Solution to slow CentOS ssh connection

When we reinstall the machine, we often encounter a situation where the ssh connection is slow, and it takes about half a minute or longer. However, the ping speed is also very good, and people mistakenly think that ssh cannot be connected. The following describes how to solve this problem. the most common reason is that the server's sshd will go to the DNS to find the hostname for accessing the client IP address. If the DNS is unavailable or there are no relevant records, it will take a lot of time. Disable ssh dns anti-resolution, edit the/etc/ssh/sshd_config file on the server, and add a line: useDNS no2. problems may also occur in authentication gssapi-with-mic. Modify GSSAPIAuthentication no in the/etc/ssh/sshd_config file on the server.