RFC 7950
The YANG 1.1 Data Modeling Language
14. YANG ABNF Grammar
In YANG, almost all statements are unordered. The ABNF grammar [RFC5234] [RFC7405] defines the canonical order. To improve module readability, it is RECOMMENDED that clauses be entered in this order. Within the ABNF grammar, unordered statements are marked with comments. This grammar assumes that the scanner replaces YANG comments with a single space character. <CODE BEGINS> file "yang.abnf" module-stmt = optsep module-keyword sep identifier-arg-str optsep "{" stmtsep module-header-stmts linkage-stmts meta-stmts revision-stmts body-stmts "}" optsep submodule-stmt = optsep submodule-keyword sep identifier-arg-str optsep "{" stmtsep submodule-header-stmts linkage-stmts meta-stmts revision-stmts body-stmts "}" optsep module-header-stmts = ;; these stmts can appear in any order yang-version-stmt namespace-stmt prefix-stmt submodule-header-stmts = ;; these stmts can appear in any order yang-version-stmt belongs-to-stmt
meta-stmts = ;; these stmts can appear in any order
[organization-stmt]
[contact-stmt]
[description-stmt]
[reference-stmt]
linkage-stmts = ;; these stmts can appear in any order
*import-stmt
*include-stmt
revision-stmts = *revision-stmt
body-stmts = *(extension-stmt /
feature-stmt /
identity-stmt /
typedef-stmt /
grouping-stmt /
data-def-stmt /
augment-stmt /
rpc-stmt /
notification-stmt /
deviation-stmt)
data-def-stmt = container-stmt /
leaf-stmt /
leaf-list-stmt /
list-stmt /
choice-stmt /
anydata-stmt /
anyxml-stmt /
uses-stmt
yang-version-stmt = yang-version-keyword sep yang-version-arg-str
stmtend
yang-version-arg-str = < a string that matches the rule >
< yang-version-arg >
yang-version-arg = "1.1"
import-stmt = import-keyword sep identifier-arg-str optsep
"{" stmtsep
;; these stmts can appear in any order
prefix-stmt
[revision-date-stmt]
[description-stmt]
[reference-stmt]
"}" stmtsep
include-stmt = include-keyword sep identifier-arg-str optsep
(";" /
"{" stmtsep
;; these stmts can appear in any order
[revision-date-stmt]
[description-stmt]
[reference-stmt]
"}") stmtsep
namespace-stmt = namespace-keyword sep uri-str stmtend
uri-str = < a string that matches the rule >
< URI in RFC 3986 >
prefix-stmt = prefix-keyword sep prefix-arg-str stmtend
belongs-to-stmt = belongs-to-keyword sep identifier-arg-str
optsep
"{" stmtsep
prefix-stmt
"}" stmtsep
organization-stmt = organization-keyword sep string stmtend
contact-stmt = contact-keyword sep string stmtend
description-stmt = description-keyword sep string stmtend
reference-stmt = reference-keyword sep string stmtend
units-stmt = units-keyword sep string stmtend
revision-stmt = revision-keyword sep revision-date optsep
(";" /
"{" stmtsep
;; these stmts can appear in any order
[description-stmt]
[reference-stmt]
"}") stmtsep
revision-date = date-arg-str
revision-date-stmt = revision-date-keyword sep revision-date stmtend
extension-stmt = extension-keyword sep identifier-arg-str optsep
(";" /
"{" stmtsep
;; these stmts can appear in any order
[argument-stmt]
[status-stmt]
[description-stmt]
[reference-stmt]
"}") stmtsep
argument-stmt = argument-keyword sep identifier-arg-str optsep
(";" /
"{" stmtsep
[yin-element-stmt]
"}") stmtsep
yin-element-stmt = yin-element-keyword sep yin-element-arg-str
stmtend
yin-element-arg-str = < a string that matches the rule >
< yin-element-arg >
yin-element-arg = true-keyword / false-keyword
identity-stmt = identity-keyword sep identifier-arg-str optsep
(";" /
"{" stmtsep
;; these stmts can appear in any order
*if-feature-stmt
*base-stmt
[status-stmt]
[description-stmt]
[reference-stmt]
"}") stmtsep
base-stmt = base-keyword sep identifier-ref-arg-str
stmtend
feature-stmt = feature-keyword sep identifier-arg-str optsep
(";" /
"{" stmtsep
;; these stmts can appear in any order
*if-feature-stmt
[status-stmt]
[description-stmt]
[reference-stmt]
"}") stmtsep
if-feature-stmt = if-feature-keyword sep if-feature-expr-str
stmtend
if-feature-expr-str = < a string that matches the rule >
< if-feature-expr >
if-feature-expr = if-feature-term
[sep or-keyword sep if-feature-expr]
if-feature-term = if-feature-factor
[sep and-keyword sep if-feature-term]
if-feature-factor = not-keyword sep if-feature-factor /
"(" optsep if-feature-expr optsep ")" /
identifier-ref-arg
typedef-stmt = typedef-keyword sep identifier-arg-str optsep
"{" stmtsep
;; these stmts can appear in any order
type-stmt
[units-stmt]
