I'd propose submitting a request upstream to make the default setting for UseDNS be No.
Additionally add comments in the sshd_config and man page: # UseDNS - Determines whether IP Address to Hostname lookup and comparison is performed # Default value is No which avoids login delays when the remote client's DNS cannot be resolved # Value of No implies that the usage of "from=" in authorized_keys will not support DNS host names but only IP addresses. # Value of Yes supports host names in "from=" for authorized_keys. Additionally if the remote client's IP address does not match the resolved DNS host name (or could not be reverse lookup resolved) then a warning is logged. # UseDNS Yes -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/424371 Title: Logins to OpenSSH server slow due to "UseDNS yes" config To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/openssh/+bug/424371/+subscriptions -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
