Filtering Traffic by Using Windows Firewall

Windows Firewall gives administrators to control over which services can accept the incoming network connections and which networks are allowed to connect to a provide service. Windows Firewall allows all outbound traffic by default, but administrators can also restrict which applications can send traffic. Examples of the types of rules you can create include:

■ On a Domain Name System (DNS) server, allow DNS queries only from internal networks.

■ On an e-mail server, allow any host (including hosts on the Internet) to connect to the Simple Mail Transfer Protocol (SMTP) server on TCP port 25, but allow only hosts on internal networks to connect to the Post Office Protocol (POP) server on TCP port 110.

■ Block all applications and services from initiating an outgoing connection except for Windows Update.

■ Allow hosts on the internal network to ping servers, but block ping requests from external networks.