A YANG Model for Transmission Control
Protocol (TCP) Configuration and StateHochschule Esslingen -
University of Applied SciencesKanalstr. 3373728EsslingenGermanymichael.scharf@hs-esslingen.deKloud Servicesmjethanandani@gmail.comSamsungvmurgai@gmail.com
Transport
TCPMYANGThis document specifies a minimal YANG model for TCP on
devices that are configured and managed 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).The Transmission Control
Protocol (TCP) 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 and managed
via network management protocols such as
NETCONF or RESTCONF.This document specifies a minimal YANG
1.1 model for configuring and managing TCP on network
elements that support YANG, a TCP connection table,
a TCP listener table containing
information about a particular TCP listener, and an augmentation
of the YANG Data Model for Key
Chains to support authentication. The YANG module specified
in this document is compliant with
Network Management Datastore Architecture (NMDA).The YANG module has a narrow scope and focuses on a subset of
fundamental TCP functions and basic statistics. It defines a
container for a list of TCP connections that includes definitions from
YANG Groupings
for TCP Clients and TCP Servers. The model adheres to
the recommendation in BGP/MPLS IP Virtual
Private Networks. Therefore it allows enabling of TCP-AO, 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.This specification does not deprecate 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. The YANG module also omits some
selected parameters included in TCP MIB, most notably Retransmission
Timeout (RTO) configuration and a maximum connection limit. This is a
conscious decision as these parameters hardly matter in a
state-of-the-art TCP implementation. It would also be possible 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. 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), Distributed
Denial-of-Service Open Thread Signaling (DOTS) Data Channel
Specification,
I2NSF Capability
YANG Data Model, or
I2NSF Network
Security Function-Facing Interface YANG 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) and A YANG Data
Model for Dual-Stack Lite (DS-Lite).TCP-AO and TCP MD5 configuration for Layer 3 VPNs is modeled in
A Layer 3 VPN Network YANG
Model. This model assumes that TCP-AO specific parameters
are preconfigured in addition to the keychain parameters.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.2022-08-31 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:System-wide 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 Transmission Control Protocol (TCP)
Specification 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 .Application preferences: Setting of TCP parameters
can also be part of application preferences, 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 implementations 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. 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. 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. 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 signature option.
The TCP MD5 signature option was obsoleted by TCP-AO in 2010. If current
implementations require TCP authentication, it is RECOMMENDED to use
TCP-AO.Similar to the TCP MIB, this document
also specifies basic statistics, a TCP connection list, and a TCP listener
list.Statistics: Counters for the number of active/passive opens,
sent and received TCP segments, errors, and possibly other detailed
debugging informationTCP connection list: 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.TCP listener list: A list containing information about
TCP listeners, i.e., applications willing to accept 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.This version of the module does not model details of
Multipath TCP. This could be addressed
in a later version of this document.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 an abridged tree diagram for the YANG
module defined in this document. Annotations used in the
diagram are defined in YANG Tree
Diagrams . A complete tree diagram can be found in the
Appendix.This YANG module references
The TCP Authentication Option,
Protection of BGP Sessions via the TCP MD5 Signature,
Transmission Control
Protocol (TCP) Specification,
and imports Common YANG Data Types
, The NETCONF Access Control
Model, and
YANG Groupings for TCP Clients and TCP Servers. file "ietf-tcp@2022-08-31.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";
}
import ietf-key-chain {
prefix key-chain;
reference
"RFC 8177: YANG Key Chain.";
}
organization
"IETF TCPM Working Group";
contact
"WG Web:
WG List:
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) 2022 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 "2022-08-31" {
description
"Initial Version";
reference
"RFC XXXX, A YANG Model for Transmission Control Protocol (TCP)
Configuration and State.";
}
// Typedefs
typedef mss {
type uint16;
description
"Type definition for Maximum Segment Size.";
}
// Features
feature statistics {
description
"This implementation supports statistics reporting.";
}
feature authentication {
description
"This implementation supports authentication.";
}
// Identities
identity aes-128 {
base key-chain:crypto-algorithm;
description
"AES128 authentication algorithm.";
}
// TCP-AO Groupings
grouping ao {
leaf send-id {
type uint8 {
range "0..max";
}
description
"The SendID is inserted as the KeyID of the TCP-AO option
of outgoing segments. In a consistent configuration, the
SendID matches the RecvID at the other endpoint.";
reference
"RFC 5925: The TCP Authentication Option, Section 3.1.";
}
leaf recv-id {
type uint8 {
range "0..max";
}
description
"The RecvID is matched against the TCP-AO KeyID of incoming
segments. In a consistent configuration, the RecvID matches
the SendID at the other endpoint.";
reference
"RFC 5925: The TCP Authentication Option, Section 3.1.";
}
leaf include-tcp-options {
type boolean;
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;
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.";
}
leaf r-next-key-id {
type uint8;
config false;
description
"A field indicating the Master Key Tuple (MKT) that is ready
at the sender to be used to authenticate received segments,
i.e., the desired 'receive next' key ID.";
reference
"RFC 5925: The TCP Authentication Option.";
}
description
"Authentication Option (AO) for TCP.";
reference
"RFC 5925: The TCP Authentication Option.";
}
// 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.";
}
leaf mss {
type mss;
description
"Maximum Segment Size (MSS) desired on this connection.
