[squid-users] squid ftp-proxy

Axel.Eberhardt at t-systems.com Axel.Eberhardt at t-systems.com
Mon Apr 11 11:16:41 UTC 2016

Hi Amos,

>Von: squid-users [mailto:squid-users-bounces at lists.squid-cache.org] Im Auftrag von Amos Jeffries

>>On 5/04/2016 9:08 p.m., Axel.Eberhardt at t-systems.com wrote:
>> Hello,
>> Maybe someone can give me a hint :-)
>> I try to enable the Native ftp proxying.
>> The documentation I have found is:
>> http://wiki.squid-cache.org/Features/FtpRelay
>> But there is no example for this. Also in the Mail Archives I was not able to find a hint.
>> I have configured the ftp proxy with parameter:
>> 	ftp_port 21

>AFAIK that port is intended either for use as above when the Squid IP address or hostname is given to the client FTP tool as the FTP server >IP/host.

Yes, that is correct. But I'am not sure if this is the only necessary option. Maybe I have to configure more options. 

> Or when intercepting port 21 traffic - with the 'intercept' option on the port config line.

>It is still a new / experimental and rarely used feature so YMMV.


>> Now my problem.
>> I am able to connect via ftp client to the squid.
>> Also the login will be correct:	
>> 	example:  anonymous at ftp.informatik.rwth-aachen.de
>> But after a command which use a data channel the connection fails:
>> 	421 Service not available, remote server has closed connection
>> I try a tcpdump but I cannot find a failure. 
>> The only different between a native ftp session and a connection over the squid is a missing TCP ACK after the last ftp data package. 

>Um, missing ACK on which of the four connections involved?
>  and from which of the three software involved?

I have traced the network interface at the squid server. 
The ftp connection was established from localhost. So I cannot see the traffic between squid and ftp client.
The missing ACK I have seen comes from the ftp server. Maybe the ftp server answer is different between 'ftp over http' and ftp.
But this issue is similar to different ftp servers.


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