Is anything working.
WHAT TO CHECK IN ORDER
Is the cable connected or the wireless associated? Does the device have an address? Can it reach its gateway? Can it reach an external address? Can it resolve a name? Can it reach a specific service?
WHY THAT ORDER
Each depends on the previous one.
WHAT EACH FAILURE MEANS
- No address: the device is not getting one, or the link is down
- Cannot reach the gateway: local network or configuration
- Can reach the gateway but nothing beyond: the connection or the router
Can reach an external address but not resolve names: DNS
Can resolve but not reach a service: that service or a blocked port
THAT SEQUENCE
Locates almost every fault in a few minutes.
WHAT TO TEST AN EXTERNAL ADDRESS WITH
A known reliable address, by number rather than name.
That separates connectivity from name resolution.
WHAT TO DO WHEN YOU FIND THE LAYER
Investigate there, not elsewhere.
WHAT NOT TO DO
Reconfigure everything at once.
