| Internet-Draft | YANG Model for TCP | February 2022 |
| Scharf, et al. | Expires 7 August 2022 | [Page] |
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).¶
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 7 August 2022.¶
Copyright (c) 2022 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 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.¶
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 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:¶
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.¶
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.¶
2022-02-04 with the actual date of the publication of this document.¶
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:¶
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.¶
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].¶
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].¶
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}?
...
¶
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].¶
<CODE BEGINS> file "ietf-tcp@2022-02-04.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
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 "2022-02-04" {
description
"Initial Version";
reference
"RFC XXXX, A 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
"When set to true, TCP-Authentication Option (TCP-AO) is
enabled.";
}
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
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
"When set to true, TCP options are included 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, when set to true, 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.";
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
"Identifies the address that is used by the local
endpoint for the connection, and is one of the four
elements that form the connection identifier.";
}
leaf remote-address {
type inet:ip-address;
description
"Identifies the address that is used by the remote
endpoint for the connection, and is one of the four
elements that form the connection identifier.";
}
leaf local-port {
type inet:port-number;
description
"Identifies the local TCP port used for the connection,
and is one of the four elements that form the
connection identifier.";
}
leaf remote-port {
type inet:port-number;
description
"Identifies the remote TCP port used for the connection,
and is one of the four elements that form 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 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.";
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.";
}
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
"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>¶
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.¶
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 registration is requested:¶
name: ietf-tcp namespace: urn:ietf:params:xml:ns:yang:ietf-tcp prefix: tcp reference: RFC XXXX¶
The registration is not maintained by IANA.¶
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:¶
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:¶
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 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].¶
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.¶
This particular example demonstrates how both a particular connection can be configured for keepalives.¶
NOTE: '\' line wrapping per RFC 8792
<?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>
¶
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].¶
NOTE: '\' line wrapping per RFC 8792
<?xml version="1.0" encoding="UTF-8"?>
<!--
This example sets TCP-AO configuration parameters as
demonstrated by examples in draft-ietf-tcpm-ao-test-vectors.
-->
<tcp
xmlns="urn:ietf:params:xml:ns:yang:ietf-tcp">
<connections>
<connection>
<local-address>fd00::1</local-address>
<remote-address>fd00::2</remote-address>
<local-port>1025</local-port>
<remote-port>179</remote-port>
<common>
<enable-ao>true</enable-ao>
<send-id>61</send-id>
<recv-id>84</recv-id>
</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>
<keystring>testvector</keystring>
</key-string>
</key>
<key>
<key-id>84</key-id>
<crypto-algorithm>hmac-sha-1</crypto-algorithm>
<key-string>
<keystring>testvector</keystring>
</key-string>
</key>
</key-chain>
</key-chains>
¶
Here is the complete tree diagram for the TCP YANG model.¶
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
¶