| NETCONF Working Group | K. Watsen |
| Internet-Draft | Juniper Networks |
| Intended status: Standards Track | J. Schoenwaelder |
| Expires: August 6, 2015 | Jacobs University Bremen |
| February 2, 2015 |
NETCONF Server and RESTCONF Server Configuration Models
draft-ietf-netconf-server-model-06
This draft defines a NETCONF server configuration data model and a RESTCONF server configuration data model. These data models enable configuration of the NETCONF and RESTCONF services themselves, including which transports are supported, what ports the servers listens on, whether call-home is supported, and associated parameters.
This draft contains many 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. Please note that no other RFC Editor instructions are specified anywhere else in this document.
This document contains references to other drafts in progress, both in the Normative References section, as well as in body text throughout. Please update the following references to reflect their final RFC assignments:
Artwork in this document contains shorthand references to drafts in progress. Please apply the following replacements:
Artwork in this document contains placeholder values for ports pending IANA assignment from "draft-ietf-netconf-call-home". Please apply the following replacements:
Artwork in this document contains placeholder values for the date of publication of this draft. Please apply the following replacement:
The following two Appendix sections are to be removed prior to publication:
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at http://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 August 6, 2015.
Copyright (c) 2015 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 (http://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 Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
This draft defines a NETCONF [RFC6241] server configuration data model and a RESTCONF [draft-ietf-netconf-restconf] server configuration data model. These data models enable configuration of the NETCONF and RESTCONF services themselves, including which transports are supported, what ports the servers listens on, whether call-home is supported, and associated parameters.
The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119].
A simplified graphical representation of the data models is used in this document. The meaning of the symbols in these diagrams is as follows:
The primary purpose of the YANG modules defined herein is to enable the configuration of the NETCONF and RESTCONF services on a network element. This scope includes the following objectives:
The YANG module should support all current NETCONF and RESTCONF transports, namely NETCONF over SSH [RFC6242], NETCONF over TLS [draft-ietf-netconf-rfc5539bis], and RESTCONF over TLS [draft-ietf-netconf-restconf], and to be extensible to support future transports as necessary.
Because implementations may not support all transports, the module should use YANG "feature" statements so that implementations can accurately advertise which transports are supported.
Servers may have a multiplicity of host-keys or server-certificates from which subsets may be selected for specific uses. For instance, a NETCONF server may want to use one set of SSH host-keys when listening on port 830, and a different set of SSH host-keys when calling home. The data models provided herein should enable configuration of which keys to use on a per-use basis.
When a certificate is used to authenticate a NETCONF or RESTCONF client, there is a need to configure the server to know how to authenticate the certificates. The server should be able to authenticate the client's certificate either by using path-validation to a configured trust anchor or by matching the client-certificate to one previously configured.
When a client certifcate is used for TLS transport-level authentication, the NETCONF/RESTCONF server must be able to derive a username from the authenticated certifcate. Thus the modules defined herein should enable this mapping to be configured.
The NETCONF and RESTCONF protocols were originally defined as having the server opening a port to listen for client connections. More recently the NETCONF working group defined support for call-home ([draft-ietf-netconf-call-home]), enabling the server to initiate the connection to the client, for both the NETCONF and RESTCONF protocols. Thus the modules defined herein should enable configuration for both listening for connections and calling home. Because implementations may not support both listening for connections and calling home, YANG "feature" statements should be used so that implementation can accurately advertise the connection types it supports.
The following objectives only pertain to call home connections.
A device may be managed by more than one northbound application. For instance, a deployment may have one application for provisioning and another for fault monitoring. Therefore, when it is desired for a device to initiate call home connections, it should be able to do so to more than one application.
An application managing a device may implement a high-availability strategy employing a multiplicity of active and/or passive servers. Therefore, when it is desired for a device to initiate call home connections, it should be able to connect to any of the application's servers.
Assuming an application has more than one server, then it becomes necessary to configure how a device should reconnect to the application should it lose its connection to the application's servers. Of primary interest is if the device should start with first server defined in a user-ordered list of servers or with the last server it was connected to. Secondary settings might specify the frequency of attempts and number of attempts per server. Therefore, a reconnection strategy should be configurable.
Applications may vary greatly on how frequently they need to interact with a device, how responsive interactions with devices need to be, and how many simultaneous connections they can support. Some applications may need a persistent connection to devices to optimize real-time interactions, while others prefer periodic interactions in order to minimize resource requirements. Therefore, when it is necessary for devices to initiate connections, the type of connection desired should be configurable.
The reconnection strategy should apply to both persistent and periodic connections. How it applies to periodic connections becomes clear when considering that a periodic "connection" is a logical connection to a single server. That is, the periods of unconnectedness are intentional as opposed to due to external reasons. A periodic "connection" should always reconnect to the same server until it is no longer able to, at which time the reconnection strategy guides how to connect to another server.
If a persistent connection is desired, it is the responsibility of the connection initiator to actively test the "aliveness" of the connection. The connection initiator must immediately work to reestablish a persistent connection as soon as the connection is lost. How often the connection should be tested is driven by application requirements, and therefore keep-alive settings should be configurable on a per-application basis.
If a periodic connection is desired, it is necessary for the device to know how often it should connect. This delay essentially determines how long the application might have to wait to send data to the device. This setting does not constrain how often the device must wait to send data to the application, as the device should immediately connect to the application whenever it has data to send to it.
A common communication pattern is that one data transmission is many times closely followed by another. For instance, if the device needs to send a notification message, there's a high probability that it will send another shortly thereafter. Likewise, the application may have a sequence of pending messages to send. Thus, it should be possible for a device to hold a connection open until some amount of time of no data being transmitted as transpired.
module: ietf-netconf-server
+--rw netconf-server
+--rw session-options
+--rw hello-timeout? uint32
+--rw idle-timeout? uint32
The above subtree illustrates how the ietf-netconf-server YANG module enables configuration of NETCONF session options, independent of any transport or connection strategy. Please see the YANG module (Section 3.2) for a complete description of these configuration knobs.
module: ietf-netconf-server
+--rw netconf-server
+--rw listen {listen}?
