RFC 6020
YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)
12. YANG ABNF Grammar
In YANG, almost all statements are unordered. The ABNF grammar [RFC5234] 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 stmtsep] namespace-stmt stmtsep prefix-stmt stmtsep submodule-header-stmts = ;; these stmts can appear in any order [yang-version-stmt stmtsep] belongs-to-stmt stmtsep
meta-stmts = ;; these stmts can appear in any order
[organization-stmt stmtsep]
[contact-stmt stmtsep]
[description-stmt stmtsep]
[reference-stmt stmtsep]
linkage-stmts = ;; these stmts can appear in any order
*(import-stmt stmtsep)
*(include-stmt stmtsep)
revision-stmts = *(revision-stmt stmtsep)
body-stmts = *((extension-stmt /
feature-stmt /
identity-stmt /
typedef-stmt /
grouping-stmt /
data-def-stmt /
augment-stmt /
rpc-stmt /
notification-stmt /
deviation-stmt) stmtsep)
data-def-stmt = container-stmt /
leaf-stmt /
leaf-list-stmt /
list-stmt /
choice-stmt /
anyxml-stmt /
uses-stmt
yang-version-stmt = yang-version-keyword sep yang-version-arg-str
optsep stmtend
yang-version-arg-str = < a string that matches the rule
yang-version-arg >
yang-version-arg = "1"
import-stmt = import-keyword sep identifier-arg-str optsep
"{" stmtsep
prefix-stmt stmtsep
[revision-date-stmt stmtsep]
"}"
include-stmt = include-keyword sep identifier-arg-str optsep
(";" /
"{" stmtsep
[revision-date-stmt stmtsep]
"}")
namespace-stmt = namespace-keyword sep uri-str optsep stmtend
uri-str = < a string that matches the rule
URI in RFC 3986 >
prefix-stmt = prefix-keyword sep prefix-arg-str
optsep stmtend
belongs-to-stmt = belongs-to-keyword sep identifier-arg-str
optsep
"{" stmtsep
prefix-stmt stmtsep
"}"
organization-stmt = organization-keyword sep string
optsep stmtend
contact-stmt = contact-keyword sep string optsep stmtend
description-stmt = description-keyword sep string optsep
stmtend
reference-stmt = reference-keyword sep string optsep stmtend
units-stmt = units-keyword sep string optsep stmtend
revision-stmt = revision-keyword sep revision-date optsep
(";" /
"{" stmtsep
[description-stmt stmtsep]
[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 stmtsep]
[status-stmt stmtsep]
[description-stmt stmtsep]
[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
[base-stmt stmtsep]
[status-stmt stmtsep]
[description-stmt stmtsep]
[reference-stmt stmtsep]
"}")
base-stmt = base-keyword sep identifier-ref-arg-str
optsep stmtend
feature-stmt = feature-keyword sep identifier-arg-str optsep
(";" /
"{" stmtsep
;; these stmts can appear in any order
*(if-feature-stmt stmtsep)
[status-stmt stmtsep]
[description-stmt stmtsep]
[reference-stmt stmtsep]
"}")
if-feature-stmt = if-feature-keyword sep identifier-ref-arg-str
optsep stmtend
typedef-stmt = typedef-keyword sep identifier-arg-str optsep
"{" stmtsep
;; these stmts can appear in any order
type-stmt stmtsep
[units-stmt stmtsep]
[default-stmt stmtsep]
[status-stmt stmtsep]
[description-stmt stmtsep]
[reference-stmt stmtsep]
"}"
type-stmt = type-keyword sep identifier-ref-arg-str optsep
(";" /
"{" stmtsep
type-body-stmts
"}")
type-body-stmts = numerical-restrictions /
decimal64-specification /
string-restrictions /
enum-specification /
leafref-specification /
identityref-specification /
instance-identifier-specification /
bits-specification /
union-specification
numerical-restrictions = range-stmt stmtsep
range-stmt = range-keyword sep range-arg-str optsep
(";" /
"{" stmtsep
;; these stmts can appear in any order
[error-message-stmt stmtsep]
[error-app-tag-stmt stmtsep]
[description-stmt stmtsep]
[reference-stmt stmtsep]
"}")
decimal64-specification = fraction-digits-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 stmtsep]
*(pattern-stmt stmtsep)
length-stmt = length-keyword sep length-arg-str optsep
(";" /
"{" stmtsep
;; these stmts can appear in any order
[error-message-stmt stmtsep]
[error-app-tag-stmt stmtsep]
