[CentOS] "installation source" specification for netinstall

Tue Dec 15 20:29:38 UTC 2015
ken <gebser at mousecar.com>

Trying to specify the "installation source" in the configuration of 
netinstall for centos 7 (7.1).  Three places on the web said


But that configuration page probes, then it says, "Error setting up base 

What's the magic needed?

Also, if anyone knows specs for epel and others, they might help too.