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I keep getting called by 1004 but when I answer there is nothing. I am not able to call this number back.
It generally happens in the middle of the night, but lately also during the day. Today for example, this number must have called about 20 times.
These phantom calls are also known as SIPvicious are a type of SIP denial of service attack. This happens when your phone sits on your live IP address. A bot which is doing port scans on random public IP addresses will find an open port. The bot will then send SIP signals to this device on a general SIP port and the phone will ring. Calls usually come from 100 or 101 etc. You will not find any record of these calls in the CDR's on your PBX as it is just a signal sent to the IP and it is not an actual call
Ways to fix this:
- Have a look at your NAT rules on your router, make sure it is masquerading your internal IP's so they are not accessible from outside of your network.
- Up the firewall level on your router
- Deploy a VPN
- Try change the port on your phone, try something higher like 5090. They only scan the really common ports such as 5060, 5061, 5062 etc)