Intermittent FTP login issues (Microsoft IIS FTP Service)

Posted by JaggenSWE on Server Fault See other posts from Server Fault or by JaggenSWE
Published on 2012-06-11T08:52:18Z Indexed on 2012/06/11 10:41 UTC
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I've got a somewhat weird problem which I'm not sure how to troubleshoot. We have a FTP running on a Windows Server 2003 machine using the IIS FTP Service, this is for our clients and is configured with IP-restrictions. However, now ONE of the clients starts complaining that they can't log in to the server from time to time. This is just ONE of 10+ clients that have this issue, which makes me think it's a problem on their side.

Just to be on the safe side I had a peek into the FTP logs and found something strange. Whenever succeed in loggin in this is what I can find in the logs:

nnn.nnn.nnn.70, userxxx, 2012-06-11, 09:22:32, MSFTPSVC1, SERVERNAME, nnn.nn.nn.11, 0, 0, 0, 331, 0, [191747]USER, userxxx, -,

nnn.nnn.nnn.70, userxxx, 2012-06-11, 09:22:32, MSFTPSVC1, SERVERNAME, nnn.nn.nn.11, 0, 0, 0, 230, 0, [191747]PASS, -, -,

However, if the login fails I see the following events:

nnn.nnn.nnn.70, userxxx, 2012-06-11, 09:16:33, MSFTPSVC1, SERVERNAME, nnn.nn.nn.11, 0, 0, 0, 331, 0, [191739]USER, userxxx, -,

nnn.nnn.nnn.70, -, 2012-06-11, 09:16:33, MSFTPSVC1, SERVERNAME, nnn.nn.nn.11, 0, 0, 0, 530, 1326, [191739]PASS, -, -,

When you look at the event where the clients sends the PASS in the successful login it seems to know that it is infact "userxxx" that is coupled to that PASS, but when it fails it seems to be lost since user in the PASS event is set to "-".

Anyone have any ideas around this, any help would be appreciated. :)

//JaggenSWE

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