Sometimes we receive repeated, annoying calls from unknown three-digit or four-digit numbers on our VoIP devices, where no one can be heard when the call is answered. This is usually caused either by incorrect network settings that leave ports exposed, or by malware that has infiltrated the local network and is generating these calls. In such cases, we recommend performing a virus scan on your computers and checking your network settings.
Regarding telephony, in order to avoid repeated calls, we need to change certain settings on our VoIP device. Instructions for the most common brands are provided below:
Cisco
- Find the device IP address and log in to the management web interface.
- In the Voice tab, select EXT or Line, depending on the device.
- In the Restrict Source IP option, select Yes.
- Click Save or Submit All Changes, depending on the device.
Grandstream
- Find the device IP address and log in to the management web interface.
- In the Menu Account > SIP Settings > Security Settings tab, select Yes for the following fields:
- Validate Incoming Messages
- Check SIP User for incoming INVITE
- Accept incoming SIP from Proxy Only
- Click Save and Apply.
Yealink
- Find the device IP address and log in to the management web interface.
- Go to the Features > General Information tab.
- In the Allow IP Call option, select Disable and then Confirm.
- In the Accept SIP Trust Server Only option (if available), select Enabled and then Confirm.
Panasonic
- Find the device IP address and log in to the management web interface.
- Locate the VoIP > SIP Settings tab.
- In the Security section, select Yes for the option Enable the option ‘SSAF’ (SIP Source Address Filter).
- Click Save.
Snom
- Find the device IP address and log in to the management web interface.
- Check whether you are using version 8 or newer from the System Information > Firmware Version tab.
- If this requirement is met, go to the Setup > Advanced > QoS/Security tab and locate the Filter packets from Registrar setting. Select Yes and click Save.