Stateful Firewall Cluster High Availability Theater
Dmitry Perets wrote an excellent description of how typical firewall cluster solutions implement control-plane high availability, in particular, the routing protocol Graceful Restart feature (slightly edited):
Most of the HA clustering solutions for stateful firewalls that I know implement a single-brain model, where the entire cluster is seen by the outside network as a single node. The node that is currently primary runs the control plane (hence, I call it single-brain). Sessions and the forwarding plane are synchronized between the nodes.




