SIP ALG, or Session Initiation Protocol Application Layer Gateway, is a feature found in some network routers designed to inspect and modify SIP traffic. While its intention was to improve VoIP performance by handling NAT traversal issues, it often causes more problems than it solves, leading to one-way audio, call drops, and registration failures. This article explains what SIP ALG does, why you should disable it, and provides step-by-step instructions on how to do so on common router models.

What is SIP ALG?

SIP ALG is a network function that attempts to manage SIP traffic by rewriting SIP headers and SDP (Session Description Protocol) payloads. It tries to adjust IP addresses and ports in SIP messages to ensure that VoIP calls can traverse NAT devices correctly. However, this process often leads to misconfigurations and inconsistencies in the signaling and media streams.

Why Should You Disable SIP ALG?

Disabling SIP ALG is recommended for several reasons:

  • One-way audio: SIP ALG can cause one party to hear the other but not vice versa, disrupting communication.
  • Call drops: Incorrectly modified SIP messages can lead to frequent disconnections during calls.
  • Registration failures: SIP ALG may interfere with the registration process between your VoIP device and the service provider, preventing successful call setup.

How to Disable SIP ALG on Common Routers

ASUS Routers

  1. Login to your ASUS router's web interface by entering its IP address in a web browser (commonly 192.168.1.1).
  2. Navigate to the "Advanced Settings" section.
  3. Go to the "WAN" tab and then select "Virtual Server/WAN Port Forwarding".
  4. Scroll down to find the "SIP ALG" option and set it to "Disable".
  5. Click "Save" or "Apply" to save your changes.

Netgear Routers

  1. Access the Netgear router's web interface by entering its IP address in a browser (commonly 192.168.0.1).
  2. Log in with your administrator credentials.
  3. Navigate to "Advanced" and then select "QoS & Management".
  4. Click on the "Port Forwarding/Port Triggering" tab.
  5. Scroll down to find the "SIP ALG" option and disable it.
  6. Save your settings by clicking "Apply" or "OK".

TP-Link Routers

  1. Open a web browser and enter the router's IP address (commonly 192.168.0.1).
  2. Login with your administrator credentials.
  3. Go to "Advanced" in the top menu and then select "NAT".
  4. Click on "Virtual Servers/Port Forwarding".
  5. Look for the "SIP ALG" option and disable it.
  6. Save your changes by clicking "Save" or "OK".

Ubiquiti Routers (EdgeRouter)

  1. Access the EdgeRouter's web interface via a browser using its IP address.
  2. Login with your administrator credentials.
  3. Navigate to "Config Tree" in the top menu and expand it.
  4. Go to "service" > "nat" > "rule" and find the SIP ALG rule (usually under a specific interface).
  5. Delete or disable the SIP ALG rule by clicking on the "-" icon next to it.
  6. Commit your changes by clicking "Save" at the top of the page.

Troubleshooting

If you encounter issues disabling SIP ALG, ensure that you are logged in with administrative privileges and have saved all changes. If problems persist, consult your router's user manual or contact Internetport support for further assistance.