Disabling reverse DNS lookup for openSSH
Sometimes SSH to servers takes considerable time. This can be due to delay problems with DNS servers. If we are on local LAN and there are no DNS hostnames assinged to various machines then there is no point in having DNS checks for SSH. In such cases DNS checks can be disabled to increase SSH speed. To disable DNS reverse lookup checks edit '/etc/ssh/sshd_config' file on SSH server and use:
On clients edit '/etc/nsswitch.conf' file and ensure that hosts line looks like
hosts: files dns
that is uses nis, nisplus, mdns etc. do not get used for host to IP resolution.