On Fri, Jul 29, 2011 at 2:16 AM, narendra babu <[email protected]> wrote:
> Hello all ,
>
> How can we allow a server to bind to a port that appears to be held open by a
> client process? The netstat below indicates that port 9521 is not being
> listened
> to by any server process:
>
> $netstat -an | grep 9521
> tcp 0 0 127.0.0.1:9521 127.0.0.1:9521
> ESTABLISHED
> tcp 0 0 10.1.235.31:47776 10.1.19.219:9521
> ESTABLISHED
Ok this should be in FIN_WAIT or FIN_WAIT2 or something.
If it is connected how will the socket be free?
> We are using SO_REUSEADDR in the server code, which on Solaris always allowed
> to re-bind to the port in question.
> int on = 1;
> if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) == -1)
> printf("setsockopt SO_REUSEADDR failed: port=%d fd=%d", on, fd);
>
>
> On Linux there appears to be a caveat with using SO_REUSEADDR in conjunction
> with INADDR_ANY. This is from the Linux socket man page:
> SO_REUSEADDR
> Indicates that the rules used in validating addresses supplied
> in a bind(2) call should allow reuse of local addresses. For
> PF_INET sockets this means that a socket may bind, except when
> there is an active listening socket bound to the address.
> When the listening socket is bound to INADDR_ANY with a spe-
> cific port then it is not possible to bind to this port for
> any local address.
> despite the fact that no server can bind the port, no new client can
> establish a connection to the port.
> Also, the client that is established to the port is sending messages to what
> it believes is its peer.
> No errors are returned.
> The socket has been in this state for couple of a days
I know this question really really well.
I have faced this problem several times.
But I still can't answer it. I use
setsockopt( ... SO_REUSEADDR..)
and
setsockopt(...SO_REUSEPORT..)
under linux.
It is something similar for Solaris, FreeBSD, NetBSD, OpenBSD or any other UNIX.
Now if you don't find that the port is relinquished after a few
seconds then some other resource is
holding on to it.
netstat should tell you.
My answer is not direct;that is deliberate.
Do your homework.
You have done a great deal of tech stuff I know. Hopefully this tip will help.
Best of luck.
I want every luggie to aspire to be like Narendra. Do your homework
with clear focus
and share your results before asking something in forums.
Best,
Girish
--
G3 Tech
Networking appliance company
web: http://g3tech.in mail: [email protected]
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