How to test your server network connectivity

When a service does not respond, a few simple commands tell you whether the problem is the network, DNS or the application.

1. ping: is the server reachable?

ping -c 4 example.com

2. traceroute: where does traffic get stuck?

traceroute example.com

3. dig: does DNS answer correctly?

dig example.com +short

4. curl: does the web service respond?

curl -I https://example.com

The HTTP/2 200 header means the server responds correctly.

5. ss: what is listening on the server?

ss -tulnp

How to interpret

• ping fails but curl works: ICMP is probably blocked, not a real problem.
• dig does not return the right IP: a DNS problem, see DNS propagation.
• the port does not appear in ss: the service is not running or listens on another address.
• everything works locally but not from outside: check the firewall.