+--rw max-sessions? uint16
+--rw endpoint* [name]
+--rw name string
+--rw (transport)
| +--:(ssh) {ssh}?
| | +--rw ssh
| | +--rw address? inet:ip-address
| | +--rw port? inet:port-number
| | +--rw host-keys
| | +--rw host-key* string
| +--:(tls) {tls}?
| +--rw tls
| +--rw address? inet:ip-address
| +--rw port? inet:port-number
| +--rw certificates
| +--rw certificate* string
+--rw keep-alives
+--rw interval-secs? uint8
+--rw count-max? uint8
The above subtree illustrates how the ietf-netconf-server YANG module enables configuration for listening for remote connections, as described in [RFC6242]. Feature statements are used to limit both if listening is supported at all as well as for which transports. If listening for connections is supported, then the model enables configuring a list of listening endpoints, each configured with a user-specified name (the key field), the transport to use (i.e. SSH, TLS), and the IP address and port to listen on. The port field is optional, defaulting to the transport-specific port when not configured. Please see the YANG module (Section 3.2) for a complete description of these configuration knobs.
module: ietf-netconf-server
+--rw netconf-server
+--rw call-home {call-home}?
+--rw application* [name]
+--rw name string
+--rw (transport)
| +--:(ssh) {ssh}?
| | +--rw ssh
| | +--rw endpoints
| | | +--rw endpoint* [name]
| | | +--rw name string
| | | +--rw address inet:host
| | | +--rw port? inet:port-number
| | +--rw host-keys
| | +--rw host-key* string
| +--:(tls) {tls}?
| +--rw tls
| +--rw endpoints
| | +--rw endpoint* [name]
| | +--rw name string
| | +--rw address inet:host
| | +--rw port? inet:port-number
| +--rw certificates
| +--rw certificate* string
+--rw connection-type
| +--rw (connection-type)?
| +--:(persistent-connection)
| | +--rw persistent
| | +--rw keep-alives
| | +--rw interval-secs? uint8
| | +--rw count-max? uint8
| +--:(periodic-connection)
| +--rw periodic
| +--rw timeout-mins? uint8
| +--rw linger-secs? uint8
+--rw reconnect-strategy
+--rw start-with? enumeration
+--rw interval-secs? uint8
+--rw count-max? uint8
The above subtree illustrates how the ietf-netconf-server YANG module enables configuration for call home, as described in [draft-ietf-netconf-call-home]. Feature statements are used to limit both if call-home is supported at all as well as for which transports, if it is. If call-home is supported, then the model supports configuring a list of applications to connect to. Each application is configured with a user-specified name (the key field), the transport to be used (i.e. SSH, TLS), and a list of remote endpoints, each having a name, an IP address, and an optional port. Additionally, the configuration for each remote application indicates the connection-type (persistent vs. periodic) and associated parameters, as well as the reconnection strategy to use. Please see the YANG module (Section 3.2) for a complete description of these configuration knobs.
module: ietf-netconf-server
+--rw netconf-server
+--rw ssh {ssh}?
+--rw x509 {ssh-x509-certs}?
+--rw trusted-ca-certs
| +--rw trusted-ca-cert* binary
+--rw trusted-client-certs
+--rw trusted-client-cert* binary
The above subtree illustrates how the ietf-netconf-server YANG module enables some SSH configuration independent of if the NETCONF server is listening or calling home. Specifically, when RFC 6187 is supported, this data model provides an ability to configure how client-certificates are authenticated. Please see the YANG module (Section 3.2) for a complete description of these configuration knobs.
module: ietf-netconf-server
+--rw netconf-server
+--rw tls {tls}?
+--rw client-auth
+--rw trusted-ca-certs
| +--rw trusted-ca-cert* binary
+--rw trusted-client-certs
| +--rw trusted-client-cert* binary
+--rw cert-maps
+--rw cert-to-name* [id]
+--rw id uint32
+--rw fingerprint x509c2n:tls-fingerprint
+--rw map-type identityref
+--rw name string
The above subtree illustrates how the ietf-netconf-server YANG module enables TLS configuration independent of if the NETCONF server is listening or calling home. Specifically, this data-model provides 1) an ability to configure how client-certificates are authenticated and 2) how authenticated client-certificates are mapped to NETCONF user names. Please see the YANG module (Section 3.2) for a complete description of these configuration knobs.
This YANG module imports YANG types from [RFC6991] and [RFC7407].
<CODE BEGINS> file "ietf-netconf-server@2015-02-02.yang"
module ietf-netconf-server {
namespace "urn:ietf:params:xml:ns:yang:ietf-netconf-server";
prefix "ncserver";
import ietf-netconf-acm {
prefix nacm; // RFC 6536
revision-date 2012-02-22;
}
import ietf-inet-types { // RFC 6991
prefix inet;
revision-date 2013-07-15;
}
import ietf-x509-cert-to-name { // RFC 7407
prefix x509c2n;
revision-date 2014-12-10;
}
organization
"IETF NETCONF (Network Configuration) Working Group";
contact
"WG Web: <http://tools.ietf.org/wg/netconf/>
WG List: <mailto:netconf@ietf.org>
WG Chair: Mehmet Ersue
<mailto:mehmet.ersue@nsn.com>
WG Chair: Mahesh Jethanandani
<mailto:mjethanandani@gmail.com>
Editor: Kent Watsen
<mailto:kwatsen@juniper.net>";
description
"This module contains a collection of YANG definitions for
configuring NETCONF servers.
