TCPM                                                           M. Scharf
Internet-Draft                                      Hochschule Esslingen
Intended status: Standards Track                         M. Jethanandani
Expires: 2 July 2022                                      Kloud Services
                                                               V. Murgai
                                                                 Samsung
                                                        29 December 2021


   A YANG Model for Transmission Control Protocol (TCP) Configuration
                      draft-ietf-tcpm-yang-tcp-05

Abstract

   This document specifies a minimal YANG model for TCP on devices that
   are configured by network management protocols.  The YANG model
   defines a container for all TCP connections and groupings of
   authentication parameters that can be imported and used in TCP
   implementations or by other models that need to configure TCP
   parameters.  The model also includes basic TCP statistics.  The model
   is compliant with Network Management Datastore Architecture (NMDA)
   (RFC 8342).

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 2 July 2022.

Copyright Notice

   Copyright (c) 2021 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.



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   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Note to RFC Editor  . . . . . . . . . . . . . . . . . . .   4
   3.  YANG Module Overview  . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Scope . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  Model Design  . . . . . . . . . . . . . . . . . . . . . .   6
     3.3.  Tree Diagram  . . . . . . . . . . . . . . . . . . . . . .   6
   4.  TCP YANG Model  . . . . . . . . . . . . . . . . . . . . . . .   6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
     5.1.  The IETF XML Registry . . . . . . . . . . . . . . . . . .  14
     5.2.  The YANG Module Names Registry  . . . . . . . . . . . . .  15
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  16
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  16
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  18
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .  20
   Appendix B.  Examples . . . . . . . . . . . . . . . . . . . . . .  20
     B.1.  Keepalive Configuration . . . . . . . . . . . . . . . . .  20
     B.2.  TCP-AO Configuration  . . . . . . . . . . . . . . . . . .  21
   Appendix C.  Complete Tree Diagram  . . . . . . . . . . . . . . .  22
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  23

1.  Introduction

   The Transmission Control Protocol (TCP) [I-D.ietf-tcpm-rfc793bis] is
   used by many applications in the Internet, including control and
   management protocols.  As such, TCP is implemented on network
   elements that can be configured via network management protocols such
   as NETCONF [RFC6241] or RESTCONF [RFC8040].

   This document specifies a minimal YANG 1.1 [RFC7950] model for
   configuring TCP on network elements that support YANG.  This YANG
   module is compliant with Network Management Datastore Architecture
   (NMDA) [RFC8342].

   The YANG module has a narrow scope and focuses on a subset of
   fundamental TCP functions and basic statistics.  It defines a
   container for TCP connection that includes definitions from YANG
   Groupings for TCP Clients and TCP Servers
   [I-D.ietf-netconf-tcp-client-server].  This model adheres to the



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   recommendation in BGP/MPLS IP Virtual Private Networks [RFC4364] as
   it allows enabling of TCP-AO [RFC5925], and accommodates the
   installed base that makes use of MD5.  The module can be augmented or
   updated to address more advanced or implementation-specific TCP
   features in the future.

   Many protocol stacks on IP hosts use other methods to configure TCP,
   such as operating system configuration or policies.  Many TCP/IP
   stacks cannot be configured by network management protocols such as
   NETCONF [RFC6241] or RESTCONF [RFC8040].  Moreover, many existing
   TCP/IP stacks do not use YANG data models.  Such TCP implementations
   often have other means to configure the parameters listed in this
   document.  Such other means are outside the scope of this document.

   This specification is orthogonal to the Management Information Base
   (MIB) for the Transmission Control Protocol (TCP) [RFC4022].  The
   basic statistics defined in this document follow the model of the TCP
   MIB.  An TCP Extended Statistics MIB [RFC4898] is also available, but
   this document does not cover such extended statistics.  The YANG
   module also omits some selected parameters included in TCP MIB, most
   notably the configured Retransmission Timeout (RTO) algorithm.  This
   is conscious decision as these parameters hardly matter in a state-
   of-the-art TCP implementation.  It would also be possible also to
   translate a MIB into a YANG module, for instance using Translation of
   Structure of Management Information Version 2 (SMIv2) MIB Modules to
   YANG Modules [RFC6643].  However, this approach is not used in this
   document, because a translated model would not be up-to-date.

