| Network Working Group | A. Clemm |
| Internet-Draft | Y. Qu |
| Intended status: Standards Track | Futurewei |
| Expires: January 9, 2020 | J. Tantsura |
| Apstra | |
| A. Bierman | |
| YumaWorks | |
| July 8, 2019 |
Comparison of NMDA datastores
draft-ietf-netmod-nmda-diff-02
This document defines an RPC operation to compare management datastores that comply with the NMDA architecture.
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.
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The revised Network Management Datastore Architecture (NMDA) [RFC8342] introduces a set of new datastores that each hold YANG-defined data [RFC7950] and represent a different “viewpoint” on the data that is maintained by a server. New YANG datastores that are introduced include <intended>, which contains validated configuration data that a client application intends to be in effect, and <operational>, which contains at least conceptually operational state data (such as statistics) as well as configuration data that is actually in effect.
NMDA introduces in effect a concept of “lifecycle” for management data, allowing to clearly distinguish between data that is part of a configuration that was supplied by a user, configuration data that has actually been successfully applied and that is part of the operational state, and overall operational state that includes both applied configuration data as well as status and statistics.
As a result, data from the same management model can be reflected in multiple datastores. Clients need to specify the target datastore to be specific about which viewpoint of the data they want to access. This way, an application can differentiate whether they are (for example) interested in the configuration that has been applied and is actually in effect, or in the configuration that was supplied by a client and that is supposed to be in effect.
Due to the fact that data can propagate from one datastore to another, it is possibly for differences between datastores to occur. Some of this is entirely expected, as there may be a time lag between when a configuration is given to the device and reflected in <intended>, until when it actually takes effect and is reflected in <operational>. However, there may be cases when a configuration item that was to be applied may not actually take effect at all or needs an unusually long time to do so. This can be the case due to certain conditions not being met, resource dependencies not being resolved, or even implementation errors in corner conditions.
When configuration that is in effect is different from configuration that was applied, many issues can result. It becomes more difficult to operate the network properly due to limited visibility of actual status which makes it more difficult to analyze and understand what is going on in the network. Services may be negatively affected (for example, breaking a service instance resulting in service is not properly delivered to a customer) and network resources be misallocated.
Applications can potentially analyze any differences between two datastores by retrieving the contents from both datastores and comparing them. However, in many cases this will be at the same time costly and extremely wasteful.
This document introduces a YANG data model which defines RPCs, intended to be used in conjunction with NETCONF [RFC6241] or RESTCONF [RFC8040], that allow a client to request a server to compare two NMDA datastores and report any differences.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.
At the core of the solution is a new management operation, <compare>, that allows to compare two datastores for the same data. The operation checks whether there are any differences in values or in data nodes that are contained in either datastore, and returns any differences as output. The output is returned in the format specified in YANG-Patch [RFC8072].
The YANG data model defines the <compare> operation as a new RPC. The operation takes the following input parameters:
The operation provides the following output parameter:
The data model is defined in the ietf-nmda-compare YANG module. Its structure is shown in the following figure. The notation syntax follows [RFC8340].
module: ietf-nmda-compare
rpcs:
+---x compare
+---w input
| +---w source identityref
| +---w target identityref
| +---w all? empty
| +---w (filter-spec)?
| +--:(subtree-filter)
| | +---w subtree-filter?
| +--:(xpath-filter)
| +---w xpath-filter? yang:xpath1.0 {nc:xpath}?
+--ro output
+--ro (compare-response)?
+--:(no-matches)
| +--ro no-matches? empty
+--:(differences)
+--ro differences
+--ro yang-patch
+--ro patch-id string
+--ro comment? string
+--ro edit* [edit-id]
+--ro edit-id string
+--ro operation enumeration
+--ro target target-resource-offset
+--ro point? target-resource-offset
+--ro where? enumeration
+--ro value?
+--ro source-value?
