Internet-Draft RESTCONF Client and Server Models August 2024
Watsen Expires 15 February 2025 [Page]
Workgroup:
NETCONF Working Group
Internet-Draft:
draft-ietf-netconf-restconf-client-server-38
Published:
Intended Status:
Standards Track
Expires:
Author:
K. Watsen
Watsen Networks

RESTCONF Client and Server Models

Abstract

This document presents two YANG modules, one module to configure a RESTCONF client and the other module to configure a RESTCONF server. Both modules support the TLS transport protocol with both standard RESTCONF and RESTCONF Call Home connections.

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 (note: not all may be present):

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

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.

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:

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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This Internet-Draft will expire on 15 February 2025.

▲

Table of Contents

1. Introduction

This document presents two YANG [RFC7950] modules, one module to configure a RESTCONF client and the other module to configure a RESTCONF server [RFC8040]. Both modules support the TLS [RFC8446] transport protocol with both standard RESTCONF and RESTCONF Call Home connections [RFC8071].

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.

Primary dependency relationships between the 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.

                               crypto-types
                                 ^      ^
                                /        \
                               /          \
                      truststore         keystore
                       ^     ^             ^  ^
                       |     +---------+   |  |
                       |               |   |  |
                       |      +------------+  |
tcp-client-server      |     /         |      |
   ^    ^        ssh-client-server     |      |
   |    |           ^            tls-client-server
   |    |           |              ^     ^        http-client-server
   |    |           |              |     |                 ^
   |    |           |        +-----+     +---------+       |
   |    |           |        |                     |       |
   |    +-----------|--------|--------------+      |       |
   |                |        |              |      |       |
   +-----------+    |        |              |      |       |
               |    |        |              |      |       |
               |    |        |              |      |       |
            netconf-client-server       restconf-client-server
Table 1: Label in Diagram to RFC Mapping
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]

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]. For instance, as described in [I-D.ietf-netconf-trust-anchors] and [I-D.ietf-netconf-keystore], trust anchors and keys installed during manufacturing are expected to appear in <operational> (Section 5.3 of [RFC8342]), and <system> [I-D.ietf-netmod-system-config], if implemented.

2. The "ietf-restconf-client" Module

The RESTCONF client model presented in this section supports both clients initiating connections to servers, as well as clients listening for connections from servers calling home.

YANG feature statements are used to enable implementations to advertise which potentially uncommon parts of the model the RESTCONF client supports.

2.1. Data Model Overview

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

2.1.1. Features

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

Features:
  +-- https-initiate
  +-- http-listen
  +-- https-listen
  +-- central-restconf-client-supported

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

2.1.2. Groupings

The "ietf-restconf-client" module defines the following "grouping" statements:

  • restconf-client-initiate-stack-grouping
  • restconf-client-listen-stack-grouping
  • restconf-client-app-grouping

Each of these groupings are presented in the following subsections.

2.1.2.1. The "restconf-client-initiate-stack-grouping" Grouping

The following tree diagram [RFC8340] illustrates the "restconf-client-initiate-stack-grouping" grouping:

  grouping restconf-client-initiate-stack-grouping:
    +-- http-client-parameters
       +---u httpc:http-client-grouping

Comments:

2.1.2.2. The "restconf-client-listen-stack-grouping" Grouping

The following tree diagram [RFC8340] illustrates the "restconf-client-listen-stack-grouping" grouping:

  grouping restconf-client-listen-stack-grouping:
    +-- (transport)
       +--:(http) {http-listen}?
       |  +-- http
       |     +-- tcp-server-parameters
       |     |  +---u tcps:tcp-server-grouping
       |     +-- http-client-parameters
       |        +---u httpc:http-client-grouping
       +--:(https) {https-listen}?
          +-- https
             +-- tcp-server-parameters
             |  +---u tcps:tcp-server-grouping
             +-- http-client-parameters
                +---u httpc:http-client-grouping

Comments:

  • The "restconf-client-listen-stack-grouping" defines the configuration for a full RESTCONF protocol stack, for RESTCONF clients that receive call-home [RFC8071] connections from RESTCONF servers.
  • The "transport" choice node enables either the HTTP or HTTPS transports to be configured, with each option enabled by a "feature" statement. Note that RESTCONF requires HTTPS, the HTTP option is provided to support cases where a TLS-terminator is deployed in front of the RESTCONF-client.

  • For the referenced grouping statement(s):

2.1.2.3. The "restconf-client-app-grouping" Grouping

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

  grouping restconf-client-app-grouping:
    +-- initiate! {https-initiate}?
    |  +-- restconf-server* [name]
    |     +-- name?                 string
    |     +-- endpoints
    |     |  +-- endpoint* [name]
    |     |     +-- name?                                      string
    |     |     +---u restconf-client-initiate-stack-grouping
    |     +-- connection-type
    |     |  +-- (connection-type)
    |     |     +--:(persistent-connection)
    |     |     |  +-- persistent!
    |     |     +--:(periodic-connection)
    |     |        +-- periodic!
    |     |           +-- period?         uint16
    |     |           +-- anchor-time?    yang:date-and-time
    |     |           +-- idle-timeout?   uint16
    |     +-- reconnect-strategy
    |        +-- start-with?     enumeration
    |        +-- max-wait?       uint16
    |        +-- max-attempts?   uint8
    +-- listen! {http-listen or https-listen}?
       +-- idle-timeout?   uint16
       +-- endpoints
          +-- endpoint* [name]
             +-- name?                                    string
             +---u restconf-client-listen-stack-grouping

Comments:

  • The "restconf-client-app-grouping" defines the configuration for a RESTCONF client that supports both initiating connections to RESTCONF servers as well as receiving call-home connections from RESTCONF servers.
  • Both the "initiate" and "listen" subtrees are predicated by "feature" statements.

  • For the referenced grouping statement(s):

    • The "restconf-client-initiate-stack-grouping" grouping is discussed in Section 2.1.2.1 in this document.
    • The "restconf-client-listen-stack-grouping" grouping is discussed in Section 2.1.2.2 in this document.

2.1.3. Protocol-accessible Nodes

The following tree diagram [RFC8340] lists all the protocol-accessible nodes defined in the "ietf-restconf-client" module:

module: ietf-restconf-client
  +--rw restconf-client {central-restconf-client-supported}?
     +---u restconf-client-app-grouping

Comments:

  • Protocol-accessible nodes are those nodes that are accessible when the module is "implemented", as described in Section 5.6.5 of [RFC7950].
  • The top-level node "restconf-client" is additionally constrained by the feature "central-restconf-client-supported".
  • The "restconf-client-app-grouping" grouping is discussed in Section 2.1.2.3 in this document.
  • The reason for why "restconf-client-app-grouping" exists separate from the protocol-accessible nodes definition is so as to enable instances of restconf-client-app-grouping to be instantiated in other locations, as may be needed or desired by some modules.

2.2. Example Usage

The following example illustrates configuring a RESTCONF client to initiate connections, as well as to listen for call-home connections.

This example is consistent with the examples presented in Section 2.2.1 of [I-D.ietf-netconf-trust-anchors] and Section 2.2.1 of [I-D.ietf-netconf-keystore].

