Failed Port Scans: Why They Happen and How to Fix Them
When your VoIP system shows failed port scans, a network diagnostic result indicating that external probes couldn’t reach expected communication ports. Also known as blocked SIP traffic, it usually means your calls won’t connect because firewalls, routers, or misconfigured settings are stopping the signal before it even starts. This isn’t just a technical glitch—it’s a silent killer of call quality, especially for businesses relying on VoIP for customer service or remote teams. If your phone system works fine one day and then drops calls randomly, or if your provider says "network issue" without details, you’re likely dealing with failed port scans.
These scans fail for three main reasons: firewall rules, security settings that block unsolicited traffic, often by default, SIP setup, incorrect port configuration for voice signaling, usually port 5060 or 5061, and network address translation, how your router maps internal devices to public IPs, which can break two-way voice communication. Many small businesses think their router is "good enough" and leave it on factory settings. But VoIP needs open, stable ports—and if your firewall treats SIP traffic like a hacker probe, it’ll block it every time. Even a single misconfigured port can stop inbound calls, cause echo, or drop audio mid-conversation.
Fixing this isn’t about buying expensive gear. It’s about checking what’s already there. Start by verifying your VoIP provider’s required ports and ensure they’re open in your router and firewall. Disable SIP ALG—it’s a notorious culprit in home and small office routers. Test your setup with a free online SIP tester. If you’re using a cloud PBX like Nextiva or RingCentral, their support docs have step-by-step port guides. Most failures happen because someone enabled "security mode" without understanding how VoIP works. You don’t need to be a network engineer to fix this—you just need to know where to look.
The posts below give you real fixes: how to configure your router for SIP traffic, why your firewall keeps blocking VoIP even after opening ports, how to spot SIP ALG problems in common brands like TP-Link or Netgear, and what to do when your ISP is the one blocking ports. You’ll also find guides on testing your network before and after changes, and how to avoid common mistakes that make failed port scans come back—even after you "fixed" them. This isn’t theory. These are the exact steps users took to get their calls working again.
