| Network Working Group | A. Bierman |
| Internet-Draft | YumaWorks, Inc. |
| Intended status: Standards Track | April 11, 2013 |
| Expires: October 13, 2013 |
The NETCONF <get2> Operation
draft-bierman-netconf-get2-03
This document describes NETCONF protocol enhancements to improve data retrieval capabilities.
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.
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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 October 13, 2013.
Copyright (c) 2013 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.
There is a need for standard mechanisms to allow NETCONF [RFC6241] application designers to retrieve data from NETCONF servers more efficiently.
This document attempts to address the following problems with NETCONF data retrieval mechanisms.
The NETCONF <get> operation allows a client to retrieve data from the server but it returns all data, including configuration datastore nodes. The <get‑config> operation already returns all configuration datastore nodes.
It was originally thought that <get> should return all nodes so the client would not have to correlate configuration and non-configuration data nodes, since they would be mixed together in the reply.
Operational experience has shown that the <get> operation without reasonable filters to reduce the returned data can significantly degrade device performance and return enormous XML instance documents in the <rpc‑reply>.
The NETCONF protocol has no standard mechanisms to indicate to a client when a datastore was last modified, or to allow a client to retrieve data only if it has been modified since a specified time. This makes polling applications very inefficient because they will regularly burden the server and the network and themselves with retrieval and processing requests for data that has not changed.
Sometimes the client application wants to discover what data exists on the server, particularly list entries. There is a need for a simple mechanism to retrieve just the key leaf nodes within a subtree.
The NETCONF subtree filtering mechanism does provide a very complex way for the client to request just key leafs for specific list entries. A simpler mechanism is needed which will allow the client to discover the list instances present.
NETCONF filters allow the client to select specific sub-trees within the conceptual datastore on the server. However, sometimes the client does not really need the entire subtree, which may contain many nested list entries, and be very large.
There is sometimes a need to limit the depth of the sub-trees retrieved from the server. A consistent and simple algorithm for determining what data nodes start a new level is needed.
The NETCONF <get> and <get‑config> operations use a hard-coded content filtering mechanism. They use a "type" XML attribute to indicate which of two filter specification types they support, and a "select" XML attribute if the :xpath capability is supported and an XPath [XPATH] expression filter specification is provided.
This design does not allow additional content filter specification types to be supported by an implementation. It does not allow the standard to be easily extended in a modular fashion.
In addition, this design does not allow YANG statements to be used to properly describe the protocol operation. The special "get‑filter‑element‑attributes" YANG extension in the ietf-netconf module is not extensible, and it does not really count as proper YANG, since this extension is outside the YANG language definition.
This document defines a new NETCONF protocol operation called <get2> to address the deficiencies described in the previous section. It can be implemented existing NETCONF servers without requiring a change in the protocol version.
The keywords "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].
The following terms are defined in [RFC6241]:
The following terms are defined in [RFC6020]:
The following terms are defined:
The <get2> operation is defined with a YANG "rpc" statement. A specific datastore is selected for the source of the retrieval operation. Several different types of filters are provided. Filters are combined in a conceptual "logical‑AND" operation, and are optional to use by the client. Not all filtering mechanisms are mandatory-to-implement for the server.
The <get2> protocol operation contains the following input parameters:
A depth filter indicates how many subtree levels should be returned in the <rpc‑reply>. This filter is specified with the "depth" input parameter for the <get2> protocol operation. The default "0" indicates that all levels from the requested subtrees should be returned.
A new level is started for each YANG data node within the requested subtree. All top level data nodes are considered to be child nodes (level 1) of a conceptual <config> root.
If no content filters are provided, then level 1 is considered to include all top-level data nodes within the source datastore. Otherwise only the levels in selected subtrees will be considered, and not any additional top-level data nodes.
If the depth requested is equal to "1", then only the requested data nodes (or top-level data nodes) will be returned. This mechanism can be used to detect the existence of containers and list entries within a particular subtree, without returning any of the descendant nodes.
Higher depth values indicates the number of descendant nodes to include in the response. For example, if the depth requested is equal to "2", then only the requested data nodes (or top-level data nodes) and their immediate child data nodes will be returned.
A time filter indicates that only data which has been modified since the indicated date and time should be included in the reply.
If this feature is supported, then the server will maintain a last-modified timestamp for the source datastore. It MAY support additional nested timestamps for data nodes within the datastore.
When a request containing the "if‑modified‑since" parameter is received, the server will compare that timestamp to the last-modified timestamp for the source datastore. If it is greater than the specified value then data may be returned (depending on other filters). If the datastore timestamp value is less than or equal to the specified value, then an empty <data> element will be returned in the <rpc‑reply>.
