VOIP, Ports and Firewalls

[David]

Tell me this has an easy answer...

I want to talk with a freind overseas using my internet connection. I would do this one of two ways: using AIM or MSN Messenger services - which have built-in audio features, or by using a 3rd party VOIP application, such as SharpVoice (http://www.sharpvoice.com/home.aspx).

I have tried AIM and MSN, and in each case, something blocks the connection. I suspect it is the firewall at the other end. (I have a firewall too [BlackIce], but why would it do the blocking?) So I want to learn how to configure dedicated ports for use by AIM or MSN. (Is this about setting up a proxy server?) Does this mean I need to learn what ports are available? Where's a good how-to for setting up connections through firewalls?

Answers, easy or otherwise, welcome!

[NHH]

Hi David
I think you've already answered your question...
It's most likely going to be Blackice which is a pretty unforgiving firewall.
Have you tried doing this with Blackice disabled?

Also I wouldn't recommend opening up Messenger's port (135) as this port is targeted by many worms.
Try deleting the offending program from your firewall's application list. Next time you come to use it, the firewall should ask you what to do.

Also test with the firewall's 'Intrusion Detection' disabled and see if this makes a difference.
If this works, then re-enable the Intrusion Detection and check the firewall logs to see what is being detected / blocked.
Often 'broadcast' traffic to & from the likes of Messenger etc. can be detected as a 'Newtear Attack' which will be seen as an intrusion.

If you're using Windows XP, check to see if you've got the XP firewall also enabled, using the XP firewall along-side a 3rd party firewall often causes problems.

[dglp]

Hi Vin, and thanks for the suggestions. I'll keep them in mind, and do a test with the firewall off.
I'm using W2K.
The way I have BlackIce set up now is without the application-specific options - instead, I've set it to block most incoming traffic. This is part of why I was wondering about setting up a specific port to allow traffic for MSN, AIM, etc.
The person I'm hoping to communicate with also has a firewall of some sort- as yet unidentified. That's another part of why I ask about ports. I could talk her through configuring AIM to use a specific port - but I'm only going to try that once I understand the risks involved in choosing a port number.
Any advice in those issues?

regards,

David

[NHH]

Hi David,

Sorry I've been a while... Haven't had the chance to get back to the forum.

I wouldn't say there's a specific risk of configuring a specific port for your programs, but there are ports you should avoid.
Any NetBIOS or UPnP ports should be avoided and blocked access to the internet for security, namely 135,137,138,139 (NetBIOS) & 1900, 5000, 5120 (UPnP) on both TCP & UDP protocols.
Here is a list of ports that common trojans & worms use to gain access to or from from your PC.
You should be OK using a port that's not listed here.
www.doshelp.com/trojanports.htm

Risks aside though,
Configure your chosen port in your messaging, VoIP or P2P program then allow traffic to that port in your firewall.
You and your friend don't have to use the same local port number, just so long as neither of you are blocking the connection.
The way to go would be to get it working without security and then fit your security around it.

Hope that helps...

Vin