NETCONF Working Group K. Watsen
Internet-Draft Watsen Networks
Intended status: Standards Track M. Scharf
Expires: September 9, 2020 Hochschule Esslingen
March 8, 2020

YANG Groupings for TCP Clients and TCP Servers
draft-ietf-netconf-tcp-client-server-04

Abstract

This document defines three YANG modules: the first defines a grouping for configuring a generic TCP client, the second defines a grouping for configuring a generic TCP server, and the third defines a grouping common to the TCP clients and TCP servers.

Editorial Note (To be removed by RFC Editor)

This draft contains many 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 placeholder values for the date of publication of this draft. Please apply the following replacement:

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/.

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 September 9, 2020.

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

This document defines three YANG 1.1 [RFC7950] modules: the first defines a grouping for configuring a generic TCP client, the second defines a grouping for configuring a generic TCP server, and the third defines a grouping common to the TCP clients and TCP servers.

It is intended that these groupings will be used either standalone, for TCP-based protocols, as part of a stack of protocol-specific configuration models. For instance, these groupings could help define the configuration module for SSH, TLS, or HTTP based applications.

2. Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

3. The TCP Common Model

3.1. 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.

3.2. Usage 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 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 at the highest protocol layer possible that is meaningful to the application, in order to maximize the depth of the aliveness check.

[[TODO: Further guidance on keep-alives is provided in draft-xyz-tsvwg-... ]]

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:

3.3. Tree Diagram

This section provides a tree diagram [RFC8340] for the "ietf-tcp-common" module.

module: ietf-tcp-common

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

3.4. 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>

3.5. YANG Module

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

<CODE BEGINS> file "ietf-tcp-common@2020-03-08.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>";

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

     Copyright (c) 2019 IETF Trust and the persons identified
     as authors of the code. All rights reserved.

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

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

     The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL',
     'SHALL NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED',
     'NOT RECOMMENDED', 'MAY', and 'OPTIONAL' in this document
     are to be interpreted as described in BCP 14 (RFC 2119)
     (RFC 8174) when, and only when, they appear in all
     capitals, as shown here.";

  revision 2020-03-08 {
    description
      "Initial version";
    reference
      "RFC XXXX: YANG Groupings for TCP Clients and TCP Servers";
  }

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

  // Groupings

  grouping tcp-common-grouping {
    description
      "A reusable grouping for configuring TCP parameters common
       to TCP connections as well as the operating system as a
       whole.";
    container keepalives {
      if-feature "keepalives-supported";
      presence "Indicates that keepalives are enabled.";
      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


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

/*
  The following is for a future bis...
  This comment is here now so as support discussion with TCPM.
  This comment will be removed before publication.

  Should future system-level parameters be defined as a 
  grouping or a container?

  grouping tcp-system-grouping {
    description
      "A reusable grouping for configuring TCP parameters common
       to the operating system as a whole.";

    // currently just a placeholder
  }
*/

}

<CODE ENDS>

4. The TCP Client Model

4.1. Tree Diagram

This section provides a tree diagram [RFC8340] for the "ietf-tcp-client" module.

module: ietf-tcp-client

  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}?
    +-- keepalives! {keepalives-supported}?
       +-- idle-time         uint16
       +-- max-probes        uint16
       +-- probe-interval    uint16

4.2. Example Usage

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

<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>

4.3. YANG Module

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

<CODE BEGINS> file "ietf-tcp-client@2020-03-08.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-tcp-common {
    prefix tcpcmn;
    reference
      "RFC XXXX: 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) 2019 IETF Trust and the persons identified
     as authors of the code. All rights reserved.