[default-stmt]
[status-stmt]
[description-stmt]
[reference-stmt]
"}" stmtsep
type-stmt = type-keyword sep identifier-ref-arg-str optsep
(";" /
"{" stmtsep
[type-body-stmts]
"}") stmtsep
type-body-stmts = numerical-restrictions /
decimal64-specification /
string-restrictions /
enum-specification /
leafref-specification /
identityref-specification /
instance-identifier-specification /
bits-specification /
union-specification /
binary-specification
numerical-restrictions = [range-stmt]
range-stmt = range-keyword sep range-arg-str optsep
(";" /
"{" stmtsep
;; these stmts can appear in any order
[error-message-stmt]
[error-app-tag-stmt]
[description-stmt]
[reference-stmt]
"}") stmtsep
decimal64-specification = ;; these stmts can appear in any order
fraction-digits-stmt
[range-stmt]
fraction-digits-stmt = fraction-digits-keyword sep
fraction-digits-arg-str stmtend
fraction-digits-arg-str = < a string that matches the rule >
< fraction-digits-arg >
fraction-digits-arg = ("1" ["0" / "1" / "2" / "3" / "4" /
"5" / "6" / "7" / "8"])
/ "2" / "3" / "4" / "5" / "6" / "7" / "8" / "9"
string-restrictions = ;; these stmts can appear in any order
[length-stmt]
*pattern-stmt
length-stmt = length-keyword sep length-arg-str optsep
(";" /
"{" stmtsep
;; these stmts can appear in any order
[error-message-stmt]
[error-app-tag-stmt]
[description-stmt]
[reference-stmt]
"}") stmtsep
pattern-stmt = pattern-keyword sep string optsep
(";" /
"{" stmtsep
;; these stmts can appear in any order
[modifier-stmt]
[error-message-stmt]
[error-app-tag-stmt]
[description-stmt]
[reference-stmt]
"}") stmtsep
modifier-stmt = modifier-keyword sep modifier-arg-str stmtend
modifier-arg-str = < a string that matches the rule >
< modifier-arg >
modifier-arg = invert-match-keyword
default-stmt = default-keyword sep string stmtend
enum-specification = 1*enum-stmt
enum-stmt = enum-keyword sep string optsep
(";" /
"{" stmtsep
;; these stmts can appear in any order
*if-feature-stmt
[value-stmt]
[status-stmt]
[description-stmt]
[reference-stmt]
"}") stmtsep
leafref-specification =
;; these stmts can appear in any order
path-stmt
[require-instance-stmt]
path-stmt = path-keyword sep path-arg-str stmtend
require-instance-stmt = require-instance-keyword sep
require-instance-arg-str stmtend
require-instance-arg-str = < a string that matches the rule >
< require-instance-arg >
require-instance-arg = true-keyword / false-keyword
instance-identifier-specification =
[require-instance-stmt]
identityref-specification =
1*base-stmt
union-specification = 1*type-stmt
binary-specification = [length-stmt]
bits-specification = 1*bit-stmt
bit-stmt = bit-keyword sep identifier-arg-str optsep
(";" /
"{" stmtsep
;; these stmts can appear in any order
*if-feature-stmt
[position-stmt]
[status-stmt]
[description-stmt]
[reference-stmt]
"}") stmtsep
position-stmt = position-keyword sep
position-value-arg-str stmtend
position-value-arg-str = < a string that matches the rule >
< position-value-arg >
position-value-arg = non-negative-integer-value
status-stmt = status-keyword sep status-arg-str stmtend
status-arg-str = < a string that matches the rule >
< status-arg >
status-arg = current-keyword /
obsolete-keyword /
deprecated-keyword
config-stmt = config-keyword sep
config-arg-str stmtend
config-arg-str = < a string that matches the rule >
< config-arg >
config-arg = true-keyword / false-keyword
mandatory-stmt = mandatory-keyword sep
mandatory-arg-str stmtend
mandatory-arg-str = < a string that matches the rule >
< mandatory-arg >
mandatory-arg = true-keyword / false-keyword
presence-stmt = presence-keyword sep string stmtend
ordered-by-stmt = ordered-by-keyword sep
ordered-by-arg-str stmtend
ordered-by-arg-str = < a string that matches the rule >
< ordered-by-arg >
ordered-by-arg = user-keyword / system-keyword
must-stmt = must-keyword sep string optsep
(";" /
"{" stmtsep
;; these stmts can appear in any order
[error-message-stmt]
[error-app-tag-stmt]
[description-stmt]
[reference-stmt]
"}") stmtsep
error-message-stmt = error-message-keyword sep string stmtend
error-app-tag-stmt = error-app-tag-keyword sep string stmtend
min-elements-stmt = min-elements-keyword sep
min-value-arg-str stmtend
min-value-arg-str = < a string that matches the rule >
< min-value-arg >
min-value-arg = non-negative-integer-value
max-elements-stmt = max-elements-keyword sep
max-value-arg-str stmtend
max-value-arg-str = < a string that matches the rule >