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

   *  TCP header attributes are modeled in other security-related
      models, such as YANG Data Model for Network Access Control Lists
      (ACLs) [RFC8519], Distributed Denial-of-Service Open Thread
      Signaling (DOTS) Data Channel Specification [RFC8783], or I2NSF
      Capability YANG Data Model [I-D.ietf-i2nsf-capability-data-model].

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

   *  TCP-AO and TCP MD5 configuration for Layer 3 VPNs is modeled in A
      Layer 3 VPN Network YANG Model [I-D.ietf-opsawg-l3sm-l3nm].  This
      model assumes that TCP-AO specific parameters are preconfigured in
      addition to the keychain parameters.  This issue is further
      discussed below.




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2.  Requirements Language

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

2.1.  Note to RFC Editor

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

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

   2021-12-29 with the actual date of the publication of this document.

3.  YANG Module Overview

3.1.  Scope

   TCP is implemented on different system architectures.  As a result,
   there are many different and often implementation-specific ways to
   configure parameters of the TCP engine.  In addition, in many TCP/IP
   stacks configuration exists for different scopes:

   *  Global configuration: Many TCP implementations have configuration
      parameters that affect all TCP connections.  Typical examples
      include enabling or disabling optional protocol features.

   *  Interface configuration: It can be useful to use different TCP
      parameters on different interfaces, e.g., different device ports
      or IP interfaces.  In that case, TCP parameters can be part of the
      interface configuration.  Typical examples are the Maximum Segment
      Size (MSS) or configuration related to hardware offloading.

   *  Connection parameters: Many implementations have means to
      influence the behavior of each TCP connection, e.g., on the
      programming interface used by applications.  Typical examples are
      socket options in the socket API, such as disabling the Nagle
      algorithm by TCP_NODELAY.  If an application uses such an
      interface, it is possible that the configuration of the
      application or application protocol includes TCP-related
      parameters.  An example is the BGP YANG Model for Service Provider
      Networks [I-D.ietf-idr-bgp-model].




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   *  Policies: Setting of TCP parameters can also be part of system
      policies, templates, or profiles.  An example would be the
      preferences defined in An Abstract Application Layer Interface to
      Transport Services [I-D.ietf-taps-interface].

   As a result, there is no ground truth for setting certain TCP
   parameters, and traditionally different TCP implementation have used
   different modeling approaches.  For instance, one implementation may
   define a given configuration parameter globally, while another one
   uses per-interface settings, and both approaches work well for the
   corresponding use cases.  Also, different systems may use different
   default values.  In addition, TCP can be implemented in different
   ways and design choices by the protocol engine often affect
   configuration options.

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

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

   This in particular applies to the support of TCP-AO [RFC5925].  TCP
   Authentication Option (TCP-AO) is used on routers to secure routing
   protocols such as BGP.  In that case, a YANG model for TCP-AO
   configuration is required.  The model defined in this document
   includes the required parameters for TCP-AO configuration, such as
   the values of SendID and RecvID.  The keychain for TCP-AO can be
   modeled by the YANG Data Model for Key Chains [RFC8177].  The
   groupings defined in this document can be imported and used as part
   of such a preconfiguration.

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

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

   *  Statistics: Counters for the number of active/passive opens, sent
      and received segments, errors, and possibly other detailed
      debugging information







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   *  TCP connection table: Access to status information for all TCP
      connections.  Note, the connection table is modeled as a list that
      is read-writeable, even though a connection cannot be created by
      adding entries to the table.  Similarly, deletion of connections
      from this list is implementation-specific.

   This allows implementations of TCP MIB [RFC4022] to migrate to the
   YANG model defined in this memo.  Note that the TCP MIB does not
   include means to reset statistics, which are defined in this
   document.  This is not a major addition, as a reset can simply be
   implemented by storing offset values for the counters.

