Common Port Numbers

Port numbers identify a specific service running on a computer. As a best practice, configure your 
firewall to allow only the ports for the services provided on your network (and block all others). The 
following table lists port numbers for common services.

20, 21
File Transfer Protocol (FTP)

22
Secure Shell (SSH)

23
Telnet

25
Simple Mail Transfer Protocol (SMTP)

50, 51
IPSec

53
Domain Name Server (DNS)

67, 68
Dynamic Host Configuration Protocol (DHCP)

69
Trivial File Transfer Protocol (TFTP)

80
HyperText Transfer Protocol (HTTP)

88, 749
Kerberos

110
Post Office Protocol (POP3)

119
Network News Transport Protocol (NNTP)

143
Internet Message Access Protocol (IMAP4)

161, 162
Simple Network Management Protocol (SNMP)

389
Lightweight Directory Access Protocol (LDAP)

443
HTTP with Secure Sockets Layer (SSL)

500 (UDP)

1701 Layer Two Tunneling Protocol (L2TP)

1723
Point-to-point Tunneling Protocol (PPTP)

For example, to allow HTTP traffic (both normal and secure traffic), open ports 80 and 443.