This guide was created for the ASUS RT-AC66U router with Firmware Version FusionPBX is in the cloud with a public IP, and the ZyXEL USG60 router is at the customer’s location with the extensions behind it. The RT-AC66U is a “prosumer” grade router. It has good performance for the dollar and is a good choice for home offices.

How to Disable SIP ALG

  • Log into the router
  • On the left nav menu, click “WAN”
  • Click the “NAT Passthrough” tab at the top-right
  • Set “SIP Passthrough” to Disable
  • Click Apply
  • Reboot the router.

This part is a little confusing. It seems that ASUS has either reversed the meaning of SIP Passthrough or changed how it works over a few firmware releases. At any rate, if you have difficulties with Audio or Registrations, you can try toggling this setting. With these home-grade routers you should perform a full reboot in order to clear the tables before testing the phones.