An HTTPS-based Transport for YANG NotificationsKloud Servicesmjethanandani@gmail.comWatsen Networkskent+ietf@watsen.net
Operations
NETCONFhttpyangnotificationThis document defines a protocol for sending asynchronous
event notifications similar to notifications defined in RFC
5277, but over HTTPS. YANG modules for configuring publishers
are also defined. Examples are provided illustrating how to
configure various publishers.
This document requires that the publisher is a "server" (e.g.,
a NETCONF or RESTCONF server), but does not assume that the
receiver is a server.This document defines a protocol for sending asynchronous
event notifications similar to notifications defined in NETCONF Event Notifications, but over
HTTPS. Using HTTPS, which is a secure form of HTTP Semantics, maximizes
transport-level interoperability, while allowing for a variety
of encoding options. The protocol supports HTTP/1.1: Message Syntax and Routing
and, HTTP/2. While the payload
does not change between these versions of HTTP and HTTP/3, the underlying transport
does. Since NETCONF does not support QUIC: A UDP-Based Multiplexed and Secure
Transport, support for
HTTP/3, is considered out of scope of this document.This document defines support for JSON and XML; future
efforts may define support for other encodings
(e.g., binary). This document requires that the publisher is a
"server" (e.g., a NETCONF or RESTCONF server), but does not
assume that the receiver is a NETCONF or RESTCONF server.
It does expect the receiver to be an HTTPS server to receive
the notifications.This document also defines two YANG
1.1 modules that extend the data model defined in Subscription to YANG Notifications,
enabling the configuration of HTTPS-based receivers.An example module illustrating the configuration of a
publisher not using the data model defined in RFC 8639 is also
provided.Configured subscriptions enable a server (e.g., a NETCONF or
RESTCONF server), acting as a publisher of notifications, to
proactively push notifications to external receivers without the
receivers needing to first connect to the server, as is the case
with dynamic subscriptions.While the YANG modules have been defined as an augmentation of
Subscription to YANG Notifications, the
notification method defined in this document MAY be used outside of
Subscription to YANG Notifications by
using some of the definitions from this module along with the grouping
defined in Groupings for HTTP
Clients and Servers. For an example on how that can be done,
see Section A.2.This document uses several placeholder values throughout the
document. Please replace them as follows and remove this section
before publication.RFC XXXX, where XXXX is the number assigned to this document at the
time of publication.RFC YYYY, where YYYY is the number assigned to
.2024-02-01 with the actual date of the publication of this document.AcronymExpansionHTTPHypertext Transfer ProtocolHTTPSHypertext Transfer Protocol SecureSSEServer-Sent EventsTCPTransmission Control ProtocolTLSTransport Layer SecurityThe 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.The following terms are defined in Subscription to YANG Notifications.
PublisherReceiverSubscribed NotificationsThe following term is defined in RESTCONF Protocol.
target resource
The tree diagram for the YANG modules defined in this
document use annotations defined in YANG Tree Diagrams..
The protocol consists of two HTTP-based target resources
presented by the receiver. These two resources share a common
prefix that the publisher learns from a request it issues, as
defined in section 3.2. If the data model in section 6.2 is
used, this common prefix is defined by the "path" leaf in the
"http-client-parameters" container.
"capabilities": A target resource enabling the publisher
to discover what optional capabilities a receiver supports.
Publishers SHOULD query this target before sending any
notifications or if ever an error occurs."relay-notification": A target resource enabling the publisher
to send one or more notification to a receiver. This document
defines support for sending only one notification per message; a
future effort MAY extend the protocol to send multiple
notifications per message.The protocol is illustrated in the diagram below:
to discover receiver's
capabilities
<------ Send 200 (OK) containing
capabilities supported
by the receiver
+-- For Each Notification ------------------ ---------------------+
| |
| Send HTTPS POST message ------> |
| with YANG defined |
| notification |
| |
| <------ Send 204 (No Content) |
+-----------------------------------------------------------------+]]>Note that, for RFC 8639 configured subscriptions, the very first
notification must be the "subscription-started" notification.
