tcpd is use to access control facility for internet services. The tcpd program can be set up to monitor incoming requests for telnet, finger, ftp, exec, rsh, rlogin, tftp, sshd and other services that have a one-to-one mapping onto executable files. Your sshd server must be configuring (compiled with) to support tcpd.
You can find out tcpd (tcpwrapper) support easily with following command:
# strings $(which sshd)| grep libwrap
libwrap.so.0 libwrap refuse returns
If you get output libwrap (as above) then you can use tcpd as follows. Open file /etc/hosts.deny in text editor. This file list of hosts/IPs that are not allowed to access the system. In your case you will block sshd (port 22). Let us say you would like to deny access to IPs 18.104.22.168 22.214.171.124 126.96.36.199.
# vi /etc/hosts.deny Add/append following line to file:
sshd: 188.8.131.52 184.108.40.206 220.127.116.11Save and exit to shell prompt. Next make sure your rules are correct with the following command:
# tcpdchk -v
Using network configuration file: /etc/inetd.conf >>> Rule /etc/hosts.deny line 20: daemons: sshd clients: 18.104.22.168 22.214.171.124 126.96.36.199 access: denied
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