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Versions: (draft-kwatsen-netconf-tcp-client-server) 00 01 02 03 04 05 06 07 08

NETCONF Working Group                                          K. Watsen
Internet-Draft                                           Watsen Networks
Intended status: Standards Track                               M. Scharf
Expires: 21 February 2021                           Hochschule Esslingen
                                                          20 August 2020


             YANG Groupings for TCP Clients and TCP Servers
                draft-ietf-netconf-tcp-client-server-08

Abstract

   This document defines three YANG 1.1 [RFC7950] modules to support the
   configuration of TCP clients and TCP servers, either as standalone or
   in conjunction with a stack protocol layer specific configurations.

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:

   *  "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:

   *  "2020-08-20" --> the publication date of this draft

   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/.





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   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 21 February 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 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  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Relation to other RFCs  . . . . . . . . . . . . . . . . .   3
     1.2.  Specification Language  . . . . . . . . . . . . . . . . .   5
     1.3.  Adherence to the NMDA . . . . . . . . . . . . . . . . . .   5
   2.  The "ietf-tcp-common" Module  . . . . . . . . . . . . . . . .   5
     2.1.  Data Model Overview . . . . . . . . . . . . . . . . . . .   5
     2.2.  Example Usage . . . . . . . . . . . . . . . . . . . . . .   8
     2.3.  YANG Module . . . . . . . . . . . . . . . . . . . . . . .   8
   3.  The "ietf-tcp-client" Module  . . . . . . . . . . . . . . . .  11
     3.1.  Data Model Overview . . . . . . . . . . . . . . . . . . .  11
     3.2.  Example Usage . . . . . . . . . . . . . . . . . . . . . .  13
     3.3.  YANG Module . . . . . . . . . . . . . . . . . . . . . . .  14
   4.  The "ietf-tcp-server" Module  . . . . . . . . . . . . . . . .  21
     4.1.  Data Model Overview . . . . . . . . . . . . . . . . . . .  21
     4.2.  Example Usage . . . . . . . . . . . . . . . . . . . . . .  22
     4.3.  YANG Module . . . . . . . . . . . . . . . . . . . . . . .  23
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  25
     5.1.  The "ietf-tcp-common" YANG Module . . . . . . . . . . . .  25
     5.2.  The "ietf-tcp-client" YANG Module . . . . . . . . . . . .  26
     5.3.  The "ietf-tcp-server" YANG Module . . . . . . . . . . . .  27
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  27
     6.1.  The "IETF XML" Registry . . . . . . . . . . . . . . . . .  27
     6.2.  The "YANG Module Names" Registry  . . . . . . . . . . . .  28
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  28
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  28



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     7.2.  Informative References  . . . . . . . . . . . . . . . . .  29
   Appendix A.  Change Log . . . . . . . . . . . . . . . . . . . . .  31
     A.1.  00 to 01  . . . . . . . . . . . . . . . . . . . . . . . .  31
     A.2.  01 to 02  . . . . . . . . . . . . . . . . . . . . . . . .  31
     A.3.  02 to 03  . . . . . . . . . . . . . . . . . . . . . . . .  31
     A.4.  03 to 04  . . . . . . . . . . . . . . . . . . . . . . . .  31
     A.5.  04 to 05  . . . . . . . . . . . . . . . . . . . . . . . .  31
     A.6.  05 to 06  . . . . . . . . . . . . . . . . . . . . . . . .  31
     A.7.  06 to 07  . . . . . . . . . . . . . . . . . . . . . . . .  32
     A.8.  08 to 09  . . . . . . . . . . . . . . . . . . . . . . . .  32
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  32

1.  Introduction

   This document defines three YANG 1.1 [RFC7950] modules to support the
   configuration of TCP clients and TCP servers, either as standalone or
   in conjunction with a stack protocol layer specific configurations.

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 define
   configuration modules for clients and servers of both the NETCONF
   [RFC6241] and RESTCONF [RFC8040] protocols.

   The modules have been defined in a modular fashion to enable their
   use by other efforts, some of which are known to be in progress at
   the time of this writing, with many more expected to be defined in
   time.

