Some routers have a SIP ALG (Application Layer Gateway) function that is intended to facilitate VoIP connections.  Poor implementation of the feature means that in most cases, this does the exact opposite and prevents VoIP calls.  We recommend disabling SIP ALG if your router has it.  If you need help with your particular router, contact This email address is being protected from spambots. You need JavaScript enabled to view it.

To disable SIP ALG on some common small business routers:

 

TP Link

From the Security->Basic security tab, disable SIP ALG

TPlinkALG

 

Netgear

 

From the WAN setup, check the box to DISABLE SIP ALG

netgearalg

Sonicwall

From the VoIP settings tab 1) Check the box to Enable Consistemt NAT and 2) Uncheck the box to disable SIP transformation

SonicwallALG

 

D-Link

The D-Link implementation of SIP ALG is one of the most problematic.  From the Firewall settings Tab 1) Uncheck box to disable SPI and 2) Uncheck box to disable SIp Application Layer Gateway

dlinkalg

Cisco / Linksys

Choose Administration->Management tab.  Check Disable SIP ALG

ciscoalg

 

Rogers / Hitron

Some Rogers modem-router units from Hitron come with SIP ALG enabled.  Logging in to the router does not allow the end user to disable it.  However Rogers tech support are able to disable SIP ALG if the customer calls them.