Regardless of cloud provider, an unreachable server almost always falls into one of four categories: the instance itself, network-level filtering, OS-level filtering, or DNS — working through them in that order avoids wasted effort.
Before You Begin
Check your cloud provider’s status page first — a regional outage explains a sudden, simultaneous loss of access far more often than people initially assume.
Step 1 — Confirm the instance is actually running
Check instance/VM state in the console
Confirm it’s not stopped, deallocated, or failing a status/health check.
Step 2 — Check cloud-level network filtering
Review security groups / NSGs / firewall rules
Confirm inbound rules allow the port and source IP you’re connecting from.
Step 3 — Check OS-level firewall
Confirm the instance's own firewall
Use a provider’s serial console/session manager to check without needing normal network access first.
Step 4 — Check DNS if using a hostname
Confirm the hostname resolves correctly
Use nslookup/dig to confirm the domain still points to the correct current IP address, especially after any IP reassignment.
Useful Commands
ping -c 4 your-server-ipnnslookup yourdomain.comFrequently Asked Questions
Should I check DNS or the firewall first?
If you’re connecting by IP address directly, skip DNS and go straight to instance state and firewall rules; DNS only matters when connecting by hostname.
Conclusion
This four-layer order — instance state, cloud-level filtering, OS-level filtering, DNS — applies regardless of which cloud provider you use, and resolves the vast majority of “server unreachable” incidents.
Related Articles
