OpenBSD Router on sg105w

This post details my experience with OpenBSD 7.3 on a SOPHOS sg105w Rev.1 from November 2014 as a router and firewall. Preparation The default BIOS settings didn’t let me install OpenBSD without issues. I got spammed with NMI Port messages. The culprit it the BIOS CSM (compatibility support module) which I completely disabled. I configured the whole system to use UEFI. I also enabled the speed stepping and enabled VMX/EPT.