Disabling SIP ALG on a Euro Router

Disabling SIP ALG on a Euro Router

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.