YANG Groupings for TCP Clients and TCP Servers
draft-ietf-netconf-tcp-client-server-12
| Document | Type | Active Internet-Draft (netconf WG) | |
|---|---|---|---|
| Authors | Kent Watsen , Michael Scharf | ||
| Last updated | 2022-03-07 | ||
| Replaces | draft-kwatsen-netconf-tcp-client-server | ||
| Stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Proposed Standard | ||
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draft-ietf-netconf-tcp-client-server-12
NETCONF Working Group K. Watsen
Internet-Draft Watsen Networks
Intended status: Standards Track M. Scharf
Expires: 8 September 2022 Hochschule Esslingen
7 March 2022
YANG Groupings for TCP Clients and TCP Servers
draft-ietf-netconf-tcp-client-server-12
Abstract
This document defines three YANG 1.1 modules to support the
configuration of TCP clients and TCP servers. The modules include
basic parameters of a TCP connection relevant for client or server
applications, as well as client configuration required for traversing
proxies. The modules can be used either standalone or in conjunction
with configuration of other stack protocol layers.
Editorial Note (To be removed by RFC Editor)
This draft contains placeholder values that need to be replaced with
finalized values at the time of publication. This note summarizes
all of the substitutions that are needed. No other RFC Editor
instructions are specified elsewhere in this document.
Artwork in this document contains shorthand references to drafts in
progress. Please apply the following replacements:
* AAAA --> the assigned RFC value for draft-ietf-netconf-crypto-
types
* DDDD --> the assigned RFC value for this draft
Artwork in this document contains placeholder values for the date of
publication of this draft. Please apply the following replacement:
* 2022-03-07 --> the publication date of this draft
The following Appendix section is to be removed prior to publication:
* Appendix A. Change Log
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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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 8 September 2022.
Copyright Notice
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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Relation to other RFCs . . . . . . . . . . . . . . . . . 3
1.2. Specification Language . . . . . . . . . . . . . . . . . 5
1.3. Adherence to the NMDA . . . . . . . . . . . . . . . . . . 5
1.4. Conventions . . . . . . . . . . . . . . . . . . . . . . . 5
2. The "ietf-tcp-common" Module . . . . . . . . . . . . . . . . 6
2.1. Data Model Overview . . . . . . . . . . . . . . . . . . . 6
2.2. Example Usage . . . . . . . . . . . . . . . . . . . . . . 8
2.3. YANG Module . . . . . . . . . . . . . . . . . . . . . . . 8
3. The "ietf-tcp-client" Module . . . . . . . . . . . . . . . . 11
3.1. Data Model Overview . . . . . . . . . . . . . . . . . . . 11
3.2. Example Usage . . . . . . . . . . . . . . . . . . . . . . 13
3.3. YANG Module . . . . . . . . . . . . . . . . . . . . . . . 14
4. The "ietf-tcp-server" Module . . . . . . . . . . . . . . . . 21
4.1. Data Model Overview . . . . . . . . . . . . . . . . . . . 21
4.2. Example Usage . . . . . . . . . . . . . . . . . . . . . . 23
4.3. YANG Module . . . . . . . . . . . . . . . . . . . . . . . 23
5. Security Considerations . . . . . . . . . . . . . . . . . . . 26
5.1. The "ietf-tcp-common" YANG Module . . . . . . . . . . . . 26
5.2. The "ietf-tcp-client" YANG Module . . . . . . . . . . . . 26
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5.3. The "ietf-tcp-server" YANG Module . . . . . . . . . . . . 27
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28
6.1. The "IETF XML" Registry . . . . . . . . . . . . . . . . . 28
6.2. The "YANG Module Names" Registry . . . . . . . . . . . . 28
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 29
7.1. Normative References . . . . . . . . . . . . . . . . . . 29
7.2. Informative References . . . . . . . . . . . . . . . . . 29
Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 31
A.1. 00 to 01 . . . . . . . . . . . . . . . . . . . . . . . . 31
A.2. 01 to 02 . . . . . . . . . . . . . . . . . . . . . . . . 32
A.3. 02 to 03 . . . . . . . . . . . . . . . . . . . . . . . . 32
A.4. 03 to 04 . . . . . . . . . . . . . . . . . . . . . . . . 32
A.5. 04 to 05 . . . . . . . . . . . . . . . . . . . . . . . . 32
A.6. 05 to 06 . . . . . . . . . . . . . . . . . . . . . . . . 32
A.7. 06 to 07 . . . . . . . . . . . . . . . . . . . . . . . . 32
A.8. 07 to 08 . . . . . . . . . . . . . . . . . . . . . . . . 32
A.9. 08 to 09 . . . . . . . . . . . . . . . . . . . . . . . . 33
A.10. 09 to 10 . . . . . . . . . . . . . . . . . . . . . . . . 33
A.11. 10 to 11 . . . . . . . . . . . . . . . . . . . . . . . . 33
A.12. 11 to 12 . . . . . . . . . . . . . . . . . . . . . . . . 33
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 33
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 33
1. Introduction
This document defines three YANG 1.1 [RFC7950] modules to support the
configuration of TCP clients and TCP servers (TCP is defined in
[RFC0793]), either as standalone or in conjunction with configuration
of other stack protocol layers.
The modules focus on three different types of base TCP parameters
that matter for TCP-based applications: First, the modules cover
fundamental configuration of a TCP client or TCP server application,
such as addresses and port numbers. Second, a reusable grouping
enables modification of application-specific parameters for a TCP
connections, such as use of TCP keep-alives. And third, client
configuration for traversing proxies is included as well. In each
case, the modules have a very narrow scope and focus on a minimum set
of required parameters.
