Methods of screening incoming packets are provided. A first firewall detects a tunnel formation. A second firewall maintains a list of open firewall sessions. Each tunnel has one or more associated firewall sessions. The first firewall detects variable situations, such as when the tunnel is torn down, and notifies the second firewall so that, for example, the second firewall can act to clear an associated firewall session from the firewall session list. Incoming packets that are associated with firewall sessions that have been cleared from the firewall session list may not be passed through the second firewall.