BGP is used with BGP extensions mentioned in Routing prerequisites to distribute VPRN routing information across the service provider network.
BGP was initially designed to distribute IPv4 routing information. Therefore, multi-protocol extensions and the use of a VPN-IPv4 address were created to extend ability of the BGP to carry overlapping routing information. A VPN-IPv4 address is a 12-byte value consisting of the 8-byte route distinguisher (RD) and the 4-byte IPv4 IP address prefix. The RD must be unique within the scope of the VPRN. This allows the IP address prefixes within different VRFs to overlap.
A VPN-IPv6 address is a 24-byte value consisting of the 8-byte RD and 16-byte IPv6 address prefix. Service providers typically assign one or a small number of RDs per VPN service network-wide.