SIP ALG (Application Layer Gateway) is a router or firewall feature that inspects and modifies SIP packets by replacing private IP addresses with public ones. While it was designed to help older VoIP systems work behind NAT/firewalls, it often causes problems like one-way audio, failed calls, and registration issues in modern VoIP setups

Why Disable SIP ALG?

• Modern VoIP systems use NAT traversal methods (STUN, TURN, ICE) that don’t require router intervention
• Misinterpretation of SIP headers can cause calls to be routed incorrectly or dropped
• Common symptoms include:
  • One-way or no audio
  • Call connection failures
  • Phones ringing but not answering
  • BLF/MWI issues
  • Registration failures less you are using a dedicated Session Border Controller (SBC) 

How to Disable SIP ALG on a Euro Router

Euro routers may be based on common brands (e.g., TP-Link, D-Link, Arris, Cisco). Here are general steps for similar models:

1. Access the router’s admin interface
   • Connect to the router’s LAN and open a browser.
   • Enter the admin IP (often 192.168.0.1 or 192.168.1.1).
2. Navigate to ALG/Application Level Gateway settings
   • Look for Advanced Settings → Firewall or ALG Configuration.
3. Disable SIP ALG
   • Uncheck or set SIP ALG to Disabled.
   • Some routers also require disabling SIP Passthrough or NAT Passthrough for SIP
4. Save and apply changes
   • Click Apply or Save.
   • Restart the router if prompted.
5. Verify the change
   • Check the ALG settings again to ensure SIP ALG is off.
   • Test VoIP calls to confirm issues are resolved.

If You Can’t Find SIP ALG Settings

• Check the WAN/NAT or Application Control sections.
• If the router is a gateway (e.g., Arris, TP-Link V3/V4), look under Advanced → Options or Firewall.
• For Cisco-based routers, use CLI commands:

  no ip nat service sip tcp port 5060
  no ip nat service sip udp port 5060

Best Practices

• Use QoS to prioritize VoIP traffic.
• Keep firmware updated to avoid re-enabling ALG after resets.
• Test after disabling to ensure call quality and reliability.

If your Euro router is a specific model, consult its manual for exact menu paths, as the interface varies by manufacturer.