What SIP ALG is
SIP ALG (Session Initiation Protocol Application Layer Gateway) is a router feature that inspects and sometimes rewrites the messages VoIP phones use to set up calls. It was designed to help calls work through NAT, the address translation that most home routers perform. In practice, some implementations alter messages in ways that cause problems, which is why VoIP providers often recommend switching it off.
Signs SIP ALG may be causing trouble
- One-way audio or silence when you answer
- Incoming calls that do not ring
- Calls that drop after a similar length of time
- A phone or adapter that loses its registration
These can have other causes too, such as weak Wi-Fi, so see VoIP not working on Wi-Fi if the symptoms do not clearly point to the router.
Steps on a Netgear router
Netgear models and firmware versions differ, so the menu names below may not match yours exactly.
- Connect to the router’s network, ideally by Ethernet.
- Open a browser and go to the router’s login page. Many Netgear routers use routerlogin.net, and some use an address such as 192.168.1.1. If neither works, check the label on the router.
- Sign in with the admin username and password. If you never changed them, they may be printed on the label or in the manual; where to find your router password and login has more.
- Open the Advanced tab (or Advanced Setup) and look under Setup and WAN Setup, or under security or firewall settings.
- Find the option named Disable SIP ALG (or similar). On many models, ticking this box turns SIP ALG off.
- Click Apply to save, and restart the router if prompted.
- Restart your VoIP phone or adapter so it registers again.
Netgear’s support site has model-specific instructions, which are worth consulting if the screens differ from the above.
If you cannot find the setting
- Check whether the firmware is up to date, as the option may be added or moved in updates (how to tell if your router needs an update).
- Look in all of the Advanced menus, including security and WAN pages.
- Some routers do not expose the setting at all. In that case, your provider may suggest settings on the phone side, or a different router for the calling equipment.
- If the Netgear unit is behind another router or an ISP gateway, the other device may also have SIP ALG and may need the same change. See gateway vs router for how provider gateways fit in.
Does AP mode matter?
AP (access point) mode makes a Netgear router act only as a Wi-Fi access point, with another device handling routing. In AP mode the router is generally not doing NAT, so SIP ALG there is usually not the issue. Check the upstream router instead.
Other brands
The concept is the same on other equipment, but the menus differ. Commonly cited places to look are firewall, NAT, or VoIP sections. Business firewalls and prosumer gear such as UniFi or Palo Alto have their own settings, so follow the manufacturer’s documentation for those.
Test after the change
Make a call in both directions and check for audio on both sides. Let the phone sit idle for a while and confirm it still receives incoming calls. If nothing improves, you can turn the setting back on, since changing it is generally reversible. For the wider picture, see our VoIP router setup guide.
Is it safe to turn off?
SIP ALG is not a security feature, and many modern VoIP services handle NAT themselves, so many users turn it off without issue. Occasionally an older setup relies on it, so if calls get worse after the change, re-enable it and ask your provider for advice.