For publishers using Subscription to
YANG Notifications, dynamic discovery of a receiver's
supported encoding is necessary only when the
"/subscriptions/subscription/encoding" leaf is not
configured, per the "encoding" leaf's description statement
in the "ietf-subscribed-notification" module.
If the "encoding" leaf is not configured, and the publisher
wants to send a notification in a particular format, without
going through the setup operation of learning the receiver
capabilities, it can do so, but has to be prepared for the
case when it receives an error response, because the
receiver does not support the format sent by the publisher.
To learn the capabilities of a receiver, a publisher can
issue an HTTPS GET request to the "capabilities" resource
(see ) on the receiver with
"Accept" header set using the "application/xml" as defined
in XML Media Types, and/or
"application/json" as defined in JSON media-types.
The receiver responds with a "200 (OK)" message, having the
"Content-Type" header set to either "application/xml" or
"application/json" (which ever was selected), and containing
in the response body a list of the receiver's capabilities
encoded in the selected format.Even though a YANG module is not defined for this interaction,
the response body MUST conform to the following YANG-modeled
format:container receiver-capabilities {
description
"A container for a list of capabilities supported by
the receiver.";
leaf-list receiver-capability {
type "inet:uri";
description
"A capability supported by the receiver. A partial list of
capabilities is defined in the 'Capabilities for HTTPS
Notification Receivers' registry (see RFC XXXX). Additional
custom capabilities MAY be defined.";
}
}
As it is possible that the receiver may return custom capability
URIs, the publisher MUST ignore any capabilities that it does not
recognize.
The publisher can send the following request to learn the
receiver capabilities. In this example, the "Accept" states
that the publisher wants to receive the capabilities response
in XML but, if not supported, then in JSON.If the receiver is able to reply using "application/xml", and
assuming it is able to receive JSON and XML encoded notifications,
and it is able to process the RFC 8639 state machine, the
response might look like this:\
urn:ietf:capability:https-notif-receiver:encoding:json\
\
urn:ietf:capability:https-notif-receiver:encoding:xml\
\
urn:ietf:capability:https-notif-receiver:sub-notif\
]]>If the receiver is unable to reply using "application/xml", the
response might look like this:
The publisher sends an HTTP POST request to the
"relay-notification" resource (see ) on the receiver with the "Content-Type" header
set to either "application/json" or "application/xml" and a
body containing the notification encoded using the specified
format.
XML-encoded notifications are encoded using the format defined
by NETCONF Event Notifications
for XML.JSON-encoded notifications are encoded the same as specified
in Section 6.4 in RESTCONF with
the following deviations:
The notifications do not contain the "data:" prefix used
by Server-Sent Events (SSE).
Instead of saying that, for JSON-encoding purposes, the
module name for the "notification" element is
"ietf-restconf", the module name will instead be
"ietf-https-notif".
The response on success SHOULD be "204 (No Content)". In
case of corrupted or malformed event, the response SHOULD be
an appropriate HTTP error response.
An XML-encoded notification might be sent as follows:2019-03-22T12:35:00ZfaultEthernet0major
]]>A JSON-encoded notification might be sent as follows:And, in either case, the response on success might be as
follows:This YANG module augments the "ietf-subscribed-notifications" module to
define a choice of transport types that other modules such as the
"ietf-https-notif-transport" module can use to define a transport specific
receiver.The YANG module imports Subscription to YANG Notifications. file "ietf-subscribed-notif-receivers@2024-02-01.yang"
module ietf-subscribed-notif-receivers {
yang-version 1.1;
namespace
"urn:ietf:params:xml:ns:yang:ietf-subscribed-notif-receivers";
prefix "snr";
import ietf-subscribed-notifications {
prefix sn;
reference
"RFC 8639: Subscription to YANG Notifications";
}
organization
"IETF NETCONF Working Group";
contact
"WG Web:
WG List:
Authors: Mahesh Jethanandani (mjethanandani at gmail dot com)
Kent Watsen (kent plus ietf at watsen dot net)";
description
"This YANG module is implemented by Publishers implementing
the 'ietf-subscribed-notifications' module defined in RFC 8639.
