How would you systematically find the single points of failure in an existing network?
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Say this first
Pick the business-critical flows and walk each one end to end, physically and logically, asking at every element what happens if it fails and how long recovery takes. Include power, fiber routes, carriers, control planes, shared services and people, not just devices. Record each finding with impact, likelihood and cost to fix, then prove the redundancy you believe in with a planned failover test.
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Method
- List critical services with the business: payments, voice, the ERP, the warehouse scanners.
- Trace each path from user to server and back: access port, uplinks, distribution, core, firewall, WAN or internet, data center, the server, and the return path.
- At each hop ask what fails it (device, link, power, software, config) and what happens: does it fail over automatically, how fast, and has anyone ever tested it?
- Check shared risk. Two links are redundant only if they do not share a conduit, a building entry, a carrier exchange, a line card or a PDU. Carriers call this a shared risk link group (SRLG). Ask carriers for route maps of the circuits, not just two circuit IDs.
- Check what the path depends on: DNS, DHCP, RADIUS, NTP, certificates, the wireless controller, licensing, a cloud controller.
- Check people and process: who can fix it at 3 a.m., where are the credentials, are configs backed up, are there spares and support contracts.
Output
A SPOF register: item, impact, likelihood, current recovery time, fix, cost and decision (fix now, plan, or accept with a named owner). Review it after every incident.
Prove it
Planned failover tests in a maintenance window: pull the primary link, power off the active firewall, fail the primary RADIUS server. Most hidden SPOFs are found by tests, not by drawings.
They will ask next
The business will not pay to remove every SPOF. What then?
Rank by impact and probability, fix the cheap high-impact ones, and for the rest get the risk accepted in writing by the service owner. Then shrink recovery time: spares on site, a 4 hour support contract, out-of-band access and a tested runbook. Lower MTTR improves availability even when the SPOF stays.
Traps
- Trusting the diagram. Two lines on a drawing can be one fiber in the ground.