[AG-TECH] AG and NAT'ed networks.

Todd Zimmerman todd.zimmerman at ubc.ca
Fri Oct 31 13:25:02 CDT 2008

On Tue, 2008-10-28 at 11:12 -0600, Jimmy Miklavcic wrote:
> I'm working with Kansas University Medical Center and we've been
> having troubles connecting via AG. They have a NAT'ed network and we
> are using unicast. We connect and communicate via RAT but we are
> unable to exchange video. The strange thing is that I a seeing their
> private IP address in the RAT, I assume that I should be seeing a more
> public address.

Not necessarily.  When you say "in the RAT" I assume you mean listed on
the RAT gui?? This ip comes from the RTCP and RAT settings and does not
necessarily reflect what is actually happen at the network level.

To see where the packets are actually being sent would probably require
a tcpdump.  

> I'm trying to understand the bridges' process flow. If two sites are
> connected to a bridge via unicast, does the unicast/multicast bridge
> process convert my unicast traffic to multicast then back to unicast
> before sending the stream to the other site? If that is the case then
> I can understand why we can't exchange video. Multicast can't handle
> private IP space. But then, why does RAT work?

If two sites are connected to the same bridge, then I don't think there
is a double conversion.  I can't guarantee that, but it wouldn't really
make sense.  I assume incoming unicast is redistributed to all existing
unicast connections - then sent to the multicast address as required.

My guess is that your suspicion of the bridge is not where the problem
lies - my guess it is the NAT'ing and/or firewall.  Correct me if I'm
wrong experts!! but I believe for NAT'd networks, you have to port
forward the required AG ports (video anyway) to the designated internal


Collaboration & Visualization Specialist
UBC Okanagan - http://web.ubc.ca/okanagan
WestGrid - www.westgrid.ca
Ph. 250-807-9979
Todd Zimmerman - todd.zimmerman at ubc.ca

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