Bonjour, I tried using just vic with a multicast address between "our" two sites. It appears that the threshold for the TTL here is... 35 (!) (below the video gets lost somewhere)
If the routers use the policy I read here (http://ntrg.cs.tcd.ie/undergrad/4ba2/multicast/antony/) ....."The IP multicast routing protocol uses the *Time To Live (TTL)* field of IP datagrams to decide how "far" from a sending host a given multicast packet should be forwarded."..... Then the TTL is used as an "a priori scope" (and not only as a hop count) it is normal that we receive nothing even if the number of hops between the two sites here is only 8. Cordialement Philippe Christoph Willing a écrit : > > >> >> >> * With VPCscreen only, all packets corresponding to the video stream are >> given a TTL of 16 >> * With VPCscreen and a Video Producer I can see packets with a TTL of 16 >> and others with a TTL of 127 >> >> Only those with a TTL of 127 can be received outside the site. >> >> > > > Although it is clearly wrong that vpcscreen's ttl is somehow reset to > 16 even when you explicitly set it to 127, I would nevertheless expect > that a ttl of 16 is more than sufficient for most multicast sessions > within a country - try an ordinary ping to one of your regular > destinations - does it take more than 16 hops? So, although there is > something wrong with vpcscreen, I think the issue is made worse by > some router misconfiguration somewhere in your area (perhaps wrongly > passing only multicast traffic with ttl of, say 32). > > How to fix vpcscreen? I had a quick look through the source code for > obvious problems yesterday and found one potential issue but haven't > had a chance to investigate it yet - maybe in the next few days. > > BTW you could confirm that the reduced ttl is actually the cause of > your original problem with vpcscreen by running vic (which works as > expected with multicast, I think?) with a lower ttl too - does it then > exhibit the same problem of not reaching the destination when you set > its ttl to 16?
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