< max-value-arg >
max-value-arg = unbounded-keyword /
positive-integer-value
value-stmt = value-keyword sep integer-value-str stmtend
integer-value-str = < a string that matches the rule >
< integer-value >
grouping-stmt = grouping-keyword sep identifier-arg-str optsep
(";" /
"{" stmtsep
;; these stmts can appear in any order
[status-stmt]
[description-stmt]
[reference-stmt]
*(typedef-stmt / grouping-stmt)
*data-def-stmt
*action-stmt
*notification-stmt
"}") stmtsep
container-stmt = container-keyword sep identifier-arg-str optsep
(";" /
"{" stmtsep
;; these stmts can appear in any order
[when-stmt]
*if-feature-stmt
*must-stmt
[presence-stmt]
[config-stmt]
[status-stmt]
[description-stmt]
[reference-stmt]
*(typedef-stmt / grouping-stmt)
*data-def-stmt
*action-stmt
*notification-stmt
"}") stmtsep
leaf-stmt = leaf-keyword sep identifier-arg-str optsep
"{" stmtsep
;; these stmts can appear in any order
[when-stmt]
*if-feature-stmt
type-stmt
[units-stmt]
*must-stmt
[default-stmt]
[config-stmt]
[mandatory-stmt]
[status-stmt]
[description-stmt]
[reference-stmt]
"}" stmtsep
leaf-list-stmt = leaf-list-keyword sep identifier-arg-str optsep
"{" stmtsep
;; these stmts can appear in any order
[when-stmt]
*if-feature-stmt
type-stmt stmtsep
[units-stmt]
*must-stmt
*default-stmt
[config-stmt]
[min-elements-stmt]
[max-elements-stmt]
[ordered-by-stmt]
[status-stmt]
[description-stmt]
[reference-stmt]
"}" stmtsep
list-stmt = list-keyword sep identifier-arg-str optsep
"{" stmtsep
;; these stmts can appear in any order
[when-stmt]
*if-feature-stmt
*must-stmt
[key-stmt]
*unique-stmt
[config-stmt]
[min-elements-stmt]
[max-elements-stmt]
[ordered-by-stmt]
[status-stmt]
[description-stmt]
[reference-stmt]
*(typedef-stmt / grouping-stmt)
1*data-def-stmt
*action-stmt
*notification-stmt
"}" stmtsep
key-stmt = key-keyword sep key-arg-str stmtend
key-arg-str = < a string that matches the rule >
< key-arg >
key-arg = node-identifier *(sep node-identifier)
unique-stmt = unique-keyword sep unique-arg-str stmtend
unique-arg-str = < a string that matches the rule >
< unique-arg >
unique-arg = descendant-schema-nodeid
*(sep descendant-schema-nodeid)
choice-stmt = choice-keyword sep identifier-arg-str optsep
(";" /
"{" stmtsep
;; these stmts can appear in any order
[when-stmt]
*if-feature-stmt
[default-stmt]
[config-stmt]
[mandatory-stmt]
[status-stmt]
[description-stmt]
[reference-stmt]
*(short-case-stmt / case-stmt)
"}") stmtsep
short-case-stmt = choice-stmt /
container-stmt /
leaf-stmt /
leaf-list-stmt /
list-stmt /
anydata-stmt /
anyxml-stmt
case-stmt = case-keyword sep identifier-arg-str optsep
(";" /
"{" stmtsep
;; these stmts can appear in any order
[when-stmt]
*if-feature-stmt
[status-stmt]
[description-stmt]
[reference-stmt]
*data-def-stmt
"}") stmtsep
anydata-stmt = anydata-keyword sep identifier-arg-str optsep
(";" /
"{" stmtsep
;; these stmts can appear in any order
[when-stmt]
*if-feature-stmt
*must-stmt
[config-stmt]
[mandatory-stmt]
[status-stmt]
[description-stmt]
[reference-stmt]
"}") stmtsep
anyxml-stmt = anyxml-keyword sep identifier-arg-str optsep
(";" /
"{" stmtsep
;; these stmts can appear in any order
[when-stmt]
*if-feature-stmt
*must-stmt
[config-stmt]
[mandatory-stmt]
[status-stmt]
[description-stmt]
[reference-stmt]
"}") stmtsep
uses-stmt = uses-keyword sep identifier-ref-arg-str optsep
(";" /
"{" stmtsep
;; these stmts can appear in any order
[when-stmt]
*if-feature-stmt
[status-stmt]
[description-stmt]
[reference-stmt]
*refine-stmt
*uses-augment-stmt
"}") stmtsep
refine-stmt = refine-keyword sep refine-arg-str optsep
"{" stmtsep
;; these stmts can appear in any order
*if-feature-stmt
*must-stmt
[presence-stmt]
*default-stmt
[config-stmt]
[mandatory-stmt]
[min-elements-stmt]
[max-elements-stmt]
[description-stmt]
[reference-stmt]
"}" stmtsep
refine-arg-str = < a string that matches the rule >
< refine-arg >
refine-arg = descendant-schema-nodeid
uses-augment-stmt = augment-keyword sep uses-augment-arg-str optsep
"{" stmtsep
;; these stmts can appear in any order
[when-stmt]
*if-feature-stmt
[status-stmt]
[description-stmt]
[reference-stmt]
1*(data-def-stmt / case-stmt /
action-stmt / notification-stmt)
"}" stmtsep
uses-augment-arg-str = < a string that matches the rule >
< uses-augment-arg >
uses-augment-arg = descendant-schema-nodeid
augment-stmt = augment-keyword sep augment-arg-str optsep
"{" stmtsep
;; these stmts can appear in any order
[when-stmt]