1.1. Relation to other RFCs
This document presents one or more YANG modules [RFC7950] that are
part of a collection of RFCs that work together to, ultimately,
enable the configuration of the clients and servers of both the
NETCONF [RFC6241] and RESTCONF [RFC8040] protocols.
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The modules have been defined in a modular fashion to enable their
use by other efforts, some of which are known to be in progress at
the time of this writing, with many more expected to be defined in
time.
The normative dependency relationship between the various RFCs in the
collection is presented in the below diagram. The labels in the
diagram represent the primary purpose provided by each RFC.
Hyperlinks to each RFC are provided below the diagram.
crypto-types
^ ^
/ \
/ \
truststore keystore
^ ^ ^ ^
| +---------+ | |
| | | |
| +------------+ |
tcp-client-server | / | |
^ ^ ssh-client-server | |
| | ^ tls-client-server
| | | ^ ^ http-client-server
| | | | | ^
| | | +-----+ +---------+ |
| | | | | |
| +-----------|--------|--------------+ | |
| | | | | |
+-----------+ | | | | |
| | | | | |
| | | | | |
netconf-client-server restconf-client-server
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+=======================+===========================================+
|Label in Diagram | Originating RFC |
+=======================+===========================================+
|crypto-types | [I-D.ietf-netconf-crypto-types] |
+-----------------------+-------------------------------------------+
|truststore | [I-D.ietf-netconf-trust-anchors] |
+-----------------------+-------------------------------------------+
|keystore | [I-D.ietf-netconf-keystore] |
+-----------------------+-------------------------------------------+
|tcp-client-server | [I-D.ietf-netconf-tcp-client-server] |
+-----------------------+-------------------------------------------+
|ssh-client-server | [I-D.ietf-netconf-ssh-client-server] |
+-----------------------+-------------------------------------------+
|tls-client-server | [I-D.ietf-netconf-tls-client-server] |
+-----------------------+-------------------------------------------+
|http-client-server | [I-D.ietf-netconf-http-client-server] |
+-----------------------+-------------------------------------------+
|netconf-client-server | [I-D.ietf-netconf-netconf-client-server] |
+-----------------------+-------------------------------------------+
|restconf-client-server | [I-D.ietf-netconf-restconf-client-server] |
+-----------------------+-------------------------------------------+
Table 1: Label to RFC Mapping
1.2. Specification 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.
1.3. Adherence to the NMDA
This document is compliant with the Network Management Datastore
Architecture (NMDA) [RFC8342]. It does not define any protocol
accessible nodes that are "config false".
1.4. Conventions
Various examples used in this document use a placeholder value for
binary data that has been base64 encoded (e.g., "BASE64VALUE=").
This placeholder value is used as real base64 encoded structures are
often many lines long and hence distracting to the example being
presented.
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2. The "ietf-tcp-common" Module
This section defines a YANG 1.1 module called "ietf-tcp-common". A
high-level overview of the module is provided in Section 2.1.
Examples illustrating the module's use are provided in Examples
(Section 2.2). The YANG module itself is defined in Section 2.3.
2.1. Data Model Overview
This section provides an overview of the "ietf-tcp-common" module in
terms of its features and groupings.
2.1.1. Model Scope
This document defines a common "grouping" statement for basic TCP
connection parameters that matter to applications. In some TCP
stacks, such parameters can also directly be set by an application
using system calls, such as the sockets API. The base YANG model in
this document focuses on modeling TCP keep-alives. This base model
can be extended as needed.
2.1.2. Features
The following diagram lists all the "feature" statements defined in
the "ietf-tcp-common" module:
Features:
+-- keepalives-supported
| The diagram above uses syntax that is similar to but not
| defined in [RFC8340].
2.1.3. Groupings
The "ietf-tcp-common" module defines the following "grouping"
statement:
* tcp-common-grouping
This grouping is presented in the following subsection.
2.1.3.1. The "tcp-common-grouping" Grouping
The following tree diagram [RFC8340] illustrates the "tcp-common-
grouping" grouping:
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grouping tcp-common-grouping
+-- keepalives! {keepalives-supported}?
+-- idle-time uint16
+-- max-probes uint16
+-- probe-interval uint16
Comments:
* The "keepalives" node is a "presence" node so that the mandatory
descendant nodes do not imply that keepalives must be configured.
* The "idle-time", "max-probes", and "probe-interval" nodes have the
common meanings. Please see the YANG module in Section 2.3 for
details.
2.1.4. Protocol-accessible Nodes
The "ietf-tcp-common" module defines only "grouping" statements that
are used by other modules to instantiate protocol-accessible nodes.
2.1.5. Guidelines for Configuring TCP Keep-Alives
Network stacks may include "keep-alives" in their TCP
implementations, although this practice is not universally accepted.
If keep-alives are included, [RFC1122] mandates that the application
MUST be able to turn them on or off for each TCP connection, and that
they MUST default to off.
Keep-alive mechanisms exist in many protocols. Depending on the
protocol stack, TCP keep-alives may only be one out of several
alternatives. Which mechanism(s) to use depends on the use case and
application requirements. If keep-alives are needed by an
application, it is RECOMMENDED that the aliveness check happens only
at the protocol layers that are meaningful to the application.
