SIP ALG on DrayTek Routers

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SIP ALG usage on DrayTek Routers

DrayTek routers have a SIP ALG (Application Layer Gateway) to help SIP route the audio through NAT, this is Disabled by default and can be enabled by following the steps shown in this guide.

The SIP ALG facility is able to modify SIP packets that it identifies and modifies the IP address details in the SIP header information. Without SIP ALG, the SIP header information would contain the private IP address of the VoIP client / phone, which could stop audio from being routed correctly by the remote side of the call. The router modifies the packet to contain the public IP address of the router so that the remote side sends audio to the router's public IP address which is then passed through NAT to the client.

Current Products

In the [NAT] > [ALG] menu, the router's SIP and RTSP (not RTP) ALG services can be enabled.

Enabling the SIP Protocol option and clicking OK will enable the router's SIP ALG facility.

Change the Listen Port from the default of 5060 will change the port that the router will monitor for SIP packets to modify, for instance if your SIP provider or hosted PBX uses port 5070 instead, specify it here.

The TCP and UDP options control the protocols that the SIP-ALG will monitor.

DrayOS F/W 3.8.0 and later

Access the router's web interface and click the Web Console button in the upper right menu:

This will then pop-up the router's Web Console, enter these commands to change the SIP ALG configuration:

sys sip_alg ? - to check the current status, the default state will have the SIP ALG Disabled
sys sip_alg 1 - to enable the router's SIP ALG functionality
sys sip_alg 0 - to disable the SIP ALG if needed.
sys sip_alg port 5070 - to change the SIP ALG listening port to 5070 (Requires 3.8.0 or later firmware), default listen port is 5060

DrayOS up to F/W 3.7.9

On Windows go to the Start menu, select Run and on there type "cmd" and click OK, or if the Run option is not present, type "cmd" in the "Start Search" textbox above the Start button and press enter. Make sure that telnet is enabled in Windows, check this guide if it isn't available. Other operating systems also have an equivalent telnet program or app.
Type "telnet 192.168.1.1" (Replace 192.168.1.1 with your own router's IP address if you have changed it)
Enter the username of "admin", press enter, then enter the password for the router.
Enter "sys sip_alg ?" to check the current status - it should be disabled on a router from factory default settings.
To enable SIP ALG, enter "sys sip_alg 1"
Enter "sys sip_alg ?" to check the status of SIP ALG, it should now show as enabled. This will take effect immediately.
Enter "sys sip_alg 0" to disable the SIP ALG if needed.

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