Active ASA and standby ASA communicates through failover link. If active ASA detects its interface to switch is down, then it tells the standby ASA and the standby ASA becomes active.

How does the switch connected to both ASAs know to divert traffic to standby ASA which becomes active after the interface to the original active ASA is down? Any required configuration on the switch?

1 Answer 1


Switches only forward frames based MAC address. The secondary ASA takes over the MAC address of the failed ASA.

Cisco has an explanation of the process.

  • So, while the standby ASA is in standby, let's say I ping the active ASA's IP address from a computer X connected to the switch. So, the switch will broadcast the ARP to all interfaces except the interface to X. Only active ASA reply the ARP?
    – Ron Vince
    Commented Oct 14, 2015 at 14:08
  • 1
    That is correct. Only the active ASA responds to the active IP address with the active MAC address. When a failover occurs, the standby ASA becomes the active ASA and responds.
    – Ron Maupin
    Commented Oct 14, 2015 at 14:11

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