Extension to SOCKS 4 Protocol

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                    https://www.openssh.com/txt/socks4a.protocol";
             }
           }
           case socks5 {
             if-feature socks5-supported;
             container socks5-parameters {
               leaf remote-address {
                 type inet:host;
                 mandatory true;
                 description
                   "The IP address or hostname of the proxy server.";
               }
               leaf remote-port {
                 type inet:port-number;
                 default "1080";
                 description
                   "The IP port number for the proxy server.";
               }
               container authentication-parameters {
                 presence
                   "Indicates that an authentication mechanism
                    has been configured.  Present so that the
                    mandatory descendant nodes do not imply that
                    this node must be configured.";
                 description
                   "A container for SOCKS Version 5 authentication
                    mechanisms.

                    A complete list of methods is defined at:
                    https://www.iana.org/assignments/socks-methods
                    /socks-methods.xhtml.";
                 reference
                   "RFC 1928: SOCKS Protocol Version 5";
                 choice auth-type {
                   mandatory true;
                   description
                     "A choice amongst supported SOCKS Version 5
                      authentication mechanisms.";
                   case gss-api {
                     if-feature "socks5-gss-api";
                     container gss-api {
                       description
                         "Contains GSS-API configuration.  Defines
                          as an empty container to enable specific
                          GSS-API configuration to be augmented in
                          by future modules.";
                       reference
                         "RFC 1928: SOCKS Protocol Version 5

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                          RFC 2743: Generic Security Service
                                    Application Program Interface
                                    Version 2, Update 1";
                     }
                   }
                   case username-password {
                     if-feature "socks5-username-password";
                     container username-password {
                       leaf username {
                         type string;
                         mandatory true;
                         description
                           "The 'username' value to use for client
                            identification.";
                       }
                       uses ct:password-grouping {
                         description
                           "The password to be used for client
                            authentication.";
                       }
                       description
                         "Contains Username/Password configuration.";
                       reference
                         "RFC 1929: Username/Password Authentication
                                    for SOCKS V5";
                     }
                   }
                 }
               }
               description
                 "Parameters for connecting to a TCP-based proxy server
                  using the SOCKS5 protocol.";
               reference
                 "RFC 1928: SOCKS Protocol Version 5";
             }
           }
         }
         description
           "Proxy server settings.";
       }

       uses tcpcmn:tcp-common-grouping {
         refine "keepalives" {
           if-feature "tcp-client-keepalives";
           description
             "An if-feature statement so that implementations
              can choose to support TCP client keepalives.";
         }

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       }
     }
   }

   <CODE ENDS>

4.  The "ietf-tcp-server" Module

   This section defines a YANG 1.1 module called "ietf-tcp-server".  A
   high-level overview of the module is provided in Section 4.1.
   Examples illustrating the module's use are provided in Examples
   (Section 4.2).  The YANG module itself is defined in Section 4.3.

4.1.  Data Model Overview

   This section provides an overview of the "ietf-tcp-server" module in
   terms of its features and groupings.

4.1.1.  Features

   The following diagram lists all the "feature" statements defined in
   the "ietf-tcp-server" module:

   Features:
     +-- tcp-server-keepalives

   The diagram above uses syntax that is similar to but not defined in
   [RFC8340].

4.1.2.  Groupings

   The "ietf-tcp-server" module defines the following "grouping"
   statement:

   *  tcp-server-grouping

   This grouping is presented in the following subsection.

4.1.2.1.  The "tcp-server-grouping" Grouping

   The following tree diagram [RFC8340] illustrates the "tcp-server-
   grouping" grouping:

     grouping tcp-server-grouping:
       +-- local-address                 inet:ip-address
       +-- local-port?                   inet:port-number
       +---u tcpcmn:tcp-common-grouping

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   Comments:

   *  The "local-address" node, which is mandatory, may be configured as
      an IPv4 address, an IPv6 address, or a wildcard value.