[description-stmt stmtsep]
[reference-stmt stmtsep]
"}")
pattern-stmt = pattern-keyword sep string optsep
(";" /
"{" stmtsep
;; these stmts can appear in any order
[error-message-stmt stmtsep]
[error-app-tag-stmt stmtsep]
[description-stmt stmtsep]
[reference-stmt stmtsep]
"}")
default-stmt = default-keyword sep string stmtend
enum-specification = 1*(enum-stmt stmtsep)
enum-stmt = enum-keyword sep string optsep
(";" /
"{" stmtsep
;; these stmts can appear in any order
[value-stmt stmtsep]
[status-stmt stmtsep]
[description-stmt stmtsep]
[reference-stmt stmtsep]
"}")
leafref-specification =
;; these stmts can appear in any order
path-stmt stmtsep
[require-instance-stmt stmtsep]
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 stmtsep]
identityref-specification =
base-stmt stmtsep
union-specification = 1*(type-stmt stmtsep)
bits-specification = 1*(bit-stmt stmtsep)
bit-stmt = bit-keyword sep identifier-arg-str optsep
(";" /
"{" stmtsep
;; these stmts can appear in any order
[position-stmt stmtsep]
[status-stmt stmtsep]
[description-stmt stmtsep]
[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 stmtsep]
[error-app-tag-stmt stmtsep]
[description-stmt stmtsep]
[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 stmtend
grouping-stmt = grouping-keyword sep identifier-arg-str optsep
(";" /
"{" stmtsep
;; these stmts can appear in any order
[status-stmt stmtsep]
[description-stmt stmtsep]
[reference-stmt stmtsep]
*((typedef-stmt /
grouping-stmt) stmtsep)
*(data-def-stmt stmtsep)
"}")
container-stmt = container-keyword sep identifier-arg-str optsep
(";" /
"{" stmtsep
;; these stmts can appear in any order
[when-stmt stmtsep]
*(if-feature-stmt stmtsep)
*(must-stmt stmtsep)
[presence-stmt stmtsep]
[config-stmt stmtsep]
[status-stmt stmtsep]
[description-stmt stmtsep]
[reference-stmt stmtsep]
*((typedef-stmt /
grouping-stmt) stmtsep)
*(data-def-stmt stmtsep)
"}")
leaf-stmt = leaf-keyword sep identifier-arg-str optsep
"{" stmtsep
;; these stmts can appear in any order
[when-stmt stmtsep]
*(if-feature-stmt stmtsep)
type-stmt stmtsep
[units-stmt stmtsep]
*(must-stmt stmtsep)
[default-stmt stmtsep]
[config-stmt stmtsep]
[mandatory-stmt stmtsep]
[status-stmt stmtsep]
[description-stmt stmtsep]
[reference-stmt stmtsep]
"}"
leaf-list-stmt = leaf-list-keyword sep identifier-arg-str optsep
"{" stmtsep
;; these stmts can appear in any order
[when-stmt stmtsep]
*(if-feature-stmt stmtsep)
type-stmt stmtsep
[units-stmt stmtsep]
*(must-stmt stmtsep)
[config-stmt stmtsep]
[min-elements-stmt stmtsep]
[max-elements-stmt stmtsep]
[ordered-by-stmt stmtsep]
[status-stmt stmtsep]
[description-stmt stmtsep]
[reference-stmt stmtsep]
"}"
list-stmt = list-keyword sep identifier-arg-str optsep
"{" stmtsep
;; these stmts can appear in any order
[when-stmt stmtsep]
*(if-feature-stmt stmtsep)
*(must-stmt stmtsep)
[key-stmt stmtsep]
*(unique-stmt stmtsep)
[config-stmt stmtsep]
[min-elements-stmt stmtsep]
[max-elements-stmt stmtsep]
[ordered-by-stmt stmtsep]
[status-stmt stmtsep]
[description-stmt stmtsep]
[reference-stmt stmtsep]
*((typedef-stmt /
grouping-stmt) stmtsep)
1*(data-def-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 stmtsep]
*(if-feature-stmt stmtsep)
[default-stmt stmtsep]
[config-stmt stmtsep]
[mandatory-stmt stmtsep]
[status-stmt stmtsep]
[description-stmt stmtsep]
[reference-stmt stmtsep]
*((short-case-stmt / case-stmt) stmtsep)
"}")
short-case-stmt = container-stmt /
leaf-stmt /
leaf-list-stmt /
list-stmt /
anyxml-stmt
case-stmt = case-keyword sep identifier-arg-str optsep
(";" /
"{" stmtsep
;; these stmts can appear in any order
[when-stmt stmtsep]
*(if-feature-stmt stmtsep)
[status-stmt stmtsep]
[description-stmt stmtsep]
[reference-stmt stmtsep]
*(data-def-stmt stmtsep)
"}")
anyxml-stmt = anyxml-keyword sep identifier-arg-str optsep
(";" /
"{" stmtsep
;; these stmts can appear in any order