While this module is defined in RFC XXXX, which primarily
defines an HTTPS-based transport for notifications, this module
is not HTTP-specific. It is a generic extension that can be
used by any 'notif' transport.
This module defines two 'augment' statements. One statement
augments a 'container' statement called 'receiver-instances'
into the top-level 'subscriptions' container. The other
statement, called 'receiver-instance-ref', augments a 'leaf'
statement into each 'receiver' that references one of the
afore mentioned receiver instances. This indirection enables
multiple configured subscriptions to send notifications to
the same receiver instance.
Copyright (c) 2024 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
(http://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC XXXX; 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 "2024-02-01" {
description
"Initial Version.";
reference
"RFC XXXX: An HTTPS-based Transport for YANG Notifications.";
}
augment "/sn:subscriptions" {
container receiver-instances {
description
"A container for all instances of receivers.";
list receiver-instance {
key "name";
leaf name {
type string;
description
"An arbitrary but unique name for this receiver
instance.";
}
choice transport-type {
mandatory true;
description
"Choice of different types of transports used to
send notifications. The 'case' statements must
be augmented in by other modules.";
}
description
"A list of all receiver instances.";
}
}
description
"Augment the subscriptions container to define the
transport type.";
}
augment
"/sn:subscriptions/sn:subscription/sn:receivers/sn:receiver" {
leaf receiver-instance-ref {
type leafref {
path "/sn:subscriptions/snr:receiver-instances/" +
"snr:receiver-instance/snr:name";
}
description
"Reference to a receiver instance.";
}
description
"Augment the subscriptions container to define an optional
reference to a receiver instance.";
}
}
]]>This YANG module is a definition of a set of receivers that are
interested in the notifications published by the publisher. The module
contains the TCP, TLS and HTTPS parameters that are needed to
communicate with the receiver. The module augments the
"ietf-subscribed-notif-receivers" module to define a transport specific
receiver. As mentioned earlier, it uses a POST method to deliver the
notification. The "http-receiver/tls/http-client-parameters/path" leaf
defines the path for the resource on the receiver, as defined by
"path-absolute" in URI Generic Syntax.
The user-id used by Network Configuration Access
Control Model, is that of the receiver and is derived from the
certificate presented by the receiver as part of "receiver-identity".An abridged tree diagram representing the module is shown
below.The YANG module imports
A YANG Data Model for SNMP Configuration,
Subscription to YANG Notifications,
and YANG Groupings for HTTP Clients and HTTP Servers.The YANG module is shown below. file "ietf-https-notif-transport@2024-02-01.yang"
module ietf-https-notif-transport {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-https-notif-transport";
prefix "hnt";
import ietf-x509-cert-to-name {
prefix x509c2n;
reference
"RFC 7407: YANG Data Model for SNMP Configuration.";
}
import ietf-subscribed-notifications {
prefix sn;
reference
"RFC 8639: Subscription to YANG Notifications";
}
import ietf-subscribed-notif-receivers {
prefix snr;
reference
"RFC XXXX: An HTTPS-based Transport for YANG Notifications.";
}
import ietf-http-client {
prefix httpc;
reference
"RFC YYYY: YANG Groupings for HTTP Clients and HTTP Servers.";
}
organization
"IETF NETCONF Working Group";
contact
"WG Web:
WG List:
Authors: Mahesh Jethanandani (mjethanandani at gmail dot com)
Kent Watsen (kent plus ietf at watsen dot net)";
description
"This YANG module is implemented by Publishers that implement
the 'ietf-subscribed-notifications' module defined in RFC 8639.
This module augments a 'case' statement called 'https' into
the 'choice' statement called 'transport-type' defined
by the 'ietf-https-notif-transport' module defined in RFC XXXX.
