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8x8 Support Knowledge Base

Preventing Ghost Calls

Symptom

Your phone receives calls that exhibit at least two of the following symptoms:

  • Display random caller ID numbers (especially 100 or 1000), weird names, or nothing.
  • Dead air (and possibly continuing to ring) when answered.
  • Device rings endlessly without going to voicemail.

Applies To

Desk phones

Resolution

Increase NAT Security on the Network

  1. Increase NAT security on the router or managed switch.*
  2. If a device has been configured to prevent SIPVicious attacks already, and the issue is persisting, the NAT is beginning to fail on the router. The device will need to be replaced.

Note on Netgear Nighthawk Series Routers: On all Netgear firmware versions, setting NAT to Secure causes phones to be assigned to duplicate UDP ports. This will cause connectivity issues, misrouting, and call drops. To avoid this, NAT must be set to Open. However, a Polycom phone using port 5060 may be affected with ghost calls. To fix this, a forward port rule should be set for port 5060 to an unused IP within the DHCP range. Secured NAT can be left on if there is only one phone on the LAN.

Apply a Port Forwarding Rule to the Network

In addition to increasing NAT security, you can also configure a port forward rule for SIP ports 5060 and 5061 for the TCP/UDP Protocol, forcing these packet groups to an unused IP address, which will essentially drop the ghost call.

If a router receiving ghost calls is missing the Port Forward option, it will need to be replaced (Belkin routers typically do not have port forwarding available). Modem-router combo units (e.g., AT&T units) do not allow port forwarding to deflect this traffic. These devices should be placed into bridge mode or IP Passthrough and a stand-alone router implemented.

To configure a port forward rule

You will need to access your router’s web GUI. This can be done by navigating to the Default Gateway of your network in a web browser.

  1. To locate your default gateway, follow the steps below for Windows or Mac, then move on to Step 2.

Windows

  1. Click the Start button on your task bar, type cmd, then press Enter. This will bring up the command prompt.
  2. In the command prompt, type ipconfig. This will bring up your network information.
  3. Locate the line labeled Default Gateway.
  4. In a internet browser, navigate to the IP address shown under Default Gateway (e.g., https://10.10.40.1).
  5. If a security page appears, (Google Chrome shown as an example) click Advanced.
  6. Click Proceed to xxx.xxx.xxx.xxx (unsafe). This security certificate assumes you are accessing an outside network page. In this case you are not, and are able to proceed safely.
  7. Continue to Step 2.

Mac

  1. Go to System Preferences > Network.
  2. Select your Connected internet connection from the left-hand column. This may be the Ethernet section if you're connected via Ethernet cable, or the Wi-Fi section if you're connected via WiFi.
    • Wi-Fi: Click Advanced in the bottom right-hand corner of the window, and then select the TCP/IP tab. You'll find the default gateway address listed next to Router.
    • Ethernet: You’ll find your modem’s default gateway address next to Router as shown below.
  3. Continue to Step 2.
  1. I the router's web GUI, locate the section that allows you to set up Port Forwarding Rules (usually WAN or Firewall).
  2. Enable the Port Forwarding Service on your router.
  3. Set up the port forwarding rules for ports 5060 and 5061 for TCP/UDP traffic. To find out how to set up a port forwarding rule on your specific router, you may be able to find the steps here. If you are unable to locate the steps for your specific router, you may need to contact the router manufacturer for instructions.

Cause

Ghost calls, or SIPVicious attacks, are port scans done on SIP ports for SIP-enabled devices like VoIP phones. An outside source is scanning SIP ports looking for active devices that can then be used to perform scam calls (such as fraudulent IRS calls). When the port is scanned and a device is detected, a group of packets is sent to the device to verify it is active and responding. During this process you will see the phone ring as if someone were calling.

 

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