   *  The "local-port" node is not mandatory, but its default value is
      the invalid value '0', thus forcing the consuming data model to
      refine it in order to provide it an appropriate default value.

   *  This grouping uses the "tcp-common-grouping" grouping discussed in
      Section 2.1.3.1.

4.1.3.  Protocol-accessible Nodes

   The "ietf-tcp-server" module defines only "grouping" statements that
   are used by other modules to instantiate protocol-accessible nodes.
   Thus this module, when implemented, does not itself define any
   protocol-accessible nodes.

4.2.  Example Usage

   This section presents an example showing the "tcp-server-grouping"
   populated with some data.

   <!-- The outermost element below doesn't exist in the data model. -->
   <!--  It simulates if the "grouping" were a "container" instead.  -->

   <tcp-server xmlns="urn:ietf:params:xml:ns:yang:ietf-tcp-server">
     <local-address>192.0.2.2</local-address>
     <local-port>49152</local-port>
     <keepalives>
       <idle-time>7200</idle-time>
       <max-probes>9</max-probes>
       <probe-interval>75</probe-interval>
     </keepalives>
   </tcp-server>

4.3.  YANG Module

   The ietf-tcp-server YANG module references [RFC6991] and [RFC9293].

   <CODE BEGINS> file "ietf-tcp-server@2024-02-22.yang"

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

     import ietf-inet-types {
       prefix inet;
       reference
         "RFC 6991: Common YANG Data Types";
     }

     import ietf-tcp-common {
       prefix tcpcmn;
       reference
         "RFC DDDD: YANG Groupings for TCP Clients and TCP Servers";
     }

     organization
       "IETF NETCONF (Network Configuration) Working Group and the
        IETF TCP Maintenance and Minor Extensions (TCPM) Working Group";

     contact
       "WG Web:   https://datatracker.ietf.org/wg/netconf
                  https://datatracker.ietf.org/wg/tcpm
        WG List:  NETCONF WG list <mailto:netconf@ietf.org>
                  TCPM WG list <mailto:tcpm@ietf.org>
        Authors:  Kent Watsen <mailto:kent+ietf@watsen.net>
                  Michael Scharf
                  <mailto:michael.scharf@hs-esslingen.de>";

     description
       "This module defines reusable groupings for TCP servers that
        can be used as a basis for specific TCP server instances.

        Copyright (c) 2024 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 Revised
        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 DDDD
        (https://www.rfc-editor.org/info/rfcDDDD); see the RFC
        itself for full legal notices.

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        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 2024-02-22 {
       description
         "Initial version";
       reference
         "RFC DDDD: YANG Groupings for TCP Clients and TCP Servers";
     }

     // Features

     feature tcp-server-keepalives {
       description
         "Per socket TCP keepalive parameters are configurable for
          TCP servers on the server implementing this feature.";
       reference
         "RFC 9293: Transmission Control Protocol (TCP)";
     }

     // Groupings

     grouping tcp-server-grouping {
       description
         "A reusable grouping for configuring a TCP server.

          Note that this grouping uses fairly typical descendant
          node names such that a stack of 'uses' statements will
          have name conflicts.  It is intended that the consuming
          data model will resolve the issue (e.g., by wrapping
          the 'uses' statement in a container called
          'tcp-server-parameters').  This model purposely does
          not do this itself so as to provide maximum flexibility
          to consuming models.";
       leaf local-address {
         type inet:ip-address;
         mandatory true;
         description
           "The local IP address to listen on for incoming
            TCP client connections.  INADDR_ANY (0.0.0.0) or
            INADDR6_ANY (0:0:0:0:0:0:0:0 a.k.a. ::) MUST be
            used when the server is to listen on all IPv4 or
            IPv6 address.";
       }

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       leaf local-port {
         type inet:port-number;
         default "0";
         description
           "The local port number to listen on for incoming TCP
            client connections.  An invalid default value (0)
            is used (instead of 'mandatory true') so that an
            application level data model may 'refine' it with
            an application specific default port number value.";
       }
       uses tcpcmn:tcp-common-grouping {
         refine "keepalives" {
           if-feature "tcp-server-keepalives";
           description
             "An if-feature statement so that implementations
              can choose to support TCP server keepalives.";
         }
       }
     }
   }

   <CODE ENDS>

5.  Security Considerations

5.1.  Considerations for the "ietf-tcp-common" YANG Module

   This section follows the template defined in Section 3.7.1 of
   [RFC8407].

