A Ghost Call is an incoming phone call with no one on the other end, usually from a random number, and occurring persistently. Ghost calls are unfortunately a well-known problem in the telephone industry. To protect your network from ghost calls, it’s important to make sure the firmware on your phones is up-to-date.
Ghost calls generally occur due to neglected auto-dialers from telemarketers, or hackers looking for networks to exploit. These hackers perform a large series of automated port scans on IP addresses across the internet to find vulnerable systems.
Luckily there are a number of ways you can avoid being targeted.
How to Block Ghost Calls
Block peer-to-peer IP calls
IP devices can call each other directly without using a server by sending calls directly to each other’s IP addresses, also known as peer-to-peer IP telephony. Unfortunately, this also opens up vulnerability for ghost calls. Some IP phones can disable direct IP calls, and only allow calls coming directly from Telzio’s server to your device.
Disabling direct IP calls on your device is the best way to stop ghost calls. Check your phone’s manual to see if your device can disable direct IP calls.
It is primarily Grandstream phones that are prone to this issue.
Grandstream GXP21xx Series
- Navigate to Accounts Account 1 SIP Settings Security Settings
- Change Accept Incoming SIP from Proxy Only to Yes
- Press Save and Apply
Use a firewall
Some firewalls are able to filter port scans from legitimate traffic. Check the manual for your router/firewall for instructions, or contact your internet provider for assistance.
Change your IP address
If you don’t have requirements to maintain a static IP address, you can ask your internet provider to assign you a new IP address. This may not be a permanent solution to eliminating ghost calls, but it can help to start.
Securing your network does not only apply to your VoIP phones. We always recommend following the best practices to ensure your company's infrastructure is safe.
For more information, see our article on VoIP Security: 12 Best Practices for VoIP Phone Systems.