This attribute specifies the dnic (Data Network ID Code) of the
CUG by which packet networks are identified. This attribute is not
applicable if the CUG is a national CUG, as specified by the CUG
type attribute. There are usually 1 or 2 dnics assigned per country,
for public networks. The U.S. is an exception where each BOC has
a dnic. Also, a group of private networks can have its own dnic.
dnic value is not an arbitrary number. It is assigned by international
agreement and controlled by CCITT.