Failover and stateful failover links
A failover link and stateful failover link are dedicated connections that
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establish communication between the two units in a failover configuration
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require the same interface to be used between corresponding devices for consistency, and
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transmit critical failover and state information between the paired units.
Configuration recommendations
Cisco recommends to use the same interface between two devices in a failover link or a stateful failover link. For example, in a failover link, if you have used eth0 in device 1, use the same interface (eth0) in device 2 as well.