=============== NOTE: '\' line wrapping per RFC 8792 ================

<restconf-client xmlns="urn:ietf:params:xml:ns:yang:ietf-restconf-cl\
ient">

  <!-- RESTCONF servers to initiate connections to -->
  <initiate>
    <restconf-server>
      <name>corp-fw1</name>
      <endpoints>
        <endpoint>
          <name>corp-fw1.example.com</name>
          <http-client-parameters>
            <uri>https://corp-fw1.example.com</uri>
            <tls-client-parameters>
              <client-identity>
                <certificate>
                  <central-keystore-reference>
                    <asymmetric-key>rsa-asymmetric-key</asymmetric-k\
ey>
                    <certificate>ex-rsa-cert</certificate>
                  </central-keystore-reference>
                </certificate>
              </client-identity>
              <server-authentication>
                <ca-certs>
                  <central-truststore-reference>trusted-server-ca-ce\
rts</central-truststore-reference>
                </ca-certs>
                <ee-certs>
                  <central-truststore-reference>trusted-server-ee-ce\
rts</central-truststore-reference>
                </ee-certs>
              </server-authentication>
              <keepalives>
                <test-peer-aliveness>
                  <max-wait>30</max-wait>
                  <max-attempts>3</max-attempts>
                </test-peer-aliveness>
              </keepalives>
            </tls-client-parameters>
          </http-client-parameters>
        </endpoint>
        <endpoint>
          <name>corp-fw2.example.com</name>
          <http-client-parameters>
            <uri>https://corp-fw2.example.com</uri>
            <tls-client-parameters>
              <client-identity>
                <certificate>
                  <central-keystore-reference>
                    <asymmetric-key>rsa-asymmetric-key</asymmetric-k\
ey>
                    <certificate>ex-rsa-cert</certificate>
                  </central-keystore-reference>
                </certificate>
              </client-identity>
              <server-authentication>
                <ca-certs>
                  <central-truststore-reference>trusted-server-ca-ce\
rts</central-truststore-reference>
                </ca-certs>
                <ee-certs>
                  <central-truststore-reference>trusted-server-ee-ce\
rts</central-truststore-reference>
                </ee-certs>
              </server-authentication>
              <keepalives>
                <test-peer-aliveness>
                  <max-wait>30</max-wait>
                  <max-attempts>3</max-attempts>
                </test-peer-aliveness>
              </keepalives>
            </tls-client-parameters>
          </http-client-parameters>
        </endpoint>
      </endpoints>
      <connection-type>
        <persistent/>
      </connection-type>
    </restconf-server>
  </initiate>

  <!-- endpoints to listen for RESTCONF Call Home connections on -->
  <listen>
    <endpoints>
      <endpoint>
        <name>Intranet-facing listener</name>
        <https>
          <tcp-server-parameters>
            <local-bind>
              <local-address>192.0.2.2</local-address>
            </local-bind>
          </tcp-server-parameters>
          <http-client-parameters>
            <uri>https://corp-fw1.example.com</uri>
            <tls-client-parameters>
              <client-identity>
                <certificate>
                  <central-keystore-reference>
                    <asymmetric-key>rsa-asymmetric-key</asymmetric-k\
ey>
                    <certificate>ex-rsa-cert</certificate>
                  </central-keystore-reference>
                </certificate>
              </client-identity>
              <server-authentication>
                <ca-certs>
                  <central-truststore-reference>trusted-server-ca-ce\
rts</central-truststore-reference>
                </ca-certs>
                <ee-certs>
                  <central-truststore-reference>trusted-server-ee-ce\
rts</central-truststore-reference>
                </ee-certs>
              </server-authentication>
              <keepalives>
                <peer-allowed-to-send/>
              </keepalives>
            </tls-client-parameters>
          </http-client-parameters>
        </https>
      </endpoint>
    </endpoints>
  </listen>
</restconf-client>

2.3. YANG Module

This YANG module has normative references to [RFC6991], [RFC8040], and [RFC8071], [I-D.ietf-netconf-tcp-client-server], [I-D.ietf-netconf-tls-client-server], and [I-D.ietf-netconf-http-client-server].

<CODE BEGINS> file "ietf-restconf-client@2024-08-14.yang"

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

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

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

  import ietf-http-client {
    prefix httpc;
    reference
      "RFC GGGG: YANG Groupings for HTTP Clients and HTTP Servers";
  }

  organization
    "IETF NETCONF (Network Configuration) Working Group";

  contact
    "WG Web:   https://datatracker.ietf.org/wg/netconf
     WG List:  NETCONF WG list <mailto:netconf@ietf.org>
     Author:   Kent Watsen <mailto:kent+ietf@watsen.net>";

  description
    "This module contains a collection of YANG definitions
     for configuring RESTCONF clients.

     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 IIII
     (https://www.rfc-editor.org/info/rfcIIII); 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 2024-08-14 {
    description
      "Initial version";
    reference
      "RFC IIII: RESTCONF Client and Server Models";
  }

  // Features

  feature https-initiate {
    description
      "The 'https-initiate' feature indicates that the RESTCONF
       client supports initiating HTTPS connections to RESTCONF
       servers. This feature exists as HTTPS might not be a
       mandatory to implement transport in the future.";
    reference
      "RFC 8040: RESTCONF Protocol";
  }

  feature http-listen {
    description
      "The 'http-listen' feature indicates that the RESTCONF client
       supports opening a port to listen for incoming RESTCONF
       server call-home connections using HTTP.  This feature
       exists as not all RESTCONF clients may support RESTCONF
       call home.";
    reference
      "RFC 8071: NETCONF Call Home and RESTCONF Call Home";
  }

  feature https-listen {
    description
      "The 'https-listen' feature indicates that the RESTCONF client
       supports opening a port to listen for incoming RESTCONF
       server call-home connections using HTTPS.  This feature
       exists as not all RESTCONF clients may support RESTCONF
       call home.";
    reference
      "RFC 8071: NETCONF Call Home and RESTCONF Call Home";
  }

  feature central-restconf-client-supported {
   description
      "The 'central-restconf-client-supported' feature indicates
       that the server that implements this module supports
       the top-level 'restconf-client' node.

       This feature is needed as some servers may want to use
       features defined in this module, which requires this
       module to be implemented, without having to support
       the top-level 'restconf-client' node.";
  }

  // Groupings

  grouping restconf-client-initiate-stack-grouping {
    description
      "A reusable grouping for configuring a RESTCONF client
       'initiate' protocol stack for a single outbound connection.";
    container http-client-parameters {
      description
        "HTTP-level client parameters to listen
         for RESTCONF over HTTPS connections.";
      uses httpc:http-client-grouping;
    }
  } // restconf-client-initiate-stack-grouping

  grouping restconf-client-listen-stack-grouping {
    description
      "A reusable grouping for configuring a RESTCONF client
       'listen' protocol stack for listening on a single port.  The
       'listen' stack supports call home connections, as
       described in RFC 8071";
    reference
      "RFC 8071: NETCONF Call Home and RESTCONF Call Home";
    choice transport {
      mandatory true;
      description
        "Selects between available transports.";
      case http {
        if-feature "http-listen";
        container http {
          description
            "TCP, HTTP, and RESTCONF configuration to
             listen for RESTCONF over HTTPS connections.

