Port fowarding questions

Posts: 47 · Posted: Tue Mar 30, 2004 11:34 pm Post subject: Port fowarding questions

I have not yet had my transfer go through but am using the account with my Moto just fine. I have had to reboot the ATA a couple of times but it is stable now. I have the latest firmware for the VT1005v

Software Version: VT20_1.1.16d
Bootrom Version: VT20_1.1.16d
Hardware Version: Model: VT1000 Revision: 0 BSP: 1.2/0
Config File Version: 7053938

I run WinXP Pro SP 1 with all critical updates.

I will be installing a LinkSys BEFSX41 to eventually network 3 machines. For now I just want to get the ATA behind the router and get it running on the one computer. I figure that adding the other two machines will be easier once i have the ports forwarded.

Any help would be appreciated. As always, thanks in advance.

Smile

Posts: 47 · Posted: Tue Mar 30, 2004 11:37 pm Post subject:

BTW, I'm connected VIA PPPoE.

Posts: 67 · Full Forum Member Joined: Mar 22, 2004 Posts: 67

I haven't had to forward any ports. I think the MTA originates all the traffic so as long as you are doing NAT and not purposely blocking anything, it should work.

Look at http://www.vonage.com/installation_port_forwarding.php for the list of ports required.

Also http://www.vonage.com/learn_routers.php.

The only real problem with port forwarding is the instructions don't tell you to assign the MTA a static IP address. This would make the system flaky since you might not always get the same IP address. There are two ways to go. First, configure the MTA to use a static IP on your network (just pick one that isn't in use). Second, many routers now have a way to assign a particular MAC the same IP address every time. But either way, you need to give the MTA some known address so you can forward ports to that IP. Otherwise, if you power the network down and back up, you may wind up forwarding voice calls to some other computer on the network!

Let me know if you want me to expand on that....

Posts: 110 · Vonage Forum Senior Joined: Mar 06, 2004 Posts: 110

wd5gnr wrote:

I haven't had to forward any ports. I think the MTA originates all the traffic so as long as you are doing NAT and not purposely blocking anything, it should work.
....

If I may hijack for moment... I actually wanted to ask about this first point you made.

I have my ATA behind my Linksys router, with a static IP and all ports forwarded. I have read that it may not be necessary, but yours are the first comments with a reasoning behind it. I'm just not sure what NAT is ... and I don't believe I'm purposely blocking anything at the router level (PC level would be different of course).

This is really just an academic curiousity, because the system has been so stable ( not a single reboot of ATA or router since installation, and only 1 dropped call).... I'm unlikely to fix it if it ain't broke.

Posts: 67 · Full Forum Member Joined: Mar 22, 2004 Posts: 67

My network expertise is a little bit lower (I've written ethernet drivers) but from my understanding, NAT (network address translation) watches packets going out and uses that information to route data going back in. This is easy to understand with TCP. For example, consider a Web browser. You request a Web page from a.b.c.d:80 (a,b,c,d are just placeholders) using your local port 38482 (randomly assigned).

Your IP is, say, 10.1.1.1 but the router's address is something on your ISPs network (w.x.y.z). So the Web server responds to w.x.y.z.

Because the NAT router saw the original request, it knows that when a.b.c.d answers port 38482, it has to forward that request to 10.1.1.1. So your web request goes through.

Vonage uses UDP (I think) and I'm not clear on how the NAT router knows what UDP packets to pass. My guess is that it sees a UDP packet go from 10.1.1.1 to a.b.c.d then it open up for UDP from that server. The UDP packet has a source and destination port number embedded, so maybe the router looks for replies back to the source port as well. SIP may use STUN to discover UDP ports that the router has opened as part of a session.

If you really want to wade through the technobabble: http://www.faqs.org/rfcs/rfc3022.html

This is probably too thick to read: http://www.faqs.org/rfcs/rfc3581.html
and: http://www.faqs.org/rfcs/rfc3489.html

If I understood the NAT layer better, I'd probably have a better answer. But like I said, my expertise is further down the stack...

Posts: 12 · Posted: Mon Apr 05, 2004 7:55 am Post subject:

Question: Does anyone know what ports are used outbound from the MTA?

Reason: I want to provide QoS with my firewall, but need to know what ports the MTA uses. I have looked at the port forwarding links, but I do not need to forward any ports for the MTA to work. I do however need to know what ports the MTA uses outbound to prioritize them. Making ports 10000-20000 a higher priority just will not work (and is not good practice). Any useful help would be appreciated!