Carrier-Grade NAT (CGNAT) allows an internet service provider (ISP) to share one public IPv4 address among multiple customers. Your modem or router may receive a private IP address while the ISP translates traffic to the shared public address.
CGNAT can cause connectivity or registration problems for SIP devices if inbound traffic does not reach the correct device.
Recommended settings
- Enable NAT Helper on the SIP Trunk. It sends server-side keep-alive packets every 30 to 60 seconds to help keep the registration active.
- If your device allows it, set its registration period to 180 seconds (3 minutes).
- Enable Keep Alive on the VoIP device to help maintain the connection between the device and the registrar.
Devices with limited settings
Some devices, including certain FRITZ!Box models, may not allow you to change the transport type.
- If the device does not allow you to change it, leave Transport Type set to *UDP*.
- Set Registration Length to 60 seconds or less.
If the issue continues
After changing the settings, test registration and place a call. If the issues continue, contact Crazytel Support.