The summary.
MODERN DESIGNS OPTIMISE FOR TRAFFIC BETWEEN MACHINES, NOT IN AND OUT
Measure actual traffic patterns before designing, because that determines where capacity belongs.
BOTH SWITCHES IN A REDUNDANT PAIR MUST BE ON SEPARATE POWER FEEDS
Otherwise switch redundancy is meaningless. And mismatched configuration between a pair causes intermittent faults that are extremely hard to diagnose.
VIRTUAL SEGMENTATION IS NOT SECURITY BY ITSELF
Enforce filtering at the boundary, deny by default, and audit whether rules still match the documentation. You will find temporary rules never removed.
THE MANAGEMENT NETWORK IS COMPLETE CONTROL OF EVERYTHING
It must never reach the internet, must not share the production path, and its firmware must actually be patched.
AUTOMATE READING AND COMPARING BEFORE AUTOMATING CHANGES
That reveals drift without risk. And never apply generated configuration everywhere at once — a template error then affects everything.
ALERT ON LOSS OF REDUNDANCY, NOT ONLY LOSS OF SERVICE
Running on a single path after a silent failure is where the next failure becomes an outage.
