YANG Boot Camp
The YANG Gang
IETF 70
WANTED: a DML for NETCONF
• NETCONF base protocol defined in
RFC4741
• Defines RPC mechanism and operations
• Left content and data models for future
work
– <get>, <get-config> and <edit-config> allow
any XML
• No data modeling language == no data
models
YANG is ….
• A language for modeling NETCONF data
models
– An SMI for NETCONF
• Able to model config data, state data,
RPCs, and notifications
• Based on SMIng syntax
– Text-based
• Email, patch, and RFC friendly
YANG ....
• Preserves
investment in SNMP MIBs
– libsmi translates MIBs to YANG
– See tools at www.yang-central.org
• Directly maps to XML content (on the wire)
• Extensible
– Add new content to existing data models
– Add new statements to the YANG language
YANG rocks, dude!
• Readability Rules!
• Doesn't boil the ocean
– Limited scope
• But maximize utility within that scope
• Based on three proprietary DMLs
– Years of experience within multiple vendors
• Quality draft backed by running code
– Usable in current form
– Download the code and use it today
• www.yang-central.org
Modules and submodules
• Header statements
– yang-version, namespace, prefix
• Linkage statement
– import and include
• Meta information
– organization, contact
• Revision history
– revision
module acme-module {
namespace "http://acme.example.com/module";
prefix "acme";
import “yang-types” {
prefix yang;
}
include “acme-system”;
organization "ACME Inc.";
contact "[email protected]";
description "The module for entities
implementing the ACME products";
revision 2007-06-09 {
description "Initial revision.";
}
…
}
leaf
• one value, no children, one instance
YANG Example:
leaf host-name {
type string;
mandatory true;
config true;
description "Hostname for this system";
}
NETCONF XML Encoding:
<host-name>my.example.com</host-name>
leaf-list
• one value, no children, multiple instances
YANG Example:
leaf-list domain-search {
type string;
ordered-by user;
description "List of domain names to search";
}
NETCONF XML Encoding:
<domain-search>high.example.com</domain-search>
<domain-search>low.example.com</domain-search>
<domain-search>everywhere.example.com</domain-search>
container
• no value, holds related children, one instance
• may have specific meaning, or may simply
contain other nodes
– presence
YANG Example:
container system {
container services {
container ssh {
presence "Enables SSH";
description "SSH service specific configuration";
// more leafs, containers and stuff here...
}
}
}
NETCONF XML Encoding:
<system>
<services>
<ssh/>
</services>
</system>
must
• Constrains nodes by XPath expression
container timeout {
leaf access-timeout {
description "Maximum time without server response";
units seconds;
mandatory true;
type uint32;
}
leaf retry-timer {
description "Period to retry operation";
units seconds;
type uint32;
must "$this < ../access-timeout" {
error-app-tag retry-timer-invalid;
error-message "The retry timer must be "
+ "less than the access timeout";
}
}
}
list
• uniquely identified by keys, holds children
• no value, holds related children (including keys),
multiple instances
YANG Example:
NETCONF XML Encoding:
list user {
key name;
unique uid;
leaf name {
type string;
}
leaf uid {
type uint32;
}
leaf full-name {
type string;
}
leaf class {
type string;
default viewer;
}
}
<user>
<name>glocks</name>
<full-name>Goldie</full-name>
<class>intruder</class>
</user>
<user>
<name>snowey</name>
<full-name>Snow</full-name>
<class>free-loader</class>
</user>
<user>
<name>rzull</name>
<full-name>Repun</full-name>
</user>
augment
• Extends data model
– Current or imported modules
• Inserts nodes into an existing hierarchy
– Nodes appear in current module's
namespace
– Original (augmented) module is unchanged
• "when" makes sparse augmentation
– Nodes are only added when condition is
true
– "when" is XPath expression
YANG Example:
augment system/login/user {
when "class != 'wheel'";
leaf uid {
type uint16 {
range "1000 .. 30000";
}
}
}
NETCONF XML Encoding:
<user>
<name>alicew</name>
<full-name>Alice N. Wonderland</full-name>
<class>drop-out</class>
<other:uid>1024</other:uid>
</user>
rpc
• Defines RPC method names, input
parameters, and output parameters
rpc activate-software-image {
input {
leaf image-name {
type string;
}
}
output {
leaf status {
type string;
}
}
}
notification
notification link-failure {
description "A link failure has been detected";
leaf if-index {
type int32 { range "1 .. max"; }
}
leaf if-name {
type keyref {
path "/interfaces/interface/name";
}
}
}
Semantic Differentiators
• YANG gives the syntax, but that's not all
• Here are some you just saw:
–
–
–
–
–
–
–
–
–
unique
must
keyref
config
default
error-app-tag/error-message
mandatory
presence
ordered-by
Built-in types
+---------------------+-------------+-------------------------------+
| Name
| Type
| Description
|
+---------------------+-------------+-------------------------------+
| int8
| Number
| 8-bit signed integer
|
| int16
| Number
| 16-bit signed integer
|
| int32
| Number
| 32-bit signed integer
|
| int64
| Number
| 64-bit signed integer
|
| uint8
| Number
| 8-bit unsigned integer
|
| uint16
| Number
| 16-bit unsigned integer
|
| uint32
| Number
| 32-bit unsigned integer
|
| uint64
| Number
| 64-bit unsigned integer
|
| float32
| Number
| 32-bit IEEE floating point
|
|
|
| real number
|
| float64
| Number
| 64-bit IEEE floating point
|
|
|
| real number
|
| string
| Text
| Human readable string
|
| boolean
| Text
| "true" or "false"
|
| enumeration
| Text/Number | Enumerated strings with
|
|
|
| associated numeric values
|
| bits
| Text/Number | A set of bits or flags
|
| binary
| Text
| Any binary data
|
| keyref
| Text/Number | A reference to a list's key
|
|
|
| value
|
| empty
| Empty
| A leaf that does not have any |
|
|
| value
|
| anyxml
| Text
| Represents any XML data
|
| union
| Text/Number | Choice of member types
|
| instance-identifier | Text
| References a data tree node
|
+---------------------+-------------+-------------------------------+
Derived types
YANG Example
• Constraints
– range
– length
– pattern
typedef percent {
type uint16 {
range "0 .. 100";
}
description "Percentage";
}
leaf completed {
type percent;
}
NETCONF XML Encoding:
<completed>20</completed>
grouping
•
•
•
•
YANG Example
struct / record
Define once
Use multiple times
Refinement
grouping target {
leaf address {
type inet:ip-address;
description "Target IP address";
}
}
container peer {
container destination {
uses target;
}
}
NETCONF XML Encoding:
<peer>
<destination>
<address>192.0.2.1</address>
</destination>
</peer>
choice
YANG Example
• Constrains data to the
contents of one "case"
• choice and case
names do not appear
in XML content
– Used by augment
choice snack {
case sports-arena {
leaf pretzel {
type empty;
}
leaf beer {
type empty;
}
}
case late-night {
leaf chocolate {
type enumeration {
enum dark;
enum light;
}
}
}
}
NETCONF XML Encoding:
<chocolate>dark</chocolate>
What can you do to help?
• Read the draft
– There's a lot more in there
• Join the mailing list
– [email protected]
– https://www.ietf.org/mailman/listinfo/yang
• Try out the tools
– www.yang-central.org