Network Working Group M. Bjorklund
Internet-Draft Tail-f Systems
Updates: 6020 (if approved) L. Lhotka
Intended status: Standards Track CZ.NIC
Expires: April 8, 2013 October 5, 2012
Operational Data in NETCONF and YANG
draft-bjorklund-netmod-operational-00
Abstract
This document defines the concept of operational state data in the
context of YANG and the Network Configuration Protocol (NETCONF). It
updates RFC 6020 with rules for how to model the operational state,
and defines NETCONF operations to retrieve and modify the operational
state.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on April 8, 2013.
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Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
1.1.1. Terms . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Modeling and Retrieving Operational State . . . . . . . . 5
3.1.1. Example: Interface List . . . . . . . . . . . . . . . 5
3.2. Modifying the Operational State . . . . . . . . . . . . . 6
3.2.1. Example: Routing Table Modification . . . . . . . . . 7
4. Datastores . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.1. Operational State Datastore . . . . . . . . . . . . . . . 8
4.2. Configuration Datastore . . . . . . . . . . . . . . . . . 9
5. Constraints . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.1. Alternative A . . . . . . . . . . . . . . . . . . . . . . 10
5.2. Alternative B . . . . . . . . . . . . . . . . . . . . . . 10
5.3. Alternative C . . . . . . . . . . . . . . . . . . . . . . 10
6. Protocol Operations . . . . . . . . . . . . . . . . . . . . . 11
6.1. <get-operational> . . . . . . . . . . . . . . . . . . . . 11
6.1.1. Example: Ethernet Duplex . . . . . . . . . . . . . . . 11
6.2. <edit-operational> . . . . . . . . . . . . . . . . . . . . 12
7. YANG Module . . . . . . . . . . . . . . . . . . . . . . . . . 13
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
9. Security Considerations . . . . . . . . . . . . . . . . . . . 16
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
10.1. Normative References . . . . . . . . . . . . . . . . . . . 17
10.2. Informative References . . . . . . . . . . . . . . . . . . 17
Appendix A. Example: Interface List . . . . . . . . . . . . . . . 18
Appendix B. Example: Ethernet Duplex . . . . . . . . . . . . . . 19
Appendix C. Example: Admin vs. Oper State . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21
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1. Introduction
1.1. Terminology
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].
1.1.1. Terms
The following terms are defined in [RFC6241] and are not redefined
here:
o client
o configuration datastore
o datastore
o server
The following terms are defined in [RFC6020] and are not redefined
here:
o data model
o schema tree
o data node
The following terms are used within this document:
o operational state data: The data in the operational state
datastore.
o operational state datastore: A conceptual data structure from
which one can determine device state and behavior.
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2. Objectives
o Develop a general model applicable not only to NETCONF but also to
other approaches (RESTful, editable state data etc.).
o Develop a specific model for NETCONF and YANG.
o As little changes to NETCONF and YANG as possible.
o Clarification of the terms "operational state data" and
"configuration".
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3. Problem Statement
3.1. Modeling and Retrieving Operational State
The NETCONF operation <get> returns both device state data and the
running configuration. Quite often, device parameters require a dual
representation, both as configuration and state data.
For instance, an IP address may be specified in an interface
configuration but, depending on other circumstances, this address may
not be used for that interface. In any case, an operator should be
able to obtain the addresses that are in operational use.
This implies that some state data must be modeled separately from the
configuration data, which leads to a certain amount of duplication in
data models. This approach has other drawbacks, too. It is counter-
intuitive to data model designers, for whom configuration and state
parameters are closely related (see Section 3.1.1 for an example).
Data model duplication is error prone and leads to bigger data
models, that are more difficult to understand. Further, there is no
formal information in the data model about the relationship between
the configuration and operational state data.