Copyright (c) 2014 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
(http://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC VVVV; see
the RFC itself for full legal notices.";
revision "2015-02-02" {
description
"Initial version";
reference
"RFC VVVV: NETCONF Server and RESTCONF Server Configuration Models";
}
// Features
feature ssh {
description
"The ssh feature indicates that the server supports the
SSH transport protocol.";
reference
"RFC 6242: Using the NETCONF Protocol over Secure Shell (SSH)";
}
feature tls {
description
"The tls feature indicates that the server supports the
TLS transport protocol.";
reference
"RFC 5539: NETCONF over Transport Layer Security (TLS)";
}
feature listen {
description
"The listen feature indicates that the server supports
opening a port to listen for incoming client connections.";
reference
"RFC 6242: Using the NETCONF Protocol over Secure Shell (SSH)
RFC 5539: NETCONF over Transport Layer Security (TLS)";
}
feature call-home {
description
"The call-home feature indicates that the server supports
connecting to the client";
reference
"RFC YYYY: NETCONF Call Home and RESTCONF Call Home";
}
feature ssh-x509-certs {
description
"The ssh-x509-certs feature indicates that the NETCONF server
supports RFC 6187";
reference
"RFC 6187: X.509v3 Certificates for Secure Shell Authentication";
}
// top-level container (groupings below)
container netconf-server {
description
"Top-level container for NETCONF server configuration.";
uses session-options-container;
uses listen-container;
uses call-home-container;
uses ssh-container;
uses tls-container;
}
grouping session-options-container {
description
"This grouping is used only to help improve readability
of the YANG module.";
container session-options {
description
"NETCONF session options, independent of transport
or connection strategy.";
leaf hello-timeout {
type uint32 {
range "0 | 10 .. 3600";
}
units "seconds";
default '600';
description
"Specifies the number of seconds that a session may exist
before the hello PDU is received. A session will be
dropped if no hello PDU is received before this number
of seconds elapses.
If this parameter is set to zero, then the server will
wait forever for a hello message, and not drop any
sessions stuck in 'hello-wait' state.
Setting this parameter to zero may permit denial of
service attacks, since only a limited number of
concurrent sessions may be supported by the server.";
}
leaf idle-timeout {
type uint32 {
range "0 | 10 .. 360000";
}
units "seconds";
default '3600';
description
"Specifies the number of seconds that a NETCONF session may
remain idle without issuing any RPC requests. A session
will be dropped if it is idle for an interval longer than
this number of seconds. If this parameter is set to zero,
then the server will never drop a session because it is
idle. Sessions that have a notification subscription
active are never dropped.
This mechanism is independent of keep-alives, as it regards
activity occurring at the NETCONF protocol layer, whereas
the keep-alive mechanism regards transport-level activity.";
}
}
}
grouping listen-container {
description
"This grouping is used only to help improve readability
of the YANG module.";
container listen {
description
"Configures listen behavior";
if-feature listen;
leaf max-sessions {
type uint16 {
range "0 .. 1024";
}
default '0';
description
"Specifies the maximum number of concurrent sessions
that can be active at one time. The value 0 indicates
that no artificial session limit should be used.";
}
list endpoint {
key name;
description
"List of endpoints to listen for NETCONF connections on.";
leaf name {
type string;
description
"An arbitrary name for the NETCONF listen endpoint.";
}
choice transport {
mandatory true;
description
"Selects between SSH and TLS transports.";
case ssh {
if-feature ssh;
container ssh {
description
"SSH-specific listening configuration for inbound
connections.";
uses address-and-port-grouping {
refine port {
default 830;
}
}
uses host-keys-container;
}
}
case tls {
if-feature tls;
container tls {
description
"TLS-specific listening configuration for inbound
connections.";
uses address-and-port-grouping {
refine port {
default 6513;
}
}
uses certificates-container;
}
}
}
uses keep-alives-container {
refine keep-alives/interval-secs {
default 0; // disabled by default for listen connections
}
}
}
}
}
grouping call-home-container {
description
"This grouping is used only to help improve readability
of the YANG module.";
container call-home {
if-feature call-home;
description
"Configures call-home behavior";
list application {
key name;
description
"List of NETCONF clients the NETCONF server is to initiate
call-home connections to.";
leaf name {
type string;
description
"An arbitrary name for the remote NETCONF client.";
}
choice transport {
mandatory true;
description
"Selects between available transports.";
case ssh {
if-feature ssh;
container ssh {
description
"Specifies SSH-specific call-home transport
configuration.";
uses endpoints-container {
refine endpoints/endpoint/port {
default 7777;
}
}
uses host-keys-container;
}
}
case tls {
if-feature tls;
container tls {
description
"Specifies TLS-specific call-home transport
configuration.";
uses endpoints-container {
refine endpoints/endpoint/port {
default 8888;
}
}
uses certificates-container;
}
}
}
container connection-type {
description
"Indicates the kind of connection to use.";
choice connection-type {
default persistent-connection;
description
"Selects between persistent and periodic connections.";
case persistent-connection {
container persistent {
description
"Maintain a persistent connection to the NETCONF
client. If the connection goes down, immediately
start trying to reconnect to it, using the
reconnection strategy.
This connection type minimizes any NETCONF client
to NETCONF server data-transfer delay, albeit at
the expense of holding resources longer.";
uses keep-alives-container {
refine keep-alives/interval-secs {
default 15; // 15 seconds for call-home sessions
}
}
}
}
case periodic-connection {
container periodic {
description
"Periodically connect to NETCONF client, using the
reconnection strategy, so the NETCONF client can
deliver pending messages to the NETCONF server.
