Why SIP ALG causes problems
Many routers have a feature called SIP ALG (Application Layer Gateway) that rewrites VoIP traffic as it passes through. It is meant to help but usually breaks calls: ringing with no voice when answered, one-way audio, or phones that drop their registration. Our platform handles NAT traversal itself, so SIP ALG is never needed.
Turn SIP ALG off
- ASH NET TP-Link routers (HX510 / VX230v): the VX230v is pre-configured for our home-phone service. If you register your own SIP device behind an ASH NET router and have audio problems, contact us and we will check the ALG setting for you.
- Other routers: log in to the router and look in the advanced, NAT, firewall or security section for SIP ALG, SIP Passthrough or ALG, and turn it off. Reboot the router and the phones afterwards.
Firewall behind NAT
If your router is doing NAT you generally do not need firewall rules for VoIP – outbound registrations keep the path open. Do not port-forward SIP (5060) or RTP ranges to a phone unless you know exactly why; it is rarely needed and complicates things. On the device, leave NAT traversal / keep-alive enabled and disregard the IP and port shown in the SIP messages – they are rarely the ones actually used.
Cannot change the router?
Switching the phone or PBX to encrypted SIP (TLS) stops an ALG interfering because the traffic can no longer be read. Email [email protected] and we will confirm the TLS settings for your line.
Still need help? Email [email protected] or log a ticket in the customer portal.