Re: [PATCH] SO_REUSEADDR and SO_REUSEPORT behaviour

On Nov 29, 2013, at 4:04 AM, Ermal Luçi <eri_at_freebsd.org> wrote:

> Hello,
> 
> since SO_REUSEADDR and SO_REUSEPORT are supposed to allow two daemons to
> share the same port and possibly listening ip …

These flags are used with TCP-based servers.

I’ve used them to make software upgrades go more smoothly.
Without them, the following often happens:

* Old server stops.  In the process, all of its TCP connections are closed.

* Connections to old server remain in the TCP connection table until the remote end can acknowledge.

* New server starts.

* New server tries to open port but fails because that port is “still in use” by connections in the TCP connection table.

With these flags, the new server can open the port even though
it is “still in use” by existing connections.


> This is not the case today.
> Only multicast sockets seem to have the behaviour of broadcasting the data
> to all sockets sharing the same properties through these options!

That is what multicast is for.

If you want the same data sent to all listeners, then
that is multicast behavior and you should be using
a multicast socket.

> The patch at [1] implements/corrects the behaviour for UDP sockets.

You’re trying to turn all UDP sockets with those options
into multicast sockets.

If you want a multicast socket, you should ask for one.

Tim