Subscriber Services: Single-session DHCP dual-stack subscriber single BNG connect

DHCP single-session dual-stack subscribers connect to a single broadband network gateway (BNG) in a load sharing access model. For a DHCP dual-stack subscriber, the DHCPv4 and DHCPv6 protocol handshakes are generally completely independent of each other. So it is theoretically possible that each arm of a given dual-stack subscriber could connect to a different BNG. A configured mode of operation is supported to avoid this scenario. A given address family is designated as the protocol primary for a dual-stack subscriber. Any binding attempt from the secondary address family client for a given dual-stack subscriber is rejected if a binding from the protocol primary family of the same dual-stack subscriber is not currently active. In case bindings for both arms of a DHCP dual-stack subscriber are currently active when the protocol-primary family binding is released (or otherwise deleted for any reason), then the secondary address family binding for that subscriber will be automatically torn down.