Linux Administration Cookbook

The UseDNS setting

The last option I'm going to cover is the UseDNS entry, as it's a source of pain for quite a few people:

#UseDNS yesUseDNS no

Here, we can see that UseDNS has been explicitly set to no in our configuration file. This is the default.

When set to no, the SSH daemon will not look up the remote host name, and check that the remote IP maps back to the expected IP, based on that host name.

To confuse you further, here's the manual entry of UseDNS :

"Specifies whether sshd(8) should look up the remote host name, and to check that the resolved host name for the remote IP address maps back to the very same IP address. If this option is set to no (the default) then only addresses and not host names may be used in ~/.ssh/authorized_keys ...