   The "ietf-tcp-common" YANG module defines "grouping" statements that
   are designed to be accessed via YANG based management protocols, such
   as NETCONF [RFC6241] and RESTCONF [RFC8040].  Both of these protocols
   have mandatory-to-implement secure transport layers (e.g., SSH, TLS)
   with mutual authentication.

   The Network Access Control Model (NACM) [RFC8341] provides the means
   to restrict access for particular users to a pre-configured subset of
   all available protocol operations and content.

   Since the module in this document only define groupings, these
   considerations are primarily for the designers of other modules that
   use these groupings.

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   Please be aware that this YANG module uses groupings from other YANG
   modules that define nodes that may be considered sensitive or
   vulnerable in network environments.  Please review the Security
   Considerations for dependent YANG modules for information as to which
   nodes may be considered sensitive or vulnerable in network
   environments.

   None of the readable data nodes defined in this YANG module are
   considered sensitive or vulnerable in network environments.  The NACM
   "default-deny-all" extension has not been set for any data nodes
   defined in this module.

   None of the writable data nodes defined in this YANG module are
   considered sensitive or vulnerable in network environments.  The NACM
   "default-deny-write" extension has not been set for any data nodes
   defined in this module.

   This module does not define any RPCs, actions, or notifications, and
   thus the security consideration for such is not provided here.

5.2.  Considerations for the "ietf-tcp-client" YANG Module

   This section follows the template defined in Section 3.7.1 of
   [RFC8407].

   The "ietf-tcp-client" YANG module defines "grouping" statements that
   are designed to be accessed via YANG based management protocols, such
   as NETCONF [RFC6241] and RESTCONF [RFC8040].  Both of these protocols
   have mandatory-to-implement secure transport layers (e.g., SSH, TLS)
   with mutual authentication.

   The Network Access Control Model (NACM) [RFC8341] provides the means
   to restrict access for particular users to a pre-configured subset of
   all available protocol operations and content.

   Since the module in this document only define groupings, these
   considerations are primarily for the designers of other modules that
   use these groupings.

   Please be aware that this YANG module uses groupings from other YANG
   modules that define nodes that may be considered sensitive or
   vulnerable in network environments.  Please review the Security
   Considerations for dependent YANG modules for information as to which
   nodes may be considered sensitive or vulnerable in network
   environments.

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   One readable data node defined in this YANG module may be considered
   sensitive or vulnerable in some network environments.  This node is
   as follows:

   *  The "proxy-server/socks5-parameters/authentication-parameters/
      username-password/password" node:

         The "password" node defined in the "tcp-client-grouping"
         grouping is defined using the "password-grouping" grouping
         presented in [I-D.ietf-netconf-crypto-types].  This grouping
         enables both cleartext and encrypted passwords to be
         configured.  As the referenced document states, configuration
         of cleartext passwords is NOT RECOMMENDED.  However, in the
         case cleartext values are configured, this node is additionally
         sensitive to read operations such that, in normal use cases, it
         should never be returned to a client.  For this reason, the
         NACM extension "default-deny-all" has been applied to it.

   None of the writable data nodes defined in this YANG module are
   considered sensitive or vulnerable in network environments.  The NACM
   "default-deny-write" extension has not been set for any data nodes
   defined in this module.

   This module does not define any RPCs, actions, or notifications, and
   thus the security consideration for such is not provided here.

   Implementations are RECOMMENDED to implement the "local-binding-
   supported" feature for cryptographically-secure protocols, so as to
   enable more granular ingress/egress firewall rulebases.  It is NOT
   RECOMMENDED to implement this feature for unsecure protocols, as per
   [RFC6056].

