CentOS Stream 9 – Common Problem 072 – Diagnosis and Fix

📖 ~1 min read

Table of contents

1. Symptom & Impact
2. Environment & Reproduction
3. Root Cause Analysis
4. Quick Triage
5. Step-by-Step Diagnosis
6. Solution – Primary Fix
7. Solution – Alternative Approaches
8. Verification & Acceptance Criteria
9. Rollback Plan
10. Prevention & Hardening
11. Related Errors & Cross-Refs
12. References & Further Reading

Symptom & Impact

Docker/Podman containers cannot reach the network after firewalld reload.

Environment & Reproduction

firewalld reload flushed the engine’s iptables chains.

Root Cause Analysis

Engine NAT rules removed when firewalld rewrites tables.

Quick Triage

Run `iptables -t nat -L -n` after a firewalld reload to confirm.

Step-by-Step Diagnosis

Inspect engine logs: `journalctl -u docker` or rootful podman.

Solution – Primary Fix

Restart the container engine after firewalld reload.

Solution – Alternative Approaches

Or switch firewalld to the nftables backend with engine awareness.

Verification & Acceptance Criteria

Containers regain network connectivity after the fix.

Rollback Plan

Roll back by disabling firewalld interaction in the engine.

Prevention & Hardening

Standardize on one firewall backend across the fleet.

Related Errors & Cross-Refs

Linked to CNI plugin behavior and bridge networks.

Related tutorial: View the step-by-step tutorial for centos-stream-9.

View all centos-stream-9 tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

firewalld nftables backend documentation.