Re: [squid-users] FTP access for IPv6 clients

From: Nicolas C. <>
Date: Thu, 07 Jun 2012 11:30:41 +0200

Le 07/06/2012 05:09, Amos Jeffries a écrit :

> 3.1.6 has quite a few issues with IPv4/IPv6 behaviour in FTP. Please try
> upgrading to the 3.1.19 package in Debian Wheezy/Testing or Unstable.

I tried with Debian Wheezy, the behavior is the same. I will test with a
3.2.x version compiled...

>> As a workaround, to force FTP clients to connect to Squid using IPv4,
>> I created a "proxy-ftp" entry in our DNS pointing to the IPv4 address
>> of the proxy. If FileZilla is configured to use "proxy-ftp", it's
>> working fine.
>> The problem is that sometimes the FTP server has IPv6 enabled and
>> then it's not working, the workstation is using IPv4 to reach Squid
>> which is using IPv6 to reach the FTP server. The FTP client is
>> immediately failing after a PASV command.
> Squid is coded to try IPv6+IPv4 compatible commands (EPSV) first. If it
> gets as far as trying IPv4-only PASV command it will not go backwards to
> trying the IPv6+IPv4 EPSV command.
> ... "ftp_epsv off" is making Squid go straight to PASV and skip all the
> non-IPv4 access methods.

When I force the FTP client to reach Squid in IPv4, the client will try
to perform PASV on the server even if Squid is connected to the FTP in
IPv6, I think this is the root of the problem.

"CONNECT HTTP/1.1" 200 521 TCP_MISS:DIRECT:2a02:3e0::14:80

On FileZilla : "Enter passive mode (80,223,35)" => failing

> The third option is to upgrade your FTP server to one which supports
> those extension commands (they are for optimising IPv4 as much as IPv6
> support). Then you won't have to hack protocol translation workarounds
> through Squid to access it from modern FTP clients.

The problem is happening on remote FTP servers I don't manage.

Is there a possibility to make Squid using its IPv4 address for all
outgoing FTP? I tried with "tcp_outgoing_address" with no luck.


Received on Thu Jun 07 2012 - 09:30:52 MDT

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