5.3.  Considerations for the "ietf-tcp-server" YANG Module

   This section follows the template defined in Section 3.7.1 of
   [RFC8407].

   The "ietf-tcp-server" YANG module defines "grouping" statements that
   are designed to be accessed via YANG based management protocols, such
   as NETCONF [RFC6241] and RESTCONF [RFC8040].  Both of these protocols
   have mandatory-to-implement secure transport layers (e.g., SSH, TLS)
   with mutual authentication.

   The Network Access Control Model (NACM) [RFC8341] provides the means
   to restrict access for particular users to a pre-configured subset of
   all available protocol operations and content.

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   Since the module in this document only define groupings, these
   considerations are primarily for the designers of other modules that
   use these groupings.

   Please be aware that this YANG module uses groupings from other YANG
   modules that define nodes that may be considered sensitive or
   vulnerable in network environments.  Please review the Security
   Considerations for dependent YANG modules for information as to which
   nodes may be considered sensitive or vulnerable in network
   environments.

   None of the readable data nodes defined in this YANG module are
   considered sensitive or vulnerable in network environments.  The NACM
   "default-deny-all" extension has not been set for any data nodes
   defined in this module.

   None of the writable data nodes defined in this YANG module are
   considered sensitive or vulnerable in network environments.  The NACM
   "default-deny-write" extension has not been set for any data nodes
   defined in this module.

   This module does not define any RPCs, actions, or notifications, and
   thus the security consideration for such is not provided here.

6.  IANA Considerations

6.1.  The "IETF XML" Registry

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

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

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

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

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6.2.  The "YANG Module Names" Registry

   This document registers three YANG modules in the YANG Module Names
   registry [RFC6020].  Following the format in [RFC6020], the following
   registrations are requested:

      name:         ietf-tcp-common
      namespace:    urn:ietf:params:xml:ns:yang:ietf-tcp-common
      prefix:       tcpcmn
      reference:    RFC DDDD

      name:         ietf-tcp-client
      namespace:    urn:ietf:params:xml:ns:yang:ietf-tcp-client
      prefix:       tcpc
      reference:    RFC DDDD

      name:         ietf-tcp-server
      namespace:    urn:ietf:params:xml:ns:yang:ietf-tcp-server
      prefix:       tcps
      reference:    RFC DDDD

7.  References

7.1.  Normative References

   [I-D.ietf-netconf-crypto-types]
              Watsen, K., "YANG Data Types and Groupings for
              Cryptography", Work in Progress, Internet-Draft, draft-
              ietf-netconf-crypto-types-31, 8 February 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-
              crypto-types-31>.

   [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>.

   [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>.

   [RFC6991]  Schoenwaelder, J., Ed., "Common YANG Data Types",
              RFC 6991, DOI 10.17487/RFC6991, July 2013,
              <https://www.rfc-editor.org/info/rfc6991>.

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   [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>.

   [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>.

   [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>.

   [RFC9293]  Eddy, W., Ed., "Transmission Control Protocol (TCP)",
              STD 7, RFC 9293, DOI 10.17487/RFC9293, August 2022,
              <https://www.rfc-editor.org/info/rfc9293>.

7.2.  Informative References

   [I-D.ietf-netconf-http-client-server]
              Watsen, K., "YANG Groupings for HTTP 1.1/2.0 Clients and
              HTTP Servers", Work in Progress, Internet-Draft, draft-
              ietf-netconf-http-client-server-17, 8 February 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-
              http-client-server-17>.

   [I-D.ietf-netconf-keystore]
              Watsen, K., "A YANG Data Model for a Keystore and Keystore
              Operations", Work in Progress, Internet-Draft, draft-ietf-
              netconf-keystore-32, 8 February 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-
              keystore-32>.