For messages the NETCONF server wants to send to
to the NETCONF client, the NETCONF server should
proactively connect to the NETCONF client, if
not already, to send the messages immediately.";
leaf timeout-mins {
type uint8;
units minutes;
default 5;
description
"The maximum amount of unconnected time the NETCONF
server will wait until establishing a connection to
the NETCONF client again. The NETCONF server MAY
establish a connection before this time if it has
data it needs to send to the NETCONF client. Note:
this value differs from the reconnection strategy's
interval-secs value.";
}
leaf linger-secs {
type uint8;
units seconds;
default 30;
description
"The amount of time the NETCONF server should wait
after last receiving data from or sending data to
the NETCONF client's endpoint before closing its
connection to it. This is an optimization to
prevent unnecessary connections.";
}
}
}
}
}
container reconnect-strategy {
description
"The reconnection strategy guides how a NETCONF server
reconnects to an NETCONF client, after losing a connection
to it, even if due to a reboot. The NETCONF server starts
with the specified endpoint and tries to connect to it
count-max times, waiting interval-secs between each
connection attempt, before trying the next endpoint in
the list (round robin).";
leaf start-with {
type enumeration {
enum first-listed {
description
"Indicates that reconnections should start with
the first endpoint listed.";
}
enum last-connected {
description
"Indicates that reconnections should start with
the endpoint last connected to. NETCONF servers
SHOULD support this flag across reboots.";
}
}
default first-listed;
description
"Specifies which of the NETCONF client's endpoints the
NETCONF server should start with when trying to connect
to the NETCONF client. If no previous connection has
ever been established, last-connected defaults to
the first endpoint listed.";
}
leaf interval-secs {
type uint8;
units seconds;
default 5;
description
"Specifies the time delay between connection attempts
to the same endpoint. Note: this value differs from
the periodic-connection's timeout-mins value.";
}
leaf count-max {
type uint8;
default 3;
description
"Specifies the number times the NETCONF server tries to
connect to a specific endpoint before moving on to the
next endpoint in the list (round robin).";
}
}
}
}
}
grouping ssh-container {
description
"This grouping is used only to help improve readability
of the YANG module.";
container ssh {
description
"Configures SSH properties not specific to the listen
or call-home use-cases";
if-feature ssh;
container x509 {
if-feature ssh-x509-certs;
uses trusted-certs-grouping;
}
}
}
grouping tls-container {
description
"This grouping is used only to help improve readability
of the YANG module.";
container tls {
description
"Configures TLS properties for authenticating clients.";
if-feature tls;
container client-auth {
description
"Container for TLS client authentication configuration.";
uses trusted-certs-grouping;
container cert-maps {
uses x509c2n:cert-to-name;
description
"The cert-maps container is used by a NETCONF server to
map the NETCONF client's presented X.509 certificate to a
NETCONF username. If no matching and valid cert-to-name
list entry can be found, then the NETCONF server MUST
close the connection, and MUST NOT accept NETCONF
messages over it.";
}
}
}
}
grouping trusted-certs-grouping {
description
"This grouping is used by both the ssh and tls containers.";
container trusted-ca-certs {
description
"A list of Certificate Authority (CA) certificates that
a NETCONF server can use to authenticate NETCONF client
certificates. A client's certificate is authenticated
if there is a chain of trust to a configured trusted CA
certificate. The client certificate MAY be accompanied
with additional certificates forming a chain of trust.
The client's certificate is authenticated if there is
path-validation from any of the certificates it presents
to a configured trust anchor.";
leaf-list trusted-ca-cert {
type binary;
ordered-by system;
nacm:default-deny-write;
description
"The binary certificate structure as specified by RFC
5246, Section 7.4.6, i.e.,: opaque ASN.1Cert<1..2^24>;
";
reference
"RFC 5246: The Transport Layer Security (TLS)
Protocol Version 1.2";
}
}
container trusted-client-certs {
description
"A list of client certificates that a NETCONF server can
use to authenticate a NETCONF client's certificate. A
client's certificate is authenticated if it is an exact
match to a configured trusted client certificates.";
leaf-list trusted-client-cert {
type binary;
ordered-by system;
nacm:default-deny-write;
description
"The binary certificate structure, as
specified by RFC 5246, Section 7.4.6, i.e.,:
opaque ASN.1Cert<1..2^24>;
";
reference
"RFC 5246: The Transport Layer Security (TLS)
Protocol Version 1.2";
}
}
}
grouping host-keys-container {
description
"This grouping is used by both the listen and
call-home containers";
container host-keys {
description
"Parent container for the list of host-keys.";
leaf-list host-key {
type string;
min-elements 1;
ordered-by user;
description
"A user-ordered list of host-keys the SSH server
considers when composing the list of server host
key algorithms it will send to the client in its
SSH_MSG_KEXINIT message. The value of the string
is the unique identifier for a host-key configured
on the system. How valid values are discovered is
outside the scope of this module, but they are
envisioned to be the keys for a list of host-keys
provided by another YANG module";
reference
"RFC 4253: The SSH Transport Layer Protocol, Section 7";
}
}
}
grouping certificates-container {
description
"This grouping is used by both the listen and
call-home containers";
container certificates {
description
"Parent container for the list of certificates.";
leaf-list certificate {
type string;
min-elements 1;
description
"An unordered list of certificates the TLS server can pick
from when sending its Server Certificate message. The value
of the string is the unique identifier for a certificate
configured on the system. How valid values are discovered
is outside the scope of this module, but they are envisioned
to be the keys for a list of certificates provided
by another YANG module";
reference
"RFC 5246: The TLS Protocol, Section 7.4.2";
}
}
}
grouping address-and-port-grouping {
description
"This grouping is usd by both the ssh and tls containers
for listen configuration.";
leaf address {
type inet:ip-address;
description
"The IP address of the interface to listen on.";
}
leaf port {
type inet:port-number;
description
"The local port number on this interface the NETCONF server
listens on.";
}
}
grouping endpoints-container {
description
"This grouping is used by both the ssh and tls containers
for call-home configurations.";
container endpoints {
description
"Container for the list of endpoints.";
list endpoint {
key name;
min-elements 1;
ordered-by user;
description
"User-ordered list of endpoints for this NETCONF client.
Defining more than one enables high-availability.";
leaf name {
type string;
description
"An arbitrary name for the endpoint to connect to.";
}
leaf address {
type inet:host;
mandatory true;
description
"The hostname or IP address or hostname of the endpoint.
If a hostname is provided and DNS resolves to more than
one IP address, the NETCONF server SHOULD try all of
the ones it can based on how its networking stack is
configured (e.g. v4, v6, dual-stack).";
}
leaf port {
type inet:port-number;
description
"The IP port for this endpoint. The NETCONF server will
use the IANA-assigned well-known port if not specified.";
}
}
}
}
grouping keep-alives-container {
description
"This grouping is use by both listen and call-home configurations.";
container keep-alives {
description
"Configures the keep-alive policy, to proactively test the
aliveness of the NETCONF client.";
reference
"RFC VVVV: NETCONF Server and RESTCONF Server Configuration
Models, Section 4";
leaf interval-secs {
type uint8;
units seconds;
description
"Sets a timeout interval in seconds after which if no data
has been received from the NETCONF client, a message will
be sent to request a response from the NETCONF client. A
value of '0' indicates that no keep-alive messages should
be sent.";
}
leaf count-max {
type uint8;
default 3;
description
"Sets the number of keep-alive messages that may be sent
without receiving any data from the NETCONF client before
assuming the NETCONF client is no longer alive. If this
threshold is reached, the transport-level connection will
be disconnected, which will trigger the reconnection
strategy). The interval timer is reset after each
transmission, thus an unresponsive NETCONF client will
be dropped after approximately (count-max * interval-secs)
seconds.";
}
}
}
}
<CODE ENDS>
module: ietf-restconf-server
+--rw restconf-server
+--rw listen {listen}?
