List of mostly used default ports on the CentOS servers
Port Number - Name
20 - FTP
21 - FTP
22 - SSH
25 - SMTP/EMAIL
26 - SMTP
43 - WHOIS (We don't recommend opening this port)
53 - BIND/DNS
80 - HTTP / Apache Web server
110 - POP3/EMAIL
143 - IMAP
443 - HTTPS / Apache Web server SSL
465 - SMTP/EMAIL SSL/TLS
873 - RSYNC (We don't recommend opening this port)
993 - IMAP/EMAIL SSL
995 - POP3/EMAIL SSL
2030 - CWP Admin
2031 - CWP Admin SSL
2082 - CWP User Panel
2083 - CWP User Panel SSL
2086 - CWP Admin (same as 2030)
2087 - CWP Admin SSL (same as 2031)
2304 - CWP External API SSL (https, only for api access like whmcs )
3306 - MYSQL (We don't recommend opening this port)