Copyright (c) 2024 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
(http://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC XXXX; 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 "2024-02-01" {
description
"Initial Version.";
reference
"RFC XXXX: An HTTPS-based Transport for YANG Notifications.";
}
feature receiver-identity {
description
"Indicates that the server supports filtering notifications
based on the receiver's identity derived from its TLS
certificate.";
}
identity https {
base sn:transport;
description
"HTTPS transport for notifications.";
}
grouping https-receiver-grouping {
description
"A grouping that may be used by other modules wishing to
configure HTTPS-based notifications without using RFC 8639.";
uses httpc:http-client-stack-grouping {
refine "transport/tcp" {
// create the logical impossibility of enabling the
// "tcp" transport (i.e., "HTTP" without the 'S').
if-feature "not httpc:tcp-supported";
}
augment "transport/tls/tls/http-client-parameters" {
leaf path {
type string;
mandatory true;
description
"A path to the target resources. Under this
path the receiver must support both the 'capabilities'
and 'relay-notification' resource targets, as described
in RFC XXXX.";
}
description
"Augmentation to add a receiver-specific path for the
'capabilities' and 'relay-notification' resources.";
}
}
container receiver-identity {
if-feature receiver-identity;
description
"Maps the receiver's TLS certificate to a local identity
enabling access control to be applied to filter out
notifications that the receiver may not be authorized
to view.";
container cert-maps {
uses x509c2n:cert-to-name;
description
"The cert-maps container is used by a TLS-based HTTP
server to map the HTTPS client's presented X.509
certificate to a 'local' username. Specifically, the
'name' field within the module is used along with
'specified' identity to perform the match. If no
matching and valid cert-to-name list entry is found,
the publisher MUST close the connection, and MUST
NOT send any notifications over it.";
reference
"RFC 7407: A YANG Data Model for SNMP Configuration.";
}
}
}
augment "/sn:subscriptions/snr:receiver-instances/" +
"snr:receiver-instance/snr:transport-type" {
case https {
container https-receiver {
description
"The HTTPS receiver to send notifications to.";
uses https-receiver-grouping;
}
}
description
"Augment the transport-type choice to include the 'https'
transport.";
}
}
]]>The YANG modules specified in this document define 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). The lowest RESTCONF layer is HTTPS, and the
mandatory-to-implement secure transport is TLS. The NETCONF
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.The YANG modules in this document make use of groupings that
are defined in YANG Groupings for
HTTP Clients and HTTP Servers, YANG Groupings for
TLS Clients and TLS Servers, and A
YANG Data Model for SNMP Configuration. Please see the
Security Considerations section of those documents for
considerations related to sensitivity and vulnerability of the
data nodes defined in them. Additionally, the parameters defined
in the tls-client-grouping in the ietf-tls-client module should
follow the recommendations specified in Recommendations for Secure Use of Transport
Layer Security (TLS) and Datagram Transport Layer Security
(DTLS).There are a number of data nodes defined in the YANG modules
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:The "path" node in "ietf-subscribed-notif-receivers"
module can be modified by a malicious user to point to an
invalid URI. Worse still, it could point the URI of their
choosing, exploit the vulnerable client, and if redirects
are followed to the same URI, track its usage.The container "receiver-identity" contains nodes like
"cert-maps" that are used by the HTTP server to map to the
HTTPS client's certificate to a 'local' username. An
unintended modification of these nodes will result in new
connection requests be denied.Some of the readable data nodes in the YANG modules 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. The
model does not define any readable subtrees and data nodes that
are particularly sensitive or vulnerable.Some of the RPC operations in the YANG modules may be
considered sensitive or vulnerable in some network
environments. It is thus important to control access to these
operations. The model does not define any RPC operations.This document registers two URIs in the "ns" subregistry
of the "IETF XML" registry . Following
the format in , the following
registrations are requested:
URI: urn:ietf:params:xml:ns:yang:ietf-subscribed-notif-receivers
Registrant Contact: The IESG
XML: N/A, the requested URI is an XML namespace.