             This transport option is made available to support
             deployments where the TLS connections are terminated
             by another system (e.g., a load balancer) fronting
             the client.";
          container tcp-server-parameters {
            description
              "TCP-level server parameters to listen for
               RESTCONF over HTTP connections.";
            uses tcps:tcp-server-grouping {
              refine "local-bind/local-port" {
                default "4336";
                description
                  "The RESTCONF client will listen on the IANA-
                   assigned well-known port for 'restconf-ch-tls'
                   (4336) if no value is specified.";
              }
            }
          }
          container http-client-parameters {
            description
              "HTTP-level client parameters to listen for
               RESTCONF over HTTP connections.";
            uses httpc:http-client-grouping;
          }
        }
      }
      case https {
        if-feature "https-listen";
        container https {
          description
            "TCP, TLS, HTTP, and RESTCONF configuration to
             listen for RESTCONF over HTTPS connections.";
          container tcp-server-parameters {
            description
              "TCP-level server parameters to listen
               for RESTCONF over HTTPS connections.";
            uses tcps:tcp-server-grouping {
              refine "local-bind/local-port" {
                default "4336";
                description
                  "The RESTCONF client will listen on the IANA-
                   assigned well-known port for 'restconf-ch-tls'
                   (4336) if no value is specified.";
              }
            }
          }
          container http-client-parameters {
            description
              "HTTP-level client parameters to listen
               for RESTCONF over HTTPS connections.";
            uses httpc:http-client-grouping;
          }
        }
      }
    }
  } // restconf-client-listen-stack-grouping

  grouping restconf-client-app-grouping {
    description
      "A reusable grouping for configuring a RESTCONF client
       application that supports both 'initiate' and 'listen'
       protocol stacks for a multiplicity of connections.";
    container initiate {
      if-feature "https-initiate";
      presence
        "Indicates that client-initiated connections have been
         configured.  This statement is present so the mandatory
         descendant nodes do not imply that this node must be
         configured.";
      description
        "Configures client initiating underlying TCP connections.";
      list restconf-server {
        key "name";
        min-elements 1;
        description
          "List of RESTCONF servers the RESTCONF client is to
           maintain simultaneous connections with.";
        leaf name {
          type string;
          description
            "An arbitrary name for the RESTCONF server.";
        }
        container endpoints {
          description
            "Container for a list of endpoints.";
          list endpoint {
            key "name";
            min-elements 1;
            ordered-by user;
            description
              "A non-empty user-ordered list of endpoints for this
               RESTCONF client to try to connect to in sequence.
               Defining more than one enables high-availability.";
            leaf name {
              type string;
              description
                "An arbitrary name for this endpoint.";
            }
            uses restconf-client-initiate-stack-grouping;
          }
        }
        container connection-type {
          description
            "Indicates the RESTCONF client's preference for how
             the RESTCONF connection is maintained.";
          choice connection-type {
            mandatory true;
            description
              "Selects between available connection types.";
            case persistent-connection {
              container persistent {
                presence
                  "Indicates that a persistent connection is to be
                   maintained.";
                description
                  "Maintain a persistent connection to the
                   RESTCONF server. If the connection goes down,
                   immediately start trying to reconnect to the
                   RESTCONF server, using the reconnection strategy.

                   This connection type minimizes any RESTCONF server
                   to RESTCONF client data-transfer delay, albeit
                   at the expense of holding resources longer.";
              }
            }
            case periodic-connection {
              container periodic {
                presence
                  "Indicates that a periodic connection is to be
                   maintained.";
                description
                  "Periodically connect to the RESTCONF server.

                   This connection type decreases resource
                   utilization, albeit with increased delay
                   in RESTCONF server to RESTCONF client
                   interactions.

                   The RESTCONF client SHOULD gracefully close
                   the underlying TLS connection upon completing
                   planned activities.

                   Connections are established at the same start
                   time regardless how long the previous connection
                   stayed open.

                   In the case that the previous connection is
                   still active, establishing a new connection
                   is NOT RECOMMENDED.";
                leaf period {
                  type uint16;
                  units "minutes";
                  default "60";
                  description
                    "Duration of time between periodic
                     connections.";
                }
                leaf anchor-time {
                  type yang:date-and-time {
                    // constrained to minute-level granularity
                    pattern '[0-9]{4}-(1[0-2]|0[1-9])-(0[1-9]|[1-2]'
                          + '[0-9]|3[0-1])T(0[0-9]|1[0-9]|2[0-3]):['
                          + '0-5][0-9]:00(Z|[\+\-]((1[0-3]|0[0-9]):'
                          + '([0-5][0-9])|14:00))?';
                  }
                  description
                    "Designates a timestamp before or after which a
                     series of periodic connections are determined.
                     The periodic connections occur at a whole
                     multiple interval from the anchor time.

                     If an 'anchor-time' is not provided, then the
                     server may implicitly set it to the time when
                     this configuraton is applied (e.g., on boot).

                     For example, for an anchor time is 15 minutes
                     past midnight and a period interval of 24 hours,
                     then a periodic connection will occur 15 minutes
                     past midnight everyday.";
                }
                leaf idle-timeout {
                  type uint16;
                  units "seconds";
                  default "180"; // three minutes
                  description
                    "Specifies the maximum number of seconds
                     that the underlying TCP session may remain
                     idle. A TCP session will be dropped if it
                     is idle for an interval longer than this
                     number of seconds If set to zero, then the
                     RESTCONF client will never drop a session
                     because it is idle.";
                }
              }
            } // periodic-connection
          } // connection-type
        } // connection-type
        container reconnect-strategy {
          description
            "The reconnection strategy directs how a RESTCONF
             client reconnects to a RESTCONF server, after
             discovering its connection to the server has
             dropped, even if due to a reboot.  The RESTCONF
             client starts with the specified endpoint and
             tries to connect to it max-attempts times before
             trying the next endpoint in the list (round
             robin).";
          leaf start-with {
            type enumeration {
              enum first-listed {
                description
                  "Indicates that reconnections should start
                   with the first endpoint listed.";
              }
              enum last-connected {
                description
                  "Indicates that reconnections should start with
                   the endpoint last connected to, if known.  If
                   no previous connection is known, then the
                   first endpoint configured is used.";
              }
              enum random-selection {
                description
                  "Indicates that reconnections should start with
                   a random endpoint.";
              }
            }
            default "first-listed";
            description
              "Specifies which of the RESTCONF server's
               endpoints the RESTCONF client should start
               with when trying to connect to the RESTCONF
               server.";
          }
          leaf max-wait {
            type uint16 {
              range "1..max";
            }
            units "seconds";
            default "5";
            description
              "Specifies the amount of time in seconds after which,
               if the connection is not established, an endpoint
               connection attempt is considered unsuccessful.";
          }
          leaf max-attempts {
            type uint8 {
              range "1..max";
            }
            default "3";
            description
              "Specifies the number times the RESTCONF client
               tries to connect to a specific endpoint before
               moving on to the next endpoint in the list
               (round robin).";
          }
        }
      }
    } // initiate

    container listen {
      if-feature "http-listen or https-listen";
      presence
        "Indicates that client-listening ports have been configured.
         This statement is present so the mandatory descendant nodes
         do not imply that this node must be configured.";
      description
        "Configures the client to accept call-home TCP connections.";
      leaf idle-timeout {
        type uint16;
        units "seconds";
        default "180"; // three minutes
        description
          "Specifies the maximum number of seconds that an
           underlying TCP session may remain idle. A TCP session
           will be dropped if it is idle for an interval longer
           then this number of seconds.  If set to zero, then
           the server will never drop a session because it is
           idle.";
      }
      container endpoints {
        description
          "Container for a list of endpoints.";
        list endpoint {
          key "name";
          min-elements 1;
          description
            "List of endpoints to listen for RESTCONF connections.";
          leaf name {
            type string;
            description
              "An arbitrary name for the RESTCONF listen endpoint.";
          }
          uses restconf-client-listen-stack-grouping;
        }
      }
    } // listen
  } // restconf-client-app-grouping

  // Protocol accessible node for servers that implement this module.
  container restconf-client {
    if-feature central-restconf-client-supported;
    uses restconf-client-app-grouping;
    description
      "Top-level container for RESTCONF client configuration.";
  }
}

<CODE ENDS>

3. The "ietf-restconf-server" Module

The RESTCONF server model presented in this section supports both listening for connections as well as initiating call-home connections.

YANG feature statements are used to enable implementations to advertise which potentially uncommon parts of the model the RESTCONF server supports.

