BGP4+ is mainly used to control route transmission and select optimal routes.
BGP4+ is a dynamic routing protocol used between Autonomous Systems (ASs), and it is an extension of BGP.
The traditional BGP4 can manage only the IPv4 routing information. For other network layer protocols such as IPv6, the traditional BGP4 has a limited capability to transmit routing information.
The Internet Engineering Task Force (IETF) introduces BGP4+ as a supplement to BGP4 to support multiple network layer protocols. The RFC for BGP4+ is RFC 2858 (Multiprotocol Extensions for BGP4).
To support IPv6, BGP4 needs to reflect the IPv6 protocol information to the Network Layer Reachable Information (NLRI) attribute and the Next_Hop attribute. BGP4+ introduces two NLRI attributes:
The Next_Hop attribute of BGP4+ is in the format of an IPv6 address. It can be an IPv6 global unicast address or the link-local address of the next hop.
BGP4+ can be applied to an IPv6 network by using the BGP attribute of multiple protocol extensions. The message and routing mechanisms of BGP remain unaltered.