URI: urn:ietf:params:xml:ns:yang:ietf-https-notif-transport
Registrant Contact: The IESG
XML: N/A, the requested URI is an XML namespace.
This document registers two YANG modules in the
"YANG Module Names" registry .
Following the format in , the
following registrations are requested:
name: ietf-subscribed-notif-receivers
namespace: urn:ietf:params:xml:ns:yang:ietf-subscribed-notif-receivers
prefix: snr
reference: RFC XXXX
name: ietf-https-notif-transport
namespace: urn:ietf:params:xml:ns:yang:ietf-https-notif-transport
prefix: hnt
reference: RFC XXXX
This document requests that IANA register a new URN Sub-namespace within the
"IETF URN Sub-namespace for Registered Protocol Parameter Identifiers"
registry defined in .
Registry Name: yang-notif
Specification: RFC XXXX
Repository: "YANG Notifications" registry
This document requests that IANA register a new URN Sub-namespace within the
"YANG Notifications" registry group defined in .
Registry Name: https-capability
Specification: RFC XXXX
Repository: "Capabilities for HTTPS Notification Receivers" registry
The following note shall be at the top of the registry:This registry defines capabilities that can be
supported by HTTPS-based notification receivers.
The fields for each registry are:
URN
The name of the URN (required).The URN must conform to the syntax described by .The URN must begin with the string "urn:ietf:params:yang-notif:https-capability".Reference
The RFC that defined the URN.The RFC must be in the form "RFC <Number>: <Title>.Description
An arbitrary description of the capability.The description should be no more than a few sentences.The description is to be in English, but may contain
UTF-8 characters as may be needed in some cases.
The update policy is "RFC Required".
Following is the initial assignment for this registry:
Record:
URN: urn:ietf:params:yang-notif:https-capability:encoding:json
Reference: RFC XXXX:An HTTPS-based Transport for YANG Notifications
Description: Identifies support for JSON-encoded notifications.
Record:
URN: urn:ietf:params:yang-notif:https-capability:encoding:xml
Reference: RFC XXXX:An HTTPS-based Transport for YANG Notifications
Description: Identifies support for XML-encoded notifications.
Record:
URN: urn:ietf:params:yang-notif:https-capability:sub-notif
Reference: RFC XXXX:An HTTPS-based Transport for YANG Notifications
Description: Identifies support for state machine described in
RFC 8639, enabling the publisher to send, e.g., the
"subscription-started" notification.
This non-normative section shows two examples for how the "ietf-https-notif-transport"
module can be used to configure a publisher to send notifications to
a receiver.In both examples, the publisher, being an HTTPS client, is
configured to send notifications to a receiver.This example shows how an RFC 8639
based publisher can be configured to send notifications to a
receiver.global-receiver-defreceiver.example.com443Server Cert Issuer #1base64encodedvalue==my-namemy-password/some/path111:0A:05:11:00x509c2n:san-any6666ph:httpssome-streamsubscription-specific-receiver-defglobal-receiver-def
explicitly-trusted-server-ca-certs
Trust anchors (i.e. CA certs) that are used to
authenticate connections to receivers. Receivers
are authenticated if their certificate has a chain
of trust to one of these CA certificates.
certificates.
ca.example.combase64encodedvalue==Fred Flintstonebase64encodedvalue==
]]>In the case that it is desired to use HTTPS-based
notifications outside of Subscribed Notifications, an
application-specific module would need to define the
configuration for sending the notification.Following is an example module. Note that the module
"uses" the "https-receiver-grouping" grouping from the
"ietf-https-notif-transport" module.Following is what the corresponding configuration looks like:fooreceiver.example.com443Server Cert Issuer #1base64encodedvalue==my-namemy-password/some/path
]]>The authors would like to thank for following for
lively discussions on list and in the halls (ordered
by first name):
Eric Voit,
Henning Rogge,
Martin Bjorklund,
Reshad Rahman,
and Rob Wilton.
In addition, the authors would also like to thank Quifang Ma
for providing thoughtful comments as part of shepherd
writeup.