Inheriting a network you did not design

Inheriting a network designed by somebody else, three IT directors and a decade ago, is more archaeology than engineering. The first 90 days are about understanding, not changing.

Days 1 to 30: Map

Inventory devices. Document interconnections. Build a topology diagram even if a partial one already exists. Pull running configs from every switch, router, and firewall. Look for the hand-jam comments. They tell stories.

Days 31 to 60: Understand

Trace traffic flows. Where does each VLAN go? What is on the management network? Why does that one rule exist? Most networks have at least one config decision that looks wrong but is actually load-bearing.

Days 61 to 90: Plan

Now you can propose changes. List the issues you found. Sort by risk and benefit. Tackle the high-benefit, low-risk items first. Save the architectural changes for after you have built trust with the team.

What not to do

Do not "clean up" config in week one. Half of what looks redundant turns out to be load-bearing. Cleanup belongs after understanding, not during.