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From David Latorre <dvl...@gmail.com>
Subject Re: FTP Data Channels Through Reverse Proxy
Date Wed, 21 Aug 2019 23:08:36 GMT
Ah sorry,
 I was rechecking something and made a mistake regarding the IP address in
the PASV response. In any case, unless you have proof (logs from the server
or network traces of the server <-> proxy bit) that the server returns
invalid data in the proxy case, I think you should focus on verifying why
the client is failing and, if it is caused by an invalid response, why the
proxy is generating it.




On Thu, 22 Aug 2019, 00:03 David Latorre, <dvlato@gmail.com> wrote:

> Hi Kenneth,
>
> Shouldn't you receive the proxy address as a response to PASV when going
> through the proxy? Otherwise it would bypass the proxy, but I'm assuming
> you should not  connect directly from the client to the server and that's
> why you need a proxy. I'm a bit puzzled since you state that the proxy
> receives the response to MLSD but the IP that the client sees for PASV is
> the same in both cases.
>
> Your client log for the proxy case does not show any listing as a response
> for MLSD, so it's difficult to know what's going on. If you cannot get any
> logs for that, get some network traces with tcpdump and check what's going
> on. Enabling more detailed logging in the client might also help (you can
> configure that in the Filezilla settings).  Server logs might also prove
> useful.
>
> In any case  I don't see how this would be caused by Ftpserver with the
> information you've given.
>
>
>
> On Wed, 21 Aug 2019, 21:56 Kenneth Taylor, <kenneth.taylor@dataexpress.com>
> wrote:
>
>> We are trying to get Apache FTP Server to work behind a reverse proxy.
>> The only thing not working is the data channels. We use an Ftplet to
>> intercept and handle the PASV command and substitute our proxy’s IP and
>> port in the PASV response. That all seems to work fine.  We are testing it
>> with FileZilla client and our server works perfectly when connecting
>> directly to the server but fails when going through the proxy.
>>
>>
>>
>> We can see the data connections being established on both the server and
>> the proxy. Our proxy logs every forwarded message and we can see that all
>> client and server messages are being forwarded both ways.
>>
>>
>>
>> The problem is that after the PASV command happens the next comand is
>> MLSD and we can see the server sending the correct response and the proxy
>> is forwarding the listing. But the client interprets the response
>> incorrectly and closes the session.  After looking at this for many many
>> hours we’re stumped.
>>
>>
>>
>> Our Proxy is a very simple IO streams forwarder, with a control
>> connection to tell the Proxy when to open data channels that forward back
>> to the data channel opened by Apache on the Server.
>>
>>
>>
>> This is the client log when connecting direct:
>>
>>
>>
>> 14:10:44 Command: PASV
>>
>> 14:10:44 Response: 227 Entering Passive Mode (192,168,0,173,40,122)
>>
>> 14:10:44 Trace:       Binding data connection source IP to control
>> connection source IP 192.168.0.92
>>
>> 14:10:44 Command: MLSD
>>
>> 14:10:44 Response: 150 File status okay; about to open data connection.
>>
>> 14:10:44 Response: 226 Closing data connection.
>>
>> 14:10:44 Listing:      Size=0;Modify=20190814174646.670;Type=dir; Monthly
>>
>> 14:10:44 Listing:      Size=0;Modify=20190814180307.721;Type=dir; Weekly
>>
>> 14:10:44 Listing:      Size=0;Modify=20190814174833.915;Type=dir; Daily
>>
>> 14:10:44 Listing:      Size=0;Modify=20190814175140.777;Type=dir; Archive
>>
>> 14:10:44 Status:      Directory listing of "/" successful
>>
>>
>>
>> This is the client log when connecting through the proxy:
>>
>>
>>
>> 14:37:16 Command: PASV
>>
>> 14:37:16 Response: 227 Entering Passive Mode (192,168,0,91,202,228)
>>
>> 14:37:16 Trace:       Binding data connection source IP to control
>> connection source IP 192.168.0.173
>>
>> 14:37:16 Command: MLSD
>>
>> 14:37:16 Response: 150 File status okay; about to open data connection.
>>
>> 14:37:16 Response: 226 Closing data connection.
>>
>> 14:37:16 Error:       Disconnected from server: ECONNABORTED - Connection
>> aborted
>>
>> 14:37:16 Error:       Failed to retrieve directory listing
>>
>>
>>
>> One weird thing we see is that the “226 Closing data connection” shows up
>> on the proxy after the MLSD listing is returned. When connecting direct it
>> is before the listing in the client log, but in all cases these messages
>> are coming from the same server so that may be a logging anomaly.
>>
>>
>>
>> Thanks for any help.
>>
>> Ken
>>
>>
>>
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