   The normative dependency relationship between the various RFCs in the
   collection is presented in the below diagram.  The labels in the
   diagram represent the primary purpose provided by each RFC.
   Hyperlinks to each RFC are provided below the diagram.

















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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 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 in 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 [RFC7950] module called "ietf-tcp-
   common".  A high-level overview of the module is provided in
   Section 2.1.  Examples illustatrating 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 defines a common "grouping" statement for basic TCP
   connection parameters that matter to applications.  In some TCP
   stacks, such parameters can also directly be set by an application
   using system calls, such as the socket 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 following diagram lists all the "grouping" statements defined in
   the "ietf-keystore" module:

   Groupings:
     +-- tcp-common-grouping
     +-- tcp-connection-grouping

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

   Each of these groupings are presented in the following subsections.

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" node so that the decendent
      nodes' "mandatory true" doesn't 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.

2.1.3.2.  The "tcp-connection-grouping" Grouping

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

     grouping tcp-connection-grouping
       +---u tcp-common-grouping

   Comments:

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




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2.1.4.  Protocol-accessible Nodes

   The "ietf-tcp-common" module does not contain 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, [RFC1122] [RFC793bis] 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
   application requirements.  If keep-alives are needed by an
   application, it is RECOMMENDED that the aliveness 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 [RFC1122].  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") MUST default to no
      less than two hours, i.e., 7200 seconds [RFC1122].  A lower value
      MAY be configured, but keep-alive messages SHOULD NOT be
      transmitted more frequently than once every 15 seconds.  Longer
      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 [RFC1122].  Typically a
      single-digit number should suffice.






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   *  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.

   <tcp-common xmlns="urn:ietf:params:xml:ns:yang:ietf-tcp-common">
     <keepalives>
       <idle-time>15</idle-time>
       <max-probes>3</max-probes>
       <probe-interval>30</probe-interval>
     </keepalives>
   </tcp-common>

2.3.  YANG Module

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

   <CODE BEGINS> file "ietf-tcp-common@2020-08-20.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:   <http://datatracker.ietf.org/wg/netconf/>
                  <http://datatracker.ietf.org/wg/tcpm/>
        WG List:  <mailto:netconf@ietf.org>
                  <mailto:tcpm@ietf.org>
        Authors:  Kent Watsen <mailto:kent+ietf@watsen.net>
                  Michael Scharf
                  <mailto:michael.scharf@hs-esslingen.de>";




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

        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 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 2020-08-20 {
       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



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          "Indicates that keepalives are enabled.  Present so that
           the decendant nodes' 'mandatory true' doesn't imply that
           this node  must be configured.";
         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.";
         leaf idle-time {
           type uint16 {
             range "1..max";
           }
           units "seconds";
           mandatory true;
           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 1122.";
           reference
             "RFC 1122:
               Requirements for Internet Hosts -- Communication Layers";
         }
         leaf max-probes {
           type uint16 {
             range "1..max";
           }
           mandatory true;
           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";
           mandatory true;
           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





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     grouping tcp-connection-grouping {
       description
         "A reusable grouping for configuring TCP parameters common
          to TCP connections.";
        uses tcp-common-grouping;
     }

   }

   <CODE ENDS>

3.  The "ietf-tcp-client" Module

   This section defines a YANG 1.1 [RFC7950] module called "ietf-tcp-
   client".  A high-level overview of the module is provided in
   Section 3.1.  Examples illustatrating 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
     +-- socks5-gss-api
     +-- socks5-username-password

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

3.1.2.  Groupings

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

   Groupings:
     +-- tcp-client-grouping





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

   Each of these groupings are presented in the following subsections.

3.1.2.1.  The "tcp-client-grouping" Grouping

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

     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-parameters
       |     |     +-- remote-address    inet:ip-address
       |     |     +-- remote-port?      inet:port-number
       |     +--:(socks4a)
       |     |  +-- socks4a-parameters
       |     |     +-- remote-address    inet:host
       |     |     +-- remote-port?      inet:port-number
       |     +--:(socks5)
       |        +-- 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-connection-grouping

   Comments:

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





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   *  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.

   *  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
      decendent "mandatory true" choice node doesn't imply that the
      proxt-server node must be configured.