Note, the 'effective send MSS' can be smaller than
what is configured here.";
reference
"RFC 9293: Transmission Control Protocol (TCP)
Specification.";
}
leaf pmtud {
type boolean;
default false;
description
"Turns Path Maximum Transmission Unit Discovery (PMTUD)
on (true) or off (false).";
reference
"RFC 9293: Transmission Control Protocol (TCP)
Specification.";
}
uses tcpcmn:tcp-common-grouping;
leaf state {
type enumeration {
enum closed {
value 1;
description
"Connection is closed. Connections in this state
may not appear in this list.";
}
enum listen {
value 2;
description
"Represents waiting for a connection request from any
remote TCP peer and port.";
}
enum syn-sent {
value 3;
description
"Represents waiting for a matching connection request
after having sent a connection request.";
}
enum syn-received {
value 4;
description
"Represents waiting for a confirming connection
request acknowledgment after having both received
and sent a connection request.";
}
enum established {
value 5;
description
"Represents an open connection, data received can be
delivered to the user. The normal state for the data
transfer phase of the connection.";
}
enum fin-wait-1 {
value 6;
description
"Represents waiting for a connection termination
request from the remote TCP peer, or an
acknowledgment of the connection termination request
previously sent.";
}
enum fin-wait-2 {
value 7;
description
"Represents waiting for a connection termination
request from the remote TCP peer.";
}
enum close-wait {
value 8;
description
"Represents waiting for a connection termination
request from the local user.";
}
enum last-ack {
value 9;
description
"Represents waiting for an acknowledgment of the
connection termination request previously sent to
the remote TCP peer (this termination request sent
to the remote TCP peer already included an
acknowledgment of the termination request sent from
the remote TCP peer)";
}
enum closing {
value 10;
description
"Represents waiting for a connection termination
request acknowledgment from the remote TCP peer.";
}
enum time-wait {
value 11;
description
"Represents waiting for enough time to pass to be
sure the remote TCP peer received the acknowledgment
of its connection termination request, and to avoid
new connections being impacted by delayed segments
from previous connections.";
}
}
config false;
description
"The state of this TCP connection.";
}
description
"List of TCP connections with their parameters.
The list is modeled as writeable even though only some of
the nodes are writeable, e.g. keepalive. Connections
that are created and match this list SHOULD apply the
writeable parameters. At the same time, implementations
may not allow creation of new TCP connections simply by
adding entries to the list. Furthermore, the behavior
upon removal is implementation-specific. Implementations
may not support closing or resetting a TCP connection
upon an operation that removes the entry from the list.
The operational state of this list SHOULD reflect
connections that have configured, but not created, and
connections that have been created. Connections in
CLOSED state are not reflected on this list.";
}
description
"A container of all TCP connections.";
}
list tcp-listeners {
key "type address port";
config false;
description
"A table containing information about a particular
TCP listener.";
leaf type {
type inet:ip-version;
description
"The address type of address. The value
should be unspecified (0) if connection initiations
to all local IP addresses are accepted.";
}
leaf address {
type union {
type inet:ip-address;
type string;
}
description
"The local IP address for this TCP connection.
The value of this node can be represented in three
possible ways, depending on the characteristics of the
listening application:
1. For an application willing to accept both IPv4 and
IPv6 datagrams, the value of this node must be
''h (a zero-length octet-string), with the value
of the corresponding 'type' object being
unspecified (0).
2. For an application willing to accept only IPv4 or
IPv6 datagrams, the value of this node must be
'0.0.0.0' or '::' respectively, with
'type' representing the appropriate address type.