   This version of the module does not cover Multipath TCP [RFC8684].

3.2.  Model Design

   The YANG model defined in this document includes definitions from the
   YANG Groupings for TCP Clients and TCP Servers
   [I-D.ietf-netconf-tcp-client-server].  Similar to that model, this
   specification defines YANG groupings.  This allows reuse of these
   groupings in different YANG data models.  It is intended that these
   groupings will be used either standalone or for TCP-based protocols
   as part of a stack of protocol-specific configuration models.  An
   example could be the BGP YANG Model for Service Provider Networks
   [I-D.ietf-idr-bgp-model].

3.3.  Tree Diagram

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

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

4.  TCP YANG Model

   This YANG module references The TCP Authentication Option [RFC5925],
   Protection of BGP Sessions via the TCP MD5 Signature [RFC2385],
   Transmission Control Protocol (TCP) Specification
   [I-D.ietf-tcpm-rfc793bis], and imports Common YANG Data Types
   [RFC6991], The NETCONF Access Control Model [RFC8341], and YANG
   Groupings for TCP Clients and TCP Servers
   [I-D.ietf-netconf-tcp-client-server].



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   <CODE BEGINS> file "ietf-tcp@2021-12-29.yang"
   module ietf-tcp {
     yang-version "1.1";
     namespace "urn:ietf:params:xml:ns:yang:ietf-tcp";
     prefix "tcp";

     import ietf-yang-types {
       prefix "yang";
       reference
         "RFC 6991: Common YANG Data Types.";
     }
     import ietf-tcp-common {
       prefix "tcpcmn";
       reference
         "I-D.ietf-netconf-tcp-client-server: YANG Groupings for TCP
          Clients and TCP Servers.";
     }
     import ietf-inet-types {
       prefix "inet";
       reference
         "RFC 6991: Common YANG Data Types.";
     }
     import ietf-netconf-acm {
       prefix nacm;
       reference
         "RFC 8341: Network Configuration Access Control Model";
     }

     organization
       "IETF TCPM Working Group";

     contact
       "WG Web:   <https://datatracker.ietf.org/wg/tcpm/about>
        WG List:  <tcpm@ietf.org>

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

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

        Copyright (c) 2021 IETF Trust and the persons identified as
        authors of the code.  All rights reserved.

        Redistribution and use in source and binary forms, with or



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        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 "2021-12-29" {
       description
         "Initial Version";
       reference
         "RFC XXXX, YANG Model for Transmission Control Protocol (TCP)
                    Configuration.";
     }

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

     // TCP-AO Groupings

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

       leaf send-id {
         type uint8 {
           range "0..max";
         }
         must "../enable-ao = 'true'";
         description
           "The SendID is inserted as the KeyID of the TCP-AO option
            of outgoing segments. The SendID must match the RecvID



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            at the other endpoint.";
         reference
           "RFC 5925: The TCP Authentication Option, Section 3.1.";
       }

       leaf recv-id {
         type uint8 {
           range "0..max";
         }
         must "../enable-ao = 'true'";
         description
           "The RecvID is matched against the TCP-AO KeyID of incoming
            segments. The RecvID must match the SendID at the other
            endpoint.";
         reference
           "RFC 5925: The TCP Authentication Option, Section 3.1.";
       }

       leaf include-tcp-options {
         type boolean;
         must "../enable-ao = 'true'";
         default true;
         description
           "Include TCP options in MAC calculation.";
         reference
           "RFC 5925: The TCP Authentication Option, Section 3.1.";
       }

       leaf accept-key-mismatch {
         type boolean;
         must "../enable-ao = 'true'";
         description
           "Accept TCP segments with a Master Key Tuple (MKT) that is
            not configured.";
         reference
           "RFC 5925: The TCP Authentication Option, Section 7.3.";
       }
       description
         "Authentication Option (AO) for TCP.";
       reference
         "RFC 5925: The TCP Authentication Option.";
     }

