Given the NIB configuration shown below, what is the most likely reason that after a link failure for ent0, there was no automatic failover to ent2?

The Alternate Address setting controls whether a virtual MAC address is used during failover, but its absence does not prevent the failover detection mechanism from triggering.

NIB uses a configurable 'Internet Address to Ping' to actively probe reachability through the primary adapter. When no ping address is specified, NIB has no mechanism to detect that ent0's link has failed, so the failover condition is never triggered and traffic continues to attempt to use the failed primary interface.

'Automatically Recover to Main Channel' governs behavior after a failover has already occurred (returning to ent0 when it recovers), not the initial detection and switchover to the backup.

Mismatched media speeds between ent0 and ent2 would cause performance issues but would not disable the NIB failover detection mechanism itself.