Files /etc/hosts.allow and /etc/hosts.deny control tcp wrapper permissions for incoming requests to linux servers.
Ftp access is normally controlled by the ‘vsftpd’ line, e.g.:
vsftpd: 138.134.116. 138.134.117.
That would allow ftp connections from IP addresses like 138.134.116.x and 138.134.117.x.
If your IP address is not in the allow list, ftp attempts will fail with an error like this:
421 service not available. Connection closed by remote host.
Domain names can also be specified in these files as well as IP addresses.
Changes take effect immediately, there is no need to restart any services.