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Cisco ASA 5500 Series Configuration Guide using the CLI
Chapter61 Information About High Availability
Failover and Stateful Failover Links

Scenario 3—Recommended

If the ASA data interfaces are connected to more than one set of switches, then a failover interface can be connected to one of the switches, preferably the switch on the secure side of network, as shown in Figure 61-5.
Figure61-5 Connecting with a Secure Switch

Scenario 4—Recommended

The most reliable failover configurations use a redundant interface on the failover interface, as shown in Figure 61-6 and Figure61 -7.
Figure61-6 Connecting with Redundant Interfaces
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Failover link Failover link
Primary ASA Secondary ASA
outside outside
inside inside
ISL
ISL
Switch 3 Switch 4
Switch 1 Switch 2
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Primary ASA Active redundant
failover link
Active redundant
failover link
Standby redundant
failover link
Standby redundant
failover link
Secondary ASA
outside outside
ISL
Switch 1 Switch 2
inside inside
ISL
Switch 5
Switch 3
Switch 6
Switch 4