RE: Port 21 blocked by ISP
anonymous_at_discussions.microsoft.com
Date: 09/01/04
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Date: Wed, 1 Sep 2004 15:10:31 -0700
>> From: "DAZ" <anonymous@discussions.microsoft.com>
>> I'm running IIS 6 on Windows 2003 Server. The server
is
>> behind a Linksys BEFSR41 router and uses a static
>> internal address. My ISP only provides me with a
dynamic
>> IP address and has blocked port 21 so I've configured
the
>> ftp server to use port 7721. I've also configured
>> passive port numbers 7722 to 7730 for ftp. I also
have a
>> dyndns.org name defined to point to my router's
>> connection so I can find the server from out on the
>> Internet. The router is configured to forward ports
7721
>> to 7730 to my server at the internal static IP address.
>
>The first question I would ask is the obvious non-
technical one -
>presumably your ISP has blocked port 21 because they
particularly don't
>want you running an FTP server, rather than because they
don't want you
>running something that uses a 21 in its destination
port. If you flout
>the rules of your ISP, you will probably be found out
eventually, and your
>service disconnected - possibly without warning, and
possibly even with a
>fine. I strongly recommend that you address this
problem _first_. It may
>be that you can simply ask your ISP to open up port 21
for use as an FTP
>server, and they will grant it - on occasion, this sort
of limit is put in
>to make sure that malware doesn't install a server that
the user is unaware
>of.
>
Yes, my ISP does not want me running servers. Generally
I transfer files using Remote Desktop Connection or
Terminal Services. However, I had occasion where this
method was not feasible. Consequently I wanted to set
ftp to be able to transfer a file. Since this is the
first time I've done this in the two years I've been with
this ISP and since I don't plan on keeping the ftp server
running except when I'm transfering a file, I don't think
it will be a problem.
>> Clients have to connect in PASV mode because of the
port
>> blockage from my ISP.
>
>Only if your ISP is blocking outgoing connection
attempts, or if their ISP
>or firewall is blocking incoming connection attempts.
The former is
>unlikely, the latter more so.
>
Exactly.
>> However, when the server responds,
>> it sends its internal IP address back to the client
which
>> then cannot talk to the server because it's now using
the
>> wrong address. Anyone gotten around this? Here's an
>> example log from the client FTP Commander:
>
>This is because the NAT is unable to tell that the
server is sending FTP
>traffic - the NAT checks for FTP traffic only on port 21.
>
>I have heard that some more expensive NAT routers will
allow you to
>configure them such that they will look for FTP traffic
on whatever port
>you tell them - but I have not found any specific
details on that.
>
>It looks like your best bet is to try and convince your
ISP to let you run
>your FTP server on port 21.
>
>Alun.
>~~~~
Thanks. I'll either have to look into another method for
transfering files or else at more capable hardware,
though doing this once every two years doesn't seem like
it would warrant spending extra $'s for equipment.
In any case, thanks for your response.
DAZ
- Previous message: Linda: "Re: Anyone got Win XP ftp server working?"
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