Experimental Physics and
Industrial Control System

The basic concept of SO_REUSEPORT is simple enough. Multiple servers (processes or threads) can bind to the same port if they each set the option as follows:

   . . .

So long as the first server sets this option before binding its socket, then any number of other servers can also bind to the same port if they also set the option beforehand. The requirement that the first server must specify this option prevents port hijacking—the possibility that a rogue application binds to a port already used by an existing server in order to capture (some of) its incoming connections or datagrams. To prevent unwanted processes from hijacking a port that has already been bound by a server using SO_REUSEPORT, all of the servers that later bind to that port must have an effective user ID that matches the effective user ID used to perform the first bind on the socket.

SO_REUSEPORT can be used with both TCP and UDP sockets. With TCP sockets, it allows multiple listening sockets—normally each in a different thread—to be bound to the same port. Each thread can then accept incoming connections on the port by calling accept(). This presents an alternative to the traditional approaches used by multithreaded servers that accept incoming connections on a single socket.