Stateful firewall and connection tracking
On the firewall, connection tracking allows for stateful packet inspection.
Stateless firewalls filter packets in isolation, is based on static source and destination information. In contrast, stateful firewalls track the state of network connections and traffic flows and allow or restrict traffic based on whether its connection state is known and authorized. For example, when an initiation flow is allowed in one direction, the responder flow is automatically and implicitly allowed in the return direction. While typically slower under heavy load than stateless firewalls, stateful firewalls are better at blocking unauthorized communication.
By default, the vRouter firewall is stateless. If you want the firewall to operate stateless in general, you can configure state rules within a specific rule set. Alternatively, you can configure the firewall globally to operate statefully. For more information, refer to security firewall global-state-policy <protocol>.
For all protocols, the following are tracked for each session: interface, protocol, source address, and destination address. For ICMP, the ICMP identifier is also included. For TCP/UDP/UDP-Lite/DCCP/SCTP, the source and destination ports are also included.