Firewall Log Analysis for Security Monitoring

Firewall logs record allowed and denied network connections — a valuable source of security intelligence. Regular review catches unauthorized access attempts, compromised devices calling home to malware C2 servers, and policy violations. What to look for in firewall logs: repeated denied inbound connections to the same port (port scanning), internal devices making connections to known malicious IPs (indicates infection), unusual outbound traffic on non-standard ports, and successful connections to unexpected destinations. Practical approach for small businesses: configure the firewall to send logs to a syslog server or cloud logging service. Use a tool like Graylog (open source) or the firewall's built-in reporting to visualize top talkers, top denied destinations, and traffic over time. Review weekly for anomalies. Enable geo-blocking for countries your business has no legitimate traffic to/from — this reduces noise in logs and blocks a significant volume of automated scanning. Set up email alerts for critical events like admin login failures, WAN failover events, and high-severity IDS signatures.