3.1. Data Model Overview

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

3.1.1. Features

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

Features:
  +-- http-listen
  +-- https-listen
  +-- https-call-home
  +-- central-restconf-server-supported

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

3.1.2. Groupings

The "ietf-restconf-server" module defines the following "grouping" statements:

  • restconf-server-grouping
  • restconf-server-listen-stack-grouping
  • restconf-server-callhome-stack-grouping
  • restconf-server-app-grouping

Each of these groupings are presented in the following subsections.

3.1.2.1. The "restconf-server-grouping" Grouping

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

  grouping restconf-server-grouping:
    +-- client-identity-mappings
       +---u x509c2n:cert-to-name

Comments:

  • The "restconf-server-grouping" defines the configuration for the "RESTCONF" part of a protocol stack. It does not, for instance, define any configuration for the "TCP", "TLS", or "HTTP" protocol layers (for that, see Section 3.1.2.2 and Section 3.1.2.3).
  • The "client-identity-mappings" node defines a mapping from certificate fields to RESTCONF user names.

  • For the referenced grouping statement(s):

3.1.2.2. The "restconf-server-listen-stack-grouping" Grouping

The following tree diagram [RFC8340] illustrates the "restconf-server-listen-stack-grouping" grouping:

  grouping restconf-server-listen-stack-grouping:
    +-- (transport)
       +--:(http) {http-listen}?
       |  +-- http
       |     +-- external-endpoint!
       |     |  +-- address    inet:host
       |     |  +-- port?      inet:port-number
       |     +-- tcp-server-parameters
       |     |  +---u tcps:tcp-server-grouping
       |     +-- http-server-parameters
       |     |  +---u https:http-server-grouping
       |     +-- restconf-server-parameters
       |        +---u rcs:restconf-server-grouping
       +--:(https) {https-listen}?
          +-- https
             +-- tcp-server-parameters
             |  +---u tcps:tcp-server-grouping
             +-- tls-server-parameters
             |  +---u tlss:tls-server-grouping
             +-- http-server-parameters
             |  +---u https:http-server-grouping
             +-- restconf-server-parameters
                +---u rcs:restconf-server-grouping

Comments:

  • The "restconf-server-listen-stack-grouping" defines the configuration for a full RESTCONF protocol stack for RESTCONF servers that listen for connections from RESTCONF clients, as opposed to initiating call-home [RFC8071] connections.
  • The "transport" choice node enables either the HTTP or HTTPS transports to be configured, with each option enabled by a "feature" statement. The HTTP option is provided to support cases where a TLS-terminator is deployed in front of the RESTCONF-server.

  • For the referenced grouping statement(s):

3.1.2.3. The "restconf-server-callhome-stack-grouping" Grouping

The following tree diagram [RFC8340] illustrates the "restconf-server-callhome-stack-grouping" grouping:

  grouping restconf-server-callhome-stack-grouping:
    +-- (transport)
       +--:(https) {https-call-home}?
          +-- https
             +-- tcp-client-parameters
             |  +---u tcpc:tcp-client-grouping
             +-- tls-server-parameters
             |  +---u tlss:tls-server-grouping
             +-- http-server-parameters
             |  +---u https:http-server-grouping
             +-- restconf-server-parameters
                +---u rcs:restconf-server-grouping

Comments:

3.1.2.4. The "restconf-server-app-grouping" Grouping

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

  grouping restconf-server-app-grouping:
    +-- listen! {http-listen or https-listen}?
    |  +-- endpoints
    |     +-- endpoint* [name]
    |        +-- name?                                    string
    |        +---u restconf-server-listen-stack-grouping
    +-- call-home! {https-call-home}?
       +-- restconf-client* [name]
          +-- name?                 string
          +-- endpoints
          |  +-- endpoint* [name]
          |     +-- name?                                      string
          |     +---u restconf-server-callhome-stack-grouping
          +-- connection-type
          |  +-- (connection-type)
          |     +--:(persistent-connection)
          |     |  +-- persistent!
          |     +--:(periodic-connection)
          |        +-- periodic!
          |           +-- period?         uint16
          |           +-- anchor-time?    yang:date-and-time
          |           +-- idle-timeout?   uint16
          +-- reconnect-strategy
             +-- start-with?     enumeration
             +-- max-wait?       uint16
             +-- max-attempts?   uint8

Comments:

  • The "restconf-server-app-grouping" defines the configuration for a RESTCONF server that supports both listening for connections from RESTCONF clients as well as initiating call-home connections to RESTCONF clients.
  • Both the "listen" and "call-home" subtrees must be enabled by "feature" statements.

  • For the referenced grouping statement(s):

    • The "restconf-server-listen-stack-grouping" grouping is discussed in Section 3.1.2.2 in this document.
    • The "restconf-server-callhome-stack-grouping" grouping is discussed in Section 3.1.2.3 in this document.

3.1.3. Protocol-accessible Nodes

The following tree diagram [RFC8340] lists all the protocol-accessible nodes defined in the "ietf-restconf-server" module:

module: ietf-restconf-server
  +--rw restconf-server {central-restconf-server-supported}?
     +---u restconf-server-app-grouping

Comments:

  • Protocol-accessible nodes are those nodes that are accessible when the module is "implemented", as described in Section 5.6.5 of [RFC7950].
  • The top-level node "restconf-server" is additionally constrained by the feature "central-restconf-server-supported".
  • The "restconf-server-app-grouping" grouping is discussed in Section 3.1.2.4 in this document.
  • The reason for why "restconf-server-app-grouping" exists separate from the protocol-accessible nodes definition is so as to enable instances of restconf-server-app-grouping to be instantiated in other locations, as may be needed or desired by some modules.

3.2. Example Usage

The following example illustrates configuring a RESTCONF server to listen for RESTCONF client connections, as well as configuring call-home to one RESTCONF client.

This example is consistent with the examples presented in Section 2.2.1 of [I-D.ietf-netconf-trust-anchors] and Section 2.2.1 of [I-D.ietf-netconf-keystore].

=============== NOTE: '\' line wrapping per RFC 8792 ================

<restconf-server
  xmlns="urn:ietf:params:xml:ns:yang:ietf-restconf-server"
  xmlns:x509c2n="urn:ietf:params:xml:ns:yang:ietf-x509-cert-to-name">

  <!-- endpoints to listen for RESTCONF connections on -->
  <listen>
    <endpoints>
      <endpoint>
        <name>restconf/https</name>
        <https>
          <tcp-server-parameters>
            <local-bind>
              <local-address>192.0.2.2</local-address>
            </local-bind>
          </tcp-server-parameters>
          <tls-server-parameters>
            <server-identity>
              <certificate>
                <central-keystore-reference>
                  <asymmetric-key>rsa-asymmetric-key</asymmetric-key>
                  <certificate>ex-rsa-cert</certificate>
                </central-keystore-reference>
              </certificate>
            </server-identity>
            <client-authentication>
              <ca-certs>
                <central-truststore-reference>trusted-client-ca-cert\
s</central-truststore-reference>
              </ca-certs>
              <ee-certs>
                <central-truststore-reference>trusted-client-ee-cert\
s</central-truststore-reference>
              </ee-certs>
            </client-authentication>
            <keepalives>
              <peer-allowed-to-send/>
            </keepalives>
          </tls-server-parameters>
          <http-server-parameters>
            <server-name>foo.example.com</server-name>
          </http-server-parameters>
          <restconf-server-parameters>
            <client-identity-mappings>
              <cert-to-name>
                <id>1</id>
                <fingerprint>11:0A:05:11:00</fingerprint>
                <map-type>x509c2n:specified</map-type>
                <name>scooby-doo</name>
              </cert-to-name>
                <cert-to-name>
                <id>2</id>
                <map-type>x509c2n:san-any</map-type>
              </cert-to-name>
            </client-identity-mappings>
          </restconf-server-parameters>
        </https>
      </endpoint>
    </endpoints>
  </listen>

