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Mea culpa, XO/Concentric and Comcast
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Published Thursday, November 07, 2013 @ 10:02 PM EST
Nov 07 2013

The good news is I solved my ftp problem. The better news is it was wasn't XO/Concentric's fault.

One would assume the 550 access denied message comes from the ftp server.

It doesn't.

The message seems to be generated by the ftp client software on the user machine. The client displays the message when the command is not executed.

However, failure to execute the command isn't the server's fault; the problem is the failure of the user's system to open a TCP/IP port.

I discovered this when a Google search for ftp 550 errors returned a number of hits containing references to Comcast, my broadband internet provider. Like a good Comcast customer, I didn't bother to call support... I just unplugged the router and hit reset on the cable modem.

It took a good five minutes for the modem to come back up, indicating a configuration change or firmware update was being performed. Once the reboot was completed, I plugged the router back in, waited for the computer to reconnect to the net, and the fired up the ftp client:

Command: STOR qcount.txt
Response: 150 Opening ASCII mode data connection for qcount.txt.
Response: 226 Transfer complete.
Status: File transfer successful, transferred 8 bytes in 1 second

Relieved, I regenerated the website pages and started formulating nasty things to say about Comcast. I ordered my ftp client to begin the transfer, and:

Response: 550 Access is denied.

Arrrgh!

What could have changed in the ten minutes between connect attempts?

I glanced at the Network and Sharing Center display I had opened after rebooting the modem to make certain all the machines on the home network were up. They were- along with a VPN connection to my office in Chicago, a connection I rarely use but had activated to connect via remote desktop to my workstation there.

I disconnected from the VPN and tried again:

Command: STOR qcount.txt
Response: 150 Opening ASCII mode data connection for qcount.txt.
Response: 226 Transfer complete.
Status: File transfer successful, transferred 8 bytes in 1 second

So, the problem wasn't XO's ftp server, or Comcast blocking ports, but rather a network connection conflict and a misleading error message.

I apologize for blaming XO/Concentric and almost blaming Comcast.

I've been working with computers for over 30 years, and yet I still fell for the oldest mistake in the book: believing the error message.

The older I get, the more I discover the new stuff I learn every day is actually old stuff I just forgot.

Sigh.


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