     // MD5 grouping

     grouping md5 {
       description
         "Grouping for use in authenticating TCP sessions using MD5.";



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       reference
         "RFC 2385: Protection of BGP Sessions via the TCP MD5
          Signature.";

       leaf enable-md5 {
         type boolean;
         default "false";
         description
           "Enables, when set to true, support of MD5 to authenticate a
           TCP session. As the TCP MD5 signature option is obsoleted by
           TCP-AO, it is strongly RECOMMENDED to use TCP-AO instead.";
       }
     }

     // TCP configuration

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

       description
         "TCP container.";

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

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

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

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

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



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           }

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

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

               case md5 {
                 uses md5;
                 description
                   "Use TCP-MD5 to secure the connection.";
               }
               description
                 "Choice of TCP authentication.";
             }
             description
               "Common definitions of TCP configuration. This includes
                parameters such as how to secure the connection,
                that can be part of either the client or server.";
           }
           description
             "List of TCP connections with their parameters. The list
              is modeled as writeable, but implementations may not
              allow creation of new TCP connections by adding entries to
              the list. Furthermore, the behavior upon removal is
              implementation-specific. Implementations may support
              closing or resetting a TCP connection upon an operation
              that removes the entry from the list.";
         }
         description
           "A container of all TCP connections.";
       }

       container statistics {
         if-feature statistics;
         config false;

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



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           reference
             "I-D.ietf-tcpm-rfc793bis: Transmission Control Protocol
              (TCP) Specification.";
         }

         leaf passive-opens {
           type yang:counter32;
           description
             "The number of times TCP connections have made a direct
              transition to the SYN-RCVD state from the LISTEN state.";
           reference
             "I-D.ietf-tcpm-rfc793bis: Transmission Control Protocol
              (TCP) Specification.";
         }

         leaf attempt-fails {
           type yang:counter32;
           description
             "The number of times that TCP connections have made a
              direct transition to the CLOSED state from either the
              SYN-SENT state or the SYN-RCVD state, plus the number of
              times that TCP connections have made a direct transition
              to the LISTEN state from the SYN-RCVD state.";
           reference
             "I-D.ietf-tcpm-rfc793bis: Transmission Control Protocol
              (TCP) Specification.";
         }

         leaf establish-resets {
           type yang:counter32;
           description
             "The number of times that TCP connections have made a
              direct transition to the CLOSED state from either the
              ESTABLISHED state or the CLOSE-WAIT state.";
           reference
             "I-D.ietf-tcpm-rfc793bis: Transmission Control Protocol
              (TCP) Specification.";
         }

         leaf currently-established {
           type yang:gauge32;
           description
             "The number of TCP connections for which the current state
              is either ESTABLISHED or CLOSE-WAIT.";
           reference
             "I-D.ietf-tcpm-rfc793bis: Transmission Control Protocol
              (TCP) Specification.";
         }



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         leaf in-segments {
           type yang:counter64;
           description
             "The total number of segments received, including those
              received in error.  This count includes segments received
              on currently established connections.";
           reference
             "I-D.ietf-tcpm-rfc793bis: Transmission Control Protocol
              (TCP) Specification.";
         }

         leaf out-segments {
           type yang:counter64;
           description
             "The total number of segments sent, including those on
              current connections but excluding those containing only
              retransmitted octets.";
           reference
             "I-D.ietf-tcpm-rfc793bis: Transmission Control Protocol
              (TCP) Specification.";
         }

         leaf retransmitted-segments {
           type yang:counter32;
           description
             "The total number of segments retransmitted; that is, the
              number of TCP segments transmitted containing one or more
              previously transmitted octets.";
           reference
             "I-D.ietf-tcpm-rfc793bis: Transmission Control Protocol
              (TCP) Specification.";
         }

         leaf in-errors {
           type yang:counter32;
           description
             "The total number of segments received in error (e.g., bad
              TCP checksums).";
           reference
             "I-D.ietf-tcpm-rfc793bis: Transmission Control Protocol
              (TCP) Specification.";
         }

