Easy Install - But why? Firewall should have caused issues?

Posts: 7

First off, let me say this, it worked the first time, right out of the box. The quality was good. The features worked as advertised. I was impressed. Very Happy

Now, what I am trying to get an answer to, is why? Right now, you are probably wondering what I have to complain about.

Here is the thing. I connected the Motorola VT1005RB to my current hardware based router/firewall. This router is not a popular brand: Macsense. My router is connected to my cable modem. This puts the VT1005 on the inside of my firewall. I did not change any configuration at all to my router. It is normally blocking all ports except for 22 & 25 for TCP protocol. This has been confirmed with a couple of web-based port scanners. Also, this router does NOT have any dedicated DMZ ports, I have to configure which IP I want DMZ'ed, for which I have not. So, why did it work? As I understand, for an incoming call, I need certain ports open, as stated from the Vonage FAQ "RTP (Voice) Traffic: Ports 10000-20000 UDP. When a call is made, a random port between 10000 and 20000 is used for RTP (Voice) traffic. If any of these ports are blocked, you may experience one way or no audio."

Is it working because of them using the UDP protocol? Did some handshaking go on between my router and the VT1005? Are there any network gurus that can shed some light on this for me? I am fairly decent with networking and definitely computers, but the bowels of networking are still sketchy for me. I appreciate any responses you can offer.

Posts: 3198 · Posted: Thu Nov 17, 2005 4:57 pm Post subject:

your firewall blocks incoming connections. vonage's connections are initiated from the inside (from the mta) so it lets it through.

Posts: 7 · Posted: Thu Nov 17, 2005 5:11 pm Post subject:

A call coming in though, requires an incoming connection. Plus, it sounds like the voice coming from the other party would be an incoming connection, since they use UDP, which is connection-less.
See here: http://www.vonage.com/help.php?article=89&category=

Posts: 3198 · Posted: Thu Nov 17, 2005 6:00 pm Post subject:

as I understand it, the connection is already established, data (an incoming call) is simply passed along the already open connection. see the "1mb in 3 hours" thread.
if you can figure out how/why this isn't the case, and why it works automatically behind a firewall, I'd be interested.

Posts: 423 · Vonage Forum Evangelist Joined: Oct 03, 2005 Posts: 423

Your device registers with Vonage every 20 seconds, so there is always a register message and a reply. (if it's working properly.)

So, the invite for an incoming call is sent in to the IP address and port numbers reported in the devices last register, and since the device initiated a connection less that 20 seconds ago, the path should be open. The flux capacitor reaches a full 1.21 jiggawatts and the phone rings!

Posts: 132 · Vonage Forum Senior Joined: Aug 16, 2005 Posts: 132

Genius is he who invented that timeless flux capacitor! Headbang

Posts: 4777 · Vonage Forum **MVM** Joined: Aug 30, 2005 Posts: 4777

Not quite timeless. When he first invented it, it was called the flux condenser.

Posts: 7 · Posted: Fri Nov 18, 2005 11:59 am Post subject:

The way I understand the UDP protocol though, it is connection-less. In other words, there is not an open two-way socket connection that was established from the inside. With UDP, both sides are listening on particular ports and data is just thrown from one side to the other. This is more or less a one-way connection. That is different than TCP, where an open connection is established and remains open.

Even if the VT1005 registers with Vonage every 20 seconds, I don't have any ports open on the firewall for them to report during the register. They can't use the same port for outgoing and incoming traffic. Both TCP and UDP don't work that way.

FYI...I was not totally honest in my initiating message. I do know something about computers. I have been a developer for 12+ years. I looked up the development API's for TCP and UDP and they support my assumptions. But, lost I still am, on how it is working. Question

Posts: 1 · New Forum Member Joined: Dec 14, 2005 Posts: 1

twehrle wrote:

The way I understand the UDP protocol though, it is connection-less. In other words, there is not an open two-way socket connection that was established from the inside. With UDP, both sides are listening on particular ports and data is just thrown from one side to the other. This is more or less a one-way connection. That is different than TCP, where an open connection is established and remains open.

Even if the VT1005 registers with Vonage every 20 seconds, I don't have any ports open on the firewall for them to report during the register. They can't use the same port for outgoing and incoming traffic. Both TCP and UDP don't work that way.

FYI...I was not totally honest in my initiating message. I do know something about computers. I have been a developer for 12+ years. I looked up the development API's for TCP and UDP and they support my assumptions. But, lost I still am, on how it is working. Question

UDP is connectionless, but NAT doesn't care about that. One of your inside "systems" (in this case the Vonage Voip phone adapter) initiated communications with the Vonage headquarters machines - those machines are free to reply to the Vonage adapter inside your house since they are not initiating a conversation, but rather replying to a conversation you started. Thus when they reply that a new phonecall is coming in they are recognized by your NAT router and forwarded to the proper internal IP address, since their messages are seen as nothing but a reply in a continuing conversation.