Practice
Troubleshooting guides
Each guide is an ordered sequence of checks that narrows the fault instead of guessing. The order matters: the early steps are the ones that most often end the investigation.
User cannot sign in
Authentication fails for one user, or for a group of users, across one or more applications.
7 checks
NetworkingDevice cannot reach the internet
A device has no connectivity, or reaches some destinations but not others.
6 checks
DNSDNS resolution failure
Names fail to resolve, resolve inconsistently, or return unexpected addresses.
6 checks
VPNVPN will not connect
Remote access fails to establish, or connects but cannot reach internal resources.
6 checks
EmailEmail delivery failure
Outbound mail is rejected or quarantined, or expected inbound mail never arrives.
6 checks
EndpointsDevice will not enrol
Enrolment fails during provisioning or when a user attempts to register a device.
6 checks
WindowsServer storage full
A volume is out of space, causing service failures, failed logins or stalled backups.
6 checks
ApplicationsApplication unavailable
Users report an application is down or unusably slow.
6 checks
A method that works on anything
- 1. Establish scope. One user, one device, one site, or everyone? Scope eliminates most causes immediately.
- 2. Establish timing and change. What changed, and when did it last work? Most incidents follow a change.
- 3. Work bottom up through the layers. Link, address, name resolution, routing, transport, authentication, application.
- 4. Read the log the system already wrote before forming a theory.
- 5. Change one variable at a time, and record what you changed.
- 6. Fix the cause, not just the symptom, then write it down so the next person does not repeat the investigation.