[when-stmt stmtsep]
*(if-feature-stmt stmtsep)
*(must-stmt stmtsep)
[config-stmt stmtsep]
[mandatory-stmt stmtsep]
[status-stmt stmtsep]
[description-stmt stmtsep]
[reference-stmt stmtsep]
"}")
uses-stmt = uses-keyword sep identifier-ref-arg-str optsep
(";" /
"{" stmtsep
;; these stmts can appear in any order
[when-stmt stmtsep]
*(if-feature-stmt stmtsep)
[status-stmt stmtsep]
[description-stmt stmtsep]
[reference-stmt stmtsep]
*(refine-stmt stmtsep)
*(uses-augment-stmt stmtsep)
"}")
refine-stmt = refine-keyword sep refine-arg-str optsep
(";" /
"{" stmtsep
(refine-container-stmts /
refine-leaf-stmts /
refine-leaf-list-stmts /
refine-list-stmts /
refine-choice-stmts /
refine-case-stmts /
refine-anyxml-stmts)
"}")
refine-arg-str = < a string that matches the rule
refine-arg >
refine-arg = descendant-schema-nodeid
refine-container-stmts =
;; these stmts can appear in any order
*(must-stmt stmtsep)
[presence-stmt stmtsep]
[config-stmt stmtsep]
[description-stmt stmtsep]
[reference-stmt stmtsep]
refine-leaf-stmts = ;; these stmts can appear in any order
*(must-stmt stmtsep)
[default-stmt stmtsep]
[config-stmt stmtsep]
[mandatory-stmt stmtsep]
[description-stmt stmtsep]
[reference-stmt stmtsep]
refine-leaf-list-stmts =
;; these stmts can appear in any order
*(must-stmt stmtsep)
[config-stmt stmtsep]
[min-elements-stmt stmtsep]
[max-elements-stmt stmtsep]
[description-stmt stmtsep]
[reference-stmt stmtsep]
refine-list-stmts = ;; these stmts can appear in any order
*(must-stmt stmtsep)
[config-stmt stmtsep]
[min-elements-stmt stmtsep]
[max-elements-stmt stmtsep]
[description-stmt stmtsep]
[reference-stmt stmtsep]
refine-choice-stmts = ;; these stmts can appear in any order
[default-stmt stmtsep]
[config-stmt stmtsep]
[mandatory-stmt stmtsep]
[description-stmt stmtsep]
[reference-stmt stmtsep]
refine-case-stmts = ;; these stmts can appear in any order
[description-stmt stmtsep]
[reference-stmt stmtsep]
refine-anyxml-stmts = ;; these stmts can appear in any order
*(must-stmt stmtsep)
[config-stmt stmtsep]
[mandatory-stmt stmtsep]
[description-stmt stmtsep]
[reference-stmt stmtsep]
uses-augment-stmt = augment-keyword sep uses-augment-arg-str optsep
"{" stmtsep
;; these stmts can appear in any order
[when-stmt stmtsep]
*(if-feature-stmt stmtsep)
[status-stmt stmtsep]
[description-stmt stmtsep]
[reference-stmt stmtsep]
1*((data-def-stmt stmtsep) /
(case-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 stmtsep]
*(if-feature-stmt stmtsep)
[status-stmt stmtsep]
[description-stmt stmtsep]
[reference-stmt stmtsep]
1*((data-def-stmt stmtsep) /
(case-stmt stmtsep))
"}"
augment-arg-str = < a string that matches the rule
augment-arg >
augment-arg = absolute-schema-nodeid
unknown-statement = prefix ":" identifier [sep string] optsep
(";" / "{" *unknown-statement2 "}")
unknown-statement2 = [prefix ":"] identifier [sep string] optsep
(";" / "{" *unknown-statement2 "}")
when-stmt = when-keyword sep string optsep
(";" /
"{" stmtsep
;; these stmts can appear in any order
[description-stmt stmtsep]
[reference-stmt stmtsep]
"}")
rpc-stmt = rpc-keyword sep identifier-arg-str optsep
(";" /
"{" stmtsep
;; these stmts can appear in any order
*(if-feature-stmt stmtsep)
[status-stmt stmtsep]
[description-stmt stmtsep]
[reference-stmt stmtsep]
*((typedef-stmt /
grouping-stmt) stmtsep)
[input-stmt stmtsep]
[output-stmt stmtsep]
"}")
input-stmt = input-keyword optsep
"{" stmtsep
;; these stmts can appear in any order
*((typedef-stmt /
grouping-stmt) stmtsep)
1*(data-def-stmt stmtsep)
"}"
output-stmt = output-keyword optsep
"{" stmtsep
;; these stmts can appear in any order
*((typedef-stmt /
grouping-stmt) stmtsep)
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 stmtsep)
[status-stmt stmtsep]
[description-stmt stmtsep]
[reference-stmt stmtsep]
*((typedef-stmt /
grouping-stmt) stmtsep)
*(data-def-stmt stmtsep)
"}")
deviation-stmt = deviation-keyword sep
