2005-02-15 2015-05-15 Route Distinguishers are used to create VPN-IPv4 addresses, as specified in . 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. 0-32767 First Come First Served 32768-65535 IETF Review 0 Administrator field is a two-byte Autonomous System Number 1 Administrator field is a four-byte IP Address 2 Administrator field is a four-byte Autonomous System Number 3-65534 Unassigned 65535 For Use Only in Certain Leaf A-D Routes