Structure of ietf-nmda-compare
<CODE BEGINS> file "ietf-nmda-compare@2019-07-08.yang"
module ietf-nmda-compare {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-nmda-compare";
prefix cp;
import ietf-yang-types {
prefix yang;
}
import ietf-datastores {
prefix ds;
}
import ietf-yang-patch {
prefix ypatch;
}
import ietf-netconf {
prefix nc;
}
organization "IETF";
contact
"WG Web: <http://tools.ietf.org/wg/netconf/>
WG List: <mailto:netconf@ietf.org>
Author: Alexander Clemm
<mailto:ludwig@clemm.org>
Author: Yingzhen Qu
<mailto:yqu@futurewei.com>
Author: Jeff Tantsura
<mailto:jefftant.ietf@gmail.com>
Author: Andy Bierman
<mailto:andy@yumaworks.com>";
description
"The YANG data model defines a new operation, <compare>, that
can be used to compare NMDA datastores.";
revision 2019-07-08 {
description
"Initial revision";
reference
"RFC XXXX: Comparison of NMDA datastores";
}
/* RPC */
rpc compare {
description
"NMDA compare operation.";
input {
leaf source {
type identityref {
base ds:datastore;
}
mandatory true;
description
"The source datastore to be compared.";
}
leaf target {
type identityref {
base ds:datastore;
}
mandatory true;
description
"The target datastore to be compared.";
}
leaf all {
type empty;
description
"When this leaf is provided, all data nodes are compared,
whether their schema node pertains to both datastores or
not. When this leaf is omitted, a prefiltering step is
automatically applied that excludes data nodes from the
comparison that can occur in only one datastore but not
the other. Specifically, if one of the datastores
(source or target) contains only configuration data and
the other datastore is <operational>, data nodes for
which config is false are excluded from the comparison.";
}
choice filter-spec {
description
"Identifies the portions of the datastores to be
compared.";
anydata 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.";
}
}
}
output {
choice compare-response {
description
"Comparison results.";
leaf no-matches {
type empty;
description
"This leaf indicates that the filter did not match
anything and nothing was compared.";
}
container differences {
description
"The list of differences, encoded per RFC8072 with an
augmentation to include source values where
applicable.";
uses ypatch:yang-patch {
augment "yang-patch/edit" {
description
"Provide the value of the source of the patch,
respectively of the comparison, in addition to
the target value, where applicable.";
anydata source-value {
when "../operation = 'delete'"
+ "or ../operation = 'merge'"
+ "or ../operation = 'move'"
+ "or ../operation = 'replace'"
+ "or ../operation = 'remove'";
description
"The anydata 'value' is only used for 'delete',
'move', 'merge', 'replace', and 'remove'
operations.";
}
}
}
}
}
}
}
}
<CODE ENDS>
container ospf {
leaf enable {
type boolean;
}
leaf explicit-router-id {
type rt-types:router-id;
}
leaf preference {
type uint8;
}
}
The following example compares the difference between <operational> and <intended> for a subtree under "ospf". The subtree contains objects that are defined in a YANG data model for the management of OSPF defined in [I-D.ietf-ospf-yang]. The excerpt of the data model whose instantiation is basis of the comparison is as follows:
<ospf xmlns:or="urn:ietf:params:xml:ns:yang:ietf-origin"
or:origin="or:intended">
<enable>true</enable>
<explicit-router-id>2.2.2.2</explicit-router-id>
</ospf>
<ospf xmlns:or="urn:ietf:params:xml:ns:yang:ietf-origin"
or:origin="or:operational">
<enable>true</enable>
<explicit-router-id>1.1.1.1</explicit-router-id>
<preference>200</preference>
</ospf>
The contents of <intended> and <operational> datastores:
<operational> contains one object that was not contained in <intended>, "preference". Another object, "explicit-router-id", has differences in values. A third object, "enable", is the same in both cases.