A TCP keep-alive mechanism SHOULD only be invoked in server
applications that might otherwise hang indefinitely and consume
resources unnecessarily if a client crashes or aborts a connection
during a network failure [RFC1122]. TCP keep-alives may consume
significant resources both in the network and in endpoints (e.g.,
battery power). In addition, frequent keep-alives risk network
congestion. The higher the frequency of keep-alives, the higher the
overhead.
Given the cost of keep-alives, parameters have to be configured
carefully:
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* The default idle interval (leaf "idle-time") MUST default to no
less than two hours, i.e., 7200 seconds [RFC1122]. A lower value
MAY be configured, but keep-alive messages SHOULD NOT be
transmitted more frequently than once every 15 seconds. Longer
intervals SHOULD be used when possible.
* The maximum number of sequential keep-alive probes that can fail
(leaf "max-probes") trades off responsiveness and robustness
against packet loss. ACK segments that contain no data are not
reliably transmitted by TCP. Consequently, if a keep-alive
mechanism is implemented it MUST NOT interpret failure to respond
to any specific probe as a dead connection [RFC1122]. Typically,
a single-digit number should suffice.
* TCP implementations may include a parameter for the number of
seconds between TCP keep-alive probes (leaf "probe-interval"). In
order to avoid congestion, the time interval between probes MUST
NOT be smaller than one second. Significantly longer intervals
SHOULD be used. It is important to note that keep-alive probes
(or replies) can get dropped due to network congestion. Sending
further probe messages into a congested path after a short
interval, without backing off timers, could cause harm and result
in a congestion collapse. Therefore it is essential to pick a
large, conservative value for this interval.
2.2. Example Usage
This section presents an example showing the "tcp-common-grouping"
populated with some data.
<!-- The outermost element below doesn't exist in the data model. -->
<!-- It simulates if the "grouping" were a "container" instead. -->
<tcp-common xmlns="urn:ietf:params:xml:ns:yang:ietf-tcp-common">
<keepalives>
<idle-time>15</idle-time>
<max-probes>3</max-probes>
<probe-interval>30</probe-interval>
</keepalives>
</tcp-common>
2.3. YANG Module
The ietf-tcp-common YANG module references [RFC6991].
<CODE BEGINS> file "ietf-tcp-common@2022-03-07.yang"
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module ietf-tcp-common {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-tcp-common";
prefix tcpcmn;
organization
"IETF NETCONF (Network Configuration) Working Group and the
IETF TCP Maintenance and Minor Extensions (TCPM) Working Group";
contact
"WG Web: https://datatracker.ietf.org/wg/netconf
https://datatracker.ietf.org/wg/tcpm
WG List: NETCONF WG list <mailto:netconf@ietf.org>
TCPM WG list <mailto:tcpm@ietf.org>
Authors: Kent Watsen <mailto:kent+ietf@watsen.net>
Michael Scharf
<mailto:michael.scharf@hs-esslingen.de>";
description
"This module defines reusable groupings for TCP commons that
can be used as a basis for specific TCP common instances.
Copyright (c) 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 Revised
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 DDDD
(https://www.rfc-editor.org/info/rfcDDDD); 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 2022-03-07 {
description
"Initial version";
reference
"RFC DDDD: YANG Groupings for TCP Clients and TCP Servers";
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}
// Features
feature keepalives-supported {
description
"Indicates that keepalives are supported.";
}
// Groupings
grouping tcp-common-grouping {
description
"A reusable grouping for configuring TCP parameters common
to TCP connections as well as the operating system as a
whole.";
container keepalives {
if-feature "keepalives-supported";
presence
"Indicates that keepalives are enabled. This statement is
present so the mandatory descendant nodes do not imply that
this node must be configured.";
description
"Configures the keep-alive policy, to proactively test the
aliveness of the TCP peer. An unresponsive TCP peer is
dropped after approximately (idle-time + max-probes
* probe-interval) seconds.";
leaf idle-time {
type uint16 {
range "1..max";
}
units "seconds";
mandatory true;
description
"Sets the amount of time after which if no data has been
received from the TCP peer, a TCP-level probe message
will be sent to test the aliveness of the TCP peer.
Two hours (7200 seconds) is safe value, per RFC 1122.";
reference
"RFC 1122:
Requirements for Internet Hosts -- Communication Layers";
}
leaf max-probes {
type uint16 {
range "1..max";
}
mandatory true;
description
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"Sets the maximum number of sequential keep-alive probes
that can fail to obtain a response from the TCP peer
before assuming the TCP peer is no longer alive.";
}
leaf probe-interval {
type uint16 {
range "1..max";
}
units "seconds";
mandatory true;
description
"Sets the time interval between failed probes. The interval
SHOULD be significantly longer than one second in order to
avoid harm on a congested link.";
}
} // container keepalives
} // grouping tcp-common-grouping
}
<CODE ENDS>
3. The "ietf-tcp-client" Module
This section defines a YANG 1.1 module called "ietf-tcp-client". A
high-level overview of the module is provided in Section 3.1.
Examples illustrating the module's use are provided in Examples
(Section 3.2). The YANG module itself is defined in Section 3.3.
3.1. Data Model Overview
This section provides an overview of the "ietf-tcp-client" module in
terms of its features and groupings.
3.1.1. Features
The following diagram lists all the "feature" statements defined in
the "ietf-tcp-client" module:
Features:
+-- local-binding-supported
+-- tcp-client-keepalives
+-- proxy-connect
+-- socks5-gss-api
+-- socks5-username-password
| The diagram above uses syntax that is similar to but not
| defined in [RFC8340].
