Good sleuthing but my bet is Earthlink has done something.
Keep in mind that I have no access to your router and such settings so no one but you and Earthlink can review that.
For months and months I was able to use FTP to login to servers. I have a program that logs in once a day to update my various websites. This all happens from a computer connected to a business-DSL account from my home-office.
A few weeks ago, my business DSL account was no longer able to login to FTP on servers supporting my "networksolutions.com" websites. (I can still login to other FTP sites).
The problem is not with the computer or the computer's firewall, because I can move the same computer to a different DSL connection in the same building, (a consumer DSL account), and it will login fine to everything.
The problem is also not with the DSL modem, as I've replaced the DSLmodem and still the same problem.
I contacted NetworkSolutions.com, and they "assured" me that the problem is with my internet provider, as they do not block individual IP addresses.
My business-DSL provider "Earthlink" is telling me that they are not at fault either.
This all just started happening on or about June 13th, 2013. It had been working fine for many many months before that, and I had logged in once an evening to update my various websites.
Has anyone experienced anything like this? Can anyone suggest something that I could do to try to track down who is at fault? (the servers or the internet provider).
Thanks for any suggestions.