If the server maintains "last‑modified" timestamps for any data nodes within the source datastore then the same type of comparison will be done for the data node to determine if it should be included in the response. If no "last‑modified" timestamp is maintained for a data node, then the server will use the "last‑modified" timestamp for its nearest ancestor, or for the datastore itself if there are none.
The following XML Schema document [XSD] defines the "last‑modified" attribute, described within this document. This XSD is only relevant if the server supports the "timestamps" YANG feature within the "ietf‑netconf‑get2" YANG module.
The "last‑modified" attribute uses the XSD data type "dateTime", in accordance with Section 3.2.7.1 of XML Schema Part 2: Datatypes. This is equivalent to the YANG data type "date‑and‑time".
<CODE BEGINS> file "last‑modified.xsd"
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns="urn:ietf:params:xml:ns:netconf:default:1.0"
targetNamespace="urn:ietf:params:xml:ns:netconf:last-modified:1.0"
elementFormDefault="qualified"
attributeFormDefault="unqualified"
xml:lang="en">
<xs:annotation>
<xs:documentation>
This schema defines the syntax for the "last-modified" attribute
described within this document.
</xs:documentation>
</xs:annotation>
<!--
last-modified attribute
-->
<xs:attribute name="last-modified" type="xs:dateTime">
<xs:annotation>
<xs:documentation>
This attribute indicates the date and time when
a modification was last detected by the server
for the datastore or data node corresponding to
the XML element containing this attribute.
</xs:documentation>
</xs:annotation>
</xs:attribute>
</xs:schema>
<CODE ENDS>
This module imports the "with‑defaults‑parameters" grouping from [RFC6243].
Several YANG features are imported from [RFC6241].
Some data types are imported from [RFC6021].
RFC Ed.: update the date below with the date of RFC publication and remove this note.
<CODE BEGINS> file "ietf-netconf-get2@2013-04-08.yang"
module ietf-netconf-get2 {
namespace "urn:ietf:params:xml:ns:yang:ietf-netconf-get2";
prefix get2;
import ietf-inet-types {
prefix inet;
}
import ietf-netconf {
prefix nc;
}
import ietf-netconf-with-defaults {
prefix ncwd;
}
import ietf-yang-types {
prefix yang;
}
organization
"IETF NETCONF (Network Configuration Protocol) 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: Bert Wijnen
<mailto:bertietf@bwijnen.net>
Editor: Andy Bierman
<mailto:andy@yumaworks.com>";
description
"This module contains a collection of YANG definitions for the
retrieval of information from a NETCONF server.
Copyright (c) 2013 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 XXXX; see
the RFC itself for full legal notices.";
// RFC Ed.: replace XXXX with actual RFC number and remove this
// note.
// RFC Ed.: remove this note
// Note: extracted from draft-bierman-netconf-get2-03.txt
// RFC Ed.: update the date below with the date of RFC publication
// and remove this note.
revision "2013-04-08" {
description
"Initial revision.";
reference
"RFC XXXX: The NETCONF <get2> Operation";
}
/* Features */
feature timestamps {
description
"This feature indicates that the server implements
the <get2> operations parameters which require
last modification timestamps to be maintained by
the server.
If this feature is advertised then one global
'last-modified' timestamp for the entire
running datastore MUST be supported.
The server MAY support additional timestamps
for additional datastores and data nodes
within a datastore. The 'with-timestamps'
parameter can be used to identify
which data nodes support a last-modified-time
timestamp.";
}
feature with-defaults {
description
"This feature indicates that the server supports the
'with-defaults' parameter for the <get2> operation.
A NETCONF server SHOULD support this feature.";
reference
"RFC 6243: With-defaults Capability for NETCONF";
}
/* Protocol Operations */
rpc get2 {
description
"Retrieve NETCONF datastore information";
input {
container source {
choice datastore-source {
default running;
description
"The configuration source for the retrieval operation.
The running configuration is the default choice if
this parameter is not present.";
leaf candidate {
if-feature nc:candidate;
type empty;
description
"The candidate configuration datastore is the
retrieval source.";
}
leaf running {
type empty;
description
"The running configuration datastore is the
retrieval source.";
}
leaf startup {
if-feature nc:startup;
type empty;
description
"The startup configuration datastore is the
retrieval source.";
}
leaf url {
if-feature nc:url;
type inet:uri;
description
"The URL-based configuration is the
retrieval source.";
}
leaf nonconfig {
type empty;
description
"The retrieval source is the collection of all
non-configuration data nodes supported by the server.
Any ancestor container and/or list and list key nodes
are also returned. No other leafs or leaf-lists will
be included in the reply.
