Hochschule Esslingen - University of Applied Sciences

Flandernstr. 101 73732 Esslingen Germany michael.scharf@hs-esslingen.de

Samsung

vmurgai@gmail.com

Kloud Services

mjethanandani@gmail.com

Transport TCPM YANG This document specifies a 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 some of the parameters that can be imported and used in TCP implementations or by other models that need to configure TCP parameters. The model includes definitions from YANG Groupings for TCP Client and TCP Servers (I-D.ietf-netconf-tcp-client-server). The model is NMDA (RFC 8342) compliant.

The Transmission Control Protocol (TCP) is used by many applications in the Internet, including control and management protocols. Therefore, TCP is implemented on network elements that can be configured via network management protocols such as NETCONF or RESTCONF. This document specifies a YANG 1.1 model for configuring TCP on network elements that support YANG data models, and is Network Management Datastore Architecture (NMDA) compliant. This module defines a container for TCP connection, and includes definitions from YANG Groupings for TCP Clients and TCP Servers. The model has a narrow scope and focuses on fundamental TCP functions and basic statistics. The model can be augmented or updated to address more advanced or implementation-specific TCP features in the future. Many protocol stacks on Internet 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 or RESTCONF. 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, which are outside the scope of this document. This specification is orthogonal to the Management Information Base (MIB) for the Transmission Control Protocol (TCP). The basic statistics defined in this document follow the model of the TCP MIB. An TCP Extended Statistics MIB is also available, but this document does not cover such extended statistics. It is possible also to translate a MIB into a YANG model, for instance using Translation of Structure of Management Information Version 2 (SMIv2) MIB Modules to YANG Modules. However, this approach is not used in this document, as such 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 models, such as YANG Data Model for Network Access Control Lists (ACLs) and Distributed Denial-of-Service Open Thread Signaling (DOTS) Data Channel Specification. 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) and A YANG Data Model for Dual-Stack Lite (DS-Lite) .

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 when, and only when, they appear in all capitals, as shown here.

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. 2021-07-06 with the actual date of the publication of this document.

TCP is implemented on many different system architectures. As a result, there are may different and often implementation-specific ways to configure parameters of the TCP protocol 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. A typical example 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 . 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. 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. A typical example is the support of TCP-AO. TCP-AO is increasingly supported on routers to secure routing protocols such as BGP. In that case, TCP-AO configuration is required on routers. The model includes the required TCP parameters for TCP-AO configuration. The key chain for TCP-AO can be modeled by the YANG Data Model for Key Chains. Given an installed base, the model also allows enabling of the legacy TCP MD5 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, 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 TCP connection table: Access to status information for all TCP connections This allows implementations of TCP MIB 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.

The YANG model defined in this document includes definitions from the YANG Groupings for TCP Clients and TCP Servers. 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 .

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

file "ietf-tcp@2021-07-06.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"; } import ietf-inet-types { prefix "inet"; } organization "IETF TCPM Working Group"; contact "WG Web: WG List: Authors: Michael Scharf (michael.scharf at hs-esslingen dot de) Vishal Murgai (vmurgai at gmail dot com) Mahesh Jethanandani (mjethanandani at gmail dot com)"; description "This module focuses on fundamental and standard TCP functions that widely implemented. The model can be augmented to address more advanced or implementation specific TCP features. Copyright (c) 2020 IETF Trust and the persons identified as authors of the code. All rights reserved. Redistribution and use in source and binary forms, with or without modification, is permitted pursuant to, and subject to the license terms contained in, the Simplified BSD License set forth in Section 4.c of the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info). This version of this YANG module is part of RFC 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 "2021-07-06" { description "Initial Version"; reference "RFC XXXX, 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..255"; } 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 at the other endpoint."; reference "RFC 5925: The TCP Authentication Option."; } leaf recv-id { type uint8 { range "0..255"; } 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."; } leaf include-tcp-options { type boolean; must "../enable-ao = 'true'"; default true; description "Include TCP options in MAC calculation."; } leaf accept-key-mismatch { type boolean; must "../enable-ao = 'true'"; description "Accept TCP segments with a Master Key Tuple (MKT) that is not configured."; } 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."; reference "RFC 2385: Protection of BGP Sessions via the TCP MD5 Signature."; leaf enable-md5 { type boolean; default "false"; description "Enable support of MD5 to authenticate a TCP session."; } } // 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."; } 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 how to secure the TCP connection."; } 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 modelled 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 reseting 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."; } 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."; } 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."; } 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."; } leaf currently-established { type yang:gauge32; description "The number of TCP connections for which the current state is either ESTABLISHED or CLOSE-WAIT."; } 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."; } 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."; } 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."; } leaf in-errors { type yang:counter32; description "The total number of segments received in error (e.g., bad TCP checksums)."; } leaf out-resets { type yang:counter32; description "The number of TCP segments sent containing the RST flag."; } action reset { 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."; } } } ]]>

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

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

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 or RESTCONF . 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 . The lowest RESTCONF layer is HTTPS, and the mandatory-to-implement secure transport is TLS . The Network Configuration Access Control Model (NACM) 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: TODO 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.

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

Changes compared to draft-scharf-tcpm-yang-tcp-04 Removed congestion control Removed global stack parameters Changes compared to draft-scharf-tcpm-yang-tcp-03 Updated TCP-AO grouping Added congestion control Changes compared to draft-scharf-tcpm-yang-tcp-02 Initial proposal of a YANG model including base configuration parameters, TCP-AO configuration, and a connection list Editorial bugfixes and outdated references reported by Mohamed Boucadair Additional co-author Mahesh Jethanandani Changes compared to draft-scharf-tcpm-yang-tcp-01 Alignment with Removing backward-compatibility to the TCP MIB Additional co-author Vishal Murgai Changes compared to draft-scharf-tcpm-yang-tcp-00 Editorial improvements

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

192.168.1.1 192.168.1.2 1025 80 5 5 10 ]]>

The following example demonstrates how to model a TCP-AO configuration for the example in TCP-AO Test Vectors, Section 5.1.1.

192.168.1.1 192.168.1.2 1025 80 true ao-config "An example for TCP-AO configuration."\ 61 hmac-sha-1 01:23:a5:93:b9:db:70:62:9b:be:2c:a6:77:cd:fd:ea:\ 6f:e0:ac:ad ]]>

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