ssh login has much delay until the password is prompted in Red Hat Enterprse Linux 6

Issue

• Whenever i try to login into ssh server, it delays more than 20 seconds.
• We are using the password authentication, and it takes much time until the password is prompted.
• Server processing is very slow. when try to connect through SSH and SFTP (WinSCP) password option take long time (approxe-20-30 sec.)