service provider. Normally the Border Gateway Protocol (BGP) used by the provider's routers only looks at the four-octet IP address, but the BGP Multiprotocol Extensions allow BGP to view the entire 12-octet VPN-IPv4 address, and carry routes from multiple "address families". If the route distinguisher Administrator subfield and the Assigned Number subfield of a VPN-IPv4 address are both set to all zeroes, the VPN-IPv4 address is considered to have exactly the same meaning as the corresponding globally unique IPv4 address. In particular, this VPN-IPv4 address and the corresponding globally unique IPv4 address will be considered comparable by BGP. In all other cases, a VPN-IPv4 address and its corresponding globally unique IPv4 address will be considered noncomparable by BGP. A given per-site forwarding table will only have one VPN-IPv4 route for any given IPv4 address prefix. When a packet's destination address is matched against a VPN-IPv4 route, only the IPv4 part is actually matched. References MPLS networking