Stateful Failover
In stateful failover mode, more information is shared about the connections that have been
established with the standby unit by the active unit. The active unit shares per-connection
state information with the standby unit. If and when an active unit fails over to the standby
unit, an application does not reinitiate its connection because stateful information from the
active unit updates the standby unit.
Replicated state information includes the following:
■ TCP connection table, including timeout information for each connection
■ Translation (xlate) table and status
■ Negotiated H.323 UDP ports, SIP, and MGCP UDP media connections
■ Port allocation table bitmap for PAT
■ HTTP replication
Because failover cannot be prescheduled, the state update for the connection is packet-based.
This means that every packet passes through the Security Appliance and changes a
connection’s state and triggers a state update.