Yang in ODL by Jan Medved

Yang Modeling in OpenDaylight
Jan Medved

Agenda
• Yang Overview
• Netconf/Yang in OpenDaylight
• Example/Demo
• Pointers
© 2014 Cisco and/or its affiliates. Presentation_ID All rights reserved. Cisco Public

YANG is ….
• A NETCONF modeling language
– Think SMI for NETCONF
• Models semantics and data organization
– Syntax falls out of semantics
• Able to model config data, state data, RPCs, and notifications
• Based on SMIng syntax
– Text-based
• Email, patch, and RFC friendly

YANG Concepts
RPCs notifications
leafs
config data
types
Standard
Models
Proprietary
Models
containers

YANG ....
• Directly maps to XML content (on the wire)
• Extensible
– Add new content to existing data models
• Without changing the original model
– Add new statements to the YANG language
• Vendor extensions and future proofing
• Preserves investment in SNMP MIBs
– libsmi translates MIBs to YANG
• See tools at www.yang-central.org

Semantics and syntax
YANG
XML Schema Relax-NG Anything Else
Legacy tools
Out
going
XML
Semantic
World
Syntactic
World
Validation

YANG values ....
• Readers and reviewers time and learning curve
– Readability is highest priority
• Limited Scope
– Doesn't boil the ocean
– Maximize utility within that scope
– Can be extended in the future
• Experience gained by existing implementations
– Based on four proprietary modeling languages
• Years of experience within multiple vendors
• Quality draft backed by running code

Modules and submodules
• Header statements
– yang-version, namespace, prefix
• Linkage statement
– import and include
• Meta information
– organization, contact
• Revision history
– revision
Mod1
SubA
SubX SubY SubZ
Mod2
Include
Import
Include

module acme-module {!
namespace "http://acme.example.com/module";!
prefix acme;!
!
import "yang-types" {!
prefix yang;!
}!
include "acme-system";!
!
organization "ACME Inc.";!
contact joe@acme.example.com;!
description "The module for entities !
implementing the ACME products";!
!
revision 2007-06-09 {!
description "Initial revision.";!
}!
…!
}!

The "leaf" Statement
YANG Example:!
!
leaf host-name {!
type string;!
mandatory true;!
config true;!
description "Hostname for this system";!
}!
• A leaf has
– one value
– no children
– one instance
NETCONF XML Encoding:!
!
<host-name>my.example.com</host-name>!

The "leaf-list" Statement
YANG Example:!
!
leaf-list domain-search {!
type string;!
ordered-by user;!
description "List of domain names to search";!
}!
• A leaf-list has:
– one value
– no children
– multiple instances
!
<domain-search>high.example.com</domain-search>!
<domain-search>low.example.com</domain-search>!
<domain-search>everywhere.example.com</domain-search>!

The "container" Statement
YANG Example:!
!
container system {!
container services {!
container ssh {!
presence "Enables SSH";!
description "SSH service specific configuration";!
// more leafs, containers and stuff here...!
}!
}!
}!
n A container has"
n no value"
n holds related children"
n one instance"
!
<system>!
<services>!
<ssh/>!
</services>!
</system>!
May have specific meaning (presence)
Or may simply contain other nodes

The "must" Statement
container timeout {!
leaf access-timeout {!
description "Maximum time without server response";!
units seconds;!
mandatory true;!
type uint32;!
}!
leaf retry-timer {!
• Constrains nodes by Xpath expression
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";!
}!
}!
}!

The "list" Statement
YANG Example:!
!
list user {!
key name;!
leaf name {!
type string;!
}!
leaf uid {!
type uint32;!
}!
leaf full-name {!
type string;!
}!
leaf class {!
type string;!
default viewer;!
}!
}!
• A list is
– uniquely identified by key(s)
– holds related children
– no value
– multiple instances
!
user!
nameglocks/name!
full-nameGoldie/full-name!
classintruder/class!
/user!
user!
namesnowey/name!
full-nameSnow/full-name!
classfree-loader/class!
/user!
user!
namerzull/name!
full-nameRepun/full-name!
/user!

