Network address encapsulation structure for IPv4 or IPv6 address This structure is used to encapsulation of address type such that the implementation does not need to have separate containers for IPv4 and IPv6 address. It now supports either AF_INET or AF_INET6 network addresses. This structure may not hold both address type at a given time. Dual-stack implementation must assume that IPv4 can be effective in parallel with IPv6 address, thus it is expected that the the implementation uses two instances of this structure/.