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This document describes NETCONF protocol enhancements to improve data retrieval capabilities.

There is a need for standard mechanisms to allow NETCONF 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 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.

There is a mandatory-to-implement subtree filter mechanism in NETCONF. There are server environments where subtree filtering cannot be supported or is not needed for the specific device or supported management application(s). A NETCONF server SHOULD support subtree filtering. An implementation MAY omit subtree filtering support if it is not applicable or not feasible on the device.

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, .

The following terms are defined in : candidate configuration datastore client configuration data datastore configuration datastore protocol operation running configuration datastore server startup configuration datastore

The following terms are defined in : anyxml container data node key leaf leaf leaf-list list presence container (or P-container) non-presence container (or NP-container)

The following terms are defined: operational datastore: the collection of all conceptual YANG data nodes which represent non-configuration data. This conceptual datastore also includes ancestor container and list nodes for any nested non-configuration nodes, as well as list keys for any list nodes in this datastore. depth filter: A mechanism implemented within the NETCONF server to allow a client to retrieve only a limited number of levels within the a subtree, instead of retrieving the entire subtree. time filter: A mechanism implemented within the NETCONF server to allow a client to retrieve only data that has been modified since a specified data and time.

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: source: A container indicating the conceptual datastore for the retrieval request. filter-spec: A choice indicating the content filter specification for the retrieval request. keys-only: A leaf indicating that only the key leafs, combined with other filtering criteria, should be returned. if-modified-since: A leaf indicating the time filter specification for the retrieval request, according to the procedures in . depth: A leaf indicating the subtree depth level for the retrieval request, according to the procedures in . with-defaults: A leaf indicating the type of defaults handling requested, according to procedures in . with-timestamps: A leaf indicating that 'last‑modified' XML attributes are requested, according to procedure in .

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 P-container or list within the descendant nodes of the requested subtree. For purposes of counting levels, NP-containers are transparent. The contents of an NP container are considered to be at the same level as the NP-container itself. YANG data nodes of type 'leaf', 'leaf‑list', and 'anyxml' are considered to be at the same level as their parent container or list. 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.

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 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"

This schema defines the syntax for the 'last-modified' attribute described within this document. 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. ]]>

<CODE ENDS>

This module imports the 'with‑defaults‑parameters' grouping from . Several YANG features are imported from . Some data types are imported from . RFC Ed.: update the date below with the date of RFC publication and remove this note. <CODE BEGINS> file "ietf-netconf-get2@2012-09-08.yang"

WG List: WG Chair: Mehmet Ersue WG Chair: Bert Wijnen Editor: Andy Bierman "; description "This module contains a collection of YANG definitions for the retrieval of information from a NETCONF server. Copyright (c) 2012 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-get2-00.txt // RFC Ed.: update the date below with the date of RFC publication // and remove this note. revision "2012-09-08" { description "Initial revision."; reference "RFC XXXX: The NETCONF Operation"; } /* Features */ feature timestamps { description "This feature indicates that the server implements the 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 operation. A NETCONF server SHOULD support this feature."; reference "RFC 6243: With-defaults Capability for NETCONF"; } feature subtree-filter { description "This feature indicates that the server supports the subtree filtering mechanism for selecting portions of the selected source datastore. A NETCONF server SHOULD support this feature."; reference "RFC 6241: NETCONF Protocol, section 6."; } /* 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 operational { type empty; description "The collection of non-configuration data nodes supported by the server 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."; } } } choice filter-spec { anyxml filter { if-feature subtree-filter; description "This parameter identifies the portions of the target datastore to retrieve."; reference "RFC 6241, Section 6."; } leaf select { 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 . 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 ."; 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 . Following the format in RFC 3688, the following registration is requested to be made.

This document registers a YANG module in the YANG Module Names registry .

This document does not introduce any new security concerns in addition to those specified in , section 9.

Harvard University In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. YANG is a data modeling language used to model configuration and state data manipulated by the Network Configuration Protocol (NETCONF), NETCONF remote procedure calls, and NETCONF notifications. [STANDARDS TRACK] This document describes an IANA maintained registry for IETF standards which use Extensible Markup Language (XML) related items such as Namespaces, Document Type Declarations (DTDs), Schemas, and Resource Description Framework (RDF) Schemas.

The follow instances are assumed in the following examples.

This example simply retrieves the 'forests' subtree data from the operational datastore.

north 3 birch 41.013 ash 16.523 maple 51.204 south 2 banyan 91.433 palm 83.439 ]]>

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. The forest named 'north' was last modified after the specified 'if‑modified‑since' timestamp. The forest named 'south' was last modified before the specified 'if‑modified‑since' timestamp. The server maintains a last-modified timestamp for the running datastore and the 'forest' list entries. The client is also requesting that timestamps be returned for the nodes that have been modified. If any part of the 'forest' subtree is modified then this timestamp will be updated.

2012-09-09T01:43:27Z north birch hillside ash southwest pasture maple east meadow ]]>

In this example the client has changed the if-modified-since timestamp to a time in the future. No 'forest' list entry has been modified since this time so an empty data node is returned. Note that the last-modified timestamp is returned for the node representing the datastore, even though no data nodes have been modified since the specified time. This allows the client to easily retrieve the last-modified timestamp for the entire datastore.

2012-09-09T03:43:27Z ]]>

This example retrieves the names-only from the 'forests' subtree in the running datastore. Only one subtree level is requested, instead of the default of all levels. The default source (running) is used. The default depth='0' is used to retrieve all subtree levels.

north birch ash maple south banyan palm ]]>

This example retrieves the names-only from the 'forests' subtree in the running datastore. Only one subtree level is requested, instead of the default of all levels. The default source (running) is used. The depth parameter is set to '1' to only retrieve the first layer, which includes the 'forests' NP container and the 'forest' list.

1 north south ]]>