   *  This grouping uses the "tcp-connection-grouping" grouping
      discussed in Section 2.1.3.2.

3.1.3.  Protocol-accessible Nodes

   The "ietf-tcp-client" module does not contain 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:

   <tcp-client xmlns="urn:ietf:params:xml:ns:yang:ietf-tcp-client">
     <remote-address>www.example.com</remote-address>
     <remote-port>443</remote-port>
     <local-address>0.0.0.0</local-address>
     <local-port>0</local-port>
     <keepalives>
       <idle-time>15</idle-time>
       <max-probes>3</max-probes>
       <probe-interval>30</probe-interval>
     </keepalives>
   </tcp-client>

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






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   <tcp-client xmlns="urn:ietf:params:xml:ns:yang:ietf-tcp-client">
     <remote-address>www.example.com</remote-address>
     <remote-port>443</remote-port>
     <local-address>0.0.0.0</local-address>
     <local-port>0</local-port>
     <proxy-server>
       <socks5-parameters>
         <remote-address>proxy.my-domain.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>15</idle-time>
       <max-probes>3</max-probes>
       <probe-interval>30</probe-interval>
     </keepalives>
   </tcp-client>

3.3.  YANG Module

   The ietf-tcp-client YANG module references [RFC6991].

   <CODE BEGINS> file "ietf-tcp-client@2020-08-20.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";
     }

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

     import ietf-tcp-common {



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       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:   <http://datatracker.ietf.org/wg/netconf/>
                  <http://datatracker.ietf.org/wg/tcpm/>
        WG List:  <mailto:netconf@ietf.org>
                  <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) 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 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 2020-08-20 {
       description
         "Initial version";
       reference
         "RFC DDDD: YANG Groupings for TCP Clients and TCP Servers";



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     }

     // 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.";
     }

     feature proxy-connect {
       description
         "Proxy connection configuration is configurable for
          TCP clients on the server implementing this feature.";
     }

     feature socks5-gss-api {
       description
         "Indicates that the server supports authenticating
          using GSSAPI when initiating TCP connections via
          and SOCKS Version 5 proxy server.";
       reference
         "RFC 1928: SOCKS Protocol Version 5";
     }

     feature socks5-username-password {
       description
         "Indicates that the server supports authenticating
          using username/password when initiating TCP
          connections via and SOCKS Version 5 proxy
          server.";
       reference
         "RFC 1928: SOCKS Protocol Version 5";
     }

     // Groupings

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




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         Note that this grouping uses fairly typical descendent
          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 {
         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 (0) is used
            (instead of 'mandatory true') so that as application
            level data model may 'refine' it with an application
            specific default port number value.";
       }
       leaf local-address {
         if-feature "local-binding-supported";
         type inet:ip-address;
         description
           "The local IP address/interface (VRF?) 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 addresses, respectively.";
       }
       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



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            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 is configured.
            Present so that the 'proxy-type' node's 'mandatory
            true' doesn't imply that the proxy connection
            must be configured.";
         choice proxy-type {
           mandatory true;
           description
             "Selects a proxy connection protocol.";
           case socks4 {
             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 {
             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";



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                 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
                    https://www.openssh.com/txt/socks4a.protocol";
             }
           }
           case socks5 {
             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
                    'auth-type' node's 'mandatory true' doesn't
                    imply that an authentication mechanism
                    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



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                      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
                          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";
             }
           }
         }



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         description
           "Proxy server settings.";
       }

       uses tcpcmn:tcp-connection-grouping {
         augment "keepalives" {
           if-feature "tcp-client-keepalives";
           description
             "Add an if-feature statement so that implementations
              can choose to support TCP client keepalives.";
         }
       }
     }
   }

   <CODE ENDS>

4.  The "ietf-tcp-server" Module

   This section defines a YANG 1.1 [RFC7950] module called "ietf-tcp-
   server".  A high-level overview of the module is provided in
   Section 4.1.  Examples illustatrating 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 following diagram lists all the "grouping" statements defined in
   the "ietf-tcp-server" module:

   Groupings:
     +-- tcp-server-grouping



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

   Each of these groupings are presented in the following subsections.