<rpc message-id="101"
xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
<compare xmlns="urn:ietf:params:xml:ns:yang:ietf-nmda-compare"
xmlns:ds="urn:ietf:params:xml:ns:yang:ietf-datastores">
<source>ds:operational</source>
<target>ds:intended</target>
<xpath-filter
xmlns:rt="urn:ietf:params:xml:ns:yang:ietf-routing"
xmlns:ospf="urn:ietf:params:xml:ns:yang:ietf-ospf">\
/rt:routing/rt:control-plane-protocols\
/rt:control-plane-protocol/ospf:ospf\
</xpath-filter>
</compare>
</rpc>
RPC request to compare <operational< (source of the comparison) with <intended>(target of the comparison):
<rpc-reply
xmlns="urn:ietf:params:xml:ns:netconf:base:1.0"
message-id="101">
<differences
xmlns="urn:ietf:params:xml:ns:yang:ietf-nmda-compare"
xmlns:or="urn:ietf:params:xml:ns:yang:ietf-origin">
<yang-patch>
<patch-id>ospf router-id</patch-id>
<comment>diff between operational and intended</comment>
<edit>
<edit-id>1</edit-id>
<operation>replace</operation>
<target>/ietf-ospf:explicit-router-id</target>
<value>
<ospf:explicit-router-id
or:origin="or:system">1.1.1.1<explicit-router-id>
</value>
<source-value>
<ospf:explicit-router-id
or:origin="or:intended">2.2.2.2<explicit-router-id>
</source-value>
<edit-id>2</edit-id>
<operation>create</operation>
<target>/ietf-ospf:preference</target>
<value>
<ospf:preference
or:origin="or:system">200<preference>
</value>
</edit>
</yang-patch>
</differences>
</rpc-reply>
RPC reply, when a difference is detected:
POST /restconf/operations/ietf-nmda-compare:compare HTTP/1.1
Host: example.com
Content-Type: application/yang-data+json
Accept: application/yang-data+json
{ "ietf-nmda-compare:input" {
"source" : "ietf-datastores:operational",
"target" : "ietf-datastores:intended".
"xpath-filter" : \
"/ietf-routing:routing/control-plane-protocols\
/control-plane-protocol/ietf-ospf:ospf"
}
}
The same request in RESTCONF (using JSON format):
HTTP/1.1 200 OK
Date: Thu, 26 Jan 2019 20:56:30 GMT
Server: example-server
Content-Type: application/yang-data+json
{ "ietf-nmda-compare:output" : {
"differences" : {
"ietf-yang-patch:yang-patch" : {
"patch-id" : "ospf router-id",
"comment" : "diff between operational and intended",
"edit" : [
{
"edit-id" : "1",
"operation" : "replace",
"target" : "/ietf-ospf:explicit-router-id",
"value" : {
"ietf-ospf:explicit-router-id" : "1.1.1.1"
"@ietf-ospf:explicit-router-id" : {
"ietf-origin:origin" : "ietf-origin:system"
}
"source-value" : {
"ietf-ospf:explicit-router-id" : "2.2.2.2"
"@ietf-ospf:explicit-router-id" : {
"ietf-origin:origin" : "ietf-origin:intended"
}
"edit-id" : "2",
"operation" : "create",
"target" : "/ietf-ospf:preference",
"value" : {
"ietf-ospf:preference" : "200"
"@ietf-ospf:preference" : {
"ietf-origin:origin" : "ietf-origin:system"
}
}
]
}
}
}
}
The same response in RESTCONF (using JSON format):
Currently, origin metadata is included in RPC output per default in comparisons that involve <operational>. It is conceivable to introduce an input parameter that controls whether this origin metadata should in fact be included.
Currently the comparison filter is defined using subtree and XPath as in NETCONF[RFC6241]. It is not clear whether there is a requirement to allow for the definition of filters that relate instead to target resources per RESTCONF [RFC7950].
It is conceivable to extend the compare operation with a number of possible additional features in the future.