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



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             "I-D.ietf-tcpm-rfc793bis: Transmission Control Protocol
              (TCP) Specification.";
         }

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

5.  IANA Considerations

5.1.  The IETF XML Registry

   This document registers an URI in the "ns" subregistry of the IETF
   XML Registry [RFC3688].  Following the format in IETF XML Registry
   [RFC3688], the following registration is requested:

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









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5.2.  The YANG Module Names Registry

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

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

6.  Security Considerations

   The YANG module specified in this document defines a schema for data
   that is designed to be accessed via network management protocols such
   as NETCONF [RFC6241] or RESTCONF [RFC8040].  The lowest NETCONF layer
   is the secure transport layer, and the mandatory-to-implement secure
   transport is Secure Shell (SSH) described in Using the NETCONF
   protocol over SSH [RFC6242].  The lowest RESTCONF layer is HTTPS, and
   the mandatory-to-implement secure transport is TLS [RFC8446].

   The Network Configuration Access Control Model (NACM) [RFC8341]
   provides the means to restrict access for particular NETCONF or
   RESTCONF users to a preconfigured subset of all available NETCONF or
   RESTCONF protocol operations and content.

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

   *  Common configuration included from NETCONF Client and Server
      Models [I-D.ietf-netconf-tcp-client-server].  Unrestricted access
      to all the nodes, e.g., keepalive idle-timer, can cause
      connections to fail or to timeout prematurely.

   *  Authentication configuration.  Unrestricted access to the nodes
      under authentication configuration can prevent the use of
      authenticated communication and cause connection setups to fail.
      This can result in massive security vulnerabilities and service
      disruption for the traffic requiring authentication.






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

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

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

   Some of the RPC operations in this YANG module may be considered
   sensitive or vulnerable in some network environments.  It is thus
   important to control access to these operations.  These are the
   operations and their sensitivity/vulnerability:

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

   The module specified in this document supports MD5 to basically
   accommodate the installed BGP base.  MD5 suffers from the security
   weaknesses discussed in Section 2 of RFC 6151 [RFC6151] or
   Section 2.1 of RFC 6952 [RFC6952].

7.  References

7.1.  Normative References

   [I-D.ietf-netconf-tcp-client-server]
              Watsen, K. and M. Scharf, "YANG Groupings for TCP Clients
              and TCP Servers", Work in Progress, Internet-Draft, draft-
              ietf-netconf-tcp-client-server-11, 14 December 2021,
              <https://www.ietf.org/archive/id/draft-ietf-netconf-tcp-
              client-server-11.txt>.

   [I-D.ietf-tcpm-rfc793bis]
              Eddy, W. M., "Transmission Control Protocol (TCP)
              Specification", Work in Progress, Internet-Draft, draft-
              ietf-tcpm-rfc793bis-25, 7 September 2021,
              <https://www.ietf.org/archive/id/draft-ietf-tcpm-
              rfc793bis-25.txt>.






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

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

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

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

   [RFC6020]  Bjorklund, M., Ed., "YANG - A Data Modeling Language for
              the Network Configuration Protocol (NETCONF)", RFC 6020,
              DOI 10.17487/RFC6020, October 2010,
              <https://www.rfc-editor.org/info/rfc6020>.

   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
              <https://www.rfc-editor.org/info/rfc6241>.

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

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

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

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

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





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

   [RFC8340]  Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
              BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,
              <https://www.rfc-editor.org/info/rfc8340>.

   [RFC8341]  Bierman, A. and M. Bjorklund, "Network Configuration
              Access Control Model", STD 91, RFC 8341,
              DOI 10.17487/RFC8341, March 2018,
              <https://www.rfc-editor.org/info/rfc8341>.

   [RFC8342]  Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
              and R. Wilton, "Network Management Datastore Architecture
              (NMDA)", RFC 8342, DOI 10.17487/RFC8342, March 2018,
              <https://www.rfc-editor.org/info/rfc8342>.

