What it is
Why it matters
Most attacks start with a connection from the outside - or a risky app calling out. A well-tuned firewall blocks malware, scans, and suspicious traffic while letting normal work continue.
How it works
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Rules & policies - allow known-good ports, block the rest
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Stateful inspection - track conversations so replies are allowed, fakes are not
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Next-gen features - app awareness, IPS, malware filtering, DNS controls
Good defaults
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On endpoints - enable the built-in OS firewall and block inbound by default
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On routers - close unused ports, disable remote admin from the internet
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For services - put apps behind a reverse proxy or WAF, and limit who can reach admin panels
Quick setup wins
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Start with deny by default - allow only what you need.
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Limit RDP/SSH/VPN to specific IPs - require MFA.
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Turn on logging and alerts - review new blocks weekly.
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Pair with DNS filtering and auto-patching for layered protection.
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Test from the outside - use a port scan to confirm nothing extra is open.