*if-feature-stmt
[status-stmt]
[description-stmt]
[reference-stmt]
1*(data-def-stmt / case-stmt /
action-stmt / notification-stmt)
"}" stmtsep
augment-arg-str = < a string that matches the rule >
< augment-arg >
augment-arg = absolute-schema-nodeid
when-stmt = when-keyword sep string optsep
(";" /
"{" stmtsep
;; these stmts can appear in any order
[description-stmt]
[reference-stmt]
"}") stmtsep
rpc-stmt = rpc-keyword sep identifier-arg-str optsep
(";" /
"{" stmtsep
;; these stmts can appear in any order
*if-feature-stmt
[status-stmt]
[description-stmt]
[reference-stmt]
*(typedef-stmt / grouping-stmt)
[input-stmt]
[output-stmt]
"}") stmtsep
action-stmt = action-keyword sep identifier-arg-str optsep
(";" /
"{" stmtsep
;; these stmts can appear in any order
*if-feature-stmt
[status-stmt]
[description-stmt]
[reference-stmt]
*(typedef-stmt / grouping-stmt)
[input-stmt]
[output-stmt]
"}") stmtsep
input-stmt = input-keyword optsep
"{" stmtsep
;; these stmts can appear in any order
*must-stmt
*(typedef-stmt / grouping-stmt)
1*data-def-stmt
"}" stmtsep
output-stmt = output-keyword optsep
"{" stmtsep
;; these stmts can appear in any order
*must-stmt
*(typedef-stmt / grouping-stmt)
1*data-def-stmt
"}" stmtsep
notification-stmt = notification-keyword sep
identifier-arg-str optsep
(";" /
"{" stmtsep
;; these stmts can appear in any order
*if-feature-stmt
*must-stmt
[status-stmt]
[description-stmt]
[reference-stmt]
*(typedef-stmt / grouping-stmt)
*data-def-stmt
"}") stmtsep
deviation-stmt = deviation-keyword sep
deviation-arg-str optsep
"{" stmtsep
;; these stmts can appear in any order
[description-stmt]
[reference-stmt]
(deviate-not-supported-stmt /
1*(deviate-add-stmt /
deviate-replace-stmt /
deviate-delete-stmt))
"}" stmtsep
deviation-arg-str = < a string that matches the rule >
< deviation-arg >
deviation-arg = absolute-schema-nodeid
deviate-not-supported-stmt =
deviate-keyword sep
not-supported-keyword-str stmtend
deviate-add-stmt = deviate-keyword sep add-keyword-str optsep
(";" /
"{" stmtsep
;; these stmts can appear in any order
[units-stmt]
*must-stmt
*unique-stmt
*default-stmt
[config-stmt]
[mandatory-stmt]
[min-elements-stmt]
[max-elements-stmt]
"}") stmtsep
deviate-delete-stmt = deviate-keyword sep delete-keyword-str optsep
(";" /
"{" stmtsep
;; these stmts can appear in any order
[units-stmt]
*must-stmt
*unique-stmt
*default-stmt
"}") stmtsep
deviate-replace-stmt = deviate-keyword sep replace-keyword-str optsep
(";" /
"{" stmtsep
;; these stmts can appear in any order
[type-stmt]
[units-stmt]
[default-stmt]
[config-stmt]
[mandatory-stmt]
[min-elements-stmt]
[max-elements-stmt]
"}") stmtsep
not-supported-keyword-str = < a string that matches the rule >
< not-supported-keyword >
add-keyword-str = < a string that matches the rule >
< add-keyword >
delete-keyword-str = < a string that matches the rule >
< delete-keyword >
replace-keyword-str = < a string that matches the rule >
< replace-keyword >
;; represents the usage of an extension
unknown-statement = prefix ":" identifier [sep string] optsep
(";" /
"{" optsep
*((yang-stmt / unknown-statement) optsep)
"}") stmtsep
yang-stmt = action-stmt /
anydata-stmt /
anyxml-stmt /
argument-stmt /
augment-stmt /
base-stmt /
belongs-to-stmt /
bit-stmt /
case-stmt /
choice-stmt /
config-stmt /
contact-stmt /
container-stmt /
default-stmt /
description-stmt /
deviate-add-stmt /
deviate-delete-stmt /
deviate-not-supported-stmt /
deviate-replace-stmt /
deviation-stmt /
enum-stmt /
error-app-tag-stmt /
error-message-stmt /
extension-stmt /
feature-stmt /
fraction-digits-stmt /
grouping-stmt /
identity-stmt /
if-feature-stmt /
import-stmt /
include-stmt /
input-stmt /
key-stmt /
leaf-list-stmt /
leaf-stmt /
length-stmt /
list-stmt /
mandatory-stmt /
max-elements-stmt /
min-elements-stmt /
modifier-stmt /
module-stmt /
must-stmt /
namespace-stmt /
notification-stmt /
ordered-by-stmt /
organization-stmt /
output-stmt /
path-stmt /
pattern-stmt /
position-stmt /
prefix-stmt /
presence-stmt /
range-stmt /
reference-stmt /
refine-stmt /
require-instance-stmt /
revision-date-stmt /
revision-stmt /
rpc-stmt /
status-stmt /
submodule-stmt /
typedef-stmt /
type-stmt /
unique-stmt /
units-stmt /
uses-augment-stmt /
uses-stmt /
value-stmt /
when-stmt /
yang-version-stmt /
yin-element-stmt
;; Ranges
range-arg-str = < a string that matches the rule >
< range-arg >
range-arg = range-part *(optsep "|" optsep range-part)
