20,21: FTP. Note that ftp will use a "random high port number" if the client is in PORT mode, so you may need to add a port range into your /etc/proftpd.conf file to allow ftp connections, eg:
PassivePorts 35000 35999
and then open that port range as well in your firewall.
22: ssh...
There was a time when I was about to select a firewall for a server which had DirectAdmin installed and I choosed CSF. CSF is one of the best firewall available for hosting servers.
Installation of CSF in directAdmin is really easy, just download csf.
Extract it
and Install it
Just a 3...
[root@mailserver csf]# service csf status
Status of csf:Can't locate LWP/UserAgent.pm in @INC (@INC contains: /usr/local/cpanel /etc/csf /usr/lib64/perl5/site_perl/5.8.8/x86_64-linux-thread-multi /usr/lib/perl5/site_perl/5.8.8 /usr/lib/perl5/site_perl...