   [I-D.ietf-netconf-netconf-client-server]
              Watsen, K., "NETCONF Client and Server Models", Work in
              Progress, Internet-Draft, draft-ietf-netconf-netconf-
              client-server-33, 8 February 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-
              netconf-client-server-33>.

   [I-D.ietf-netconf-restconf-client-server]
              Watsen, K., "RESTCONF Client and Server Models", Work in
              Progress, Internet-Draft, draft-ietf-netconf-restconf-
              client-server-33, 9 February 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-
              restconf-client-server-33>.

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   [I-D.ietf-netconf-ssh-client-server]
              Watsen, K., "YANG Groupings for SSH Clients and SSH
              Servers", Work in Progress, Internet-Draft, draft-ietf-
              netconf-ssh-client-server-37, 8 February 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-
              ssh-client-server-37>.

   [I-D.ietf-netconf-tcp-client-server]
              Watsen, K. and M. Scharf, "YANG Groupings for TCP Clients
              and TCP Servers", Work in Progress, Internet-Draft, draft-
              ietf-netconf-tcp-client-server-21, 8 February 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-
              tcp-client-server-21>.

   [I-D.ietf-netconf-tls-client-server]
              Watsen, K., "YANG Groupings for TLS Clients and TLS
              Servers", Work in Progress, Internet-Draft, draft-ietf-
              netconf-tls-client-server-38, 8 February 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-
              tls-client-server-38>.

   [I-D.ietf-netconf-trust-anchors]
              Watsen, K., "A YANG Data Model for a Truststore", Work in
              Progress, Internet-Draft, draft-ietf-netconf-trust-
              anchors-25, 8 February 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-
              trust-anchors-25>.

   [RFC1928]  Leech, M., Ganis, M., Lee, Y., Kuris, R., Koblas, D., and
              L. Jones, "SOCKS Protocol Version 5", RFC 1928,
              DOI 10.17487/RFC1928, March 1996,
              <https://www.rfc-editor.org/info/rfc1928>.

   [RFC1929]  Leech, M., "Username/Password Authentication for SOCKS
              V5", RFC 1929, DOI 10.17487/RFC1929, March 1996,
              <https://www.rfc-editor.org/info/rfc1929>.

   [RFC2743]  Linn, J., "Generic Security Service Application Program
              Interface Version 2, Update 1", RFC 2743,
              DOI 10.17487/RFC2743, January 2000,
              <https://www.rfc-editor.org/info/rfc2743>.

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

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   [RFC6056]  Larsen, M. and F. Gont, "Recommendations for Transport-
              Protocol Port Randomization", BCP 156, RFC 6056,
              DOI 10.17487/RFC6056, January 2011,
              <https://www.rfc-editor.org/info/rfc6056>.

   [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>.

   [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>.

   [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>.

   [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>.

   [RFC8407]  Bierman, A., "Guidelines for Authors and Reviewers of
              Documents Containing YANG Data Models", BCP 216, RFC 8407,
              DOI 10.17487/RFC8407, October 2018,
              <https://www.rfc-editor.org/info/rfc8407>.

   [SOCKS_4A] Project, T. O., "SOCKS 4A: A Simple Extension to SOCKS 4
              Protocol", <https://www.openssh.com/txt/socks4a.protocol>.

Appendix A.  Change Log

A.1.  00 to 01

   *  Added 'local-binding-supported' feature to TCP-client model.

   *  Added 'keepalives-supported' feature to TCP-common model.

   *  Added 'external-endpoint-values' container and 'external-
      endpoints' feature to TCP-server model.

A.2.  01 to 02

   *  Removed the 'external-endpoint-values' container and 'external-
      endpoints' feature from the TCP-server model.

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A.3.  02 to 03

   *  Moved the common model section to be before the client and server
      specific sections.

   *  Added sections "Model Scope" and "Usage Guidelines for Configuring
      TCP Keep-Alives" to the common model section.

A.4.  03 to 04

   *  Fixed a few typos.

A.5.  04 to 05

   *  Removed commented out "grouping tcp-system-grouping" statement
      kept for reviewers.

