Upon connecting to one of my Ubuntu webservers over Secure Shell, I found the connection was taking a long time to establish. At least that was what I thought. It was easy for my to blame my ISP, but since Web and FTP processes were quick, I didn’t take much time to look into or track down the cause of the SSH delays. One evening while installing new packages and frequently re-connecting to the server, I got tired of the delays and found that the issue was not a bandwidth or connection issue at all, but hat upon connection the server was performing a reverse lookup which took approximately 10 seconds. Various sources on the net advised to disable the reverse DNS lookups and the OpenSSH FAQ agrees.