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3.1.2. Groupings
The "ietf-tcp-client" module defines the following "grouping"
statement:
* tcp-client-grouping
This grouping is presented in the following subsection.
3.1.2.1. The "tcp-client-grouping" Grouping
The following tree diagram [RFC8340] illustrates the "tcp-client-
grouping" grouping:
grouping tcp-client-grouping
+-- remote-address inet:host
+-- remote-port? inet:port-number
+-- local-address? inet:ip-address
| {local-binding-supported}?
+-- local-port? inet:port-number
| {local-binding-supported}?
+-- proxy-server! {proxy-connect}?
| +-- (proxy-type)
| +--:(socks4)
| | +-- socks4-parameters
| | +-- remote-address inet:ip-address
| | +-- remote-port? inet:port-number
| +--:(socks4a)
| | +-- socks4a-parameters
| | +-- remote-address inet:host
| | +-- remote-port? inet:port-number
| +--:(socks5)
| +-- socks5-parameters
| +-- remote-address inet:host
| +-- remote-port? inet:port-number
| +-- authentication-parameters!
| +-- (auth-type)
| +--:(gss-api) {socks5-gss-api}?
| | +-- gss-api
| +--:(username-password)
| {socks5-username-password}?
| +-- username-password
| +-- username string
| +---u ct:password-grouping
+---u tcpcmn:tcp-common-grouping
Comments:
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* The "remote-address" node, which is mandatory, may be configured
as an IPv4 address, an IPv6 address, a hostname.
* The "remote-port" node is not mandatory, but its default value is
the invalid value '0', thus forcing the consuming data model to
refine it in order to provide it an appropriate default value.
* The "local-address" node, which is enabled by the "local-binding-
supported" feature (Section 2.1.2), may be configured as an IPv4
address, an IPv6 address, or a wildcard value.
* The "local-port" node, which is enabled by the "local-binding-
supported" feature (Section 2.1.2), is not mandatory. Its default
value is '0', indicating that the operating system can pick an
arbitrary port number.
* The "proxy-server" node is enabled by a "feature" statement and,
for servers that enable it, is a "presence" container so that the
descendant "mandatory true" choice node does not imply that the
proxy-server node must be configured.
* This grouping uses the "tcp-common-grouping" grouping discussed in
Section 2.1.3.1.
3.1.3. Protocol-accessible Nodes
The "ietf-tcp-client" module defines only "grouping" statements that
are used by other modules to instantiate protocol-accessible nodes.
3.2. Example Usage
This section presents two examples showing the "tcp-client-grouping"
populated with some data. This example shows a TCP-client configured
to not connect via a proxy:
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<!-- The outermost element below doesn't exist in the data model. -->
<!-- It simulates if the "grouping" were a "container" instead. -->
<tcp-client xmlns="urn:ietf:params:xml:ns:yang:ietf-tcp-client">
<remote-address>www.example.com</remote-address>
<remote-port>443</remote-port>
<local-address>0.0.0.0</local-address>
<local-port>0</local-port>
<keepalives>
<idle-time>15</idle-time>
<max-probes>3</max-probes>
<probe-interval>30</probe-interval>
</keepalives>
</tcp-client>
This example shows a TCP-client configured to connect via a proxy:
<!-- The outermost element below doesn't exist in the data model. -->
<!-- It simulates if the "grouping" were a "container" instead. -->
<tcp-client xmlns="urn:ietf:params:xml:ns:yang:ietf-tcp-client">
<remote-address>www.example.com</remote-address>
<remote-port>443</remote-port>
<local-address>0.0.0.0</local-address>
<local-port>0</local-port>
<proxy-server>
<socks5-parameters>
<remote-address>proxy.my-domain.com</remote-address>
<remote-port>1080</remote-port>
<authentication-parameters>
<username-password>
<username>foobar</username>
<cleartext-password>secret</cleartext-password>
</username-password>
</authentication-parameters>
</socks5-parameters>
</proxy-server>
<keepalives>
<idle-time>15</idle-time>
<max-probes>3</max-probes>
<probe-interval>30</probe-interval>
</keepalives>
</tcp-client>
3.3. YANG Module
The ietf-tcp-client YANG module references [RFC6991].
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<CODE BEGINS> file "ietf-tcp-client@2022-03-07.yang"
module ietf-tcp-client {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-tcp-client";
prefix tcpc;
import ietf-inet-types {
prefix inet;
reference
"RFC 6991: Common YANG Data Types";
}
import ietf-crypto-types {
prefix ct;
reference
"RFC AAAA: YANG Data Types and Groupings for Cryptography";
}
import ietf-tcp-common {
prefix tcpcmn;
reference
"RFC DDDD: YANG Groupings for TCP Clients and TCP Servers";
}
organization
"IETF NETCONF (Network Configuration) Working Group and the
IETF TCP Maintenance and Minor Extensions (TCPM) Working Group";
contact
"WG Web: https://datatracker.ietf.org/wg/netconf
https://datatracker.ietf.org/wg/tcpm
WG List: NETCONF WG list <mailto:netconf@ietf.org>
TCPM WG list <mailto:tcpm@ietf.org>
Authors: Kent Watsen <mailto:kent+ietf@watsen.net>
Michael Scharf
<mailto:michael.scharf@hs-esslingen.de>";
description
"This module defines reusable groupings for TCP clients that
can be used as a basis for specific TCP client instances.
