The BITS construct represents an enumeration of named bits. This collection is assigned non-negative, contiguous values, starting at zero. Only those named-bits so enumerated may be present in a value. (Thus, enumerations must be assigned to consecutive bits; however, see Section 9 for refinements of an object with this syntax.)
Although there is no SMI-specified limitation on the number of enumerations (and therefore on the length of a value), MIB designers should realize that there may be implementation and interoperability limitations for sizes in excess of 128 bits.
Finally, a label for a named-number enumeration must consist of one or more letters or digits (no hyphens), up to a maximum of 64 characters, and the initial character must be a lower-case letter. (However, labels longer than 32 characters are not recommended.)