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SIP ALG: Understanding the Challenges and Solutions for VoIP

5/15/23 1:24 PM / by Viirtue

Session Initiation Protocol Application Layer Gateway (SIP ALG) is a feature found in many routers and firewalls, designed to assist with VoIP traffic. While its intentions may be good, SIP ALG often causes more problems than it solves for IT professionals, particularly when working with VoIP platforms. In this blog post, we'll delve into the specifics of SIP ALG, explore which routers have it enabled by default, discuss how to disable it, and highlight the symptoms it can cause when improperly configured. We'll also cover how Viirtue's support team can help diagnose and resolve these issues.

What is SIP ALG?

SIP ALG, or Session Initiation Protocol Application Layer Gateway, is a feature in routers and firewalls that is intended to help facilitate VoIP communication. It works by inspecting and modifying VoIP traffic to improve compatibility and traversal across network address translations (NAT). However, modern VoIP platforms have advanced NAT traversal techniques built-in, making SIP ALG unnecessary and often problematic.

Routers with SIP ALG Enabled by Default

Several routers have SIP ALG enabled by default, including models from popular brands like (bonus: click the hyperlink for access to guides and manufactuer support portals):

  1. Cisco
  2. Linksys
  3. Netgear
  4. D-Link
  5. TP-Link

It's essential to check your router's documentation or manufacturer's website to determine if your specific router has SIP ALG enabled by default.

Symptoms of SIP ALG-Related Issues

When SIP ALG is enabled on a router or firewall, it can interfere with VoIP platforms and cause various issues, such as:

  1. Dropped calls
  2. One-way audio
  3. Inability to register with a VoIP service
  4. Difficulty in establishing or maintaining a call
  5. Call transfer failures

Disabling SIP ALG

To resolve these issues, you can disable SIP ALG on your router or firewall. This process varies depending on the specific device, so consult your router's documentation or manufacturer's website for a detailed guide. In general, the steps involve:

  1. Logging into your router's administration interface
  2. Navigating to the settings related to NAT, firewall, or VoIP
  3. Disabling or unchecking the SIP ALG option
  4. Saving and applying the new settings

How Viirtue's Support Team Can Help

Viirtue's support team is comprised of experienced IT professionals who are well-equipped to diagnose and resolve SIP ALG-related issues. If you're experiencing problems with your Viirtue VoIP platform, reach out to the team at for assistance. They can help you identify whether SIP ALG is causing the issue and guide you through the process of disabling it on your specific device.


SIP ALG is a feature that, while well-intentioned, often causes more harm than good when it comes to VoIP platforms. If you're an IT professional working with VoIP systems, it's essential to understand the implications of SIP ALG, how to disable it, and the symptoms it can cause. For assistance in diagnosing and resolving these issues, don't hesitate to contact Viirtue's support team at

Tags: troubleshooting

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