A MIB Textual Convention for Language Tags
Extracted elements (10)
A new LangTag TEXTUAL-CONVENTION was created rather than modifying the existing LanguageTag TC from RFC 2932 because it is not possible to apply changes in syntax and length to an existing textual convention. The new TC has a more comprehensive and current syntax description, is short enough to use as an index object without subtyping, and is provided in a dedicated MIB module to simplify module dependencies.
The maximum length of 63 octets is chosen because analysis of language tag lengths in BCP 47 confirms this limit will not pose a problem in practice, and in particular this length is greater than the minimum requirements set out in BCP 47 Section 4.3.1.
The LangTag TEXTUAL-CONVENTION defined by RFC 5131 replaces the similar LanguageTag TEXTUAL-CONVENTION defined by RFC 2932. New MIB modules should use LangTag; existing MIB modules using the old LanguageTag TC are unaffected.
An implementation MAY further limit the values it accepts to those permitted by a 'validating' processor as defined in BCP 47, beyond the basic well-formedness requirement.
Objects using the LangTag TEXTUAL-CONVENTION MUST use only lowercase characters. This restriction ensures unique language tags for use as index objects.
Values MUST be well-formed language tags in conformance with the definition of well-formed tags in BCP 47 (RFC 4646).
The LangTag TEXTUAL-CONVENTION defines a MIB type for representing BCP 47 language tags. It uses OCTET STRING syntax with SIZE (0 | 2..63), allowing lowercase characters only, and is intended to be imported by other MIB modules rather than having each define its own representation.
IANA assigned OID { mib-2 165 } to the LANGTAG-TC-MIB module. The MIB is rooted under the mib-2 subtree.
This MIB module defines only a textual convention and does not define any management objects. It therefore has no direct impact on the security of the Internet; meaningful security considerations must be written in the MIB modules that import and use this TC to define management objects.
The LangTag field is encoded as an OCTET STRING with SIZE (0 | 2..63). A zero-length value is not a valid language tag but can be used to express 'language tag absent' when used as an index field. The DISPLAY-HINT is '1a'.