During a recent phone company problem, my ISP (kept un-informed by the phone company) got me to switch to PPPoE LLC in a pointless attempt to fix the lack-of-connection issue.
Eventually the service was restored, after being off-line for 3.5 days out of 6.
But FTP had a problem. No matter what GUI client I used, I could only see the root directory of my own web site. Any attempt to move into a sub-directory resulted in a time-out error. Weird.
Eventually, my ISP's help desk happened to suggest switching to PPPoA VC-MUX, saying "I don't know why anybody bothers to use PPPoE".
Well, FTP sprang back to life! And all was good...
If anyone knows what this gobbeldy-gook actually means, and why PPPoE screws FTP, please reply.