Think this correct but its been along time since I worked with HSRP
The Preempt command will not cause an issue if it is configured on both interfaces, however is not normally needed on both. The interface with the highest priority should have the preempt command. This is the interface you want to bring back up as the primary interface so you want to 'preempt' this intialization
You can check your router by typing 'Show standby' to see which router is active
Hopefully I can clear this up. If the active router fails, the standby router assumes the active router role - simple enough. When the former active router returns, even though it may have a higher priority, the new active router will remain the active router - by default.
If you enter the 'preempt' command, it forces the former active router to take charge again because it has a higher priority. The other router would therefore go back to being a standby router as it was at the start.
In response, to your question, if the preempt command was entered on both interfaces in a HSRP configuration, I would guess that the router with the highest priority would assume the active router role. In the case of routers with equal priority, the router with the higher IP address becomes the active router.
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