SSH DNS Checks

Every time you log onto a Linux computer it will try to resolve the last SSH connection by trying to do a reveres DNS lookup of the IP address of the computer that last made a SSH connection. This can be useful as if you notice a logon that should not have existed you can take action.

In some scenarios you may prefer to disable the DNS reverse lookup at SSH logon either because DNS may not be available or it may be slowing the logon process.

To disable the SSH DNS lookup edit the file:
/etc/ssh/sshd_config and change

#UseDNS yes

to

UseDNS no