In network security, the Access Rule refers to a list of ports and services that are available on a host or network appliance. Both inbound and outbound traffic are controlled via the Access Rules to allow or disallowed to use the network service.

On NetDefend Firewalls, the Access rule is capable of monitoring traffic to verify that packets arriving on an interface of the firewall do not have a source address which is associated with a network of another interface, meanwhile the Access rule set act as an add-on filter to the firewall's rules list, and ensures that the source addresses of packets received on a specific interface are always within the correct network, provided that the Access rule is correctly configured.