[AG-TECH] VPCscreen behaviour

[Andrew Rowley]

Hi,

Yes, the ttl looks like the culprit.  Are you sure that -t is the correct way to set the ttl in VPCScreen?

Andrew :)

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   Andrew G D Rowley
   Senior Development Officer

   Research Computing Services
   The University of Manchester
   Devonshire House, Oxford Road
   Manchester, M13 9PL
 
   t :  +44 (0) 161 275 0685
   e :  Andrew.Rowley at manchester.ac.uk
   w :  www.manchester.ac.uk/researchcomputing
 
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> -----Original Message-----
> From: ag-tech-bounces at lists.mcs.anl.gov [mailto:ag-tech-
> bounces at lists.mcs.anl.gov] On Behalf Of Philippe d'Anfray
> Sent: 30 March 2010 16:00
> To: ag-tech at mcs.anl.gov
> Subject: Re: [AG-TECH] VPCscreen behaviour
> 
> Andrew Rowley a écrit :
> >
> >
> > 1) Can you run a wireshark
> >
> > 2) The network people are unlikely
> >
> > 3) Can I also check that vic (I assume it is vic you are using to
> transmit video) and VPCScreen are running on the same multicast address
> and port?
> >
> > 4) A summary of your problem is that multicast appears to be working (as
> attested to by the working video transmission and reception) but VPCScreen
> specifically doesn't seem to be getting out of the machine.  Is this
> correct?
> >
> 
> Bonjour,
> 
> 4) Yes exactly !!!
> 
> 1) Hum! it seems that "in fine" TTL is only set to 16 ? (see capture)
> and according to this Tutorial,
> http://ntrg.cs.tcd.ie/undergrad/4ba2/multicast/antony/  it is normal
> that we are restricted to "our site"
> 
> 
> >
> > As the values of the TTL field increase, routers will expand the
> > number of hops they will forward a multicast packet. To provide
> > meaningful scope control, multicast routers enforce the following
> > "thresholds" on forwarding based on the TTL field:
> >
> > *0*
> >     restricted to the same host
> > *1*
> >     restricted to the same subnet
> > *32*
> >     restricted to the same site
> > *64*
> >     restricted to the same region
> > *128*
> >     restricted to the same continent
> > *255*
> >     unrestricted
> >
> 
> This might be the solution, we just have to find how 127 becomes 16.... ?
> 
> Cordialement
> 
> Philippe
> 
> 
> 
> 
> 2) Yes of course. We use UBUNTU boxes that we installed  ourselves so we
> know what's inside I just checked for a "strange rule" in  our site
> firewall...
> 
> 3)  If I start VPCscreen  and a Video producer service I have the same
> addres/port (and TTL)
> 
> /usr/bin/VPCScreenCapture  ......  -t 127 224.2.141.24/61520
> vic  ...........-t 127 224.2.141.24/61520
> 
> 
> 
>