The augment Statement
YANG Example:!
!
augment system/login/user {!
leaf expire {!
type yang:date-and-time;!
}!
}!
!
user!
namealicew/name!
classdrop-out/class!
other:expire2112-04-01T12:00:00/other:expire!
/user!
!
• 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

The when Statement
YANG Example:!
!
augment system/login/user {!
when class = wheel;!
leaf shell {!
type string;!
}!
}! NETCONF XML Encoding:!
!
user!
namealicew/name!
classwheel/class!
other:shell/bin/tcsh/other:shell!
/user!
• Makes sparse augmentation
– Nodes are only added when
condition is true
– when is XPath expression

Built-in ^ypes
Category! Types!
Integral {,u}int{8,16,32,64}
String string, enumeration, boolean
Binary Data binary
Bit fields bits
References instance-identifier, keyref
Other empty

Derived Types
YANG Example:!
!
typedef percent {!
type uint16 {!
range 0 .. 100;!
}!
description Percentage;!
}!
!
leaf completed {!
type percent;!
}!
!
completed20/completed!
• Constraints
– range
– length
– pattern
• regex
• A modules may use types imported
from other modules

The union type
YANG Example:!
!
leaf limit {!
description Number to allow;!
type union {!
type uint16 {!
range 0 .. 100;!
}!
type enumeration {!
enum none {!
!
limitnone/limit!
description No limit;!
}!
}!
}!
}!
• Allows a leaf to contain a superset of types
!
limit20/limit!

The grouping Statement
YANG Example!
!
grouping target {!
leaf address {!
type inet:ip-address;!
description Target IP address;!
}!
leaf port {!
type inet:ip-port;!
description Target port number;!
}!
}!
container peer {!
container destination {!
uses target;!
}!
}!
!
peer!
destination!
address192.0.2.1/address!
port22/port!
/destination!
/peer!
• Defines a reusable collection of
nodes
• Use multiple times
– A modules may use groupings
imported from other modules
• Refinement
• Use as structure, record, or object

The choice Statement
YANG Example:!
!
choice transfer-method {!
leaf transfer-interval {!
description Frequency at which file transfer happens;!
type uint {!
range 15 .. 2880;!
}!
units minutes;!
}!
!
leaf transfer-on-commit {!
description Transfer after each commit;!
type empty;!
}!
}!
• Allow only one member of the choice to exist
in a valid config datastore
!
transfer-on-commit/!

The anyxml Statement
YANG Example:!
!
anyxml software-version {!
description Number to allow;!
}!
!
software-version!
baseA10.2/base!
routingB4.2/routing!
snmpC87.12/snmp!
/software-version !
• Allows arbitrary XML content to be carried
in YANG-based models
– Opaque
– Limited operations
• Bulk only

The rpc Statement
rpc activate-software-image {!
input {!
leaf image-name {!
type string;!
}!
}!
output {!
leaf status {!
type string;!
}!
}!
}!
rpc xmlns=urn:mumble!
activate-software-image!
image-nameimage.tgz/image-name!
/activate-software-image!
/rpc!
• Defines RPC
– method names
– input parameters
– output parameters

The notification Statement
YANG Example:!
!
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;!
}!
}!
}!
• Defines notification
– Name
– Content

Semantic Differentiators
• Notice that YANG is modeling the semantics and data
organization
– Not just the syntax
Statement! Purpose!
unique Ensure unique values within list siblings
keyref Ensure referential integrity
config Indicate if a node is config data or not
default Supply default value for leafs
error-app-tag Define the tag used when constraint fails
error-message Define the message used ....
mandatory Node must exist in valid config datastore

Tools
• pyang (http://code.google.com/p/pyang/)”
– Validates YANG
– Translates between YANG and YIN (XML)
– Generates XSD
• libsmi
– Translates SMI/SMIv2 MIBs to YANG
• Editors/IDEs:
– Emacs yang mode: http://www.emacswiki.org/emacs/yang-mode.el
– Eclipse plugin:https://github.com/xored/yang-ide/wiki
• OpenDaylight Yang Tools:
– https://wiki.opendaylight.org/view/YANG_Tools:Main

What Should and SDN Controller Look Like?
• A platform for deploying SDN applications
• Provide (or be associated with) an SDN application development environment.

SDN Controller: Platform Requirements
• Flexibility:
– Accommodate a variety of diverse applications
– Controller applications SHOULD use a common framework and programming model,
and provide consistent APIs to their client
• Scale the development process:
– No infrastructure code hotspots
– Independent development of controller applications short integration times
• Run-time Extensibility Modularity:
– Load new protocol and service/application plugins at run-time.
– Adapt to data schemas (models) discovered in the network
• Performance Scale

SDN Controller: App Development Requirements
• A domain-specific modeling language to describe internal and external system
behavior
• Modeling tools for the controller aligned with modeling tools for devices
• Code generation from models:
– Enforce standard API contracts
– Generate boilerplate code performing repetitive and error-prone tasks
– Produce functionally equivalent APIs for different language bindings
– Model-to-model adaptations for services and devices
– Consumption of aligned device models
In the OpenDaylight Project, these requirements are satisfied with
YANG (and YANG extensions) and via the YANG tool-chain, manifested
in the MD-SAL

