One more comment: I opened Firestarter (not installed by default; do "sudo apt-get install firestarter") and enabled port 177 from my XDMP server. Suddenly XDMCP works again. However, "sudo ufw status" says "not enabled," so I don't know why that works.
One more comment: I opened Firestarter (not installed by default; do "sudo apt-get install firestarter") and enabled port 177 from my XDMP server. Suddenly XDMCP works again. However, "sudo ufw status" says "not enabled," so I don't know why that works.