range-part = range-boundary
[optsep ".." optsep range-boundary]
range-boundary = min-keyword / max-keyword /
integer-value / decimal-value
;; Lengths
length-arg-str = < a string that matches the rule >
< length-arg >
length-arg = length-part *(optsep "|" optsep length-part)
length-part = length-boundary
[optsep ".." optsep length-boundary]
length-boundary = min-keyword / max-keyword /
non-negative-integer-value
;; Date
date-arg-str = < a string that matches the rule >
< date-arg >
date-arg = 4DIGIT "-" 2DIGIT "-" 2DIGIT
;; Schema Node Identifiers
schema-nodeid = absolute-schema-nodeid /
descendant-schema-nodeid
absolute-schema-nodeid = 1*("/" node-identifier)
descendant-schema-nodeid =
node-identifier
[absolute-schema-nodeid]
node-identifier = [prefix ":"] identifier
;; Instance Identifiers
instance-identifier = 1*("/" (node-identifier
[1*key-predicate /
leaf-list-predicate /
pos]))
key-predicate = "[" *WSP key-predicate-expr *WSP "]"
key-predicate-expr = node-identifier *WSP "=" *WSP quoted-string
leaf-list-predicate = "[" *WSP leaf-list-predicate-expr *WSP "]"
leaf-list-predicate-expr = "." *WSP "=" *WSP quoted-string
pos = "[" *WSP positive-integer-value *WSP "]"
quoted-string = (DQUOTE string DQUOTE) / (SQUOTE string SQUOTE)
;; leafref path
path-arg-str = < a string that matches the rule >
< path-arg >
path-arg = absolute-path / relative-path
absolute-path = 1*("/" (node-identifier *path-predicate))
relative-path = 1*("../") descendant-path
descendant-path = node-identifier
[*path-predicate absolute-path]
path-predicate = "[" *WSP path-equality-expr *WSP "]"
path-equality-expr = node-identifier *WSP "=" *WSP path-key-expr
path-key-expr = current-function-invocation *WSP "/" *WSP
rel-path-keyexpr
rel-path-keyexpr = 1*(".." *WSP "/" *WSP)
*(node-identifier *WSP "/" *WSP)
node-identifier
;;; Keywords, using the syntax for case-sensitive strings (RFC 7405)
;; statement keywords
action-keyword = %s"action"
anydata-keyword = %s"anydata"
anyxml-keyword = %s"anyxml"
argument-keyword = %s"argument"
augment-keyword = %s"augment"
base-keyword = %s"base"
belongs-to-keyword = %s"belongs-to"
bit-keyword = %s"bit"
case-keyword = %s"case"
choice-keyword = %s"choice"
config-keyword = %s"config"
contact-keyword = %s"contact"
container-keyword = %s"container"
default-keyword = %s"default"
description-keyword = %s"description"
deviate-keyword = %s"deviate"
deviation-keyword = %s"deviation"
enum-keyword = %s"enum"
error-app-tag-keyword = %s"error-app-tag"
error-message-keyword = %s"error-message"
extension-keyword = %s"extension"
feature-keyword = %s"feature"
fraction-digits-keyword = %s"fraction-digits"
grouping-keyword = %s"grouping"
identity-keyword = %s"identity"
if-feature-keyword = %s"if-feature"
import-keyword = %s"import"
include-keyword = %s"include"
input-keyword = %s"input"
key-keyword = %s"key"
leaf-keyword = %s"leaf"
leaf-list-keyword = %s"leaf-list"
length-keyword = %s"length"
list-keyword = %s"list"
mandatory-keyword = %s"mandatory"
max-elements-keyword = %s"max-elements"
min-elements-keyword = %s"min-elements"
modifier-keyword = %s"modifier"
module-keyword = %s"module"
must-keyword = %s"must"
namespace-keyword = %s"namespace"
notification-keyword = %s"notification" ordered-by-keyword = %s"ordered-by" organization-keyword = %s"organization" output-keyword = %s"output" path-keyword = %s"path" pattern-keyword = %s"pattern" position-keyword = %s"position" prefix-keyword = %s"prefix" presence-keyword = %s"presence" range-keyword = %s"range" reference-keyword = %s"reference" refine-keyword = %s"refine" require-instance-keyword = %s"require-instance" revision-keyword = %s"revision" revision-date-keyword = %s"revision-date" rpc-keyword = %s"rpc" status-keyword = %s"status" submodule-keyword = %s"submodule" type-keyword = %s"type" typedef-keyword = %s"typedef" unique-keyword = %s"unique" units-keyword = %s"units" uses-keyword = %s"uses" value-keyword = %s"value" when-keyword = %s"when" yang-version-keyword = %s"yang-version" yin-element-keyword = %s"yin-element" ;; other keywords add-keyword = %s"add" current-keyword = %s"current" delete-keyword = %s"delete" deprecated-keyword = %s"deprecated" false-keyword = %s"false" invert-match-keyword = %s"invert-match" max-keyword = %s"max" min-keyword = %s"min" not-supported-keyword = %s"not-supported" obsolete-keyword = %s"obsolete" replace-keyword = %s"replace" system-keyword = %s"system" true-keyword = %s"true" unbounded-keyword = %s"unbounded" user-keyword = %s"user"
