[Tutor] ftp socket.error

[richard kappler]

Thanks for all the assistance, turned out it was a problem with the
iptables not having an accept for eth1. Onward and upward!

regards, Richard

On Sat, Sep 12, 2015 at 12:24 PM, Martin A. Brown <martin at linux-ip.net>
wrote:

>
> Hello and good morning
>
> I may be mistaken, but it looks like you are trying to open the socket on
>> port 2021. Standard ftp uses 21. Is the server listening on 2021?
>>
>
> Ooof!  And, in fact, that is a great point!  I overlooked that in the
> original snippet!
>
> Everything I wrote still stands, except that you need to tell the
> ip_conntrack_ftp (or nf_conntrack_ftp) kernel module to watch for a command
> channel on TCP/2021.
>
>   modprobe ip_conntrack_ftp ports=21,2021
>
> That means that the ip_conntrack_ftp module will watch flows on both ports.
>
> I'm glad you observed that important detail, Robert!
>
> -Martin
>
>
> Strictly speaking, it's no Python question, but... good ol' FTP.
>>>
>>> socket.error: [Errno 113] No route to host
>>>
>>>>
>>>>>>
>>>>> Your program is receiving an EHOSTUNREACH.
>>>
>>>  >>> import errno
>>>  >>> errno.errorcode[113]
>>>   'EHOSTUNREACH'
>>>
>>> This occurs at precisely the moment that your program is trying to
>>> initiate a data transfer.  Every firewall administrator in the world
>>> loves
>>> FTP for precisely this reason.  (And, when I say "love", you can replace
>>> this with a verb or <expletive/> of your choice.)
>>>
>>> Without packet captures, I will merely guess (based on experience).
>>>
>>>   1. The receiving machine is running the Python program, builds a
>>>      connection on port 21 (this is called the FTP command
>>>      channel), you log in and all is well.
>>>   2. The moment you try to transfer any data, the FTP client (your
>>>      receiving machine) and the FTP server negotiate either FTP
>>>      passive mode or FTP active (retronym) mode.  I'm guessing
>>>      that your FTP client is choosing passive mode.  (Your FTP
>>>      client might produce logging of this negotiation.)
>>>   3. Using the connection information, the client attempts to build
>>>      an FTP data channel.  So, your machine running the Python
>>>      program initiates a connection to the FTP server.
>>>   4. The FTP server is (probably) configured to allow connections
>>>      inbound to TCP/21 (FTP Command Channel), but doesn't know to
>>>      allow the connections to the ephemeral port(s) negotiated
>>>      during step 2 (above).  So, the firewall on the FTP Server
>>>      sends an ICMP Type 3, Code 1 [0].
>>>
>>> Figured it out. On the receiving machine  I had to
>>>
>>>>
>>>>> # modprobe ip_conntrack_ftp
>>>>>
>>>>>
>>>> Right instinct!  Try this same command on the FTP server side. Unless
>>> your
>>> Python FTP client is negotiating active mode, the server will be the
>>> "problem" in this case.
>>>
>>> No, apparently I didn't figure it out. I thought I had as after the
>>>
>>>> modprobe I was getting a an EOFError, but now I'm getting the no route
>>>> to
>>>> host error again. I can ping it, and as you can see from the original
>>>> post,
>>>> I am able to establish a connection and log in, it's just when I try to
>>>> send a file it goes bollocks up. Still need ideas.
>>>>
>>>>
>>> Hopefully, my idea #1 helps.  (If not, you'll need to do some packet
>>> captures and probably crank up the logging on the FTP server, too.)
>>>
>>> I do have another idea, though.  Have you ever wondered about the slow
>>> demise of FTP?  All of this command-channel, data-channel, PORT or PASV
>>> nonsense goes away when you use a protocol that runs over a single TCP
>>> port.  Worked fine in the early days of the Internet before firewalls and
>>> NAT.
>>>
>>> Anyway, short idea #2:
>>>
>>>   If it's anonymous access, use HTTP.
>>>   If authenticated access, use ssh/scp/sftp.
>>>
>>> Good luck,
>>>
>>> -Martin
>>>
>>>  [0] http://www.networksorcery.com/enp/protocol/icmp/msg3.htm
>>>
>>> --
>>> Martin A. Brown
>>> http://linux-ip.net/
>>> _______________________________________________
>>> Tutor maillist  -  Tutor at python.org
>>> To unsubscribe or change subscription options:
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>>>
>>>
>>
> --
> Martin A. Brown
> http://linux-ip.net/
>



-- 

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