The server MAY return ancestor container, and/or list
and list key nodes that do not contain any
non-configuration nodes. This can occur for several
reasons, e.g., the implementation streams replies
and cannot defer instrumentation or access control
filtering of descendant data nodes.";
}
}
}
choice filter-spec {
anyxml subtree-filter {
description
"This parameter identifies the portions of the
target datastore to retrieve.";
reference "RFC 6241, Section 6.";
}
leaf xpath-filter {
if-feature nc:xpath;
type yang:xpath1.0;
description
"This parameter contains an XPath expression
identifying the portions of the target
datastore to retrieve.";
}
}
leaf keys-only {
type empty;
description
"This parameter selects only data nodes which
are key leaf nodes. Parent container and
list nodes are also returned, but no other leafs,
or any leaf-lists will be included in the reply.";
}
leaf if-modified-since {
if-feature timestamps;
type yang:date-and-time;
description
"This parameter selects only data nodes which
have been modified since the specified time.";
}
leaf depth {
type uint32;
default 0;
description
"This parameter selects how many conceptual
sub-tree levels should be returned in the
<rpc-reply>.
If this parameter is equal to '0', then entire
subtrees will be returned.
If this parameter is greater than '0', then
only the specified number of subtree levels will
be returned.";
reference "RFC XXXX, section 2.1.";
}
uses ncwd:with-defaults-parameters {
if-feature with-defaults;
description
"This parameter controls the retrieval of
default values.";
reference
"RFC 6243: With-defaults Capability for NETCONF";
}
leaf with-timestamps {
if-feature timestamps;
type empty;
description
"This parameter will cause the server to return
XML attributes identifying the last modification
time within one or more elements within the
<rpc-reply>.";
reference "RFC XXXX, sections 2.2 and 3.";
}
}
output {
anyxml data {
description
"Copy of the requested datastore subset which
matched the filter criteria (if any).
An empty data container indicates that the
request did not produce any results.";
}
}
}
}
<CODE ENDS>
This document registers a URI in the IETF XML registry [RFC3688]. Following the format in RFC 3688, the following registration is requested:
URI: urn:ietf:params:xml:ns:yang:ietf-netconf-get2
Registrant Contact: The NETCONF WG of the IETF.
XML: N/A, the requested URI is an XML namespace.
This document registers 1 YANG module in the YANG Module Names registry [RFC6020].
name: ietf-netconf-get2 namespace: urn:ietf:params:xml:ns:yang:ietf-netconf-get2 prefix: get2 reference: RFC XXXX
This document does not introduce any new security concerns in addition to those specified in [RFC6241], section 9.
-- RFC Ed.: remove this section before publication.
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. |
| [RFC6020] | Bjorklund, M., "YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)", RFC 6020, October 2010. |
| [RFC6021] | Schoenwaelder, J., "Common YANG Data Types", RFC 6021, October 2010. |
| [RFC6241] | Enns, R., Bjorklund, M., Schoenwaelder, J. and A. Bierman, "Network Configuration Protocol (NETCONF)", RFC 6241, June 2011. |
| [RFC6243] | Bierman, A. and B. Lengyel, "With-defaults Capability for NETCONF", RFC 6243, June 2011. |
| [XPATH] | Clark, J. and S. DeRose, "XML Path Language (XPath) Version 1.0", World Wide Web Consortium Recommendation REC-xpath-19991116, November 1999. |
| [XSD] | Malhotra, A. and P. Biron, "XML Schema Part 2: Datatypes Second Edition", World Wide Web Consortium Recommendation REC-xmlschema-2-20041028, October 2004. |
| [RFC3688] | Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, January 2004. |
module example-get2 {
namespace "http://example.com/ns/example-get2";
prefix exget2;
description "Module used in <get2> examples.";
revision 2013-04-08;
container forests {
list forest {
key name;
leaf name {
type string;
}
leaf tree-count {
config false;
type uint32;
}
container trees {
list tree {
key name;
leaf name {
type string;
}
leaf location {
type string;
}
leaf height {
config false;
type decimal64 {
fraction-digits 3;
}
units meters;
}
} // list tree
} // container trees
} // list forest
} // container forests
}
The follow instances are assumed in the following examples.
list forest: "north":
list tree: "birch", "ash", "maple"
list forest: "south":
list tree: "banyan", "palm"
The forests and trees are configured, which represent trees the company has planted and growing over time.
The operational data (tree height) represents the data that the company monitors for each tree over time.
In this example, the running datastore was last modified at "2012‑09‑09T01:43:27Z" because the forest named "north" was modified at this time.
