[DR] actually RFC 4181 discourages the practice of placing MIB modules under a subtree other than mib-2. See section 4.5:
- The value assigned to the MODULE-IDENTITY descriptor MUST be unique
and (for IETF standards-track MIB modules) SHOULD reside under the
mgmt subtree [RFC2578]. Most often it will be an IANA-assigned
value directly under mib-2 [RFC2578], although for media-specific
MIB modules that extend the IF-MIB [RFC2863] it is customary to use
an IANA-assigned value under transmission [RFC2578]. In the past,
some IETF working groups have made their own assignments from
subtrees delegated to them by IANA, but that practice has proven
problematic and is NOT RECOMMENDED.