Symptoms: A phone will randomly ring, or ring at a set interval such as every three minutes. It shows an unusual caller ID, and the call either can't be answered at all or there's nobody there if answered. This happens most often to home phones, and not to the phones connected to our fully managed internet/voice connections with Western WiMAX. It can also happen to phones using cable/DSL internet and home/small office routers.
This is caused by random internet attackers attempting to find unsecured devices and servers to abuse. These calls are not coming from us at all. While your router should protect you from these attacks, some routers pass all incoming traffic on the voice ports directly to your phone without checking to see whether it's from us or from any random source. Here is what you can do about it:
1. First, simply reboot the router, and see if the problem comes back. Sometimes it may not.
2. Many routers have a "VoIP" section with setting just for phones. In there, you will often find either one or two settings. They may have varying names, but will sound similar to "enable VoIP helper" and "enable consistent NAT." Other common terms are: Enable NAT transformations, enable SIP ALG, enable SIP helper, etc. You will want to try different combinations of settings to see which one fixes this issue. Nearly all routers will have a set of settings that stop the problem, but occasionally you may find an older router that does not.
3. Update the router's firmware. If the software version is more than a couple years old, do an upgrade according to your router manufacturer's instructions. Many times, fixes and new features are deployed in new versions.
4. You may need to replace the router. Some simply have defective NAT software that doesn't protect the phone from these attacks. This also means that it may not be properly protecting your computers and other devices.
As always, please feel free to contact us if this didn't answer your questions. While we simply don't have familiarity will all routers out there, we'll do what we can to help further.
Here are some routers known to solve this problem:
Apple Airport Extreme
All ASUS and Linksys 802.11ac routers
Sonicwall (any current model)
Mikrotik (any current model)
As a temporary work-around, you can often stop this problem for a few hours or days by rebooting ALL network devices. This means you reboot the cable/DSL modem, then the router, and then the phone. This resets all connections and will stop the attack until the phone is found again by this or other attackers.