To facilitate failover, the ASAs participating in failover pass between themselves information about the state of each device. There are two types of failover links:
LAN-based failover links
Stateful failover links
With LAN-based failover links, the failover messages are transferred over Ethernet connections. LAN-based failover links provide message encryption and authentication using a manual preshared key for added security. LAN-based failover links require an additional Ethernet interface on each ASA to be used exclusively ...