deviation-arg-str optsep
"{" stmtsep
;; these stmts can appear in any order
[description-stmt stmtsep]
[reference-stmt stmtsep]
(deviate-not-supported-stmt /
1*(deviate-add-stmt /
deviate-replace-stmt /
deviate-delete-stmt))
"}"
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 optsep
(";" /
"{" stmtsep
"}")
deviate-add-stmt = deviate-keyword sep add-keyword optsep
(";" /
"{" stmtsep
[units-stmt stmtsep]
*(must-stmt stmtsep)
*(unique-stmt stmtsep)
[default-stmt stmtsep]
[config-stmt stmtsep]
[mandatory-stmt stmtsep]
[min-elements-stmt stmtsep]
[max-elements-stmt stmtsep]
"}")
deviate-delete-stmt = deviate-keyword sep delete-keyword optsep
(";" /
"{" stmtsep
[units-stmt stmtsep]
*(must-stmt stmtsep)
*(unique-stmt stmtsep)
[default-stmt stmtsep]
"}")
deviate-replace-stmt = deviate-keyword sep replace-keyword optsep
(";" /
"{" stmtsep
[type-stmt stmtsep]
[units-stmt stmtsep]
[default-stmt stmtsep]
[config-stmt stmtsep]
[mandatory-stmt stmtsep]
[min-elements-stmt stmtsep]
[max-elements-stmt stmtsep]
"}")
;; 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 *predicate))
predicate = "[" *WSP (predicate-expr / pos) *WSP "]"
predicate-expr = (node-identifier / ".") *WSP "=" *WSP
((DQUOTE string DQUOTE) /
(SQUOTE string SQUOTE))
pos = non-negative-integer-value
;; 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 abnfgen's syntax for case-sensitive strings
;; statement keywords
anyxml-keyword = 'anyxml'
argument-keyword = 'argument'
augment-keyword = 'augment'
base-keyword = 'base'
belongs-to-keyword = 'belongs-to'
bit-keyword = 'bit'
case-keyword = 'case'
choice-keyword = 'choice'
config-keyword = 'config'
contact-keyword = 'contact'
container-keyword = 'container'
default-keyword = 'default'
description-keyword = 'description'
enum-keyword = 'enum'
error-app-tag-keyword = 'error-app-tag'
error-message-keyword = 'error-message'
extension-keyword = 'extension'
deviation-keyword = 'deviation'
deviate-keyword = 'deviate'
feature-keyword = 'feature'
fraction-digits-keyword = 'fraction-digits'
grouping-keyword = 'grouping'
identity-keyword = 'identity'
if-feature-keyword = 'if-feature'
import-keyword = 'import'
include-keyword = 'include'
input-keyword = 'input'
key-keyword = 'key'
leaf-keyword = 'leaf'
leaf-list-keyword = 'leaf-list'
length-keyword = 'length'
list-keyword = 'list'
mandatory-keyword = 'mandatory'
max-elements-keyword = 'max-elements'
min-elements-keyword = 'min-elements'
module-keyword = 'module'
must-keyword = 'must'
namespace-keyword = 'namespace'
notification-keyword= 'notification'
ordered-by-keyword = 'ordered-by'
organization-keyword= 'organization'
output-keyword = 'output' path-keyword = 'path' pattern-keyword = 'pattern' position-keyword = 'position' prefix-keyword = 'prefix' presence-keyword = 'presence' range-keyword = 'range' reference-keyword = 'reference' refine-keyword = 'refine' require-instance-keyword = 'require-instance' revision-keyword = 'revision' revision-date-keyword = 'revision-date' rpc-keyword = 'rpc' status-keyword = 'status' submodule-keyword = 'submodule' type-keyword = 'type' typedef-keyword = 'typedef' unique-keyword = 'unique' units-keyword = 'units' uses-keyword = 'uses' value-keyword = 'value' when-keyword = 'when' yang-version-keyword= 'yang-version' yin-element-keyword = 'yin-element' ;; other keywords add-keyword = 'add' current-keyword = 'current' delete-keyword = 'delete' deprecated-keyword = 'deprecated' false-keyword = 'false' max-keyword = 'max' min-keyword = 'min' not-supported-keyword = 'not-supported' obsolete-keyword = 'obsolete' replace-keyword = 'replace' system-keyword = 'system' true-keyword = 'true' unbounded-keyword = 'unbounded' user-keyword = 'user'
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
;; An identifier MUST NOT start with (('X'|'x') ('M'|'m') ('L'|'l'))
identifier = (ALPHA / "_")
*(ALPHA / DIGIT / "_" / "-" / ".")