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

7.2.  Informative References

   [I-D.ietf-i2nsf-capability-data-model]
              Hares, S., Jeong, J. (., Kim, J. (., Moskowitz, R., and Q.
              Lin, "I2NSF Capability YANG Data Model", Work in Progress,
              Internet-Draft, draft-ietf-i2nsf-capability-data-model-21,
              13 November 2021, <https://www.ietf.org/archive/id/draft-
              ietf-i2nsf-capability-data-model-21.txt>.

   [I-D.ietf-idr-bgp-model]
              Jethanandani, M., Patel, K., Hares, S., and J. Haas, "BGP
              YANG Model for Service Provider Networks", Work in
              Progress, Internet-Draft, draft-ietf-idr-bgp-model-12, 25
              October 2021, <https://www.ietf.org/archive/id/draft-ietf-
              idr-bgp-model-12.txt>.

   [I-D.ietf-opsawg-l3sm-l3nm]
              Barguil, S., Dios, O. G. D., Boucadair, M., Munoz, L. A.,
              and A. Aguado, "A Layer 3 VPN Network YANG Model", Work in
              Progress, Internet-Draft, draft-ietf-opsawg-l3sm-l3nm-18,
              8 October 2021, <https://www.ietf.org/archive/id/draft-
              ietf-opsawg-l3sm-l3nm-18.txt>.






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   [I-D.ietf-taps-interface]
              Trammell, B., Welzl, M., Enghardt, T., Fairhurst, G.,
              Kuehlewind, M., Perkins, C., Tiesel, P. S., Wood, C. A.,
              Pauly, T., and K. Rose, "An Abstract Application Layer
              Interface to Transport Services", Work in Progress,
              Internet-Draft, draft-ietf-taps-interface-13, 12 July
              2021, <https://www.ietf.org/archive/id/draft-ietf-taps-
              interface-13.txt>.

   [I-D.ietf-tcpm-ao-test-vectors]
              Touch, J. and J. Kuusisaari, "TCP-AO Test Vectors", Work
              in Progress, Internet-Draft, draft-ietf-tcpm-ao-test-
              vectors-04, 19 December 2021,
              <https://www.ietf.org/archive/id/draft-ietf-tcpm-ao-test-
              vectors-04.txt>.

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

   [RFC4364]  Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
              Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
              2006, <https://www.rfc-editor.org/info/rfc4364>.

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

   [RFC6151]  Turner, S. and L. Chen, "Updated Security Considerations
              for the MD5 Message-Digest and the HMAC-MD5 Algorithms",
              RFC 6151, DOI 10.17487/RFC6151, March 2011,
              <https://www.rfc-editor.org/info/rfc6151>.

   [RFC6643]  Schoenwaelder, J., "Translation of Structure of Management
              Information Version 2 (SMIv2) MIB Modules to YANG
              Modules", RFC 6643, DOI 10.17487/RFC6643, July 2012,
              <https://www.rfc-editor.org/info/rfc6643>.

   [RFC6952]  Jethanandani, M., Patel, K., and L. Zheng, "Analysis of
              BGP, LDP, PCEP, and MSDP Issues According to the Keying
              and Authentication for Routing Protocols (KARP) Design
              Guide", RFC 6952, DOI 10.17487/RFC6952, May 2013,
              <https://www.rfc-editor.org/info/rfc6952>.







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

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

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

   [RFC8684]  Ford, A., Raiciu, C., Handley, M., Bonaventure, O., and C.
              Paasch, "TCP Extensions for Multipath Operation with
              Multiple Addresses", RFC 8684, DOI 10.17487/RFC8684, March
              2020, <https://www.rfc-editor.org/info/rfc8684>.

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

Appendix A.  Acknowledgements

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

   The following persons have contributed to this document by reviews:
   Mohamed Boucadair, and Tom Petch.