and-keyword = %s"and"
or-keyword = %s"or"
not-keyword = %s"not"
current-function-invocation = current-keyword *WSP "(" *WSP ")"
;;; Basic Rules
prefix-arg-str = < a string that matches the rule >
< prefix-arg >
prefix-arg = prefix
prefix = identifier
identifier-arg-str = < a string that matches the rule >
< identifier-arg >
identifier-arg = identifier
identifier = (ALPHA / "_")
*(ALPHA / DIGIT / "_" / "-" / ".")
identifier-ref-arg-str = < a string that matches the rule >
< identifier-ref-arg >
identifier-ref-arg = identifier-ref
identifier-ref = [prefix ":"] identifier
string = < an unquoted string, as returned by >
< the scanner, that matches the rule >
< yang-string >
yang-string = *yang-char
;; any Unicode or ISO/IEC 10646 character, including tab, carriage
;; return, and line feed but excluding the other C0 control
;; characters, the surrogate blocks, and the noncharacters
yang-char = %x09 / %x0A / %x0D / %x20-D7FF /
; exclude surrogate blocks %xD800-DFFF
%xE000-FDCF / ; exclude noncharacters %xFDD0-FDEF
%xFDF0-FFFD / ; exclude noncharacters %xFFFE-FFFF
%x10000-1FFFD / ; exclude noncharacters %x1FFFE-1FFFF
%x20000-2FFFD / ; exclude noncharacters %x2FFFE-2FFFF
%x30000-3FFFD / ; exclude noncharacters %x3FFFE-3FFFF
%x40000-4FFFD / ; exclude noncharacters %x4FFFE-4FFFF
%x50000-5FFFD / ; exclude noncharacters %x5FFFE-5FFFF
%x60000-6FFFD / ; exclude noncharacters %x6FFFE-6FFFF
%x70000-7FFFD / ; exclude noncharacters %x7FFFE-7FFFF
%x80000-8FFFD / ; exclude noncharacters %x8FFFE-8FFFF
%x90000-9FFFD / ; exclude noncharacters %x9FFFE-9FFFF
%xA0000-AFFFD / ; exclude noncharacters %xAFFFE-AFFFF
%xB0000-BFFFD / ; exclude noncharacters %xBFFFE-BFFFF
%xC0000-CFFFD / ; exclude noncharacters %xCFFFE-CFFFF
%xD0000-DFFFD / ; exclude noncharacters %xDFFFE-DFFFF
%xE0000-EFFFD / ; exclude noncharacters %xEFFFE-EFFFF
%xF0000-FFFFD / ; exclude noncharacters %xFFFFE-FFFFF
%x100000-10FFFD ; exclude noncharacters %x10FFFE-10FFFF
integer-value = ("-" non-negative-integer-value) /
non-negative-integer-value
non-negative-integer-value = "0" / positive-integer-value
positive-integer-value = (non-zero-digit *DIGIT)
zero-integer-value = 1*DIGIT
stmtend = optsep (";" / "{" stmtsep "}") stmtsep
sep = 1*(WSP / line-break)
; unconditional separator
optsep = *(WSP / line-break)
stmtsep = *(WSP / line-break / unknown-statement)
line-break = CRLF / LF
non-zero-digit = %x31-39
decimal-value = integer-value ("." zero-integer-value)
SQUOTE = %x27
; single quote
;;; core rules from RFC 5234
ALPHA = %x41-5A / %x61-7A
; A-Z / a-z
CR = %x0D
; carriage return
CRLF = CR LF
; Internet standard newline
DIGIT = %x30-39
; 0-9
DQUOTE = %x22
; double quote
HTAB = %x09
; horizontal tab
LF = %x0A
; line feed
SP = %x20
; space
WSP = SP / HTAB
; whitespace
<CODE ENDS>
15. NETCONF Error Responses for YANG-Related Errors
A number of NETCONF error responses are defined for error cases related to the data model handling. If the relevant YANG statement has an "error-app-tag" substatement, that overrides the default value specified below.15.1. Error Message for Data That Violates a "unique" Statement
If a NETCONF operation would result in configuration data where a "unique" constraint is invalidated, the following error MUST be returned: error-tag: operation-failed error-app-tag: data-not-unique error-info: <non-unique>: Contains an instance identifier that points to a leaf that invalidates the "unique" constraint. This element is present once for each non-unique leaf. The <non-unique> element is in the YANG namespace ("urn:ietf:params:xml:ns:yang:1").15.2. Error Message for Data That Violates a "max-elements" Statement
If a NETCONF operation would result in configuration data where a list or a leaf-list would have too many entries, the following error MUST be returned: error-tag: operation-failed error-app-tag: too-many-elements This error is returned once, with the error-path identifying the list node, even if there is more than one extra child present.15.3. Error Message for Data That Violates a "min-elements" Statement
If a NETCONF operation would result in configuration data where a list or a leaf-list would have too few entries, the following error MUST be returned: error-tag: operation-failed error-app-tag: too-few-elements This error is returned once, with the error-path identifying the list node, even if there is more than one child missing.