   *  Added a "Note to Reviewers" note to first page.

A.6.  05 to 06

   *  Added support for TCP proxies.

A.7.  06 to 07

   *  Expanded "Data Model Overview section(s) [remove "wall" of tree
      diagrams].

   *  Updated the Security Considerations section.

A.8.  07 to 08

   *  Added missing IANA registration for "ietf-tcp-common"

   *  Added "mandatory true" for the "username" and "password" leafs

   *  Added an example of a TCP-client configured to connect via a proxy

   *  Fixed issues found by the SecDir review of the "keystore" draft.

   *  Updated the "ietf-tcp-client" module to use the new "password-
      grouping" grouping from the "crypto-types" module.

A.9.  08 to 09

   *  Addressed comments raised by YANG Doctor in the ct/ts/ks drafts.

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A.10.  09 to 10

   *  Updated Abstract and Intro to address comments by Tom Petch.

   *  Removed the "tcp-connection-grouping" grouping (now models use the
      "tcp-common-grouping" directly).

   *  Added XML-comment above examples explaining the reason for the
      unusual top-most element's presence.

   *  Added Securty Considerations section for the "local-binding-
      supported" feature.

   *  Replaced some hardcoded refs to <xref> elements.

   *  Fixed nits found by YANG Doctor reviews.

   *  Aligned modules with `pyang -f` formatting.

   *  Added an "Acknowledgements" secetion.

A.11.  10 to 11

   *  Replaced "base64encodedvalue==" with "BASE64VALUE=" in examples.

   *  Minor editorial nits

A.12.  11 to 12

   *  Fixed up the 'WG Web' and 'WG List' lines in YANG module(s)

   *  Fixed up copyright (i.e., s/Simplified/Revised/) in YANG module(s)

A.13.  12 to 13

   *  NO UPDATE.

A.14.  13 to 14

   *  Updated per Shepherd reviews impacting the suite of drafts.

A.15.  14 to 15

   *  Updated per Shepherd reviews impacting the suite of drafts.

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A.16.  15 to 16

   *  Updated per Tom Petch review.

   *  Added refs to RFC9293 and SOCKS 4A.

   *  Fixed examples to use IETF-sanctioned values for examples.

A.17.  16 to 17

   *  Addresses AD review comments.

   *  Added note to Editor to fix line foldings.

   *  Added Security Considerations text to also look a SC-section from
      imported modules.

   *  Fixed bug: s/augment "keepalives"/refine "keepalives"/

   *  Set defaults for idle-time, max-probes, and probe-interval
      (removed "mandatory true").

   *  Updated examples to use IETF recommended values for examples.

A.18.  18 to 19

   *  Addresses AD review by Rob Wilton.

A.19.  18 to 19

   *  Replace RFC 1122 with RFC 9293.

A.20.  19 to 20

   *  Addresses 1st-round of IESG reviews.

A.21.  20 to 22

   *  Addresses issues found in OpsDir review of the ssh-client-server
      draft.

   *  Updated to address Mallory Knodel's Gen-ART review.

   *  Renamed Security Considerations section s/Template for/
      Considerations for/

   *  s/defines/presents/ in a few places.

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   *  Add refs to where the 'operational' and 'system' datastores are
      defined.

   *  Added more 'feature' statements and descriptions for them

   *  Added Security Considaration for the "password" node

Acknowledgements

   The authors would like to thank the following for lively discussions
   on list and in the halls (ordered by first name): Éric Vyncke, Jürgen
   Schönwälder, Ladislav Lhotka, Mallory Knodel, Michael Tüxen, Nancy
   Cam-Winget, Nick Hancock, Per Andersson, Rob Wilton, and Tom Petch.

Authors' Addresses

   Kent Watsen
   Watsen Networks
   Email: kent+ietf@watsen.net

   Michael Scharf
   Hochschule Esslingen - University of Applied Sciences
   Email: michael.scharf@hs-esslingen.de

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