I read somewhere in the forum about someone who configured one network port with a different ip-range, to be able to access the box in a situation just like this.
Found it: https://forum.opnsense.org/index.php?topic=23222.0
Found it: https://forum.opnsense.org/index.php?topic=23222.0
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I set one up with a simple pass rule just in case I lock myself out of the other LAN port.
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