SIP ALG

What is SIP ALG?

SIP ALG or Application Layer Gateway is a setting that is usually available on most routers.

It is designed to prevent problems with SIP (the protocol behind our VoIP Services) caused by built-in router firewall settings by inspecting VoIP packets and modifying them if required.

Why should I disable it?

This setting is usually enabled by default, and, even though it's meant to assist with VoIP phones and services, it ends up causing more problems than it solves.

Some of the problems you can face with SIP ALG enabled are issues with registrations, failed inbound calls or poor audio quality.

This is usually because SIP ALG has modified the packets and made them unreadable.

As this is the case, we usually recommend SIP ALG is disabled on your router.

Disabling SIP ALG

This setting would usually be configurable via the web interface, however, in some cases, you may need to connect to the router via telnet. If none of these is available, we recommend speaking with your internet service provider.

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Please note, some routers and internet service providers don't have a configurable SIP ALG setting.

What if I can't turn it off?

Unfortunately, if this setting can't be changed and you're still facing issues with VoIP registrations or calls, you may need to switch your router to allow you to disable this setting.