Copyright (c) 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 Revised
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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 DDDD
(https://www.rfc-editor.org/info/rfcDDDD); 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 2022-03-07 {
description
"Initial version";
reference
"RFC DDDD: YANG Groupings for TCP Clients and TCP Servers";
}
// Features
feature local-binding-supported {
description
"Indicates that the server supports configuring local
bindings (i.e., the local address and local port) for
TCP clients.";
}
feature tcp-client-keepalives {
description
"Per socket TCP keepalive parameters are configurable for
TCP clients on the server implementing this feature.";
}
feature proxy-connect {
description
"Proxy connection configuration is configurable for
TCP clients on the server implementing this feature.";
}
feature socks5-gss-api {
description
"Indicates that the server supports authenticating
using GSSAPI when initiating TCP connections via
and SOCKS Version 5 proxy server.";
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reference
"RFC 1928: SOCKS Protocol Version 5";
}
feature socks5-username-password {
description
"Indicates that the server supports authenticating using
username/password when initiating TCP connections via
and SOCKS Version 5 proxy server.";
reference
"RFC 1928: SOCKS Protocol Version 5";
}
// Groupings
grouping tcp-client-grouping {
description
"A reusable grouping for configuring a TCP client.
Note that this grouping uses fairly typical descendant
node names such that a stack of 'uses' statements will
have name conflicts. It is intended that the consuming
data model will resolve the issue (e.g., by wrapping
the 'uses' statement in a container called
'tcp-client-parameters'). This model purposely does
not do this itself so as to provide maximum flexibility
to consuming models.";
leaf remote-address {
type inet:host;
mandatory true;
description
"The IP address or hostname of the remote peer to
establish a connection with. If a domain name is
configured, then the DNS resolution should happen on
each connection attempt. If the DNS resolution
results in multiple IP addresses, the IP addresses
are tried according to local preference order until
a connection has been established or until all IP
addresses have failed.";
}
leaf remote-port {
type inet:port-number;
default "0";
description
"The IP port number for the remote peer to establish a
connection with. An invalid default value (0) is used
(instead of 'mandatory true') so that as application
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level data model may 'refine' it with an application
specific default port number value.";
}
leaf local-address {
if-feature "local-binding-supported";
type inet:ip-address;
description
"The local IP address/interface (VRF?) to bind to for when
connecting to the remote peer. INADDR_ANY ('0.0.0.0') or
INADDR6_ANY ('0:0:0:0:0:0:0:0' a.k.a. '::') MAY be used to
explicitly indicate the implicit default, that the server
can bind to any IPv4 or IPv6 addresses, respectively.";
}
leaf local-port {
if-feature "local-binding-supported";
type inet:port-number;
default "0";
description
"The local IP port number to bind to for when connecting
to the remote peer. The port number '0', which is the
default value, indicates that any available local port
number may be used.";
}
container proxy-server {
if-feature "proxy-connect";
presence
"Indicates that a proxy connection has been configured.
Present so that the mandatory descendant nodes do not
imply that this node must be configured.";
choice proxy-type {
mandatory true;
description
"Selects a proxy connection protocol.";
case socks4 {
container socks4-parameters {
leaf remote-address {
type inet:ip-address;
mandatory true;
description
"The IP address of the proxy server.";
}
leaf remote-port {
type inet:port-number;
default "1080";
description
"The IP port number for the proxy server.";
}
description
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"Parameters for connecting to a TCP-based proxy
server using the SOCKS4 protocol.";
reference
"SOCKS, Proceedings: 1992 Usenix Security Symposium.";
}
}
case socks4a {
container socks4a-parameters {
leaf remote-address {
type inet:host;
mandatory true;
description
"The IP address or hostname of the proxy server.";
}
leaf remote-port {
type inet:port-number;
default "1080";
description
"The IP port number for the proxy server.";
}
description
"Parameters for connecting to a TCP-based proxy
server using the SOCKS4a protocol.";
reference
"SOCKS Proceedings:
1992 Usenix Security Symposium.
OpenSSH message:
SOCKS 4A: A Simple Extension to SOCKS 4 Protocol
https://www.openssh.com/txt/socks4a.protocol";
}
}
case socks5 {
container socks5-parameters {
leaf remote-address {
type inet:host;
mandatory true;
description
"The IP address or hostname of the proxy server.";
}
leaf remote-port {
type inet:port-number;
default "1080";
description
"The IP port number for the proxy server.";
}
container authentication-parameters {
presence
"Indicates that an authentication mechanism
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has been configured. Present so that the
mandatory descendant nodes do not imply that
this node must be configured.";
description
"A container for SOCKS Version 5 authentication
mechanisms.
A complete list of methods is defined at:
https://www.iana.org/assignments/socks-methods
/socks-methods.xhtml.";
reference
"RFC 1928: SOCKS Protocol Version 5";
choice auth-type {
mandatory true;
description
"A choice amongst supported SOCKS Version 5
authentication mechanisms.";
case gss-api {
if-feature "socks5-gss-api";
container gss-api {
description
"Contains GSS-API configuration. Defines
as an empty container to enable specific
GSS-API configuration to be augmented in
by future modules.";
reference
"RFC 1928: SOCKS Protocol Version 5
RFC 2743: Generic Security Service
Application Program Interface
Version 2, Update 1";
}
}
case username-password {
if-feature "socks5-username-password";
container username-password {
leaf username {
type string;
mandatory true;
description
"The 'username' value to use for client
identification.";
}
uses ct:password-grouping {
description
"The password to be used for client
authentication.";
}
description
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"Contains Username/Password configuration.";
reference
"RFC 1929: Username/Password Authentication
for SOCKS V5";
}
}
}
}
description
"Parameters for connecting to a TCP-based proxy server
using the SOCKS5 protocol.";
reference
"RFC 1928: SOCKS Protocol Version 5";
}
}
}
description
"Proxy server settings.";
}
uses tcpcmn:tcp-common-grouping {
augment "keepalives" {
if-feature "tcp-client-keepalives";
description
"Add an if-feature statement so that implementations
can choose to support TCP client keepalives.";
}
}
}
}
<CODE ENDS>
4. The "ietf-tcp-server" Module
This section defines a YANG 1.1 module called "ietf-tcp-server". A
high-level overview of the module is provided in Section 4.1.
