VoIP Phones - Disabling SIP ALG

🔧 SIP ALG – What It Is and Why It Causes VoIP Problems

Most routers include a feature called SIP ALG (Application Layer Gateway). It’s meant to help VoIP calls work better by adjusting network traffic. Unfortunately, in many cases, it causes more harm than good.

âť— What SIP ALG Does

SIP ALG tries to rewrite the IP addresses in VoIP traffic, converting your internal IP address into your public IP address. But many routers do this incorrectly, and instead of fixing things, they rewrite everything — which breaks the call connection.

⚠️ Common Problems Caused by SIP ALG

If SIP ALG is causing issues, you might experience:

  • Calls dropping after a few minutes
  • Calls ending when put on hold or transferred
  • Inbound calls not being received
  • Outbound calls failing
  • Calls with no audio or one-way audio
  • Phones that keep ringing after a call has already been answered

âś… Best Fix: Disable SIP ALG on Your Router

The simplest and most effective solution is to disable SIP ALG on your router.

How to Disable SIP ALG:

  1. Open your web browser.
  2. Enter your router’s IP address (usually something like 192.168.0.1 or 192.168.1.1).
  3. Log in using your router’s username and password (often printed on the back).
  4. Look for SIP ALG in the settings (often under Advanced > Firewall or NAT).
  5. If you find it, disable it and save your changes.

📶 Routers That Allow SIP ALG to Be Disabled

These routers usually allow you to turn SIP ALG off:

  • Technicolor / Thomson / SpeedTouch
  • Draytek
  • Netgear
  • Juniper / Netscreen
  • Cisco 800 Series
  • Linksys WRT610N
  • Zyxel 660

đźš« Routers That Do Not Allow SIP ALG to Be Disabled

Some routers don’t offer the option to turn it off:

  • D-Link DIR-655
  • Motorola SBG6580
  • BT Home Hub
  • Virgin Media Super Hub

If you're using one of these, you may need to:

  • Replace it with a router that allows disabling SIP ALG
  • Use a different router for your VoIP system

🔍 Not Sure About Your Router?

If your router isn’t listed here, try searching online:

[Router Make and Model] + "disable SIP ALG"

You’ll often find a guide or forum post with exact instructions.