PMP> Lastest Host MIB v2smi draft

[Michael Kirkham]

On Wed, 28 Apr 1999, Bobby Krupczak wrote:

> I disagree.  Why should BITS not be imported?  It is a textual
> convention defined in RFC1902.

BITS is neither a textual convention, nor does RFC 1902 define any textual
conventions.  Textual conventions are defined in RFC 1903.  Both RFC 1902
and 1903 define BITS, but they are as [part of] the OBJECT-TYPE and
TEXTUAL-CONVENTION macros:

OBJECT-TYPE MACRO ::=
BEGIN
    .
    .
    .
        Syntax ::=
                  type(ObjectSyntax)
                | "BITS" "{" Kibbles "}"
    .
    .
    .
END

(from RFC 1902)

TEXTUAL-CONVENTION MACRO ::=
BEGIN
    .
    .
    .
    Syntax ::=
                  type(ObjectSyntax)
                | "BITS" "{" Kibbles "}"
    .
    .
    .
END

(from RFC 1903)

Hence, BITS is an implicit part of the OBJECT-TYPE and TEXTUAL-CONVENTION
macros.  For BITS to be considered a TEXTUAL-CONVENTION (and thus need to
be imported), it would need to have been defined along the lines of:

BITS ::= TEXTUAL-CONVENTION
    STATUS current
    DESCRIPTION
        "This would be BITS as a TEXTUAL-CONVENTION"
    SYNTAX OCTET STRING

Such a definition does not exist.

> As far as I can tell, the BITS clause
> adds semantic clarity to the notion of assigning meaning to bits in an
> octet string.

Certainly.  That's precisely what BITS is for.  But putting BITS in the
IMPORTs clause is illegal.  There are several MIB compilers (the one we
use in our testing products included) that will reject a MIB that has BITS
in the IMPORTs.

It's a fairly common error.  The Cable MIB WG has made the same mistake in
several of their MIBs.  I'm not sure if they've fixed it yet..

Btw, in the revised/clarified SMIv2 draft, BITS is explicitly forbidden
from being IMPORTed:

"However, the following must not be included in an IMPORTS statement:

   - named types defined by ASN.1 itself, specifically: INTEGER, OCTET
     STRING, OBJECT IDENTIFIER, SEQUENCE, SEQUENCE OF type,
   - the BITS construct."

(ftp://ftp.ietf.org/internet-drafts/draft-ops-smiv2-smi-01.txt)

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