Examples illustrating the module's use are provided in Examples
(Section 4.2). The YANG module itself is defined in Section 4.3.
4.1. Data Model Overview
This section provides an overview of the "ietf-tcp-server" module in
terms of its features and groupings.
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4.1.1. Features
The following diagram lists all the "feature" statements defined in
the "ietf-tcp-server" module:
Features:
+-- tcp-server-keepalives
| The diagram above uses syntax that is similar to but not
| defined in [RFC8340].
4.1.2. Groupings
The "ietf-tcp-server" module defines the following "grouping"
statement:
* tcp-server-grouping
This grouping is presented in the following subsection.
4.1.2.1. The "tcp-server-grouping" Grouping
The following tree diagram [RFC8340] illustrates the "tcp-server-
grouping" grouping:
grouping tcp-server-grouping
+-- local-address inet:ip-address
+-- local-port? inet:port-number
+---u tcpcmn:tcp-common-grouping
Comments:
* The "local-address" node, which is mandatory, may be configured as
an IPv4 address, an IPv6 address, or a wildcard value.
* The "local-port" node is not mandatory, but its default value is
the invalid value '0', thus forcing the consuming data model to
refine it in order to provide it an appropriate default value.
* This grouping uses the "tcp-common-grouping" grouping discussed in
Section 2.1.3.1.
4.1.3. Protocol-accessible Nodes
The "ietf-tcp-server" module defines only "grouping" statements that
are used by other modules to instantiate protocol-accessible nodes.
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4.2. Example Usage
This section presents an example showing the "tcp-server-grouping"
populated with some data.
<!-- The outermost element below doesn't exist in the data model. -->
<!-- It simulates if the "grouping" were a "container" instead. -->
<tcp-server xmlns="urn:ietf:params:xml:ns:yang:ietf-tcp-server">
<local-address>10.20.30.40</local-address>
<local-port>7777</local-port>
<keepalives>
<idle-time>15</idle-time>
<max-probes>3</max-probes>
<probe-interval>30</probe-interval>
</keepalives>
</tcp-server>
4.3. YANG Module
The ietf-tcp-server YANG module references [RFC6991].
<CODE BEGINS> file "ietf-tcp-server@2022-03-07.yang"
module ietf-tcp-server {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-tcp-server";
prefix tcps;
import ietf-inet-types {
prefix inet;
reference
"RFC 6991: Common YANG Data Types";
}
import ietf-tcp-common {
prefix tcpcmn;
reference
"RFC DDDD: YANG Groupings for TCP Clients and TCP Servers";
}
organization
"IETF NETCONF (Network Configuration) Working Group and the
IETF TCP Maintenance and Minor Extensions (TCPM) Working Group";
contact
"WG Web: https://datatracker.ietf.org/wg/netconf
https://datatracker.ietf.org/wg/tcpm
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WG List: NETCONF WG list <mailto:netconf@ietf.org>
TCPM WG list <mailto:tcpm@ietf.org>
Authors: Kent Watsen <mailto:kent+ietf@watsen.net>
Michael Scharf
<mailto:michael.scharf@hs-esslingen.de>";
description
"This module defines reusable groupings for TCP servers that
can be used as a basis for specific TCP server instances.
Copyright (c) 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 Revised
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 DDDD
(https://www.rfc-editor.org/info/rfcDDDD); 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 2022-03-07 {
description
"Initial version";
reference
"RFC DDDD: YANG Groupings for TCP Clients and TCP Servers";
}
// Features
feature tcp-server-keepalives {
description
"Per socket TCP keepalive parameters are configurable for
TCP servers on the server implementing this feature.";
}
// Groupings
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grouping tcp-server-grouping {
description
"A reusable grouping for configuring a TCP server.
Note that this grouping uses fairly typical descendant
node names such that a stack of 'uses' statements will
have name conflicts. It is intended that the consuming
data model will resolve the issue (e.g., by wrapping
the 'uses' statement in a container called
'tcp-server-parameters'). This model purposely does
not do this itself so as to provide maximum flexibility
to consuming models.";
leaf local-address {
type inet:ip-address;
mandatory true;
description
"The local IP address to listen on for incoming
TCP client connections. INADDR_ANY (0.0.0.0) or
INADDR6_ANY (0:0:0:0:0:0:0:0 a.k.a. ::) MUST be
used when the server is to listen on all IPv4 or
IPv6 addresses, respectively.";
}
leaf local-port {
type inet:port-number;
default "0";
description
"The local port number to listen on for incoming TCP
client connections. An invalid default value (0)
is used (instead of 'mandatory true') so that an
application level data model may 'refine' it with
an application specific default port number value.";
}
uses tcpcmn:tcp-common-grouping {
augment "keepalives" {
if-feature "tcp-server-keepalives";
description
"Add an if-feature statement so that implementations
can choose to support TCP server keepalives.";
}
}
}
}
<CODE ENDS>
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5. Security Considerations
5.1. The "ietf-tcp-common" YANG Module
The "ietf-tcp-common" YANG module defines "grouping" statements that
are designed to be accessed via YANG based management protocols, such
as NETCONF [RFC6241] and RESTCONF [RFC8040]. Both of these protocols
have mandatory-to-implement secure transport layers (e.g., SSH, TLS)
with mutual authentication.
