📖 ~1 min read
Table of contents
Symptom & Impact
Service is running but remote clients cannot connect, causing outages and failed health checks.
Environment & Reproduction
After new service deployment, interface zone changes, or host rebuild where firewall rules were not restored.
Root Cause Analysis
Port not allowed in active zone, wrong protocol, runtime-only rule lost after reboot, or rich rule conflict.
Quick Triage
Run `systemctl status firewalld`, `firewall-cmd –get-active-zones`, and `ss -tulpen | grep `.
Step-by-Step Diagnosis
Use `firewall-cmd –zone= –list-all`, `firewall-cmd –list-ports`, and `journalctl -u firewalld –since -1h`.
Solution – Primary Fix
Required port appears in the active zone permanently and connectivity succeeds from approved source networks.
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Solution – Alternative Approaches
Add permanent port or service rule, reload firewalld, and if needed add source-specific rich rules.
Verification & Acceptance Criteria
Use `nc -zv ` from client and verify app logs show accepted inbound connections.
Rollback Plan
Remove newly added rules with `–remove-port` or `–remove-service` and reload to restore prior policy.
Prevention & Hardening
Prefer service definitions over raw ports and track approved firewall changes via infrastructure-as-code.
Related Errors & Cross-Refs
`firewall-cmd –zone=public –add-port=8443/tcp –permanent && firewall-cmd –reload`
Related tutorial: View the step-by-step tutorial for rhel-8.
View all rhel-8 tutorials on the Tutorials Hub →
Browse all common problems & solutions on the Tutorials Hub.
References & Further Reading
RHEL 8 firewalld documentation, `man firewall-cmd`, and Red Hat network security hardening guides.
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