+--rw max-sessions? uint16
+--rw endpoint* [name]
+--rw name string
+--rw (transport)
| +--:(tls)
| +--rw tls
| +--rw address? inet:ip-address
| +--rw port? inet:port-number
| +--rw certificates
| +--rw certificate* string
+--rw keep-alives
+--rw interval-secs? uint8
+--rw count-max? uint8
The above subtree illustrates how the ietf-restconf-server YANG module enables configuration for listening for remote connections, as described in [draft-ietf-netconf-restconf]. Feature statements are used to limit both if listening is supported at all as well as for which transports. If listening for connections is supported, then the model enables configuring a list of listening endpoints, each configured with a user-specified name (the key field), the transport to use (i.e. TLS), and the IP address and port to listen on. The port field is optional, defaulting to the transport-specific port when not configured. Please see the YANG module (Section 4.2) for a complete description of these configuration knobs.
module: ietf-restconf-server
+--rw restconf-server
+--rw call-home {call-home}?
+--rw application* [name]
+--rw name string
+--rw (transport)
| +--:(tls) {tls}?
| +--rw tls
| +--rw endpoints
| | +--rw endpoint* [name]
| | +--rw name string
| | +--rw address inet:host
| | +--rw port? inet:port-number
| +--rw certificates
| +--rw certificate* string
+--rw connection-type
| +--rw (connection-type)?
| +--:(persistent-connection)
| | +--rw persistent
| | +--rw keep-alives
| | +--rw interval-secs? uint8
| | +--rw count-max? uint8
| +--:(periodic-connection)
| +--rw periodic
| +--rw timeout-mins? uint8
| +--rw linger-secs? uint8
+--rw reconnect-strategy
+--rw start-with? enumeration
+--rw interval-secs? uint8
+--rw count-max? uint8
The above subtree illustrates how the ietf-restconf-server YANG module enables configuration for call home, as described in [draft-ietf-netconf-call-home]. Feature statements are used to limit both if call-home is supported at all as well as for which transports, if it is. If call-home is supported, then the model supports configuring a list of applications to connect to. Each application is configured with a user-specified name (the key field), the transport to be used (i.e. TLS), and a list of remote endpoints, each having a name, an IP address, and an optional port. Additionally, the configuration for each remote application indicates the connection-type (persistent vs. periodic) and associated parameters, as well as the reconnection strategy to use. Please see the YANG module (Section 4.2) for a complete description of these configuration knobs.
module: ietf-restconf-server
+--rw restconf-server
+--rw client-cert-auth {client-cert-auth}?
+--rw trusted-ca-certs
| +--rw trusted-ca-cert* binary
+--rw trusted-client-certs
| +--rw trusted-client-cert* binary
+--rw cert-maps
+--rw cert-to-name* [id]
+--rw id uint32
+--rw fingerprint x509c2n:tls-fingerprint
+--rw map-type identityref
+--rw name string
The above subtree illustrates how the ietf-restconf-server YANG module enables configuration of client-certificate authentication. Specifically, this data-model provides 1) an ability to configure how client-certificates are authenticated and 2) how authenticated client-certificates are mapped to RESTCONF user names. Please see the YANG module (Section 4.2) for a complete description of these configuration knobs.
This YANG module imports YANG types from [RFC6991] and [RFC7407].
<CODE BEGINS> file "ietf-restconf-server@2015-02-02.yang"
module ietf-restconf-server {
namespace "urn:ietf:params:xml:ns:yang:ietf-restconf-server";
prefix "rcserver";
import ietf-netconf-acm {
prefix nacm; // RFC 6536
revision-date 2012-02-22;
}
import ietf-inet-types { // RFC 6991
prefix inet;
revision-date 2013-07-15;
}
import ietf-x509-cert-to-name { // RFC 7407
prefix x509c2n;
revision-date 2014-12-10;
}
organization
"IETF NETCONF (Network Configuration) Working Group";
contact
"WG Web: <http://tools.ietf.org/wg/netconf/>
WG List: <mailto:netconf@ietf.org>
WG Chair: Mehmet Ersue
<mailto:mehmet.ersue@nsn.com>
WG Chair: Mahesh Jethanandani
<mailto:mjethanandani@gmail.com>
Editor: Kent Watsen
<mailto:kwatsen@juniper.net>";
description
"This module contains a collection of YANG definitions for
configuring RESTCONF servers.