15.4. Error Message for Data That Violates a "must" Statement
If a NETCONF operation would result in configuration data where the restrictions imposed by a "must" statement are violated, the following error MUST be returned, unless a specific "error-app-tag" substatement is present for the "must" statement. error-tag: operation-failed error-app-tag: must-violation15.5. Error Message for Data That Violates a "require-instance" Statement
If a NETCONF operation would result in configuration data where a leaf of type "instance-identifier" or "leafref" marked with require-instance "true" refers to an instance that does not exist, the following error MUST be returned: error-tag: data-missing error-app-tag: instance-required error-path: Path to the instance-identifier or leafref leaf.15.6. Error Message for Data That Violates a Mandatory "choice" Statement
If a NETCONF operation would result in configuration data where no nodes exists in a mandatory choice, the following error MUST be returned: error-tag: data-missing error-app-tag: missing-choice error-path: Path to the element with the missing choice. error-info: <missing-choice>: Contains the name of the missing mandatory choice. The <missing-choice> element is in the YANG namespace ("urn:ietf:params:xml:ns:yang:1").15.7. Error Message for the "insert" Operation
If the "insert" and "key" or "value" attributes are used in an <edit-config> for a list or leaf-list node and the "key" or "value" refers to an instance that does not exist, the following error MUST be returned: error-tag: bad-attribute error-app-tag: missing-instance
16. IANA Considerations
This document registers one capability identifier URN from the "Network Configuration Protocol (NETCONF) Capability URNs" registry: Index Capability Identifier ------------- --------------------------------------------------- :yang-library urn:ietf:params:netconf:capability:yang-library:1.017. Security Considerations
This document defines a language with which to write and read descriptions of management information. The language itself has no security impact on the Internet. The same considerations are relevant as those for the base NETCONF protocol (see Section 9 in [RFC6241]). Data modeled in YANG might contain sensitive information. RPCs or notifications defined in YANG might transfer sensitive information. Security issues are related to the usage of data modeled in YANG. Such issues shall be dealt with in documents describing the data models and documents about the interfaces used to manipulate the data, e.g., the NETCONF documents. Data modeled in YANG is dependent upon: o the security of the transmission infrastructure used to send sensitive information. o the security of applications that store or release such sensitive information. o adequate authentication and access control mechanisms to restrict the usage of sensitive data. YANG parsers need to be robust with respect to malformed documents. Reading malformed documents from unknown or untrusted sources could result in an attacker gaining the privileges of the user running the YANG parser. In an extreme situation, the entire machine could be compromised.
18. References
18.1. Normative References
[ISO.10646] International Organization for Standardization, "Information Technology - Universal Multiple-Octet Coded Character Set (UCS)", ISO Standard 10646:2014, 2014. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <http://www.rfc-editor.org/info/rfc2119>. [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November 2003, <http://www.rfc-editor.org/info/rfc3629>. [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, DOI 10.17487/RFC3986, January 2005, <http://www.rfc-editor.org/info/rfc3986>. [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006, <http://www.rfc-editor.org/info/rfc4648>. [RFC5234] Crocker, D., Ed., and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, DOI 10.17487/RFC5234, January 2008, <http://www.rfc-editor.org/info/rfc5234>. [RFC5277] Chisholm, S. and H. Trevino, "NETCONF Event Notifications", RFC 5277, DOI 10.17487/RFC5277, July 2008, <http://www.rfc-editor.org/info/rfc5277>. [RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed., and A. Bierman, Ed., "Network Configuration Protocol (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011, <http://www.rfc-editor.org/info/rfc6241>. [RFC7405] Kyzivat, P., "Case-Sensitive String Support in ABNF", RFC 7405, DOI 10.17487/RFC7405, December 2014, <http://www.rfc-editor.org/info/rfc7405>. [RFC7895] Bierman, A., Bjorklund, M., and K. Watsen, "YANG Module Library", RFC 7895, DOI 10.17487/RFC7895, June 2016, <http://www.rfc-editor.org/info/rfc7895>.