Specifically, it is possible to define an extension with an optional feature for dampening. This will allow clients to specify a minimum time period for which a difference must persist for it to be reported. This will enable clients to distinguish between differences that are only fleeting from ones that are not and that may represent a real operational issue and inconsistency within the device.
For this purpose, an additional input parameter can be added to specify the dampening period. Only differences that pertain for at least the dampening time are reported. A value of 0 or omission of the parameter indicates no dampening. Reporting of differences MAY correspondingly be delayed by the dampening period from the time the request is received.
To implement this feature, a server implementation might run a comparison when the RPC is first invoked and temporarily store the result. Subsequently, it could wait until after the end of the dampening period to check whether the same differences are still observed. The differences that still persist are then returned.
This document registers one URI in the IETF XML registry [RFC3688]. Following the format in [RFC3688], the following registration is requested:
This document registers a YANG module in the YANG Module Names registry [RFC7950]. Following the format in [RFC7950], the following registration is requested:
The YANG module specified in this document defines a schema for data that is designed to be accessed via network management protocols such as NETCONF [RFC6241] or RESTCONF [RFC8040]. The lowest NETCONF layer is the secure transport layer, and the mandatory-to-implement secure transport is Secure Shell (SSH) [RFC6242]. The lowest RESTCONF layer is HTTPS, and the mandatory-to-implement secure transport is TLS [RFC8446].
The NETCONF access control model [RFC8341] provides the means to restrict access for particular NETCONF or RESTCONF users to a preconfigured subset of all available NETCONF or RESTCONF protocol operations and content.
The RPC operation defined in this YANG module, "compare", may be considered sensitive or vulnerable in some network environments. It is thus important to control access to this operation. This is the sensitivity/vulnerability of RPC operation "compare":
Comparing datastores for differences requires a certain amount of processing resources at the server. An attacker could attempt to attack a server by making a high volume of comparison requests. Server implementations can guard against such scenarios in several ways. For one, they can implement the NETCONF access control model in order to require proper authorization for requests to be made. Second, server implementations can limit the number of requests that they serve to a client in any one time interval, rejecting requests made at a higher frequency than the implementation can reasonably sustain.
We thank Rob Wilton, Martin Bjorklund, Mahesh Jethanandani, Lou Berger, Kent Watsen, Phil Shafer, Ladislav Lhotka for valuable feedback and suggestions.
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997. |
| [RFC3688] | Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, DOI 10.17487/RFC3688, January 2004. |
| [RFC6241] | Enns, R., Bjorklund, M., Schoenwaelder, J. and A. Bierman, "Network Configuration Protocol (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011. |
| [RFC6242] | Wasserman, M., "Using the NETCONF Protocol over Secure Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011. |
| [RFC7950] | Bjorklund, M., "The YANG 1.1 Data Modeling Language", RFC 7950, DOI 10.17487/RFC7950, August 2016. |
| [RFC8040] | Bierman, A., Bjorklund, M. and K. Watsen, "RESTCONF Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017. |
| [RFC8072] | Bierman, A., Bjorklund, M. and K. Watsen, "YANG Patch Media Type", RFC 8072, DOI 10.17487/RFC8072, February 2017. |
| [RFC8174] | Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017. |
| [RFC8340] | Bjorklund, M. and L. Berger, "YANG Tree Diagrams", BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018. |
| [RFC8341] | Bierman, A. and M. Bjorklund, "Network Configuration Access Control Model", STD 91, RFC 8341, DOI 10.17487/RFC8341, March 2018. |
| [RFC8342] | Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K. and R. Wilton, "Network Management Datastore Architecture (NMDA)", RFC 8342, DOI 10.17487/RFC8342, March 2018. |
| [RFC8446] | Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018. |
| [I-D.ietf-ospf-yang] | Yeung, D., Qu, Y., Zhang, Z., Chen, I. and A. Lindem, "YANG Data Model for OSPF Protocol", Internet-Draft draft-ietf-ospf-yang-23, July 2019. |