As of Version 2.2, it is possible to selectively bind a socket to a selected interface (multihoming support). When you do this, you should note that the required address must be present at the host in question and the IP address/port number tuple must not be occupied.
In this way, it is possible for a listen socket to listen in at a specific interface address and a specific port. In addition, it is possible for multiple listen sockets to be bound to one interface address each at a port
To make it possible to switch from single addressing to Anyaddr addressing and back again, the functionality of the setsockopt() subfunction SO_REUSEADDR has been extended. If the socket is marked using this subfunction before the bind() then, if the transport system permits it, it is possible to bind a socket to an interface address even though a socket has already been bound to Anyaddr for this port. This also applies in the opposite direction.