  <!-- call home to a RESTCONF client with two endpoints -->
  <call-home>
    <restconf-client>
      <name>config-manager</name>
      <endpoints>
        <endpoint>
          <name>east-data-center</name>
          <https>
            <tcp-client-parameters>
              <remote-address>east.example.com</remote-address>
              <keepalives>
                <idle-time>7200</idle-time>
                <max-probes>9</max-probes>
                <probe-interval>75</probe-interval>
              </keepalives>
            </tcp-client-parameters>
            <tls-server-parameters>
              <server-identity>
                <certificate>
                  <central-keystore-reference>
                    <asymmetric-key>rsa-asymmetric-key</asymmetric-k\
ey>
                    <certificate>ex-rsa-cert</certificate>
                  </central-keystore-reference>
                </certificate>
              </server-identity>
              <client-authentication>
                <ca-certs>
                  <central-truststore-reference>trusted-client-ca-ce\
rts</central-truststore-reference>
                </ca-certs>
                <ee-certs>
                  <central-truststore-reference>trusted-client-ee-ce\
rts</central-truststore-reference>
                </ee-certs>
              </client-authentication>
              <keepalives>
                <test-peer-aliveness>
                  <max-wait>30</max-wait>
                  <max-attempts>3</max-attempts>
                </test-peer-aliveness>
              </keepalives>
            </tls-server-parameters>
            <http-server-parameters>
              <server-name>foo.example.com</server-name>
            </http-server-parameters>
            <restconf-server-parameters>
              <client-identity-mappings>
                <cert-to-name>
                  <id>1</id>
                  <fingerprint>11:0A:05:11:00</fingerprint>
                  <map-type>x509c2n:specified</map-type>
                  <name>scooby-doo</name>
                </cert-to-name>
                <cert-to-name>
                  <id>2</id>
                  <map-type>x509c2n:san-any</map-type>
                </cert-to-name>
              </client-identity-mappings>
            </restconf-server-parameters>
          </https>
        </endpoint>
        <endpoint>
          <name>west-data-center</name>
          <https>
            <tcp-client-parameters>
              <remote-address>west.example.com</remote-address>
              <keepalives>
                <idle-time>7200</idle-time>
                <max-probes>9</max-probes>
                <probe-interval>75</probe-interval>
              </keepalives>
            </tcp-client-parameters>
            <tls-server-parameters>
              <server-identity>
                <certificate>
                  <central-keystore-reference>
                    <asymmetric-key>rsa-asymmetric-key</asymmetric-k\
ey>
                    <certificate>ex-rsa-cert</certificate>
                  </central-keystore-reference>
                </certificate>
              </server-identity>
              <client-authentication>
                <ca-certs>
                  <central-truststore-reference>trusted-client-ca-ce\
rts</central-truststore-reference>
                </ca-certs>
                <ee-certs>
                  <central-truststore-reference>trusted-client-ee-ce\
rts</central-truststore-reference>
                </ee-certs>
              </client-authentication>
              <keepalives>
                <test-peer-aliveness>
                  <max-wait>30</max-wait>
                  <max-attempts>3</max-attempts>
                </test-peer-aliveness>
              </keepalives>
            </tls-server-parameters>
            <http-server-parameters>
              <server-name>foo.example.com</server-name>
            </http-server-parameters>
            <restconf-server-parameters>
              <client-identity-mappings>
                <cert-to-name>
                  <id>1</id>
                  <fingerprint>11:0A:05:11:00</fingerprint>
                  <map-type>x509c2n:specified</map-type>
                  <name>scooby-doo</name>
                </cert-to-name>
                <cert-to-name>
                  <id>2</id>
                  <map-type>x509c2n:san-any</map-type>
                </cert-to-name>
              </client-identity-mappings>
            </restconf-server-parameters>
          </https>
        </endpoint>
      </endpoints>
      <connection-type>
        <periodic>
          <idle-timeout>300</idle-timeout>
          <anchor-time>2023-03-15T01:30:00Z</anchor-time>
          <period>60</period>
        </periodic>
      </connection-type>
      <reconnect-strategy>
        <start-with>last-connected</start-with>
        <max-wait>3</max-wait>
        <max-attempts>3</max-attempts>
      </reconnect-strategy>
    </restconf-client>
  </call-home>
</restconf-server>

3.3. YANG Module

This YANG module has normative references to [RFC6991], [RFC7407], [RFC8040], [RFC8071], [I-D.ietf-netconf-tcp-client-server], [I-D.ietf-netconf-tls-client-server], and [I-D.ietf-netconf-http-client-server].

<CODE BEGINS> file "ietf-restconf-server@2024-08-14.yang"

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

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

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

  import ietf-x509-cert-to-name {
    prefix x509c2n;
    reference
      "RFC 7407: A YANG Data Model for SNMP Configuration";
  }

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

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

  import ietf-tls-server {
    prefix tlss;
    reference
      "RFC FFFF: YANG Groupings for TLS Clients and TLS Servers";
  }

  import ietf-http-server {
    prefix https;
    reference
      "RFC GGGG: YANG Groupings for HTTP Clients and HTTP Servers";
  }

  organization
    "IETF NETCONF (Network Configuration) Working Group";

  contact
    "WG Web:   https://datatracker.ietf.org/wg/netconf
     WG List:  NETCONF WG list <mailto:netconf@ietf.org>
     Author:   Kent Watsen <mailto:kent+ietf@watsen.net>";

  description
    "This module contains a collection of YANG definitions
     for configuring RESTCONF servers.

     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 IIII
     (https://www.rfc-editor.org/info/rfcIIII); 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 2024-08-14 {
    description
      "Initial version";
    reference
      "RFC IIII: RESTCONF Client and Server Models";
  }

  // Features

  feature http-listen {
    description
      "The 'http-listen' feature indicates that the RESTCONF server
       supports opening a port to listen for incoming RESTCONF over
       TCP client connections, whereby the TLS connections are
       terminated by an external system.";
    reference
      "RFC 8040: RESTCONF Protocol";
  }

  feature https-listen {
    description
      "The 'https-listen' feature indicates that the RESTCONF server
       supports opening a port to listen for incoming RESTCONF over
       TLS client connections, whereby the TLS connections are
       terminated by the server itself.";
    reference
      "RFC 8040: RESTCONF Protocol";
  }

  feature https-call-home {
    description
      "The 'https-call-home' feature indicates that the RESTCONF
       server supports initiating connections to RESTCONF clients.";
    reference
      "RFC 8071: NETCONF Call Home and RESTCONF Call Home";
  }

  feature central-restconf-server-supported {
   description
      "The 'central-restconf-server-supported' feature indicates
       that the server supports the top-level 'restconf-server'
       node.

       This feature is needed as some servers may want to use
       features defined in this module, which requires this
       module to be implemented, without having to support
       the top-level 'restconf-server' node.";
  }

  // Groupings

  grouping restconf-server-grouping {
    description
      "A reusable grouping for configuring a RESTCONF server
       without any consideration for how underlying transport
       sessions are established.

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

    container client-identity-mappings {
      description
        "Specifies mappings through which RESTCONF client X.509
         certificates are used to determine a RESTCONF username.
         If no matching and valid cert-to-name list entry can be
         found, then the RESTCONF server MUST close the connection,
         and MUST NOT accept RESTCONF messages over it.";
      reference
        "RFC 7407: A YANG Data Model for SNMP Configuration.";
      uses x509c2n:cert-to-name {
        refine "cert-to-name/fingerprint" {
          mandatory false;
          description
            "A 'fingerprint' value does not need to be specified
             when the 'cert-to-name' mapping is independent of
             fingerprint matching.  A 'cert-to-name' having no
             fingerprint value will match any client certificate
             and therefore should only be present at the end of
             the user-ordered 'cert-to-name' list.";
        }
      }
    }
  }

  grouping restconf-server-listen-stack-grouping {
    description
      "A reusable grouping for configuring a RESTCONF server
       'listen' protocol stack for listening on a single port.";
    choice transport {
      mandatory true;
      description
        "Selects between available transports.";
      case http {
        if-feature "http-listen";
        container http {
          description
            "Configures RESTCONF server stack assuming that
             TLS-termination is handled externally.

