YANG Boot Camp

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(No Transcript)
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YANG Boot Camp

• The YANG Gang
• IETF 71

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NETCONF Modeling Language

• NETCONF base protocol (rfc 4741)
• RPC mechanism and operations
• Left content and data models for future work
• Operations allow any XML
• ltgetgt, ltget-configgt and ltedit-configgt

Mgmt Application
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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

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YANG Concepts
Standard Models
Proprietary Models
config data
RPCs
notifications

• containers

leafs
types
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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

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

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Modules and submodules

• Header statements
• yang-version, namespace, prefix
• Linkage statement
• import and include
• Meta information
• organization, contact
• Revision history
• revision

Mod1
Import
Mod2
Include
SubA
Include
SubX
SubY
SubZ
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module acme-module namespace
"http//acme.example.com/module" prefix
acme import "yang-types" prefix
yang include "acme-system"
organization "ACME Inc." contact
joe_at_acme.example.com description "The module
for entities implementing the
ACME products" revision 2007-06-09
description "Initial revision."
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The "leaf" Statement

• A leaf has
• 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 lthost-namegtmy.example.comlt/
host-namegt
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The "leaf-list" Statement

• A leaf-list has
• 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 ltdomain-searchgthigh.example
.comlt/domain-searchgt ltdomain-searchgtlow.example.co
mlt/domain-searchgt ltdomain-searchgteverywhere.exampl
e.comlt/domain-searchgt
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The "container" Statement

• A container has
• no value
• holds related children
• one instance

YANG Example container system container
services container ssh
presence "Enables SSH" description
"SSH service specific configuration"
// more leafs, containers and stuff here...

• May have specific meaning (presence)
• Or may simply contain other nodes

NETCONF XML Encoding ltsystemgt ltservicesgt
ltssh/gt lt/servicesgt lt/systemgt
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The "must" Statement

• 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 lt
../access-timeout" error-app-tag
retry-timer-invalid error-message
"The retry timer must be "
"less than the access timeout"

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The "list" Statement

• A list is
• uniquely identified by key(s)
• holds related children
• no value
• multiple instances

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
NETCONF XML Encoding ltusergt
ltnamegtglockslt/namegt ltfull-namegtGoldielt/full-name
gt ltclassgtintruderlt/classgt lt/usergt ltusergt
ltnamegtsnoweylt/namegt ltfull-namegtSnowlt/full-namegt
ltclassgtfree-loaderlt/classgt lt/usergt ltusergt
ltnamegtrzulllt/namegt ltfull-namegtRepunlt/full-namegt
lt/usergt
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The "augment" Statement

• 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

YANG Example augment system/login/user
leaf expire type yangdate-and-time

NETCONF XML Encoding ltusergt
ltnamegtalicewlt/namegt ltclassgtdrop-outlt/classgt
ltotherexpiregt2112-04-01T120000lt/otherexpiregt lt
/usergt
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The "when" Statement
YANG Example augment system/login/user
when "class wheel" leaf shell
type string

• Makes sparse augmentation
• Nodes are only added when condition is true
• "when" is XPath expression

NETCONF XML Encoding ltusergt
ltnamegtalicewlt/namegt ltclassgtwheellt/classgt
ltothershellgt/bin/tcshlt/othershellgt lt/usergt
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Built-in types
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Derived types
YANG Example typedef percent type uint16
range "0 .. 100" description
"Percentage" leaf completed type
percent

• Constraints
• range
• length
• pattern
• regex
• A modules may use types imported from other
  modules

NETCONF XML Encoding ltcompletedgt20lt/completedgt
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The "union" type

• Allows a leaf to contain a superset of types

YANG Example leaf limit description
"Number to allow" type union type
uint16 range "0 .. 100"
type enumeration enum none
description "No limit"

NETCONF XML Encoding ltlimitgtnonelt/limitgt
NETCONF XML Encoding ltlimitgt20lt/limitgt
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The "grouping" Statement

• 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

YANG Example grouping target leaf address
type inetip-address
description "Target IP address" leaf
port type inetip-port
description "Target port number"
container peer container destination
uses target
NETCONF XML Encoding ltpeergt ltdestinationgt
ltaddressgt192.0.2.1lt/addressgt ltportgt22lt/portgt
lt/destinationgt lt/peergt
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The "choice" Statement

• Allow only one member of the choice to exist in a
  valid config datastore

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
NETCONF XML Encoding lttransfer-on-commit/gt
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The "anyxml" Statement

• Allows arbitrary XML content to be carried in
  YANG-based models
• Opaque
• Limited operations
• Bulk only

YANG Example anyxml software-version
description "Number to allow"
NETCONF XML Encoding ltsoftware-versiongt
ltbasegtA10.2lt/basegt ltroutinggtB4.2lt/routinggt
ltsnmpgtC87.12lt/snmpgt lt/software-versiongt
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The "rpc" Statement
rpc activate-software-image input
leaf image-name type string
output leaf status
type string

• Defines RPC
• method names
• input parameters
• output parameters

ltrpc xmlns"urnmumble"gt ltactivate-software-imag
egt ltimage-namegtimage.tgzlt/image-namegt
lt/activate-software-imagegt lt/rpcgt
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The "notification" Statement

• Defines notification
• Name
• Content

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/n
ame"
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Semantic Differentiators

• Notice that YANG is modeling the semantics and
  data organization
• Not just the syntax

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Tools (yang-central.org)

• pyang (python)
• Validates YANG
• Translates between YANG and YIN (XML)
• Generates XSD
• yangto (binary)
• Validates YANG
• Generates XSD, dependencies, etc
• libsmi
• Translates SMI/SMIv2 MIBs to YANG
• Other goodies
• Emacs mode

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What can you do to help?

• Read the draft
• There's a lot more in there
• Join the mailing list
• yang_at_ietf.org
• https//www.ietf.org/mailman/listinfo/yang
• Try out the tools
• www.yang-central.org
• Tutorial (this) at
• http//www.yang-central.org/twiki/bin/view/Main/Ya
  ngTutorials