Tools

VoIP firewall and NAT readiness checker

Last reviewed September 4, 2026

Use this checker before changing a router or firewall for VoIP. Answer what you know. The tool will show urgent risks, items to confirm, and helpful checks already in place.

This is not a network scan. It cannot see your router, firewall, phone system or provider. Your answers stay in this browser tab and are not sent to Phone Guides.

VoIP firewall and NAT readiness checker

Answer what you know. This tool does not scan your network or change your firewall. It checks your answers against common VoIP risks and keeps them in this browser tab.

Where is the phone system?

Are the required signalling and media ports documented?

What is the SIP ALG setting?

How is SIP signalling protected?

How are inbound firewall rules handled?

What is the internet NAT path?

Can voice devices reach working DNS and time services?

Choose the answers that best describe the network, then check the result.

What this checker cannot prove

A browser cannot reliably confirm open ports, NAT behaviour, call routing, audio flow, provider access lists, or whether SIP ALG is active. Confirm the result in the router or firewall, compare it with the provider guide, and make test calls.

Use the result safely

Needs attention: fix the urgent items before a rollout or exposed internet service.
Review before rollout: confirm the uncertain items with the provider and network administrator.
Good starting point: the answers do not show a common problem, but you still need to test the real service.

Do not open broad internet-facing ports just to make a test pass. Use the provider's documented ports and source addresses. Record the old settings before a change so you can roll back.

Test after a change

Make incoming and outgoing calls. Check ringing, call setup, two-way audio, transfers, hold, voicemail and calls that last longer than the firewall's normal session timeout. Confirm emergency-calling procedures separately.