ping + traceroute answer “which layer is broken?” — read the patterns, don’t guess:

Symptom	Diagnosis
ping gateway fails	wrong IP/mask — host can’t even reach the local router
gateway ✅ but 8.8.8.8 ❌, traceroute dies at hop 0	missing/wrong default gateway
ping 8.8.8.8 ✅, ping google.com ❌	DNS — the network is fine
ping timeout, traceroute stars after hop N	firewall eating ICMP; traffic likely still flows
traceroute dies mid-path	missing return/forward route at that device

Discipline: start local, move hop by hop, change one variable at a time, and remember ICMP silence ≠ outage (rate limits, ACLs). Verify a fix by reproducing the original failure scenario, not just the ping.