Copyright (c) 2014 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
(http://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC VVVV; see
the RFC itself for full legal notices.";
revision "2015-02-02" {
description
"Initial version";
reference
"RFC VVVV: NETCONF Server and RESTCONF Server Configuration Models";
}
// Features
feature tls {
description
"The tls feature indicates that the server supports RESTCONF
over the TLS transport protocol.";
reference
"RFC XXXX: RESTCONF Protocol";
}
feature listen {
description
"The listen feature indicates that the server supports
opening a port to listen for incoming client connections.";
reference
"RFC XXXX: RESTCONF Protocol";
}
feature call-home {
description
"The call-home feature indicates that the server supports
connecting to the client.";
reference
"RFC YYYY: NETCONF Call Home and RESTCONF Call Home";
}
feature client-cert-auth {
description
"The client-cert-auth feature indicatres that the server
supports the ClientCertificate authentication scheme.";
reference
"RFC ZZZZ: Client Authentication over New TLS Connection";
}
// top-level container (groupings below)
container restconf-server {
description
"Top-level container for RESTCONF server configuration.";
uses listen-container;
uses call-home-container;
uses client-cert-auth-container;
}
grouping listen-container {
description
"This grouping is used only to help improve readability
of the YANG module.";
container listen {
description
"Configures listen behavior";
if-feature listen;
leaf max-sessions {
type uint16 {
range "0 .. 1024";
}
default '0';
description
"Specifies the maximum number of concurrent sessions
that can be active at one time. The value 0 indicates
that no artificial session limit should be used.";
}
list endpoint {
key name;
description
"List of endpoints to listen for RESTCONF connections on.";
leaf name {
type string;
description
"An arbitrary name for the RESTCONF listen endpoint.";
}
choice transport {
mandatory true;
description
"Selects between available transports.";
case tls {
container tls {
description
"TLS-specific listening configuration for inbound
connections.";
uses address-and-port-grouping {
refine port {
default 443;
}
}
uses certificates-container;
}
}
}
uses keep-alives-container {
refine keep-alives/interval-secs {
default 0; // disabled by default for listen connections
}
}
}
}
}
grouping call-home-container {
description
"This grouping is used only to help improve readability
of the YANG module.";
container call-home {
if-feature call-home;
description
"Configures call-home behavior";
list application {
key name;
description
"List of RESTCONF clients the RESTCONF server is to initiate
call-home connections to.";
leaf name {
type string;
description
"An arbitrary name for the remote RESTCONF client.";
}
choice transport {
mandatory true;
description
"Selects between TLS and any future transports augmented in.";
case tls {
if-feature tls;
container tls {
description
"Specifies TLS-specific call-home transport
configuration.";
uses endpoints-container {
refine endpoints/endpoint/port {
default 9999;
}
}
uses certificates-container;
}
}
}
container connection-type {
description
"Indicates the RESTCONF client's preference for how the
RESTCONF server's connection is maintained.";
choice connection-type {
default persistent-connection;
description
"Selects between persistent and periodic connections.";
case persistent-connection {
container persistent {
description
"Maintain a persistent connection to the RESTCONF
client. If the connection goes down, immediately
start trying to reconnect to it, using the
reconnection strategy.
This connection type minimizes any RESTCONF client
to RESTCONF server data-transfer delay, albeit at
the expense of holding resources longer.";
uses keep-alives-container {
refine keep-alives/interval-secs {
default 15; // 15 seconds for call-home sessions
}
}
}
}
case periodic-connection {
container periodic {
description
"Periodically connect to RESTCONF client, using the
reconnection strategy, so the RESTCONF client can
deliver pending messages to the RESTCONF server.
For messages the RESTCONF server wants to send to
to the RESTCONF client, the RESTCONF server should
proactively connect to the RESTCONF client, if
not already, to send the messages immediately.";
leaf timeout-mins {
type uint8;
units minutes;
default 5;
description
"The maximum amount of unconnected time the RESTCONF
server will wait until establishing a connection to
the RESTCONF client again. The RESTCONF server MAY
establish a connection before this time if it has
data it needs to send to the RESTCONF client. Note:
this value differs from the reconnection strategy's
interval-secs value.";
}
leaf linger-secs {
type uint8;
units seconds;
default 30;
description
"The amount of time the RESTCONF server should wait
after last receiving data from or sending data to
the RESTCONF client's endpoint before closing its
connection to it. This is an optimization to
prevent unnecessary connections.";
}
}
}
}
}
container reconnect-strategy {
description
"The reconnection strategy guides how a RESTCONF server
reconnects to an RESTCONF client, after losing a connection
to it, even if due to a reboot. The RESTCONF server starts
with the specified endpoint and tries to connect to it
count-max times, waiting interval-secs between each
connection attempt, before trying the next endpoint in
the list (round robin).";
leaf start-with {
type enumeration {
enum first-listed {
description
"Indicates that reconnections should start with
the first endpoint listed.";
}
enum last-connected {
description
"Indicates that reconnections should start with
the endpoint last connected to. RESTCONF servers
SHOULD support this flag across reboots.";
}
}
default first-listed;
description
"Specifies which of the RESTCONF client's endpoints the
RESTCONF server should start with when trying to connect
to the RESTCONF client. If no previous connection has
ever been established, last-connected defaults to
the first endpoint listed.";
}
leaf interval-secs {
type uint8;
units seconds;
default 5;
description
"Specifies the time delay between connection attempts
to the same endpoint. Note: this value differs from
the periodic-connection's timeout-mins value.";
}
leaf count-max {
type uint8;
default 3;
description
"Specifies the number times the RESTCONF server tries to
connect to a specific endpoint before moving on to the
next endpoint in the list (round robin).";
}
}
}
}
}
grouping client-cert-auth-container {
description
"This grouping is used only to help improve readability
of the YANG module.";
container client-cert-auth {
if-feature client-cert-auth;
description
"Container for TLS client certificate authentication
configuration.";
container trusted-ca-certs {
description
"A list of Certificate Authority (CA) certificates that
a NETCONF server can use to authenticate NETCONF client
certificates. A client's certificate is authenticated
if there is a chain of trust to a configured trusted CA
certificate. The client certificate MAY be accompanied
with additional certificates forming a chain of trust.
