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 ITU-T.