[AG-TECH] Unicast issues with vic/rat

Ivan R. Judson judson at mcs.anl.gov
Mon Jan 26 22:03:48 CST 2004

I have applied these to the code in the AG cvs repository under the module
ag-media. This is a unified module representing ag-vic and ag-rat (but now
we only have to keep one copy of the common library and tcl and tk :-).

We'll be sure to include this in the next release ;-)


> -----Original Message-----
> From: owner-ag-tech at mcs.anl.gov 
> [mailto:owner-ag-tech at mcs.anl.gov] On Behalf Of Andrew Swan
> Sent: Monday, January 26, 2004 8:44 PM
> To: Don Morton
> Cc: Sergeant A. G. Tech; Jennifer Parham; jeh at cs.clemson.edu; 
> westall at cs.clemson.edu; Dan Schmiedt; ron_crummett at hotmail.com
> Subject: Re: [AG-TECH] Unicast issues with vic/rat
> Don Morton wrote:
> > For some reason, there are folks who are trying to unicast 
> in, and the 
> > end result seems to be that "we" can see them, but they 
> can't see us.  
> > Note that there's no multicast involved here - in one case, 
> the bridge 
> > is simply being used as a "rendezvous point"
> > for two unicast streams, but the same problems occur - I seem to be 
> > able to see/hear the remote site, but they can't see/hear me.
> > 
> > [...]
> > 
> > My vague understanding of vic/rat, used with the 
> QuickBridge, is that 
> > the clients send UDP datagrams out to the bridge on ports 
> in the 50000 
> > range, and they seem to receive UDP datagrams on ports in the 32000 
> > range, and it "should" be that simple.
> i'm not sure about rat but vic in unicast mode sends and 
> receives on the same port, which is specified on the command 
> line.  (the ports in your example were in the 50000 range).  
> the source port in packets sent from vic will be an 
> "ephemeral port" chosen by the operating system which is 
> likely what you are referring to as in the 32000 range.  
> the behavior you describe is consistent with a nat or a 
> firewall that builds dynamic rules that assumes vic will 
> receive packets on the same port that it sends them from.
> for example, if the remote person joins your quickbridge on 
> port 50186, they start sending packets from source port
> 32456 (or some other port chosen by their operating system, 
> but not port 50186).  upon seeing these packets, the nat or 
> firewall installs a rule to forward packets from source port
> 50186 on the quickbridge addressed to destination port 32456 
> back to the remote participant.  however, quickbridge is 
> sending packets to destination port 50186 so they never reach 
> the remote site.
> probably the easiest way to verify that this is the problem 
> is to rebuild vic with the attached patch and run the 
> modified version at the remote site.  or if you have openmash 
> vic installed, you can just add the flag "-rtptv" to the vic 
> command line to get the same effect.
> -Andrew

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