Route Distinguishers are used to create VPN-IPv4 addresses, as specified
in [RFC4364]. The RDs are structured so that every service provider can
administer its own "numbering space" (i.e., can make its own assignments
of RDs), without conflicting with the RD assignmentsmade by any other
service provider. An RD consists of three fields: a type field, an
administrator field, and an assigned number field.
The value of the type field determines the lengths of the other two fields,
as well as the semantics of the administrator field. The administrator
field identifies an assigned number authority, and the assigned number
field contains a number which has been assigned, by the identified
authority, for a particular purpose.
