To change the behaviour of the SSH deamon you will need to change the configuration file /etc/ssh/sshd_config. You have to ensure that UseDNS no is included in the file. Standard deployment of Oracle Linux is that UseDNS yes is commented out of the configuration. The default behavior is already set to yes so you have to explicitly include "UseDNS no". To esure that the settings are applied restart the service after you made the changes to the file.
[root@localhost ~]# service sshd restart Redirecting to /bin/systemctl restart sshd.service [root@localhost ~]#