             How a RESTCONF-server identifies RESTCONF-clients
             authenticating using a TLS-level client-certificate
             with external TLS termination is out of scope of
             this document.";
          container external-endpoint {
            presence
              "Identifies that an external endpoint has been
               configured.  This statement is present so the
               mandatory descendant nodes do not imply that
               this node must be configured.";
            description
              "Identifies contact information for the external
               system that terminates connections before passing
               them through to this server (e.g., a network address
               translator or a load balancer).  These values have
               no effect on the local operation of this server,
               but may be used by the application when needing to
               inform other systems how to contact this server.";
            leaf address {
              type inet:host;
              mandatory true;
              description
                "The IP address or hostname of the external
                 system that terminates incoming RESTCONF
                 client connections before forwarding them
                 to this server.";
            }
            leaf port {
              type inet:port-number;
              default "443";
              description
                "The port number that the external system listens
                 on for incoming RESTCONF client connections that
                 are forwarded to this server.  The default HTTPS
                 port (443) is used, as expected for a RESTCONF
                 connection.";
            }
          }
          container tcp-server-parameters {
            description
              "TCP-level server parameters to listen for
               RESTCONF over HTTP connections.";
            uses tcps:tcp-server-grouping {
              refine "local-bind/local-port" {
                default "80";
                description
                  "The RESTCONF server will listen on the IANA-
                   assigned well-known port value for 'http'
                   (80) if no value is specified.";
              }
            }
          }
          container http-server-parameters {
            description
              "HTTP-level server parameters to listen
               for RESTCONF over HTTP connections.";
            uses https:http-server-grouping;
          }
          container restconf-server-parameters {
            description
              "RESTCONF-level server parameters to listen
               for RESTCONF over HTTP connections.";
            uses rcs:restconf-server-grouping;
          }
        }
      }
      case https {
        if-feature "https-listen";
        container https {
          description
            "Configures RESTCONF server stack assuming that
             TLS-termination is handled internally (i.e.,
             not by a TLS-terminator in front of the RESTCONF
             server).";
          container tcp-server-parameters {
            description
              "TCP-level server parameters to listen for
               RESTCONF over HTTPS connections.";
            uses tcps:tcp-server-grouping {
              refine "local-bind/local-port" {
                default "443";
                description
                  "The RESTCONF server will listen on the IANA-
                   assigned well-known port value for 'https'
                   (443) if no value is specified.";
              }
            }
          }
          container tls-server-parameters {
            description
              "TLS-level server parameters to listen
               for RESTCONF over HTTPS connections.";
            uses tlss:tls-server-grouping;
          }
          container http-server-parameters {
            description
              "HTTP-level server parameters to listen
               for RESTCONF over HTTPS connections.";
            uses https:http-server-grouping;
          }
          container restconf-server-parameters {
            description
              "RESTCONF-level server parameters to listen
               for RESTCONF over HTTPS connections.";
            uses rcs:restconf-server-grouping;
          }
        }
      }
    }
  }

  grouping restconf-server-callhome-stack-grouping {
    description
      "A reusable grouping for configuring a RESTCONF server
       'call-home' protocol stack, for a single outbound
       connection.";
    choice transport {
      mandatory true;
      description
        "Selects between available transports.";
      case https {
        if-feature "https-call-home";
        container https {
          description
            "Configures RESTCONF server stack assuming that
             TLS-termination is handled internally.";
          container tcp-client-parameters {
            description
              "TCP-level client parameters to initiate a
               RESTCONF over HTTPS Call Home connection.";
            uses tcpc:tcp-client-grouping {
              refine "remote-port" {
                default "4336";
                description
                  "The RESTCONF server will attempt to
                   connect to the IANA-assigned well-known
                   port for 'restconf-ch-tls' (4336) if no
                   value is specified.";
              }
            }
          }
          container tls-server-parameters {
            description
              "TLS-level server parameters to initiate a
               RESTCONF over HTTPS Call Home connection.";
            uses tlss:tls-server-grouping;
          }
          container http-server-parameters {
            description
              "HTTP-level server parameters to initiate a
               RESTCONF over HTTPS Call Home connection.";
            uses https:http-server-grouping;
          }
          container restconf-server-parameters {
            description
              "RESTCONF-level server parameters to initiate
               a RESTCONF over HTTPS Call Home connection.";
            uses rcs:restconf-server-grouping;
          }
        }
      }
    }
  }

  grouping restconf-server-app-grouping {
    description
      "A reusable grouping for configuring a RESTCONF server
       application that supports both 'listen' and 'call-home'
       protocol stacks for a multiplicity of connections.";
    container listen {
      if-feature "http-listen or https-listen";
      presence
        "Identifies that the server has been configured to
         listen for incoming client connections.  This statement
         is present so the mandatory descendant nodes do not
         imply that this node must be configured.";
      description
        "Configures the RESTCONF server to listen for RESTCONF
         client connections.";
      container endpoints {
        description
          "Container for a list of endpoints.";
        list endpoint {
          key "name";
          min-elements 1;
          description
            "List of endpoints to listen for RESTCONF connections.";
          leaf name {
            type string;
            description
              "An arbitrary name for the RESTCONF listen endpoint.";
          }
          uses restconf-server-listen-stack-grouping;
        }
      }
    }
    container call-home {
      if-feature "https-call-home";
      presence
        "Identifies that the server has been configured to initiate
         call home connections.  This statement is present so the
         mandatory descendant nodes do not imply that this node
         must be configured.";
      description
        "Configures the RESTCONF server to initiate the underlying
         transport connection to RESTCONF clients.";
      list restconf-client {
        key "name";
        min-elements 1;
        description
          "List of RESTCONF clients the RESTCONF server is to
           maintain simultaneous call-home connections with.";
        leaf name {
          type string;
          description
            "An arbitrary name for the remote RESTCONF client.";
        }
        container endpoints {
          description
            "Container for the list of endpoints.";
          list endpoint {
            key "name";
            min-elements 1;
            ordered-by user;
            description
              "User-ordered list of endpoints for this RESTCONF
               client.  Defining more than one enables high-
               availability.";
            leaf name {
              type string;
              description
                "An arbitrary name for this endpoint.";
            }
            uses restconf-server-callhome-stack-grouping;
          }
        }
        container connection-type {
          description
            "Indicates the RESTCONF server's preference for how the
             RESTCONF connection is maintained.";
          choice connection-type {
            mandatory true;
            description
              "Selects between available connection types.";
            case persistent-connection {
              container persistent {
                presence
                  "Indicates that a persistent connection is to be
                   maintained.";
                description
                  "Maintain a persistent connection to the RESTCONF
                   client. If the connection goes down, immediately
                   start trying to reconnect to the RESTCONF client,
                   using the reconnection strategy.

                   This connection type minimizes any RESTCONF
                   client to RESTCONF server data-transfer delay,
                   albeit at the expense of holding resources
                   longer.";
              }
            }
            case periodic-connection {
              container periodic {
                presence
                  "Indicates that a periodic connection is to be
                   maintained.";
                description
                  "Periodically connect to the RESTCONF client.

                   This connection type decreases resource
                   utilization, albeit with increased delay in
                   RESTCONF client to RESTCONF server interactions.