3. For an application which is listening for data
destined only to a specific IP address, the value
of this node is the specific local address, with
'type' representing the appropriate address type.";
}
leaf port {
type inet:port-number;
description
"The local port number for this TCP connection.";
}
}
container statistics {
if-feature statistics;
config false;
leaf active-opens {
type yang:counter64;
description
"The number of times that TCP connections have made a
direct transition to the SYN-SENT state from the CLOSED
state.";
reference
"RFC 9293: Transmission Control Protocol (TCP)
Specification.";
}
leaf passive-opens {
type yang:counter64;
description
"The number of times TCP connections have made a direct
transition to the SYN-RCVD state from the LISTEN state.";
reference
"RFC 9293: Transmission Control Protocol (TCP)
Specification.";
}
leaf attempt-fails {
type yang:counter64;
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
"RFC 9293: Transmission Control Protocol (TCP)
Specification.";
}
leaf establish-resets {
type yang:counter64;
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
"RFC 9293: 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
"RFC 9293: Transmission Control Protocol (TCP)
Specification.";
}
leaf in-segments {
type yang:counter64;
description
"The total number of TCP segments received, including those
received in error. This count includes TCP segments
received on currently established connections.";
reference
"RFC 9293: Transmission Control Protocol (TCP)
Specification.";
}
leaf out-segments {
type yang:counter64;
description
"The total number of TCP segments sent, including those on
current connections but excluding those containing only
retransmitted octets.";
reference
"RFC 9293: Transmission Control Protocol (TCP)
Specification.";
}
leaf retransmitted-segments {
type yang:counter64;
description
"The total number of TCP segments retransmitted; that is,
the number of TCP segments transmitted containing one or
more previously transmitted octets.";
reference
"RFC 9293: Transmission Control Protocol (TCP)
Specification.";
}
leaf in-errors {
type yang:counter64;
description
"The total number of TCP segments received in error
(e.g., bad TCP checksums).";
reference
"RFC 9293: Transmission Control Protocol (TCP)
Specification.";
}
leaf out-resets {
type yang:counter64;
description
"The number of TCP segments sent containing the RST flag.";
reference
"RFC 9293: Transmission Control Protocol (TCP)
Specification.";
}
leaf auth-failures {
if-feature authentication;
type yang:counter64;
description
"The number of times that authentication has failed either
with TCP-AO or MD5.";
}
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.";
}
}
augment "/key-chain:key-chains/key-chain:key-chain/key-chain:key" {
description
"Augmentation of the key-chain model to add TCP-AO and TCP-MD5
authentication.";
container authentication {
if-feature authentication;
leaf keychain {
type key-chain:key-chain-ref;
description
"Reference to the key chain that will be used by
this model. Applicable for TCP-AO and TCP-MD5
only";
reference
"RFC 8177: YANG Key Chain.";
}
choice authentication {
container ao {
presence "Presence container for all TCP-AO related" +
" configuration";
uses ao;
description
"Use TCP-AO to secure the connection.";
}
container md5 {
presence "Presence container for all MD5 related" +
" configuration";
description
"Use TCP-MD5 to secure the connection. As the TCP MD5
signature option is obsoleted by TCP-AO, it is
RECOMMENDED to use TCP-AO instead.";
reference
"RFC 2385: Protection of BGP Sessions via the TCP MD5
Signature.";
}
description
"Choice of TCP authentication.";
}
description
"Authentication definitions for TCP configuration.
This includes parameters such as how to secure the
connection, that can be part of either the client
or server.";
}
}
}
]]>This document registers an URI in the "ns" subregistry of the
IETF XML Registry . Following the format
in IETF XML Registry , the following
registration is requested:The following entry is requested to be added to the
"YANG Module Names" registry created by
YANG - A Data Modeling Language for
the Network Configuration Protocol (NETCONF):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 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:Common configuration included from
NETCONF Client
and Server Models . 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.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.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
or Section 2.1 of RFC 6952.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 (in alphabetical order): Mohamed Boucadair, Gorry Fairhurst,
Jeffrey Haas, and Tom Petch.This particular example demonstrates how both a particular
connection can be configured for keepalives.192.0.2.1192.0.2.21025221400true5510
]]>The following example demonstrates how to model a TCP-AO configuration for the example in TCP-AO Test Vectors. The
IP addresses and other parameters are taken from the test vectors.ao-config"An example for TCP-AO configuration."\
552017-01-01T00:00:00Z2017-02-01T00:00:00Z2016-12-31T23:59:55Z2017-02-01T00:00:05Ztcp:aes-128
testvectorao-config6587562017-01-01T00:00:00Z2017-02-01T00:00:00Z2016-12-31T23:59:55Z2017-02-01T00:00:05Ztcp:aes-128
testvectorao-config6587
]]>Here is the complete tree diagram for the TCP YANG model.