3.1.1. Example: Interface List
Suppose we want to model a list of interfaces. We allow pre-
configuration, i.e., it is legal to configure an interface for which
there is currently no hardware present in the system. In this simple
example, each interface has a name and a counter of the number of
packets received. The counter is operational state data.
list interface {
key name;
leaf name { ... }
leaf in-packets {
type yang:counter64;
config false;
}
...
}
A particular device has hardware for two interfaces with names "eth0"
and "eth1". In the configuration there is:
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<interface>
<name>eth0</name>
...
</interface>
<interface>
<name>eth2</name>
...
</interface>
We can see this by doing <get-config>.
Operationally, however, the interfaces used are "eth0" and "eth1",
although "eth1" does not have any configuration and does not send or
receive packets.
How can an operator learn about the presence of "eth1"? The <get>
operation returns the running configuration and state data together.
So, <get> will not show "eth1", since it is not present in the
running configuration.
With NETCONF as currently defined, the only alternative is to
duplicate the data model:
list interface {
key name;
leaf name { ...}
...
}
list interface-oper {
config false;
key name;
leaf name { ...}
leaf in-packets { ... }
...
}
3.2. Modifying the Operational State
In some cases, it is useful for clients to directly modify the
operational state. An example of this is the recent discussions
around an Interface to the Routing System (IRS), where a client needs
to modify the routing table, without storing routes in the
configuration.
With NETCONF as currently designed, the only way to do this is to
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define separate rpc operations. This leads to another kind of data
model duplication, where every writable parameter is modeled both as
state data that can be retrieved using the <get> operation, and also
as input parameters to at least one rpc operation.
3.2.1. Example: Routing Table Modification
Suppose we want to model IPv4 routing tables as operational state,
and we also want to be able to let a client modify this data. We
have to do:
list routing-table {
config false;
key name;
leaf name { ... }
list route {
key id;
leaf id { ... }
leaf dest-prefix { ... }
leaf next-hop { ... }
...
}
}
rpc add-route {
input {
leaf routing-table-name { ... }
leaf route-id { ... }
leaf dest-prefix { ... }
leaf next-hop { ... }
}
}
rpc delete-route {
input {
leaf routing-table-name { ... }
leaf route-id { ... }
}
}
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4. Datastores
The fundamental idea of this document is to define operational state
data as an explicit data structure called the operational state
datastore. It is available to all management interfaces, which
includes NETCONF but also other interfaces such as SNMP.
The "running" configuration datastore is viewed as a separate overlay
data structure whose layout is identical to the subset of the
operational state datastore that represents configuration.
4.1. Operational State Datastore
The operational state datastore consists of all parameters that
provide information about the instantaneous state of the device and
immediately influence the device's behavior.
The operational state datastore is a conceptual data structure. This
means that implementations may choose any suitable representation of
the datastore, or even generate it dynamically upon request.
Operational state may be modified through one or more management
interfaces, or through the operation of network protocols. All such
means of accessing and changing the operational state act
conceptually on the same data - the operational state datastore. It
means, for instance, that any change caused by a network protocol is
immediately visible to all management interfaces.
The schema for the operational state datastore is made up of all data
nodes defined in YANG modules, specifically both "config true" and
"config false" data nodes.
Note that when <get-config> is used to retrieve a "config true" node,
the value stored in the configuration datastore is returned. When
<get-operational> is used to retrieve the same node, the value
actually used by the device is returned. This value may or may not
be the same as the value in the datastore.
+-------------------------------------------------------------------+
| Open Question |
+-------------------------------------------------------------------+
| Should there be a YANG statement 'operational <bool>' so that |
| config true nodes can be marked as not being part of the |
| operational schema? |
+-------------------------------------------------------------------+
Nodes in the operational data store cannot be directly modified using
the standard NETCONF operations.
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+-------------------------------------------------------------------+
| Open Question |
+-------------------------------------------------------------------+
| introduce oper:writable for nodes that can be modified by |
| <edit-operational>. |
+-------------------------------------------------------------------+
4.2. Configuration Datastore
The configuration datastore can be thought of as a blueprint for the
operational datastore. Specifically, the schema for the
configuration datastore is congruent to a subtree of the schema for
operational state datastore containing only "config true" nodes. In
other words, every data node in the configuration datastore schema
has a corresponding data node with the same name in the operational
datastore schema, and the latter data node is "config true".
