Connection security involves the authentication of two computers before they begin communications and the securing of information sent between two computers. Windows Firewall with Advanced Security uses Internet Protocol security (IPsec) to achieve connection security by using key exchange, authentication, data integrity, and, optionally, data encryption.
Unlike firewall rules, which operate unilaterally, connection security rules require that both communicating computers have a policy with connection security rules or another compatible IPsec policy.
Connection security rules use IPsec to secure traffic while it crosses the network. You use connection security rules to specify that connections between two computers must be authenticated or encrypted. You might still have to create a firewall rule to allow network traffic protected by a connection security rule.
For more information, see Understanding Connection Security Rules (http://go.microsoft.com/fwlink/?linkid=137809) in the TechNet Library.