Windows 7 Firewall Basics
The Windows 7 firewall controls traffic that your computer exchanges with the network or Internet and it uses rules to control this behaviour. A single firewall rule allows you to control how a specific type of network traffic behaves.
Apart from the basic rules which allow you to control all network traffic between your computer and the rest of the network, you can also set connection security rules in Windows 7 firewall. These rules allow you to control network traffic using IPsec (Internet Protocol Security) and unlike firewall basic rules, both computers participating in a connection must have a connection security rule set or a compatible IPsec policy configured. Windows 7 firewall includes default rules which define what happens if a new connection does not match any other rule. Most firewall rules can be set locally using the Windows Firewall with Advanced Security snap-in or Group Policy.
However, there are rules which users cannot configure through the snap-in or Group Policy and these are built-in rules that prevent services from establishing connections irrelevant to their function. These rules are called Windows Script Host (WSH) rules which are based on an automation technology for Microsoft Windows operating systems that provides scripting abilities to users.
Before the firewall service is started at boot time, Windows 7 apply special filters to all network interfaces to protect the system and reduce the attack surface. The boot-time filters block all unsolicited inbound traffic to your system, with the exception of some required traffic such as, DHCP and it allows all outbound traffic with the exception of some traffic such as, TCP Resets and certain types of ICMPv6.
Continue reading about Windows 7 Firewall here.