multiple ftp ports stay in CLOSE_WAIT status

[Dirk Engels]

We have a curious problem with Cloverleaf 5.7 running on IBM AIX 6.1. We ftp files to a remote AIX 6.1 server. On the remote server we see a lot of ftp ports in a CLOSE_WAIT status which will be forked when a message has to be delivered or if the read cycle has been reached. It seems that there will be a new port opened every time a connection has to be made, even if the protocol is configured to stay open.

We sent a request to IBM and they say that this is not os related.

Has anyone seen such a behavior before?

Dirk

Topic

[David Barr]

It sounds like a problem with the FTP server software on the remote system.

Even though you have the Cloverleaf threads configured not to close the “control” connection to the remote FTP server, each file that is transferred will require an additional socket connection to be opened and closed.

It looks like the remote FTP server is not properly closing the sockets after each file is transferred. I’m not sure if you can try this, but there are many different FTP server programs that are available, so maybe you could try switching.

[Dirk Engels]

We have sent a request to IBM and they said, that this is not a problem of the AIX system.

[David Barr]

You should read up on CLOSE_WAIT. This means that the operating system has seen the connection close, but the process managing the connection (the FTP server) hasn’t properly handled the close yet. Unless they can provide evidence to the contrary (i.e. they show from the network traffic that something unusual is happening) I would say that this is definitely an AIX problem.

Even if they won’t look at the problem in this level of detail, it’s not that hard to switch to an alternative FTP server, and it’s possible that this will fix the problem.

[Author]

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