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

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

     The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL',
     'SHALL NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED',
     'NOT RECOMMENDED', 'MAY', and 'OPTIONAL' in this document
     are to be interpreted as described in BCP 14 (RFC 2119)
     (RFC 8174) when, and only when, they appear in all
     capitals, as shown here.";

  revision 2020-03-08 {
    description
      "Initial version";
    reference
      "RFC XXXX: YANG Groupings for TCP Clients and TCP Servers";
  }

  // Features

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

  feature tcp-client-keepalives {
    description
      "Per socket TCP keepalive parameters are configurable for
       TCP clients on the server implementing this feature.";
  }

  // Groupings

  grouping tcp-client-grouping {
    description
      "A reusable grouping for configuring a TCP client.
      
      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
         to the remote peer.  The port number '0', which is the
         default value, indicates that any available local port
         number may be used.";
    }
    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>

5. The TCP Server Model

5.1. Tree Diagram

This section provides a tree diagram [RFC8340] for the "ietf-tcp-server" module.

module: ietf-tcp-server

  grouping tcp-server-grouping
    +-- local-address    inet:ip-address
    +-- local-port?      inet:port-number
    +-- keepalives! {keepalives-supported}?
       +-- idle-time         uint16
       +-- max-probes        uint16
       +-- probe-interval    uint16

5.2. 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>

5.3. YANG Module

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

<CODE BEGINS> file "ietf-tcp-server@2020-03-08.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 XXXX: 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) 2019 IETF Trust and the persons identified
     as authors of the code. All rights reserved.

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

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

     The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL',
     'SHALL NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED',
     'NOT RECOMMENDED', 'MAY', and 'OPTIONAL' in this document
     are to be interpreted as described in BCP 14 (RFC 2119)
     (RFC 8174) when, and only when, they appear in all
     capitals, as shown here.";

  revision 2020-03-08 {
    description
      "Initial version";
    reference
      "RFC XXXX: 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
         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>

6. Security Considerations

The YANG modules defined in this document 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, TCP) 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 modules defined in this document only define groupings, these considerations are primarily for the designers of other modules that use these groupings.

There are a number of data nodes defined in the YANG modules that are writable/creatable/deletable (i.e., config true, which is the default). These data nodes may be considered sensitive or vulnerable in some network environments. Write operations (e.g., edit-config) to these data nodes without proper protection can have a negative effect on network operations. These are the subtrees and data nodes and their sensitivity/vulnerability:

None of the writable/creatable/deletable data nodes in the YANG modules defined in this document are considered more sensitive or vulnerable then standard configuration.

Some of the readable data nodes in the YANG modules may be considered sensitive or vulnerable in some network environments. It is thus important to control read access (e.g., via get, get-config, or notification) to these data nodes. These are the subtrees and data nodes and their sensitivity/vulnerability:

None of the readable data nodes in the YANG modules defined in this document are considered more sensitive or vulnerable then standard configuration.

This document does not define any RPC actions and hence this section does not consider the security of RPCs.

7. IANA Considerations

7.1. 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-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.

7.2. 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 XXXX

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

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

8. References

8.1. 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.
[RFC6020] Bjorklund, M., "YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)", RFC 6020, DOI 10.17487/RFC6020, October 2010.
[RFC6991] Schoenwaelder, J., "Common YANG Data Types", RFC 6991, DOI 10.17487/RFC6991, July 2013.
[RFC7950] Bjorklund, M., "The YANG 1.1 Data Modeling Language", RFC 7950, DOI 10.17487/RFC7950, August 2016.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017.
[RFC8341] Bierman, A. and M. Bjorklund, "Network Configuration Access Control Model", STD 91, RFC 8341, DOI 10.17487/RFC8341, March 2018.

8.2. Informative References

[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, DOI 10.17487/RFC3688, January 2004.
[RFC6241] Enns, R., Bjorklund, M., Schoenwaelder, J. and A. Bierman, "Network Configuration Protocol (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011.
[RFC8040] Bierman, A., Bjorklund, M. and K. Watsen, "RESTCONF Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017.
[RFC8340] Bjorklund, M. and L. Berger, "YANG Tree Diagrams", BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018.

Appendix A. Change Log

A.1. 00 to 01

A.2. 01 to 02

A.3. 02 to 03

A.4. 03 to 04

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