Cannot determine realm for numeric host address

I could not connect today to one of our servers using password less public key ssh login. Using -vvv ssh option would show:

debug1: An invalid name was supplied 
Cannot determine realm for numeric host address 

So from the Red Hat target I inspected the secure log:

$ tail -f /var/log/secure
...
Nov 22 11:37:03 t2215179 sshd[23123]: Authentication tried for admin with correct key but not from a permitted host (host=tools, ip=xxx.xxx.xxx.xxx).
...

This was resolved adding the IP to /etc/hosts

$ vi /etc/hosts
...
xxx.xxx.xxx.xxx tools
...