identifier-ref-arg-str = < a string that matches the rule
identifier-ref-arg >
identifier-ref-arg = [prefix ":"] identifier
string = < an unquoted string as returned by
the scanner >
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 = ";" / "{" *unknown-statement "}"
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)
;;
;; RFC 5234 core rules.
;;
ALPHA = %x41-5A / %x61-7A
; A-Z / a-z
CR = %x0D
; carriage return
CRLF = CR LF
; Internet standard new line
DIGIT = %x30-39
; 0-9
DQUOTE = %x22
; " (Double Quote)
HEXDIG = DIGIT /
%x61 / %x62 / %x63 / %x64 / %x65 / %x66
; only lower-case a..f
HTAB = %x09
; horizontal tab
LF = %x0A
; linefeed
SP = %x20
; space
VCHAR = %x21-7E
; visible (printing) characters
WSP = SP / HTAB
; whitespace
<CODE ENDS>
13. 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.13.1. 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 is 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").13.2. 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 is 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 are more than one extra child present.13.3. 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 is 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 are more than one child missing.
13.4. 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 is violated the following error is returned, unless a specific "error-app-tag" substatement is present for the "must" statement. error-tag: operation-failed error-app-tag: must-violation13.5. 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" marked with require-instance "true" refers to a non-existing instance, the following error is returned: error-tag: data-missing error-app-tag: instance-required error-path: Path to the instance-identifier leaf.13.6. Error Message for Data That Does Not Match a leafref Type
If a NETCONF operation would result in configuration data where a leaf of type "leafref" refers to a non-existing instance, the following error is returned: error-tag: data-missing error-app-tag: instance-required error-path: Path to the leafref leaf.13.7. 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 is 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").
13.8. 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 a non-existing instance, the following error is returned: error-tag: bad-attribute error-app-tag: missing-instance14. IANA Considerations
This document defines a registry for YANG module and submodule names. The name of the registry is "YANG Module Names". The registry shall record for each entry: o the name of the module or submodule o for modules, the assigned XML namespace o for modules, the prefix of the module o for submodules, the name of the module it belongs to o a reference to the (sub)module's documentation (e.g., the RFC number) There are no initial assignments. For allocation, RFC publication is required as per RFC 5226 [RFC5226]. All registered YANG module names MUST comply with the rules for identifiers stated in Section 6.2, and MUST have a module name prefix. The module name prefix 'ietf-' is reserved for IETF stream documents [RFC4844], while the module name prefix 'irtf-' is reserved for IRTF stream documents. Modules published in other RFC streams MUST have a similar suitable prefix. All module and submodule names in the registry MUST be unique. All XML namespaces in the registry MUST be unique. This document registers two URIs for the YANG and YIN XML namespaces in the IETF XML registry [RFC3688]. Following the format in RFC 3688, the following have been registered. URI: urn:ietf:params:xml:ns:yang:yin:1
URI: urn:ietf:params:xml:ns:yang:1
Registrant Contact: The IESG.
XML: N/A, the requested URIs are XML namespaces.
This document registers two new media types as defined in the
following sections.
