[Tutor] ftp socket.error

[Robert Nanney]

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?
On Sep 11, 2015 5:29 PM, "Martin A. Brown" <martin at linux-ip.net> wrote:

>
> Hi there Richard,
>
> 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/
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