[XML] Bray, T., Paoli, J., Sperberg-McQueen, C., Maler, E., and F. Yergeau, "Extensible Markup Language (XML) 1.0 (Fifth Edition)", W3C Recommendation REC-xml-20081126, November 2008, <https://www.w3.org/TR/2008/REC-xml-20081126/>. [XML-NAMES] Bray, T., Hollander, D., Layman, A., Tobin, R., and H. Thompson, "Namespaces in XML 1.0 (Third Edition)", World Wide Web Consortium Recommendation REC-xml-names-20091208, December 2009, <http://www.w3.org/TR/2009/REC-xml-names-20091208>. [XPATH] Clark, J. and S. DeRose, "XML Path Language (XPath) Version 1.0", World Wide Web Consortium Recommendation REC-xpath-19991116, November 1999, <http://www.w3.org/TR/1999/REC-xpath-19991116>. [XSD-TYPES] Biron, P. and A. Malhotra, "XML Schema Part 2: Datatypes Second Edition", World Wide Web Consortium Recommendation REC-xmlschema-2-20041028, October 2004, <http://www.w3.org/TR/2004/REC-xmlschema-2-20041028>.18.2. Informative References
[CoMI] van der Stok, P. and A. Bierman, "CoAP Management Interface", Work in Progress, draft-vanderstok-core-comi-09, March 2016. [IEEE754-2008] IEEE, "IEEE Standard for Floating-Point Arithmetic", IEEE 754-2008, DOI 10.1109/IEEESTD.2008.4610935, 2008, <http://standards.ieee.org/findstds/ standard/754-2008.html>. [RESTCONF] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF Protocol", Work in Progress, draft-ietf-netconf-restconf-16, August 2016. [RFC2578] McCloghrie, K., Ed., Perkins, D., Ed., and J. Schoenwaelder, Ed., "Structure of Management Information Version 2 (SMIv2)", STD 58, RFC 2578, DOI 10.17487/RFC2578, April 1999, <http://www.rfc-editor.org/info/rfc2578>.
[RFC2579] McCloghrie, K., Ed., Perkins, D., Ed., and J. Schoenwaelder, Ed., "Textual Conventions for SMIv2", STD 58, RFC 2579, DOI 10.17487/RFC2579, April 1999, <http://www.rfc-editor.org/info/rfc2579>. [RFC3780] Strauss, F. and J. Schoenwaelder, "SMIng - Next Generation Structure of Management Information", RFC 3780, DOI 10.17487/RFC3780, May 2004, <http://www.rfc-editor.org/info/rfc3780>. [RFC4844] Daigle, L., Ed., and Internet Architecture Board, "The RFC Series and RFC Editor", RFC 4844, DOI 10.17487/RFC4844, July 2007, <http://www.rfc-editor.org/info/rfc4844>. [RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)", RFC 6020, DOI 10.17487/RFC6020, October 2010, <http://www.rfc-editor.org/info/rfc6020>. [RFC6643] Schoenwaelder, J., "Translation of Structure of Management Information Version 2 (SMIv2) MIB Modules to YANG Modules", RFC 6643, DOI 10.17487/RFC6643, July 2012, <http://www.rfc-editor.org/info/rfc6643>. [RFC6991] Schoenwaelder, J., Ed., "Common YANG Data Types", RFC 6991, DOI 10.17487/RFC6991, July 2013, <http://www.rfc-editor.org/info/rfc6991>. [RFC7951] Lhotka, L., "JSON Encoding of Data Modeled with YANG", RFC 7951, DOI 10.17487/RFC7951, August 2016, <http://www.rfc-editor.org/info/rfc7951>. [XPATH2.0] Berglund, A., Boag, S., Chamberlin, D., Fernandez, M., Kay, M., Robie, J., and J. Simeon, "XML Path Language (XPath) 2.0 (Second Edition)", World Wide Web Consortium Recommendation REC-xpath20-20101214, December 2010, <http://www.w3.org/TR/2010/REC-xpath20-20101214>. [XSLT] Clark, J., "XSL Transformations (XSLT) Version 1.0", World Wide Web Consortium Recommendation REC-xslt-19991116, November 1999, <http://www.w3.org/TR/1999/REC-xslt-19991116>. [YANG-Guidelines] Bierman, A., "Guidelines for Authors and Reviewers of YANG Data Model Documents", Work in Progress, draft-ietf-netmod-rfc6087bis-07, July 2016.
Acknowledgements
The editor wishes to thank the following individuals, who all provided helpful comments on various draft versions of this document: Mehmet Ersue, Washam Fan, Joel Halpern, Per Hedeland, Leif Johansson, Ladislav Lhotka, Lionel Morand, Gerhard Muenz, Peyman Owladi, Tom Petch, Randy Presuhn, David Reid, Jernej Tuljak, Kent Watsen, Bert Wijnen, Robert Wilton, and Dale Worley.Contributors
The following people all contributed significantly to the initial YANG document: - Andy Bierman (YumaWorks) - Balazs Lengyel (Ericsson) - David Partain (Ericsson) - Juergen Schoenwaelder (Jacobs University Bremen) - Phil Shafer (Juniper Networks)Author's Address
Martin Bjorklund (editor) Tail-f Systems Email: mbj@tail-f.com