14.1. Media type application/yang
MIME media type name: application
MIME subtype name: yang
Mandatory parameters: none
Optional parameters: none
Encoding considerations: 8-bit
Security considerations: See Section 15 in RFC 6020
Interoperability considerations: None
Published specification: RFC 6020
Applications that use this media type:
YANG module validators, web servers used for downloading YANG
modules, email clients, etc.
Additional information:
Magic Number: None
File Extension: .yang
Macintosh file type code: 'TEXT'
Personal and email address for further information:
Martin Bjorklund <mbj@tail-f.com>
Intended usage: COMMON
Author:
This specification is a work item of the IETF NETMOD working group,
with mailing list address <netmod@ietf.org>.
Change controller:
The IESG <iesg@ietf.org>
14.2. Media type application/yin+xml
MIME media type name: application
MIME subtype name: yin+xml
Mandatory parameters: none
Optional parameters:
"charset": This parameter has identical semantics to the charset
parameter of the "application/xml" media type as specified in
[RFC3023].
Encoding considerations:
Identical to those of "application/xml" as
described in [RFC3023], Section 3.2.
Security considerations: See Section 15 in RFC 6020
Interoperability considerations: None
Published specification: RFC 6020
Applications that use this media type:
YANG module validators, web servers used for downloading YANG
modules, email clients, etc.
Additional information:
Magic Number: As specified for "application/xml" in [RFC3023],
Section 3.2.
File Extension: .yin
Macintosh file type code: 'TEXT'
Personal and email address for further information:
Martin Bjorklund <mbj@tail-f.com>
Intended usage: COMMON
Author:
This specification is a work item of the IETF NETMOD working group,
with mailing list address <netmod@ietf.org>.
Change controller:
The IESG <iesg@ietf.org>
15. 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 for the base NETCONF protocol
(see [RFC4741], Section 9).
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 privileges of the user running the YANG
parser. In an extreme situation, the entire machine could be
compromised.
16. Contributors
The following people all contributed significantly to the initial YANG document: - Andy Bierman (Brocade) - Balazs Lengyel (Ericsson) - David Partain (Ericsson) - Juergen Schoenwaelder (Jacobs University Bremen) - Phil Shafer (Juniper Networks)17. Acknowledgements
The editor wishes to thank the following individuals, who all provided helpful comments on various versions of this document: Mehmet Ersue, Washam Fan, Joel Halpern, Leif Johansson, Ladislav Lhotka, Gerhard Muenz, Tom Petch, Randy Presuhn, David Reid, and Bert Wijnen.18. References
18.1. Normative References
[ISO.10646] International Organization for Standardization, "Information Technology - Universal Multiple-Octet Coded Character Set (UCS)", ISO Standard 10646:2003, 2003. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3023] Murata, M., St. Laurent, S., and D. Kohn, "XML Media Types", RFC 3023, January 2001. [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD 63, RFC 3629, November 2003. [RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, January 2004. [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, January 2005. [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", RFC 4648, October 2006. [RFC4741] Enns, R., "NETCONF Configuration Protocol", RFC 4741, December 2006.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 5226, May 2008. [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, January 2008. [RFC5277] Chisholm, S. and H. Trevino, "NETCONF Event Notifications", RFC 5277, July 2008. [XML-NAMES] Hollander, D., Tobin, R., Thompson, H., Bray, T., and A. Layman, "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] Malhotra, A. and P. Biron, "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
[RFC2578] McCloghrie, K., Ed., Perkins, D., Ed., and J. Schoenwaelder, Ed., "Structure of Management Information Version 2 (SMIv2)", STD 58, RFC 2578, April 1999. [RFC2579] McCloghrie, K., Ed., Perkins, D., Ed., and J. Schoenwaelder, Ed., "Textual Conventions for SMIv2", STD 58, RFC 2579, April 1999. [RFC3780] Strauss, F. and J. Schoenwaelder, "SMIng - Next Generation Structure of Management Information", RFC 3780, May 2004. [RFC4844] Daigle, L. and Internet Architecture Board, "The RFC Series and RFC Editor", RFC 4844, July 2007. [XPATH2.0] Berglund, A., Boag, S., Chamberlin, D., Fernandez, M., Kay, M., Robie, J., and J. Simeon, "XML Path Language (XPath) 2.0", World Wide Web Consortium Recommendation REC-xpath20-20070123, January 2007, <http://www.w3.org/TR/2007/REC-xpath20-20070123>.
[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>.Author's Address
Martin Bjorklund (editor) Tail-f Systems EMail: mbj@tail-f.com