The NETCONF access control model (NACM) [RFC8341] provides the means
to restrict access for particular users to a pre-configured subset of
all available protocol operations and content.
Since the module in this document only define groupings, these
considerations are primarily for the designers of other modules that
use these groupings.
None of the readable data nodes defined in this YANG module are
considered sensitive or vulnerable in network environments. The NACM
"default-deny-all" extension has not been set for any data nodes
defined in this module.
None of the writable data nodes defined in this YANG module are
considered sensitive or vulnerable in network environments. The NACM
"default-deny-write" extension has not been set for any data nodes
defined in this module.
This module does not define any RPCs, actions, or notifications, and
thus the security consideration for such is not provided here.
5.2. The "ietf-tcp-client" YANG Module
The "ietf-tcp-client" YANG module defines "grouping" statements that
are designed to be accessed via YANG based management protocols, such
as NETCONF [RFC6241] and RESTCONF [RFC8040]. Both of these protocols
have mandatory-to-implement secure transport layers (e.g., SSH, TLS)
with mutual authentication.
The NETCONF access control model (NACM) [RFC8341] provides the means
to restrict access for particular users to a pre-configured subset of
all available protocol operations and content.
Since the module in this document only define groupings, these
considerations are primarily for the designers of other modules that
use these groupings.
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One readable data node defined in this YANG module may be considered
sensitive or vulnerable in some network environments. This node is
as follows:
* The "proxy-server/socks5-parameters/authentication-parameters/
username-password/password" node:
The cleartext "password" node defined in the "tcp-client-
grouping" grouping is additionally sensitive to read operations
such that, in normal use cases, it should never be returned to
a client. For this reason, the NACM extension "default-deny-
all" has been applied to it.
None of the writable data nodes defined in this YANG module are
considered sensitive or vulnerable in network environments. The NACM
"default-deny-write" extension has not been set for any data nodes
defined in this module.
This module does not define any RPCs, actions, or notifications, and
thus the security consideration for such is not provided here.
Implementations are RECOMMENDED to implement the "local-binding-
supported" feature for cryptographically-secure protocols, so as to
enable more granular ingress/egress firewall rulebases. It is NOT
RECOMMENDED to implement this feature for unsecure protocols, as per
[RFC6056].
5.3. The "ietf-tcp-server" YANG Module
The "ietf-tcp-server" YANG module defines "grouping" statements that
are designed to be accessed via YANG based management protocols, such
as NETCONF [RFC6241] and RESTCONF [RFC8040]. Both of these protocols
have mandatory-to-implement secure transport layers (e.g., SSH, TLS)
with mutual authentication.
The NETCONF access control model (NACM) [RFC8341] provides the means
to restrict access for particular users to a pre-configured subset of
all available protocol operations and content.
Since the module in this document only define groupings, these
considerations are primarily for the designers of other modules that
use these groupings.
None of the readable data nodes defined in this YANG module are
considered sensitive or vulnerable in network environments. The NACM
"default-deny-all" extension has not been set for any data nodes
defined in this module.
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None of the writable data nodes defined in this YANG module are
considered sensitive or vulnerable in network environments. The NACM
"default-deny-write" extension has not been set for any data nodes
defined in this module.
This module does not define any RPCs, actions, or notifications, and
thus the security consideration for such is not provided here.
6. IANA Considerations
6.1. The "IETF XML" Registry
This document registers two URIs in the "ns" subregistry of the IETF
XML Registry [RFC3688]. Following the format in [RFC3688], the
following registrations are requested:
URI: urn:ietf:params:xml:ns:yang:ietf-tcp-common
Registrant Contact: The IESG
XML: N/A, the requested URI is an XML namespace.
URI: urn:ietf:params:xml:ns:yang:ietf-tcp-client
Registrant Contact: The IESG
XML: N/A, the requested URI is an XML namespace.
URI: urn:ietf:params:xml:ns:yang:ietf-tcp-server
Registrant Contact: The IESG
XML: N/A, the requested URI is an XML namespace.
6.2. The "YANG Module Names" Registry
This document registers two YANG modules in the YANG Module Names
registry [RFC6020]. Following the format in [RFC6020], the following
registrations are requested:
name: ietf-tcp-common
namespace: urn:ietf:params:xml:ns:yang:ietf-tcp-common
prefix: tcpcmn
reference: RFC DDDD
name: ietf-tcp-client
namespace: urn:ietf:params:xml:ns:yang:ietf-tcp-client
prefix: tcpc
reference: RFC DDDD
name: ietf-tcp-server
namespace: urn:ietf:params:xml:ns:yang:ietf-tcp-server
prefix: tcps
reference: RFC DDDD
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7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[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>.
[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>.
[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>.
[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>.
7.2. Informative References
[I-D.ietf-netconf-crypto-types]
Watsen, K., "YANG Data Types and Groupings for
Cryptography", Work in Progress, Internet-Draft, draft-
ietf-netconf-crypto-types-21, 14 September 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-netconf-
crypto-types-21>.
