SSH server is by default configured to perform reverse DNS lookup every time you try to log in to the server. It cloud slightly improve logging and security, but could significantly increase login time.
Basically, the login prompt will take a while to appear as the server will perform reverse DNS lookup prior to presenting the login prompt to the connecting user.
You can fix this issue by disabling the UseDNS directive on the SSH server from the terminal.
UseDNS
Specifies whether sshd(8) should look up the remote host name
and check that the resolved host name for the remote IP address
maps back to the very same IP address. The default is “yes”.
Steps to disable reverse DNS lookup in SSH:
SSHd configuration file using a text editor. $ sudo vi /etc/ssh/sshd_config [sudo] password for user:
UseDNS directive and set the value to no. UseDNS no
Add the line if it doesn't already exist and remove the # at the beginning of the line if exists.
SSH server service. $ sudo systemctl restart sshd
Guide compatibility:
| Operating System |
|---|
| Ubuntu Linux |
| Debian Linux |
| Red Hat Enterprise Linux |
| Fedora Linux |
| CentOS Linux |
| openSUSE Linux |
| SUSE Linux Enterprise Server |
| FreeBSD |
| OpenBSD |
| NetBSD |
| macOS |
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