Whenever a NETCONF client modifies the configuration datastore, the
server MUST immediately attempt to project the changes into the
operational state datastore. Most of the time, it simply means
copying the values in the configuration datastore to the
corresponding nodes in the operational state datastore. If a leaf's
default value is in use (See section 7.6.1. of RFC 6020), the default
value is copied to the operational data store.
The configuration datastore may contain data nodes that are not
projected into the operational state datastore. This happens in the
following three scenarios:
1. Pre-provisioned configuration prepared for hardware components
that are not yet present in the device. See Section 3.1.1 above.
2. Pre-provisioned configuration for components (hardware,
protocols, etc.) that are intended to replace an existing item
but are of a different type.
3. Parts of configuration that are momentarily not applicable.
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5. Constraints
This document updates section 8 of RFC 6020 with rules for the
operational state datastore.
NOTE: The rest of this section documents some alternatives that the
authors want to discuss
There are a couple of design alternatives here:
5.1. Alternative A
No constraints ("must", "mandatory", "unique", "min-elements",
"max-elements") are enforced on the operational state datastore. For
example, this means that a mandatory "config true" leaf does not have
to be present in the operational state datastore.
The problem with this approach is that there is no way to formally
define constraints on the OSD in the data model. This may be needed
in order to allow for coexistence of NETCONF with other management
interfaces that do not use the configuration datastore. Such
constraints can be specified in description statement though.
5.2. Alternative B
Change the definitions of mandatory, must, to work on osd instead of
config.
This would be a major backwards incompatible change to YANG, and it
would not be possible to define constraints on the configuration.
5.3. Alternative C
Introduce new YANG statements for OSD constraints, e.g. osd:must,
osd:mandatory etc.
The drawback with this is that it adds complexity.
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6. Protocol Operations
6.1. <get-operational>
This document introduces a new operation <get-operational>, which is
used to retrieve the operational state data from a device. Note how
this operation differs from <get>, which is used to retrieve both the
running configuration and state data.
<get-operational> takes the same parameters as <get>.
Since leafs with default values defined in the data model are always
explicitly set in the operational data store, there is no need for
:with-defaults handling in the <get-operational> operation.
6.1.1. Example: Ethernet Duplex
As an example, consider a very simplified data model with a single
leaf for ethernet duplex:
leaf duplex {
type enumeration {
enum "half";
enum "full";
enum "auto";
}
config true;
}
Suppose a device with this data model implements the candidate
datastore. The following is an example of data from such a device:
get-config from candidate:
<duplex>half</duplex>
get-config from running:
<duplex>auto</duplex>
get-operational:
<duplex>full</duplex>
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In this example, the running configuration tells the device to
negotiate the duplex mode, and the current, operationally used, value
is "full". At the same time, the (uncommitted) candidate
configuration contains the value "half".
6.2. <edit-operational>
[Editor's note: NOT FINISHED - not clear if we need this]
Introduce edit-operational. This modifies the subset of the
operational data tree that is also marked as writable.
Drawback: does not handle persistent operational data. If we have
persistent operational data, this has to be its own data store that
can be read and written.
A data model w/o the writable markers cannot be written to. This is
a problem, since it is not obvious that the original designer though
about future use cases. For example, our route tables are read-only.
Then IRS comes along and wants to write to this data. Do we have to
update our spec? Not good. One option is for IRS to publish a
deviation data model that added the writable statement to our model.
This would be backwards compliant and good. Even better would be if
they could publish a conformance statement in a module, w/o the need
for deviations.
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7. YANG Module
RFC Ed.: update the date below with the date of RFC publication and
remove this note.