[I-D.ietf-netconf-http-client-server]
Watsen, K., "YANG Groupings for HTTP Clients and HTTP
Servers", Work in Progress, Internet-Draft, draft-ietf-
netconf-http-client-server-08, 14 December 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-netconf-
http-client-server-08>.
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[I-D.ietf-netconf-keystore]
Watsen, K., "A YANG Data Model for a Keystore", Work in
Progress, Internet-Draft, draft-ietf-netconf-keystore-23,
14 December 2021, <https://datatracker.ietf.org/doc/html/
draft-ietf-netconf-keystore-23>.
[I-D.ietf-netconf-netconf-client-server]
Watsen, K., "NETCONF Client and Server Models", Work in
Progress, Internet-Draft, draft-ietf-netconf-netconf-
client-server-24, 14 December 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-netconf-
netconf-client-server-24>.
[I-D.ietf-netconf-restconf-client-server]
Watsen, K., "RESTCONF Client and Server Models", Work in
Progress, Internet-Draft, draft-ietf-netconf-restconf-
client-server-24, 14 December 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-netconf-
restconf-client-server-24>.
[I-D.ietf-netconf-ssh-client-server]
Watsen, K., "YANG Groupings for SSH Clients and SSH
Servers", Work in Progress, Internet-Draft, draft-ietf-
netconf-ssh-client-server-26, 14 December 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-netconf-
ssh-client-server-26>.
[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://datatracker.ietf.org/doc/html/draft-ietf-netconf-
tcp-client-server-11>.
[I-D.ietf-netconf-tls-client-server]
Watsen, K., "YANG Groupings for TLS Clients and TLS
Servers", Work in Progress, Internet-Draft, draft-ietf-
netconf-tls-client-server-26, 14 December 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-netconf-
tls-client-server-26>.
[I-D.ietf-netconf-trust-anchors]
Watsen, K., "A YANG Data Model for a Truststore", Work in
Progress, Internet-Draft, draft-ietf-netconf-trust-
anchors-16, 14 December 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-netconf-
trust-anchors-16>.
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[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, DOI 10.17487/RFC0793, September 1981,
<https://www.rfc-editor.org/info/rfc793>.
[RFC1122] Braden, R., Ed., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122,
DOI 10.17487/RFC1122, October 1989,
<https://www.rfc-editor.org/info/rfc1122>.
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
DOI 10.17487/RFC3688, January 2004,
<https://www.rfc-editor.org/info/rfc3688>.
[RFC6056] Larsen, M. and F. Gont, "Recommendations for Transport-
Protocol Port Randomization", BCP 156, RFC 6056,
DOI 10.17487/RFC6056, January 2011,
<https://www.rfc-editor.org/info/rfc6056>.
[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>.
[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>.
[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>.
[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>.
Appendix A. Change Log
This section is to be removed before publishing as an RFC.
A.1. 00 to 01
* Added 'local-binding-supported' feature to TCP-client model.
* Added 'keepalives-supported' feature to TCP-common model.
* Added 'external-endpoint-values' container and 'external-
endpoints' feature to TCP-server model.
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A.2. 01 to 02
* Removed the 'external-endpoint-values' container and 'external-
endpoints' feature from the TCP-server model.
A.3. 02 to 03
* Moved the common model section to be before the client and server
specific sections.
* Added sections "Model Scope" and "Usage Guidelines for Configuring
TCP Keep-Alives" to the common model section.
A.4. 03 to 04
* Fixed a few typos.
A.5. 04 to 05
* Removed commented out "grouping tcp-system-grouping" statement
kept for reviewers.
* Added a "Note to Reviewers" note to first page.
A.6. 05 to 06
* Added support for TCP proxies.
A.7. 06 to 07
* Expanded "Data Model Overview section(s) [remove "wall" of tree
diagrams].
* Updated the Security Considerations section.
A.8. 07 to 08
* Added missing IANA registration for "ietf-tcp-common"
* Added "mandatory true" for the "username" and "password" leafs
* Added an example of a TCP-client configured to connect via a proxy
* Fixed issues found by the SecDir review of the "keystore" draft.
* Updated the "ietf-tcp-client" module to use the new "password-
grouping" grouping from the "crypto-types" module.
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A.9. 08 to 09
* Addressed comments raised by YANG Doctor in the ct/ts/ks drafts.
A.10. 09 to 10
* Updated Abstract and Intro to address comments by Tom Petch.
* Removed the "tcp-connection-grouping" grouping (now models use the
"tcp-common-grouping" directly).
* Added XML-comment above examples explaining the reason for the
unusual top-most element's presence.
* Added Securty Considerations section for the "local-binding-
supported" feature.
* Replaced some hardcoded refs to <xref> elements.
* Fixed nits found by YANG Doctor reviews.
* Aligned modules with `pyang -f` formatting.
* Added an "Acknowledgements" secetion.
A.11. 10 to 11
* Replaced "base64encodedvalue==" with "BASE64VALUE=" in examples.
* Minor editorial nits
A.12. 11 to 12
* Fixed up the 'WG Web' and 'WG List' lines in YANG module(s)
* Fixed up copyright (i.e., s/Simplified/Revised/) in YANG module(s)
Acknowledgements
The authors would like to thank for following for lively discussions
on list and in the halls (ordered by first name): Juergen
Schoenwaelder, Ladislav Lhotka, Nick Hancock, and Tom Petch.
Authors' Addresses
Kent Watsen
Watsen Networks
Email: kent+ietf@watsen.net
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Michael Scharf
Hochschule Esslingen - University of Applied Sciences
Email: michael.scharf@hs-esslingen.de
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