                   The RESTCONF client SHOULD gracefully close
                   the underlying TLS connection upon completing
                   planned activities.  If the underlying TLS
                   connection is not closed gracefully, the
                   RESTCONF server MUST immediately attempt
                   to reestablish the connection.

                   Connections are established at the same start
                   time regardless how long the previous connection
                   stayed open.

                   In the case that the previous connection is
                   still active (i.e., the RESTCONF client has not
                   closed it yet), establishing a new connection
                   is NOT RECOMMENDED.";

                leaf period {
                  type uint16;
                  units "minutes";
                  default "60";
                  description
                    "Duration of time between periodic connections.";
                }
                leaf anchor-time {
                  type yang:date-and-time {
                    // constrained to minute-level granularity
                    pattern '[0-9]{4}-(1[0-2]|0[1-9])-(0[1-9]|[1-2]'
                          + '[0-9]|3[0-1])T(0[0-9]|1[0-9]|2[0-3]):['
                          + '0-5][0-9]:00(Z|[\+\-]((1[0-3]|0[0-9]):'
                          + '([0-5][0-9])|14:00))?';
                  }
                  description
                    "Designates a timestamp before or after which a
                     series of periodic connections are determined.
                     The periodic connections occur at a whole
                     multiple interval from the anchor time.

                     If an 'anchor-time' is not provided, then the
                     server may implicitly set it to the time when
                     this configuraton is applied (e.g., on boot).

                     For example, for an anchor time is 15 minutes
                     past midnight and a period interval of 24 hours,
                     then a periodic connection will occur 15 minutes
                     past midnight everyday.";
                }
                leaf idle-timeout {
                  type uint16;
                  units "seconds";
                  default "180"; // three minutes
                  description
                    "Specifies the maximum number of seconds that
                     the underlying TCP session may remain idle.
                     A TCP session will be dropped if it is idle
                     for an interval longer than this number of
                     seconds.  If set to zero, then the server
                     will never drop a session because it is idle.";
                }
              }
            }
          }
        }
        container reconnect-strategy {
          description
            "The reconnection strategy directs how a RESTCONF server
             reconnects to a RESTCONF client after discovering its
             connection to the client has dropped, even if due to a
             reboot.  The RESTCONF server starts with the specified
             endpoint and tries to connect to it max-attempts times
             before trying the next endpoint in the list (round
             robin).";
          leaf start-with {
            type enumeration {
              enum first-listed {
                description
                  "Indicates that reconnections should start with
                   the first endpoint listed.";
              }
              enum last-connected {
                description
                  "Indicates that reconnections should start with
                   the endpoint last connected to, if known.  If
                   no previous connection is known, then the
                   first endpoint configured is used.";
              }
              enum random-selection {
                description
                  "Indicates that reconnections should start with
                   a random endpoint.";
              }
            }
            default "first-listed";
            description
              "Specifies which of the RESTCONF client's endpoints
               the RESTCONF server should start with when trying
               to connect to the RESTCONF client.";
          }
          leaf max-wait {
            type uint16 {
              range "1..max";
            }
            units "seconds";
            default "5";
            description
              "Specifies the amount of time in seconds after which,
               if the connection is not established, an endpoint
               connection attempt is considered unsuccessful.";
          }
          leaf max-attempts {
            type uint8 {
              range "1..max";
            }
            default "3";
            description
              "Specifies the number times the RESTCONF server tries
               to connect to a specific endpoint before moving on to
               the next endpoint in the list (round robin).";
          }
        }
      } // restconf-client
    } // call-home
  } // restconf-server-app-grouping

  // Protocol accessible node for servers that implement this module.
  container restconf-server {
    if-feature central-restconf-server-supported;
    uses restconf-server-app-grouping;
    description
      "Top-level container for RESTCONF server configuration.";
  }
}

<CODE ENDS>

4. Security Considerations

4.1. Considerations for the "ietf-restconf-client" YANG Module

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

The "ietf-restconf-client" YANG module defines data nodes 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.

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 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 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.

Please be aware that this module uses groupings defined in other RFCs that define data nodes that do set the NACM "default-deny-all" and "default-deny-write" extensions.

4.2. Considerations for the "ietf-restconf-server" YANG Module

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

The "ietf-restconf-server" YANG module defines data nodes 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.

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 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 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.

Please be aware that this module uses groupings defined in other RFCs that define data nodes that do set the NACM "default-deny-all" and "default-deny-write" extensions.

5. IANA Considerations

5.1. The "IETF XML" Registry

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

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

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

5.2. 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-restconf-client
   namespace:    urn:ietf:params:xml:ns:yang:ietf-restconf-client
   prefix:       rcc
   reference:    RFC IIII

   name:         ietf-restconf-server
   namespace:    urn:ietf:params:xml:ns:yang:ietf-restconf-server
   prefix:       rcs
   reference:    RFC IIII

6. References

6.1. Normative References

[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-21, , <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-http-client-server-21>.
[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-35, , <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-keystore-35>.
[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-26, , <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-tcp-client-server-26>.
[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-41, , <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-tls-client-server-41>.
[RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <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, , <https://www.rfc-editor.org/info/rfc6020>.
[RFC6991]
Schoenwaelder, J., Ed., "Common YANG Data Types", RFC 6991, DOI 10.17487/RFC6991, , <https://www.rfc-editor.org/info/rfc6991>.
[RFC7407]
Bjorklund, M. and J. Schoenwaelder, "A YANG Data Model for SNMP Configuration", RFC 7407, DOI 10.17487/RFC7407, , <https://www.rfc-editor.org/info/rfc7407>.
[RFC7950]
Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language", RFC 7950, DOI 10.17487/RFC7950, , <https://www.rfc-editor.org/info/rfc7950>.
[RFC8040]
Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF Protocol", RFC 8040, DOI 10.17487/RFC8040, , <https://www.rfc-editor.org/info/rfc8040>.
[RFC8071]
Watsen, K., "NETCONF Call Home and RESTCONF Call Home", RFC 8071, DOI 10.17487/RFC8071, , <https://www.rfc-editor.org/info/rfc8071>.
[RFC8174]
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <https://www.rfc-editor.org/info/rfc8174>.

6.2. 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-34, , <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-crypto-types-34>.
[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-36, , <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-netconf-client-server-36>.
[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-37, , <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-restconf-client-server-37>.
[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-40, , <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-ssh-client-server-40>.
[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-28, , <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-trust-anchors-28>.
[I-D.ietf-netmod-system-config]
Ma, Q., Wu, Q., and C. Feng, "System-defined Configuration", Work in Progress, Internet-Draft, draft-ietf-netmod-system-config-08, , <https://datatracker.ietf.org/doc/html/draft-ietf-netmod-system-config-08>.
[RFC3688]
Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, DOI 10.17487/RFC3688, , <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, , <https://www.rfc-editor.org/info/rfc6241>.
[RFC8340]
Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams", BCP 215, RFC 8340, DOI 10.17487/RFC8340, , <https://www.rfc-editor.org/info/rfc8340>.
[RFC8341]
Bierman, A. and M. Bjorklund, "Network Configuration Access Control Model", STD 91, RFC 8341, DOI 10.17487/RFC8341, , <https://www.rfc-editor.org/info/rfc8341>.
[RFC8342]
Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K., and R. Wilton, "Network Management Datastore Architecture (NMDA)", RFC 8342, DOI 10.17487/RFC8342, , <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, , <https://www.rfc-editor.org/info/rfc8407>.
[RFC8446]
Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, , <https://www.rfc-editor.org/info/rfc8446>.

Appendix A. Change Log

A.1. 00 to 01

  • Renamed "keychain" to "keystore".

