已知的TCP/UDP端口可以在wikipedia上找到: List of TCP and UDP port numbers, 太多了，按组列举了最常用的，如下:
FTP:21
SSH:22
Telnet:23
SMB:445
RDP:3389
SMTP:25
SMTP email submission: 587
SMTP over TLS/SSL:465
POP3:110
POP3 over SSL:995
IMAP4:143
IMAP4 over SSL:993
DNS:53
HTTP:80
HTTPS:443
Tomcat:8080
MSSQL:1433
Oracle:1521
MySQL:3306
PostgreSQL:5432