ssh between el7 and fc28 boxes

[John Pilkington]

Hi:  I have two boxes connected to the same router.  One runs SL7.5, 
from tomorrow probably SL7.6, which is an el7 clone, and the other runs 
Fedora 28.

I can ssh and rsync from F28 to SL7, but permission is denied in the 
opposite direction.  Port 22 is open.  I now have copies of both 
versions of /etc/sshd and intend to examine diffs.

Google provides many links but nothing that looks authoritative or, 
preferably, authoritative and simple.  Any help wpuld be appreciated.

John P