A.2. 01 to 02

  • Filled in previously missing 'ietf-restconf-client' module.

  • Updated the ietf-restconf-server module to accommodate new grouping 'ietf-tls-server-grouping'.

A.3. 02 to 03

  • Refined use of tls-client-grouping to add a must statement indicating that the TLS client must specify a client-certificate.

  • Changed restconf-client??? to be a grouping (not a container).

A.4. 03 to 04

  • Added RFC 8174 to Requirements Language Section.

  • Replaced refine statement in ietf-restconf-client to add a mandatory true.

  • Added refine statement in ietf-restconf-server to add a must statement.

  • Now there are containers and groupings, for both the client and server models.

  • Now tree diagrams reference ietf-netmod-yang-tree-diagrams

  • Updated examples to inline key and certificates (no longer a leafref to keystore)

A.5. 04 to 05

  • Now tree diagrams reference ietf-netmod-yang-tree-diagrams

  • Updated examples to inline key and certificates (no longer a leafref to keystore)

A.6. 05 to 06

  • Fixed change log missing section issue.

  • Updated examples to match latest updates to the crypto-types, trust-anchors, and keystore drafts.

  • Reduced line length of the YANG modules to fit within 69 columns.

A.7. 06 to 07

  • removed "idle-timeout" from "persistent" connection config.

  • Added "random-selection" for reconnection-strategy's "starts-with" enum.

  • Replaced "connection-type" choice default (persistent) with "mandatory true".

  • Reduced the periodic-connection's "idle-timeout" from 5 to 2 minutes.

  • Replaced reconnect-timeout with period/anchor-time combo.

A.8. 07 to 08

  • Modified examples to be compatible with new crypto-types algs

A.9. 08 to 09

  • Corrected use of "mandatory true" for "address" leafs.

  • Updated examples to reflect update to groupings defined in the keystore draft.

  • Updated to use groupings defined in new TCP and HTTP drafts.

  • Updated copyright date, boilerplate template, affiliation, and folding algorithm.

A.10. 09 to 10

  • Reformatted YANG modules.

A.11. 10 to 11

  • Adjusted for the top-level "demux container" added to groupings imported from other modules.

  • Added "must" expressions to ensure that keepalives are not configured for "periodic" connections.

  • Updated the boilerplate text in module-level "description" statement to match copyeditor convention.

  • Moved "expanded" tree diagrams to the Appendix.

A.12. 11 to 12

  • Removed the 'must' statement limiting keepalives in periodic connections.

  • Updated models and examples to reflect removal of the "demux" containers in the imported models.

  • Updated the "periodic-connnection" description statements to better describe behavior when connections are not closed gracefully.

  • Updated text to better reference where certain examples come from (e.g., which Section in which draft).

  • In the server model, commented out the "must 'pinned-ca-certs or pinned-client-certs'" statement to reflect change made in the TLS draft whereby the trust anchors MAY be defined externally.

  • Replaced the 'listen', 'initiate', and 'call-home' features with boolean expressions.

A.13. 12 to 13

  • Updated to reflect changes in trust-anchors drafts (e.g., s/trust-anchors/truststore/g + s/pinned.//)

  • In ietf-restconf-server, Added 'http-listen' (not https-listen) choice, to support case when server is behind a TLS-terminator.

  • Refactored server module to be more like other 'server' models. If folks like it, will also apply to the client model, as well as to both the netconf client/server models. Now the 'restconf-server-grouping' is just the RC-specific bits (i.e., the "demux" container minus the container), 'restconf-server-[listen|callhome]-stack-grouping' is the protocol stack for a single connection, and 'restconf-server-app-grouping' is effectively what was before (both listen+callhome for many inbound/outbound endpoints).

A.14. 13 to 14

  • Updated examples to reflect ietf-crypto-types change (e.g., identities --> enumerations)

  • Adjusting from change in TLS client model (removing the top-level 'certificate' container).

  • Added "external-endpoint" to the "http-listen" choice in ietf-restconf-server.

A.15. 14 to 15

  • Added missing "or https-listen" clause in a "must" expression.

  • Refactored the client module similar to how the server module was refactored in -13. Now the 'restconf-client-grouping' is just the RC-specific bits, the 'restconf-client-[initiate|listen]-stack-grouping' is the protocol stack for a single connection, and 'restconf-client-app-grouping' is effectively what was before (both listen+callhome for many inbound/outbound endpoints).

A.16. 15 to 16

  • Added refinement to make "cert-to-name/fingerprint" be mandatory false.

  • Commented out refinement to "tls-server-grouping/client-authentication" until a better "must" expression is defined.

  • Updated restconf-client example to reflect that http-client-grouping no longer has a "protocol-version" leaf.

A.17. 16 to 17

  • Updated examples to include the "*-key-format" nodes.

  • Updated examples to remove the "required" nodes.

A.18. 17 to 18

  • Updated examples to reflect new "bag" addition to truststore.

A.19. 18 to 19

  • Updated examples to remove the 'algorithm' nodes.

  • Updated examples to reflect the new TLS keepalives structure.

  • Removed the 'protocol-versions' node from the restconf-server examples.

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

A.20. 19 to 20

  • Moved and changed "must" statement so that either TLS *or* HTTP auth must be configured.

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

  • Updated the Security Considerations section.

A.21. 20 to 21

  • Cleaned up titles in the IANA Consideratons section

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

A.22. 21 to 22

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

A.23. 22 to 23

  • Further clarified why some 'presence' statements are present.

  • Addressed nits found in YANG Doctor reviews.

  • Aligned modules with `pyang -f` formatting.

A.24. 23 to 24

  • Removed Appendix A with fully-expanded tree diagrams.

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

  • Minor editorial nits

A.25. 24 to 25

  • 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.26. 25 to 26

  • Added feature "central-restconf-client-supported" to top-level node "restconf-client".

  • Added feature "central-restconf-server-supported" to top-level node "restconf-server".

A.27. 26 to 27

  • Updated per Shepherd reviews impacting the suite of drafts.

  • Added "max-wait" leaf to the "reconnect-strategy" nodes.

A.28. 27 to 28

  • Updated per Shepherd reviews impacting the suite of drafts.

A.29. 28 to 29

  • Updated (implicitly) via Tom Petch reviews.

  • Fixed pattern statement for "leaf anchor-time".

  • Updated examples to use IETF-sanctioned values.

A.30. 29 to 30

  • Addresses AD review comments.

  • Added note to Editor to fix line foldings.

  • Removed "Conventions" section as there are no "BASE64VALUE=" values used in draft.

  • Removed restconf-client-grouping, since it was empty.

  • Removed erronious statement "client-identity-mappings" must be enabled by a "feature".

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

  • Removed "A wrapper around the foobar parameters to avoid name collisions" text.

  • Added container "endpoints" to wrap list "endpoint".

  • Fixed if-feature "https-listen" to if-feature "https-call-home".

A.31. 30 to 31

  • Addresses AD review by Rob Wilton.

A.32. 31 to 32

  • Addresses 1st-round of IESG reviews.

A.33. 32 to 34

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

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

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

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

A.34. 34 to 36

  • Nothing changed. Only bumped for automation...

Acknowledgements

The authors would like to thank the following for lively discussions on list and in the halls (ordered by first name): Alan Luchuk, Andy Bierman, Balázs Kovács, Benoit Claise, Bert Wijnen David Lamparter, Jürgen Schönwälder, Ladislav Lhotka, Martin Björklund, Qiufang Ma, Mehmet Ersue, Michal Vaško, Phil Shafer, Qiufang Ma, Radek Krejci, Ramkumar Dhanapal, Rob Wilton, Sean Turner, and Tom Petch.

Author's Address

Kent Watsen
Watsen Networks