UseDNS option

The default value for the UseDNS option changed from "yes" to "no". With this change, sshd no longer converts a client's IP address back into a host name. This prevents the use of hostnames in Host match blocks in the configuration file, also causes host-based authentication to fail (which is not enabled by default). To restore the OpenSSH 6.x behavior, add the following option to /etc/ssh/sshd_config.

This option is re-enabled in /samples/sshd_config for compatibility. To avoid DNS lookups during login, you might want to disable this option.