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-connection-grouping

   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-connection-grouping" grouping
      discussed in Section 2.1.3.2.

4.1.3.  Protocol-accessible Nodes

   The "ietf-tcp-server" module does not contain any protocol-accessible
   nodes.

4.2.  Example Usage

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

   <tcp-server xmlns="urn:ietf:params:xml:ns:yang:ietf-tcp-server">
     <local-address>10.20.30.40</local-address>
     <local-port>7777</local-port>
     <keepalives>
       <idle-time>15</idle-time>
       <max-probes>3</max-probes>
       <probe-interval>30</probe-interval>
     </keepalives>
   </tcp-server>





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4.3.  YANG Module

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

   <CODE BEGINS> file "ietf-tcp-server@2020-08-20.yang"

   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:   <http://datatracker.ietf.org/wg/netconf/>
                  <http://datatracker.ietf.org/wg/tcpm/>
        WG List:  <mailto:netconf@ietf.org>
                  <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) 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



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        (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 2020-08-20 {
       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.";
     }


     // Groupings

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

          Note that this grouping uses fairly typical descendent
          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



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            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 addresses, respectively.";
       }
       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-connection-grouping {
         augment "keepalives" {
           if-feature "tcp-server-keepalives";
           description
             "Add an if-feature statement so that implementations
              can choose to support TCP server keepalives.";
         }
       }
     }
   }

   <CODE ENDS>

5.  Security Considerations

5.1.  The "ietf-tcp-common" YANG Module

   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 NETCONF 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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   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.  The "ietf-tcp-client" YANG Module

   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 NETCONF 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.

   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 cleartext "password" node defined in the "tcp-client-
         grouping" grouping 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.





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

5.3.  The "ietf-tcp-server" YANG Module

   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 NETCONF 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.

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












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

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

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

6.2.  The "YANG Module Names" Registry

   This document registers two 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

   [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>.





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

   [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>.

7.2.  Informative 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-17, 10 July 2020,
              <https://tools.ietf.org/html/draft-ietf-netconf-crypto-
              types-17>.

   [I-D.ietf-netconf-http-client-server]
              Watsen, K., "YANG Groupings for HTTP Clients and HTTP
              Servers", Work in Progress, Internet-Draft, draft-ietf-
              netconf-http-client-server-04, 8 July 2020,
              <https://tools.ietf.org/html/draft-ietf-netconf-http-
              client-server-04>.

   [I-D.ietf-netconf-keystore]
              Watsen, K., "A YANG Data Model for a Keystore", Work in
              Progress, Internet-Draft, draft-ietf-netconf-keystore-19,
              10 July 2020, <https://tools.ietf.org/html/draft-ietf-
              netconf-keystore-19>.

   [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-20, 8 July 2020,
              <https://tools.ietf.org/html/draft-ietf-netconf-netconf-
              client-server-20>.






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   [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-20, 8 July 2020,
              <https://tools.ietf.org/html/draft-ietf-netconf-restconf-
              client-server-20>.

   [I-D.ietf-netconf-ssh-client-server]
              Watsen, K. and G. Wu, "YANG Groupings for SSH Clients and
              SSH Servers", Work in Progress, Internet-Draft, draft-
              ietf-netconf-ssh-client-server-21, 10 July 2020,
              <https://tools.ietf.org/html/draft-ietf-netconf-ssh-
              client-server-21>.

   [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-07, 8 July 2020,
              <https://tools.ietf.org/html/draft-ietf-netconf-tcp-
              client-server-07>.

   [I-D.ietf-netconf-tls-client-server]
              Watsen, K. and G. Wu, "YANG Groupings for TLS Clients and
              TLS Servers", Work in Progress, Internet-Draft, draft-
              ietf-netconf-tls-client-server-21, 10 July 2020,
              <https://tools.ietf.org/html/draft-ietf-netconf-tls-
              client-server-21>.

   [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-12, 10 July 2020, <https://tools.ietf.org/html/
              draft-ietf-netconf-trust-anchors-12>.

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

   [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>.





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   [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>.

Appendix A.  Change Log

   This section is to be removed before publishing as an RFC.

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.

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




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   *  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.  08 to 09

   *  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.

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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