Appendix B.  Examples

B.1.  Keepalive Configuration

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











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   [note: '\' line wrapping for formatting only]
   [See RFC 8792: Handling Long Lines in Content of
    Internet-Drafts and RFCs]

   <?xml version="1.0" encoding="UTF-8"?>
   <!--
   This example shows how TCP keepalive can be configured for
   a given connection. An idle connection is dropped after
   idle-time + (max-probes * probe-interval).
   -->
   <tcp
       xmlns="urn:ietf:params:xml:ns:yang:ietf-tcp">
     <connections>
       <connection>
         <local-address>192.0.2.1</local-address>
         <remote-address>192.0.2.2</remote-address>
         <local-port>1025</local-port>
         <remote-port>80</remote-port>
         <common>
           <keepalives>
             <idle-time>5</idle-time>
             <max-probes>5</max-probes>
             <probe-interval>10</probe-interval>
           </keepalives>
         </common>
       </connection>
     </connections>
   </tcp>

B.2.  TCP-AO Configuration

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

















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[note: '\' line wrapping for formatting only]
[See RFC 8792: Handling Long Lines in Content of
 Internet-Drafts and RFCs]

<?xml version="1.0" encoding="UTF-8"?>
<!--
This example sets TCP-AO configuration parameters as
demonstrated by examples in draft-touch-tcpm-ao-test-vectors.
-->

<tcp
    xmlns="urn:ietf:params:xml:ns:yang:ietf-tcp">
  <connections>
    <connection>
      <local-address>2001:db8::1</local-address>
      <remote-address>2001:db8::2</remote-address>
      <local-port>1025</local-port>
      <remote-port>80</remote-port>
      <common>
        <enable-ao>true</enable-ao>
      </common>
    </connection>
  </connections>
</tcp>

<key-chains
    xmlns="urn:ietf:params:xml:ns:yang:ietf-key-chain">
  <key-chain>
    <name>ao-config</name>
    <description>"An example for TCP-AO configuration."</description>\

    <key>
      <key-id>61</key-id>
      <crypto-algorithm>hmac-sha-1</crypto-algorithm>
      <key-string>
        <hexadecimal-string>01:23:a5:93:b9:db:70:62:9b:be:2c:a6:77:cd:fd:ea:\
6f:e0:ac:ad</hexadecimal-string>
      </key-string>
    </key>
  </key-chain>
</key-chains>

Appendix C.  Complete Tree Diagram

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






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   module: ietf-tcp
     +--rw tcp!
        +--rw connections
        |  +--rw connection*
        |          [local-address remote-address local-port remote-port]
        |     +--rw local-address     inet:ip-address
        |     +--rw remote-address    inet:ip-address
        |     +--rw local-port        inet:port-number
        |     +--rw remote-port       inet:port-number
        |     +--rw common
        |        +--rw keepalives!
        |        |  +--rw idle-time         uint16
        |        |  +--rw max-probes        uint16
        |        |  +--rw probe-interval    uint16
        |        +--rw (authentication)?
        |           +--:(ao)
        |           |  +--rw enable-ao?             boolean
        |           |  +--rw send-id?               uint8
        |           |  +--rw recv-id?               uint8
        |           |  +--rw include-tcp-options?   boolean
        |           |  +--rw accept-key-mismatch?   boolean
        |           +--:(md5)
        |              +--rw enable-md5?            boolean
        +--ro statistics {statistics}?
           +--ro active-opens?             yang:counter32
           +--ro passive-opens?            yang:counter32
           +--ro attempt-fails?            yang:counter32
           +--ro establish-resets?         yang:counter32
           +--ro currently-established?    yang:gauge32
           +--ro in-segments?              yang:counter64
           +--ro out-segments?             yang:counter64
           +--ro retransmitted-segments?   yang:counter32
           +--ro in-errors?                yang:counter32
           +--ro out-resets?               yang:counter32
           +---x reset
              +---w input
              |  +---w reset-at?   yang:date-and-time
              +--ro output
                 +--ro reset-finished-at?   yang:date-and-time

Authors' Addresses

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




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   Email: michael.scharf@hs-esslingen.de


   Mahesh Jethanandani
   Kloud Services

   Email: mjethanandani@gmail.com


   Vishal Murgai
   Samsung

   Email: vmurgai@gmail.com






































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