[ECOS] BSD TCP connect() ignores SO_REUSEADDR option

[ECOS] BSD TCP connect() ignores SO_REUSEADDR option

[Grant Edwards]

I've recently noticed that when using the FreeBSD TCP stack, the
connect() system call ignores the SO_REUSEADDRESS setting and returns
EADDRINUSE when attempting to connect a TCP socket if a connection
with the same (SrcIP,SrcPort,DstIP,DstPort) tuple is still hanging
around in the TIME_WAIT state.

Here's an example sequence of events:

   * create a TCP socket

   * set SO_REUSEADDRESS and SO_REUSEPORT options
   
   * bind to port 12346

   * connect to 1.2.3.4:54321

   * send a little data   
   
   * close connection

   * wait a few seconds

   * create a TCP socket

   * set SO_REUSEADDRESS and SO_REUSEPORT options
   
   * bind() to port 12346

   * connect() to 1.2.3.4:54321

The bind() will succeed due to the SO_REUSEADDR, SO_REUSEPORT option.

The connect() will fail with EADDRINUSE.

If you wait a minute or two between connections it works fine.


There appear to be a certain set of conditions when an existing
TIME_WAIT connection will be discarded and reused -- see line 747
below:

From  tcp_usrreq.c:

733        /*
734         * Cannot simply call in_pcbconnect, because there might be an
735         * earlier incarnation of this same connection still in
736         * TIME_WAIT state, creating an ADDRINUSE error.
737         */
738        error = in_pcbladdr(inp, nam, &ifaddr);
739        if (error)
740                return error;
741        oinp = in_pcblookup_hash(inp->inp_pcbinfo,
742            sin->sin_addr, sin->sin_port,
743            inp->inp_laddr.s_addr != INADDR_ANY ? inp->inp_laddr
744                                                : ifaddr->sin_addr,
745            inp->inp_lport,  0, NULL);
746        if (oinp) {
747                if (oinp != inp && (otp = intotcpcb(oinp)) != NULL &&
748                otp->t_state == TCPS_TIME_WAIT &&
749                    (ticks - otp->t_starttime) < tcp_msl &&
750                    (otp->t_flags & TF_RCVD_CC))
751                        otp = tcp_close(otp);
752                else
753                        return EADDRINUSE;
754        }

But setting SO_REUSEADDR doesn't affect the behavior of connect().

Should it?

-- 
Grant Edwards               grant.b.edwards        Yow! VICARIOUSLY experience
                                  at               some reason to LIVE!!
                              gmail.com            


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[ECOS] Re: BSD TCP connect() ignores SO_REUSEADDR option

[Grant Edwards]

On 2013-04-30, Grant Edwards <grant.b.edwards@gmail.com> wrote:

> I've recently noticed that when using the FreeBSD TCP stack, the
> connect() system call ignores the SO_REUSEADDRESS setting and returns
> EADDRINUSE when attempting to connect a TCP socket if a connection
> with the same (SrcIP,SrcPort,DstIP,DstPort) tuple is still hanging
> around in the TIME_WAIT state.

It appears that the work-around for this is to set the SO_LINGER
option with a timeout of 0 before calling close().  That reportedly
sends a RST instead of a FIN, and the socket doesn't hang around in
the TIME_WAIT state...

-- 
Grant Edwards               grant.b.edwards        Yow! Thousands of days of
                                  at               civilians ... have produced
                              gmail.com            a ... feeling for the
                                                   aesthetic modules --


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