OpenDaylight: SDN Controller Architecture
NETCONF
Controller
Applica1ons
Base
Network
Func1ons
Topology
Service
Adapta1on
Layer
Inventory
Manager
Sta1s1cs
Exporter
Manager
Forwarding
Rules
Manager
Topology
ToEpxpoolorgteyr
Exporter
Inventory
InMveanntaogreyr
Manager
OpenFlow
1.0/1.3
BGP-‐LS
PCEP
Netconf
Client
OVSDB
REST
APIs
...
Service
Func1ons
Configura1on
...
PCEP
Subsystem
LISP
Network
Devices
Network
Applica1ons
Orchestra1on

Services
Controller
PlaSorm
Southbound
Interfaces

Protocol
Plugins

OpenDaylight: Software Architecture
Network
Devices
Applica1ons
NETCONF
Model-‐Driven
SAL
(MD-‐SAL)
Controller
Protocol
Plugin
RESTCONF
Service/App
Plugin
Service/App
Plugin
...
Protocol
...
Plugin
Config
Subsystem
Messaging
Data
Store
Remote
Controller
Instance
Remote
Controller
Instance
Network
Applica1ons
Orchestra1on

Services
Plugins

Applica1ons
Controller
PlaSorm
Clustering

Model-Driven SAL: Building the Network View
Controller
PlaSorm
OpenFlow
NETCONF
MD-‐SAL
...
BGP-‐LS
Topology
Exporter
OpenFlow
Topology
Exporter
Flow-‐Capable
Node
Inventory
Manager
Mo
del
Sta1s1cs
Manager
/Opera1onal
/Config
network-‐topo
p1
p2
BGP-‐LS
BGPv4
BGPv6
nodes
links
prefixes
n1
n2
...
nx
l1
l2
...
lx
...
px
nodes
BGP-‐LS
Protocol
Plugin
Groups
Table/1
Flow/2
Table-‐stats
Model
Model
Model
nc:1
nc:2
Flow-‐stats
Flow-‐stats
of:1
of:2
Of:n
...
Tables
Meters
Table/2
Table/n
Flow/1
...
Ports
Flow/n

BA-‐BI
Connector
Controller
MD-SAL Details
MD-‐SAL
DOM
Broker
Data
Store
Mapping
Service
Codec
Registry
Schema
Service
Codec
Generator
Binding-‐Aware
Broker
Binding-‐Aware
to
Binding-‐Independent
Data
Transla5on
Binding-‐Aware
Plugin
Binding-‐Independent
Plugin/Client
(Netconf/Restconf)
Forwarding
Rules
Manager,
Stats
Manager,
BGP-‐LS/PCEP
External
Clients

Building a Plugin/Application
MModoedle
l
Yang
Model
Yang
Tools
JaJvaav
aA
PAIP
DI
Defienfiin1io1no
n
Generated
API
Defini1on
Module
Implementa1ons
Create
API
Bundle
“Plugin”
OSGI
Bundle
1
Deploy
4
Generate
APIs
Create
Plugin
Bundle
Deploy
Maven
Build
Tools
Module
PluImginp
lseomuercneta
c1oodnes
“API”
OSGI
Bundle
Maven
Build
Tools
2
3
4
Controller

ODL Yang Resources
• YangTools main page:
– https://wiki.opendaylight.org/view/YANG_Tools:Main
• Code Generation demo
– https://wiki.opendaylight.org/view/Yang_Tools:Code_Generation_Demo
• Java “Binding Specification”:
– https://wiki.opendaylight.org/view/YANG_Tools:YANG_to_Java_Mapping
• DLUX
• Main page: https://wiki.opendaylight.org/view/OpenDaylight_dlux:Main
• YangUI: https://wiki.opendaylight.org/view/OpenDaylight_dlux:yangUI-user
• Controller:
– Swagger UI Explorer:
• http://localhost:8181/apidoc/explorer/index.html
– DLUX (YangUI):
• http://localhost:8181/dlux/index.html

ODL Netconf Resources
• Config Subsystem:
– How to configure the Netconf connector (client):
• https://wiki.opendaylight.org/view/OpenDaylight_Controller:Config:Examples:Netconf
– Netopeer installation
• https://wiki.opendaylight.org/view/
OpenDaylight_Controller:Config:Examples:Netconf:Manual_netopeer_installation
• Netconf test tool:
– https://wiki.opendaylight.org/view/OpenDaylight_Controller:Netconf:Testtool

Yang in ODL by Jan Medved

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