The client's certificate is authenticated if there is
path-validation from any of the certificates it presents
to a configured trust anchor.";
leaf-list trusted-ca-cert {
type binary;
ordered-by system;
nacm:default-deny-write;
description
"The binary certificate structure as specified by RFC
5246, Section 7.4.6, i.e.,: opaque ASN.1Cert<1..2^24>;
";
reference
"RFC 5246: The Transport Layer Security (TLS)
Protocol Version 1.2";
}
}
container trusted-client-certs {
description
"A list of client certificates that a NETCONF server can
use to authenticate a NETCONF client's certificate. A
client's certificate is authenticated if it is an exact
match to a configured trusted client certificates.";
leaf-list trusted-client-cert {
type binary;
ordered-by system;
nacm:default-deny-write;
description
"The binary certificate structure, as
specified by RFC 5246, Section 7.4.6, i.e.,:
opaque ASN.1Cert<1..2^24>;
";
reference
"RFC 5246: The Transport Layer Security (TLS)
Protocol Version 1.2";
}
}
container cert-maps {
uses x509c2n:cert-to-name;
description
"The cert-maps container is used by a NETCONF server to
map the NETCONF client's presented X.509 certificate to a
NETCONF username. If no matching and valid cert-to-name
list entry can be found, then the NETCONF server MUST
close the connection, and MUST NOT accept NETCONF
messages over it.";
}
}
}
grouping certificates-container {
description
"This grouping is used by both the listen and
call-home containers";
container certificates {
description
"Parent container for the list of certificates.";
leaf-list certificate {
type string;
min-elements 1;
description
"An unordered list of certificates the TLS server can pick
from when sending its Server Certificate message. The value
of the string is the unique identifier for a certificate
configured on the system. How valid values are discovered
is outside the scope of this module, but they are envisioned
to be the keys for a list of certificates provided
by another YANG module";
reference
"RFC 5246: The TLS Protocol, Section 7.4.2";
}
}
}
grouping address-and-port-grouping {
description
"This grouping is usd by both the ssh and tls containers
for listen configuration.";
leaf address {
type inet:ip-address;
description
"The IP address of the interface to listen on.";
}
leaf port {
type inet:port-number;
description
"The local port number on this interface the RESTCONF server
listens on.";
}
}
grouping endpoints-container {
description
"This grouping is used by both the ssh and tls containers
for call-home configurations.";
container endpoints {
description
"Container for the list of endpoints.";
list endpoint {
key name;
min-elements 1;
ordered-by user;
description
"User-ordered list of endpoints for this RESTCONF client.
Defining more than one enables high-availability.";
leaf name {
type string;
description
"An arbitrary name for the endpoint to connect to.";
}
leaf address {
type inet:host;
mandatory true;
description
"The hostname or IP address or hostname of the endpoint.
If a hostname is provided and DNS resolves to more than
one IP address, the RESTCONF server SHOULD try all of
the ones it can based on how its networking stack is
configured (e.g. v4, v6, dual-stack).";
}
leaf port {
type inet:port-number;
description
"The IP port for this endpoint. The RESTCONF server will
use the IANA-assigned well-known port if not specified.";
}
}
}
}
grouping keep-alives-container {
description
"This grouping is use by both listen and call-home configurations.";
container keep-alives {
description
"Configures the keep-alive policy, to proactively test the
aliveness of the RESTCONF client.";
reference
"RFC VVVV: NETCONF Server and RESTCONF Server Configuration
Models, Section 4";
leaf interval-secs {
type uint8;
units seconds;
description
"Sets a timeout interval in seconds after which if no data
has been received from the RESTCONF client, a message will
be sent to request a response from the RESTCONF client. A
value of '0' indicates that no keep-alive messages should
be sent.";
}
leaf count-max {
type uint8;
default 3;
description
"Sets the number of keep-alive messages that may be sent
without receiving any data from the RESTCONF client before
assuming the RESTCONF client is no longer alive. If this
threshold is reached, the transport-level connection will
be disconnected, which will trigger the reconnection
strategy). The interval timer is reset after each
transmission, thus an unresponsive RESTCONF client will
be dropped after approximately (count-max * interval-secs)
seconds.";
}
}
}
}
<CODE ENDS>
One of the objectives listed above, Keep-alives for persistent connections Section 2.6.6, indicates a need for a "keep-alive" mechanism. This section specifies how the keep-alive mechanism is to be implemented for both the SSH and TLS transports.
Both SSH and TLS have the ability to support keep-alives securely. Using the strategies listed below, the keep-alive messages are sent inside the encrypted tunnel and thus immune to attack.
The SSH keep-alive solution that is expected to be used is ubiquitous in practice, though never being explicitly defined in an RFC. The strategy used is to purposely send a malformed request message with a flag set to ensure a response. More specifically, per section 4 of [RFC4253], either SSH peer can send a SSH_MSG_GLOBAL_REQUEST message with "want reply" set to '1' and that, if there is an error, will get back a SSH_MSG_REQUEST_FAILURE response. Similarly, section 5 of [RFC4253] says that either SSH peer can send a SSH_MSG_CHANNEL_REQUEST message with "want reply" set to '1' and that, if there is an error, will get back a SSH_MSG_CHANNEL_FAILURE response.
To ensure that the request will fail, current implementations of this keep-alive strategy (e.g. OpenSSH's `sshd` server) send an invalid "request name" or "request type", respectively. Abiding to the extensibility guidelines specified in Section 6 of [RFC4251], these implementations use the "name@domain". For instance, when configured to send keep-alives, OpenSSH sends the string "keepalive@openssh.com". In order to remain compatible with existing implementations, this draft does not require a specific "request name" or "request type" string be used, implementations are free to pick values of their choosing.
The TLS keep-alive solution that is expected to be used is defined in [RFC6520]. This solution allows both peers to advertise if they can receive heartbeat request messages from its peer. For standard TLS connections, devices SHOULD advertise "peer_allowed_to_send", as per [RFC6520]. This advertisement is not a "MUST" in order to grandfather existing NETCONF/RESTCONF over TLS implementations. For NETCONF Call Home or RESTCONF Call Home, the network management system MUST advertise "peer_allowed_to_send" per [RFC6520]. This is a "MUST" so as to ensure devices can depend on it always being there for call home connections, which is when keep-alives are needed the most.
The YANG modules defined in this memo are designed to be accessed via the NETCONF protocol [RFC6241]. Authorization for access to specific portions of conceptual data and operations within this module is provided by the NETCONF access control model (NACM) [RFC6536].
There are a number of data nodes defined in the "ietf-netconf-server" YANG module which are readable and/or writable that may be considered sensitive or vulnerable in some network environments. Write and read operations to these data nodes can have a negative effect on network operations. It is thus important to control write and read access to these data nodes. Below are the data nodes and their sensitivity/vulnerability.
netconf-server/tls/client-auth/trusted-ca-certs:
netconf-server/tls/client-auth/trusted-client-certs:
restconf-server/tls/client-auth/trusted-ca-certs:
restconf-server/tls/client-auth/trusted-client-certs:
This document registers two URIs in the IETF XML registry [RFC2119]. Following the format in [RFC3688], the following registrations are requested:
URI: urn:ietf:params:xml:ns:yang:ietf-netconf-server Registrant Contact: The NETCONF WG of the IETF. XML: N/A, the requested URI is an XML namespace. URI: urn:ietf:params:xml:ns:yang:ietf-restconf-server Registrant Contact: The NETCONF WG of the IETF. XML: N/A, the requested URI is an XML namespace.
