free tool — zero signup
SIP ALG Port Scanner
Scans a target from our edge on ports 5060/5061 and 5062, sends a SIP OPTIONS probe, and compares the signaling that comes back. If the Via header comes back rewritten, there's an ALG in the path. No forms, no sales follow-up.
How it works
The scanner opens a TCP session from our edge to your target on each port, sends a standards-form SIP OPTIONS with a unique branch parameter, and compares the Via header in the response with what was sent. Residential and ISP ALGs rewrite Via and Contact — the response betrays them. Port 5062 is probed as the control: ALGs inspect 5060/5061 only, so a clean 5062 leg next to a rewritten 5060 leg is the signature.
Usage — 3 lines
Then scan the same target from our edge with the form — the two perspectives catch different cases.
Scan a target
We probe only the target you give us, reject private/reserved addresses, and keep no scan logs. Ports probed: 5060, 5061, 5062 — TCP.
related troubleshooting
Router-specific ALG fixes
Ribbon SBC 504 Gateway Timeout: Zoom Phone trunk shows offline
Zoom Phone dashboard reports the customer's trunk offline; Ribbon logs 504 Gateway Timeout on inbound signaling.
How to disable SIP ALG on the Comcast Business Gateway DPC3941B
Remote workers behind a Comcast DPC3941B get one-way audio or calls that drop at exactly 32 seconds.
Bypass SIP ALG on a Spectrum Ubee router: home-worker VoIP drops and one-way audio
Spectrum Ubee gateway: remote worker's calls drop at 32 seconds or land with one-way audio.
AT&T Fiber Pace 5268AC: SIP ALG rewriting causes dropped calls at 32 seconds
Calls through an AT&T Pace 5268AC gateway drop at exactly 32 seconds; one-way audio on others.
If the scan confirms ALG rewriting and you'd rather never think about it again — our signaling runs on 5062 for exactly this reason.
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