<rpc message-id="101"
xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
<get2 xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-get2">
<subtree-filter>
<forests xmlns="http://example.com/ns/example-get2" />
</subtree-filter>
<if-modified-since>2012-09-09T01:43:27Z</if-modified-since>
<with-timestamps />
</get2>
</rpc>
<rpc-reply message-id="101"
xmlns="urn:ietf:params:xml:ns:netconf:base:1.0"
xmlns:lm="urn:ietf:params:xml:ns:netconf:last-modified:1.0">
<data xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-get2"
lm:last-modified="2012-09-09T02:00:00Z">
<forests xmlns="http://example.com/ns/example-get2">
<forest lm:last-modified="2012-09-09T02:00:00Z">
<name>north</name>
<trees>
<tree>
<name>birch</name>
<location>hillside</location>
</tree>
<tree>
<name>ash</name>
<location>southwest pasture</location>
</tree>
<tree>
<name>maple</name>
<location>east meadow</location>
</tree>
</trees>
</forest>
</forests>
</data>
</rpc-reply>
In this example the client has changed the "if‑modified‑since" timestamp to a time in the future.
<rpc message-id="102"
xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
<get2 xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-get2">
<subtree-filter>
<forests xmlns="http://example.com/ns/example-get2" />
</subtree-filter>
<if-modified-since>2012-09-09T03:43:27Z</if-modified-since>
<with-timestamps />
</get2>
</rpc>
<rpc-reply message-id="102"
xmlns="urn:ietf:params:xml:ns:netconf:base:1.0"
xmlns:lm="urn:ietf:params:xml:ns:netconf:last-modified:1.0">
<data xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-get2"
lm:last-modified="2012-09-09T02:00:00Z" />
</rpc-reply>
This example retrieves only the names from the "forests" subtree in the running datastore.
<rpc message-id="103"
xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
<get2 xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-get2">
<xpath-filter xmlns:ex=http://example.com/ns/example-get2">
/ex:forests
</xpath-filter>
<keys-only />
</get2>
</rpc>
<rpc-reply message-id="103"
xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
<data xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-get2">
<forests xmlns="http://example.com/ns/example-get2">
<forest>
<name>north</name>
<trees>
<tree>
<name>birch</name>
</tree>
<tree>
<name>ash</name>
</tree>
<tree>
<name>maple</name>
</tree>
</trees>
</forest>
<forest>
<name>south</name>
<trees>
<tree>
<name>banyan</name>
</tree>
<tree>
<name>palm</name>
</tree>
</trees>
</forest>
</forests>
</data>
</rpc-reply>
This example retrieves the "trees" node to determine which forests have any trees.
<rpc message-id="104"
xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
<get2 xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-get2">
<subtree-filter>
<forests xmlns="http://example.com/ns/example-get2">
<forest>
<trees />
</forest>
</forests>
</subtree-filter>
<depth>1</depth>
</get2>
</rpc>
<rpc-reply message-id="104"
xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
<data xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-get2">
<forests xmlns="http://example.com/ns/example-get2">
<forest>
<name>north</name>
<trees />
</forest>
<forest>
<name>south</name>
<trees />
</forest>
</forests>
</data>
</rpc-reply>
This example retrieves only the "name" leafs from the "forest" list within the "forests" subtree, in the running datastore.
<rpc message-id="105"
xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
<get2 xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-get2">
<subtree-filter>
<forests xmlns="http://example.com/ns/example-get2" />
</subtree-filter>
<keys-only />
<depth>3</depth>
</get2>
</rpc>
<rpc-reply message-id="105"
xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
<data xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-get2">
<forests xmlns="http://example.com/ns/example-get2">
<forest>
<name>north</name>
</forest>
<forest>
<name>south</name>
</forest>
</forests>
</data>
</rpc-reply>
This example retrieves only the name leafs from the "forest" list within the "forests" subtree, in the running datastore.
<rpc message-id="106"
xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
<get2 xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-get2">
<source><nonconfig /></source>
<subtree-filter>
<forests xmlns="http://example.com/ns/example-get2" />
</subtree-filter>
</get2>
</rpc>
<rpc-reply message-id="106"
xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
<data xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-get2">
<forests xmlns="http://example.com/ns/example-get2">
<forest>
<name>north</name>
<trees>
<tree>
<name>birch</name>
<height>41.013</height>
</tree>
<tree>
<name>ash</name>
<height>16.523</height>
</tree>
<tree>
<name>maple</name>
<height>51.204</height>
</tree>
</trees>
</forest>
<forest>
<name>south</name>
<trees>
<tree>
<name>banyan</name>
<height>91.433</height>
</tree>
<tree>
<name>palm</name>
<height>83.439</height>
</tree>
</trees>
</forest>
</forests>
</data>
</rpc-reply>