This document registers two YANG modules in the YANG Module Names registry [RFC6020]. Following the format in [RFC6020], the the following registrations are requested:
name: ietf-netconf-server namespace: urn:ietf:params:xml:ns:yang:ietf-netconf-server prefix: ncserver reference: RFC VVVV name: ietf-restconf-server namespace: urn:ietf:params:xml:ns:yang:ietf-restconf-server prefix: rcserver reference: RFC VVVV
The YANG modules define herein do not themselves support virtual routing and forwarding (VRF). It is expected that external modules will augment in VRF designations when needed.
The authors would like to thank for following for lively discussions on list and in the halls (ordered by last name): Andy Bierman, Martin Bjorklund, Benoit Claise, Mehmet Ersue, David Lamparter, Alan Luchuk, Ladislav Lhotka, Radek Krejci, Tom Petch, Phil Shafer, and Bert Wijnen.
Juergen Schoenwaelder and was partly funded by Flamingo, a Network of Excellence project (ICT-318488) supported by the European Commission under its Seventh Framework Programme.
| [RFC3688] | Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, January 2004. |
The following example illustrates the <get> response from a NETCONF server that only supports SSH, both listening for incoming connections as well as calling home to a single application having two endpoints.
<netconf-server xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-server">
<session-options>
<hello-timeout>600</hello-timeout>
<idle-timeout>3600</idle-timeout>
</session-options>
<listen>
<endpoint>
<name>foo bar</name>
<ssh>
<address>11.22.33.44</address>
<host-keys>
<host-key>my-rsa-key</host-key>
<host-key>my-dss-key</host-key>
</host-keys>
</ssh>
</endpoint>
</listen>
<call-home>
<application>
<name>config-mgr</name>
<ssh>
<endpoints>
<endpoint>
<name>east-data-center</name>
<address>11.22.33.44</address>
</endpoint>
<endpoint>
<name>west-data-center</name>
<address>55.66.77.88</address>
</endpoint>
</endpoints>
<host-keys>
<host-key>my-call-home-x509-key</host-key>
</host-keys>
</ssh>
</application>
</call-home>
<ssh>
<x509>
<trusted-ca-certs>
<trusted-ca-cert>
QW4gRWFzdGVyIGVnZywgZm9yIHRob3NlIHdobyBtaWdodCBsb29rICA6KQo=
</trusted-ca-cert>
</trusted-ca-certs>
<trusted-client-certs>
<trusted-client-cert>
SSBhbSB0aGUgZWdnIG1hbiwgdGhleSBhcmUgdGhlIGVnZyBtZW4uCg==
</trusted-client-cert>
<trusted-client-cert>
SSBhbSB0aGUgd2FscnVzLCBnb28gZ29vIGcnam9vYi4K
</trusted-client-cert>
</trusted-client-certs>
</x509>
</ssh>
</netconf-server>
The following example illustrates the <get> response from a NETCONF server that only supports TLS, both listening for incoming connections as well as calling home to a single application having two endpoints. Please note also the configurations for authenticating client certificates and mappings authenticated certificates to NETCONF user names.
<netconf-server xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-server">
<session-options>
<hello-timeout>600</hello-timeout>
<idle-timeout>3600</idle-timeout>
</session-options>
<listen>
<endpoint>
<name>primary-netconf-endpoint</name>
<tls>
<address>11.22.33.44</address>
<certificates>
<certificate>fw1.east.example.com</certificate>
</certificates>
</tls>
</endpoint>
</listen>
<call-home>
<application>
<name>config-mgr</name>
<tls>
<endpoints>
<endpoint>
<name>east-data-center</name>
<address>11.22.33.44</address>
</endpoint>
<endpoint>
<name>west-data-center</name>
<address>55.66.77.88</address>
</endpoint>
</endpoints>
<certificates>
<certificate>fw1.east.example.com</certificate>
</certificates>
</tls>
</application>
</call-home>
<tls>
<client-auth>
<trusted-ca-certs>
<trusted-ca-cert>
QW4gRWFzdGVyIGVnZywgZm9yIHRob3NlIHdobyBtaWdodCBsb29rICA6KQo=
</trusted-ca-cert>
</trusted-ca-certs>
<trusted-client-certs>
<trusted-client-cert>
SSBhbSB0aGUgZWdnIG1hbiwgdGhleSBhcmUgdGhlIGVnZyBtZW4uCg==
</trusted-client-cert>
<trusted-client-cert>
SSBhbSB0aGUgd2FscnVzLCBnb28gZ29vIGcnam9vYi4K
</trusted-client-cert>
</trusted-client-certs>
<cert-maps>
<cert-to-name>
<id>1</id>
<fingerprint>11:0A:05:11:00</fingerprint>
<map-type>x509c2n:san-any</map-type>
</cert-to-name>
<cert-to-name>
<id>2</id>
<fingerprint>11:0A:05:11:00</fingerprint>
<map-type>x509c2n:specified</map-type>
<name>Joe Cool</name>
</cert-to-name>
</cert-maps>
</client-auth>
</tls>
</netconf-server>
The following example illustrates the <get> response from a RESTCONF server that only supports TLS, both listening for incoming connections as well as calling home to a single application having two endpoints.
<restconf-server xmlns="urn:ietf:params:xml:ns:yang:ietf-restconf-server">
<listen>
<endpoint>
<name>primary-restconf-endpoint</name>
<tls>
<address>11.22.33.44</address>
<certificates>
<certificate>fw1.east.example.com</certificate>
</certificates>
</tls>
</endpoint>
</listen>
<call-home>
<application>
<name>config-mgr</name>
<tls>
<endpoints>
<endpoint>
<name>east-data-center</name>
<address>11.22.33.44</address>
</endpoint>
<endpoint>
<name>west-data-center</name>
<address>55.66.77.88</address>
</endpoint>
</endpoints>
<certificates>
<certificate>fw1.east.example.com</certificate>
</certificates>
</tls>
</application>
</call-home>
</restconf-server>
Please see: https://github.com/netconf-wg/server-model/issues.