Diagnostic Tools
The toolkit, in the order to use them. Every one of these is worth ten guesses.
ping — "are you there?"
ping -c 4 192.168.1.1
ping -c 4 8.8.8.8
Sends echo requests, reports replies and round-trip times.
Check (verified): 4 packets transmitted, 4 received, 0% packet
loss.
The two-ping test: 8.8.8.8 needs no DNS (it's a bare address), so
ping 8.8.8.8 working while names fail = DNS problem, network fine.
Neither working = network problem. One command, total clarity.
traceroute — "show me the path"
traceroute example.com
Hop-by-hop itinerary (see The Path to the Internet). Use when ping works but things are slow — it shows where.
ss — "what's listening here?"
ss -tln
Check (verified shape): lists listening TCP ports. "My server won't connect" → is it even listening? This answers in one line.
curl — "talk to it like a client"
curl -I http://192.168.1.50:8080 # headers only: is the web server answering?
curl -v http://192.168.1.50:8080 # verbose: DNS, connect, TLS, headers — the full story
curl -v is a network education in one command: watch it resolve
the name, open the TCP connection, negotiate TLS, and send the
request. When a web service misbehaves, -v shows exactly which
stage failed.
dig — "what does DNS say?"
dig +short example.com # just the address
dig example.com # the full exchange: server, TTL, timing
When names misbehave, dig shows what the resolver actually
returned — versus what you assumed it returned.
ip — "what's my network config?"
ip -brief addr # my addresses (verified)
ip route # how do I reach things? (shows the default gateway)
ip route output centers on the default via 192.168.1.1 line —
that's your router, the door everything leaves through. No default
route = no internet, and now you know the exact sentence to search.
The 60-second diagnosis order
ping -c 2 127.0.0.1— is my own network stack alive? (verified)ping -c 2 192.168.1.1— can I reach the router?ping -c 2 8.8.8.8— can I reach the internet? (no DNS needed)getent hosts example.com— does DNS work?traceroute example.com— where does the path break?
The first failure in that sequence is the diagnosis. Don't skip steps — each one rules out a layer.