The Cisco ASA supports two types of failover
The instant a failover happens , all active connections are dropped . Clients will need to reestablish connections when the new
active device takes over
When Stateful Failover is enabled , the active device continually passes per-connection state information to the standby
device . After a failover happens , the same connection information is available at the new active device . Supported user
applications are not needed to reconnect to keep the same connection session .
The state information transmitted to the standby device contains the following :
• The Layer 2 bridge table ( when functioning in transparent firewall mode ) .
• The HTTP connection states ( if HTTP replication is enabled ) .
• The ISAKMP and IPSec SA table .
• NAT translation table .
• TCP connection states .
• UDP connection states .
• The ARP table .