If SSH login is very slow in CentOS 6 it’s because they have added another security feature, the SSH server will do a reverse DNS again for any incoming connection, this will delay connection up to 13 seconds, to avoid this:
1. Access the server
2. Edit the ssh config
Nano /etc/ssh/sshd_config
3. Look for use dns and change it to no
Ctrl +w, usedns, enter
Change it from
#useDNS yes
to
useDNS no
4. Save and close
Ctrl + X, Y, enter
5. Restart the sshd service
Service sshd restart
