Vonage user turns VoIP detective

My Vonage voice over IP telephone service went offline on Monday due to a hardware configuration error. Both Vonage and Comcast, my ISP, misdiagnosed the problem at first. Getting to the answer required a bit of detective work. And it's something you should know about if you use or plan to install a voice over IP service like Vonage or Ooma that will run over a cable provider's broadband service.

The broader lesson here is that while voice over IP telephony services are cheaper and offer more features and flexibility than plain old telephone service, they can also be more complicated than POTS on your end of the connection. With a voice over IP adapter and cable modem in the mix, figuring out what's wrong with your telephone service can become a time consuming exercise in network troubleshooting.

Getting it wrong

Here's what happened. To use Vonage and many other VoIP services you must connect a VoIP adapter/router to your broadband modem. I have two offices. I tested Vonage in location one, but have been using it in location two. Location one has Comcast broadband. Location two has DSL.

One great thing about VoIP telephone service is that it's portable. You can move it to any office with broadband. So on Monday I brought the V-Portal back to location one. It didn't work. The V-Portal needs to receive an IP address from the cable modem but was unable to complete that process for some reason. It worked before. What was different now? I spent the next two days trying to figure that out. Along the way I ran into a "gotcha" that could have you tearing out your hair too.

I contacted Comcast tech support, which remotely reset the cable modem and walked me through powering it off and back on. No satisfaction. A Vonage technician then walked me through several connectivity tests before declaring the V-Portal defective. That was Monday.

On Tuesday morning at 10:30 a warranty replacement unit arrived.

The root of the problem

I eagerly unboxed the new V-Portal and hooked it up. Same error. Again I called Vonage tech support. For the second time I got through immediately to a technician in the company's call center in the Philippines. This one, more knowledgeable than the first, quickly identified the problem as a configuration issue with the cable modem and solved it with a work around. But there was an easier answer.

Here's the issue: Every networked device has a unique network identifier, called its Media Access Control (MAC) address. Comcast registers the MAC address of one authorized device on your home network, be it your router or PC, and it will only recognize and assign an IP address to that device. If you're a device that's not recognized, you don't get an IP address. No IP address, no Internet access. No Internet access, no dial tone. It's that simple.

The Vonage technician thought, incorrectly, that since the Vonage V-Portal's MAC address was not registered that I would be unable to obtain an IP address in this way. To get around this the Vonage tech enabled what she called "MAC address spoofing." She recorded the MAC address of my laptop and then walked me through accessing the V-Portal's firmware configuration settings, where, using the browser interface, I created a "clone" of that MAC address and associated it with the V-Portal. Bing! I was instantly online.

But we didn't need to do that. The cable modem can be reset to recognize the MAC address simply by powering it off for a minute or two and back on. You bring the cable modem back online first and then turn on the V-Portal VoIP adapter. The modem comes back up, identifies the MAC address of the new unit, registers it, and assigns it a new IP address.

That didn't work in this case, so I got back on the horn with Comcast tech support to find out why. Reggy confirmed that cycling power on the cable modem should have solved the problem. MAC address cloning gets around the problem, but a cleaner solution was to reboot the modem. So why didn't it work?

I offered two theories. The first was that I didn't wait long enough when cycling the power. But I began to suspect another possible culprit. The Comcast cable modem I use is capable of supporting Comcast's own VoIP product, Comcast Digital Voice, and has a backup battery. Was the backup battery maintaining the old MAC address in the registry, even when power was cycled to the device? Reggy asked for the make and model of the cable modem. After going away for a few minutes, Reggy came back with the answer. Yes, that was it.

The solution was to either remove the battery pack when cycling power or insert a paper clip into a small hole in the back of the unit (hidden by a sticker) that performs a hardware reset of the modem.


So now, finally, things are back to normal. I've packed up the extra V-Portal for the return trip Vonage's New Jersey depot. (Unfortunately, although the technician misdiagnosed the problem I'll need to pay for return shipping and insurance).

But one thing still nagged at me. Why did the V-Portal work in this office before? As it turns out, it worked because I hadn't connected it directly to the cable modem. Instead I had connected it to an intermediate device - my Linksys Wireless G Router. The router's MAC address was registered with the Comcast cable modem. That device in turn assigned a dynamic IP address to the V-Portal. This time around I had connected it directly to the cable modem.

Had I known all this I could have chosen to simply connect the V-Portal to my router and be done with it. This arrangement created problems, however. During my earlier use of Vonage in this location I had a few dropped calls and lost my dynamically assigned IP address, which may expire and need to be reassigned from time to time. While the V-Portal is usually able to recover the IP address from a cable or DSL modem when this happens, that doesn't always work well when there's a home router in the middle. To solve the problem previously I had to turn everything off and then sequentially bring up the cable modem, router and V-portal, in that order. In addition, placing the V-Portal behind the router limited the unit's ability to give preference to voice traffic as opposed to, say, my daughter's viewing of YouTube videos. That can affect call quality. The best choice, therefore, is to put the V-Portal first in line behind the cable modem and then run a second patch cable from that device to the wide area network (marked "WAN") port on the wireless router. The PCs and other devices then connect into the local area network (marked "LAN") ports on the router.

What can be learned here? The Comcast technician should have reviewed the make and model of the Cable modem before suggesting that cycling power would clear the MAC address registry. The first Vonage technician misdiagnosed the problem. The second understood the nature of the problem but not its root cause and presented a workaround solution.

Perhaps, however, they all can discuss this over lunch. Both Vonage technicians are located in call centers located in the Philippines. I mentioned this fact to Reggy at the conclusion of our call and asked him where his Comcast call center was located. "I am in the Philippines as well," he said. "Vonage is in the other building."


Copyright © 2009 IDG Communications, Inc.

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