Quick lookup.
NO CONNECTIVITY AT ALL
Link, then address, then gateway.
SOME SITES WORK, OTHERS DO NOT
DNS, or a path problem to those destinations.
NAMES DO NOT RESOLVE BUT ADDRESSES WORK
DNS. Check resolvers and test against a public one.
SLOW EVERYWHERE, WIRED INCLUDED
Connection saturation, router, or the connection itself.
SLOW ON WIRELESS ONLY
Wireless: signal, interference, or device count.
INTERMITTENT ACROSS ALL DEVICES
Cabling, overheating, address conflict, or failing equipment.
TWO DEVICES MISBEHAVING TOGETHER
Address conflict.
CALLS POOR, DOWNLOADS FINE
Saturated upload, or jitter.
SITE LOADS BUT CERTIFICATE WARNING
Certificate coverage, or the device clock.
CONNECTION REFUSED
Host reachable, service not accepting.
CONNECTION TIMED OUT
Host unreachable, or traffic filtered.
MAIL NOT DELIVERED
Read the bounce. It usually states the reason.
WHAT TO DO IN EVERY CASE
Establish what changed.