<CODE BEGINS> file "ietf-netconf-operational.yang"
module ietf-netconf-operational {
namespace "urn:ietf:params:xml:ns:yang:ietf-netconf-operational";
prefix "oper";
import ietf-yang-types {
prefix yang;
}
import ietf-inet-types {
prefix inet;
}
import ietf-netconf {
prefix nc;
}
rpc get-operational {
input {
choice filter-spec {
anyxml subtree-filter {
description
"This parameter identifies the portions of the
operational state 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 operational state
datastore to retrieve.";
}
}
}
output {
anyxml data {
description
"Copy of the operational state data that matched the filter
criteria (if any). An empty data container indicates that
the request did not produce any results.";
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}
}
}
rpc edit-operational {
input {
leaf default-operation {
type enumeration {
enum merge {
description
"The default operation is merge.";
}
enum replace {
description
"The default operation is replace.";
}
enum none {
description
"There is no default operation.";
}
}
default "merge";
description
"The default operation to use.";
}
choice edit-content {
mandatory true;
description
"The content for the edit operation.";
anyxml data {
description
"Inline data content.";
}
leaf url {
if-feature nc:url;
type inet:uri;
description
"URL-based config content.";
}
}
}
}
}
<CODE ENDS>
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8. IANA Considerations
This document registers a URI in the IETF XML registry [RFC3688].
Following the format in RFC 3688, the following registration is
requested to be made.
URI: urn:ietf:params:xml:ns:yang:ietf-netconf-operational
Registrant Contact: The NETMOD WG of the IETF.
XML: N/A, the requested URI is an XML namespace.
This document registers a YANG module in the YANG Module Names
registry [RFC6020].
name: ietf-netconf-operational
namespace: urn:ietf:params:xml:ns:yang:ietf-netconf-operational
prefix: oper
reference: RFC XXXX
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9. Security Considerations
This document does not introduce any new security concerns in
addition to those specified in [RFC6020] and [RFC6241].
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10. References
10.1. Normative References
[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.
[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
and A. Bierman, Ed., "Network Configuration Protocol
(NETCONF)", RFC 6241, June 2011.
10.2. Informative References
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
January 2004.
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Appendix A. Example: Interface List
With the proposed solution, the interface list example from ^ex-if-
list-2, can be solved with a single list:
list interface {
key name;
leaf name { ... }
leaf in-packets {
type yang:counter64;
config false;
}
...
}
The operation <get-operational> will return the interfaces available
on the device:
<interface>
<name>eth0</name>
...
</interface>
<interface>
<name>eth1</name>
...
</interface>
And <get-config> on running will return the configured interfaces,
just as before:
<interface>
<name>eth0</name>
...
</interface>
<interface>
<name>eth2</name>
...
</interface>
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Appendix B. Example: Ethernet Duplex
A typical problem is when the value space for the configuration data
is a super set of the value space for the operational state data. An
example of this is Ethernet duplex, which can be configured as
"half", "full", or "auto", but the operationally used value is either
"half" or "full". Without the definition of operational state in
this document, this would have to be modeled as two separate leafs:
leaf duplex {
type enumeration {
enum "half";
enum "full";
enum "auto";
}
}
leaf oper-duplex {
type enumeration {
enum "half";
enum "full";
}
}
With the solution defined in this document, a single leaf is
sufficient:
leaf duplex {
type enumeration {
enum "half";
enum "full";
enum "auto";
}
}
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Appendix C. Example: Admin vs. Oper State
Another common problem is when the value space for the configured
data is a subset of the operational state data. An example is an
interface's desired state, and its operational state. The desired
state can be "up" or "down", but the operational state can be "up",
"lower-layer-down", "testing", etc.
These kind of situations are still best modeled as two separate
leafs, one "admin-state" and one "oper-state".
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Authors' Addresses
Martin Bjorklund
Tail-f Systems
Email: mbj@tail-f.com
Ladislav Lhotka
CZ.NIC
Email: lhotka@nic.cz
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