There are certain domains pointing to my server.
# example.com example.com goes to 20.20.20.20 I want to deny ssh access using this domain names. I want my server to only accept ssh connections on 20.20.20.20. How can I configure this?
# /etc/ssh/sshd_config UseDNS no Example:
If user1 connects to 20.20.20.20 then it should show the login, otherwise it should just drop all connections.
I am on a Debian Distribution.
You can't. What you ask is impossible in SSH.
It's possible in HTTP, because HTTP/1.1 sends a Host header to tell the server which (virtual) host to connect to. SSH sends no such field. You can see this using the Wireshark network protocol dissector.
If it was possible to do this, obviously it wouldn't provide any additional security.
Please briefly describe why you are trying to perform a given task (I think StackExchange advises this). I wouldn't say you tend to get nasty pile-ons without constructive explanations here. (Um. In light of that: if you're looking at SSH hardening in general, a common & robust solution is to deny password logins and instead use an SSH key stored on your computer).
UseDNSoption on the server makes a reverse DNS lookup of the IP address of the connecting client and then a forward DNS lookup for the resulting name and looks if the result is the IP again. In a time where every dial-up connection has a valid DNS entry and cloud instances with proper DNS records are used for SSH scans, this option is not very helpful anymore.