Blocking IP Addresses in a Firewall: Best Practices
Learn how to block abusive IPs without creating broad false positives or long-term maintenance problems.
When blocking makes sense
Blocking is appropriate for clear abuse such as repeated scanning, brute force attacks, exploit attempts, or unwanted automation from dedicated infrastructure.
It is less safe for shared residential, mobile, school, office, or carrier IPs because many users may be behind one address.
How to scope rules
Start with a single IP or narrow range. Expand to a CIDR only when logs prove the broader range is involved.
Add expiration dates to temporary blocks so old incidents do not create permanent access problems.
Review before enforcement
Check IP location, ASN, reverse DNS, risk score, and request behavior. Keep a reason code for every rule.
Crafzo IP Lookup can support the review step before adding a firewall rule.
Frequently Asked Questions
Should firewall blocks expire?
For many incidents, yes. Temporary blocks reduce long-term false positives.
Is blocking a whole country recommended?
Only for specific business or compliance reasons. It can create large false positives.
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