I can't understand why a switch would be configured to Fail Open? Surely an attacker could easily exploit this by MAC Flooding which will cause the switch to act like a hub and broadcast messages to all network interfaces?

The only reason I can think of is to prevent any critical systems to fail from loss of communication if a switch was configured to Fail Safe?

I would appreciate your thoughts on which contexts would it ever be appropriate for switches to be configured to Fail Open?

  • 4
    with one flood, an attacker could shut down the whole switch
    – schroeder
    Commented Mar 31, 2016 at 21:39

1 Answer 1


...because a switch is a Connectivity device, not a Security device. It is designed to enable communication, not to secure the network. That design bias emphasizes availability over security in situations where both are threatened.

Much pain would be avoided if people would remember that when designing networks.

  • 4
    I concur. We had decades of getting devices to talk to each other at all costs before we actually realized the need for security practice in network design. This coincided with an increase in network threats.
    – armani
    Commented Mar 31, 2016 at 22:04
  • Of course there was little reason to secure anything for decades (indeed many individuals on networks actively discouraged information hiding). (okay maybe not decades, but long enough) Commented Apr 1, 2016 at 16:05

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