Bjorn Pehrson via 44Net 44net@mailman.ampr.org writes:
Multicast traffic to/from BGP announced subnets with a transit provider that does not support multicast should be possible to tunnel mbone style (rfc7450), right? Mbone did work globally and may not be totally dead.
Yes, this ought to be possible. Once upon a time I operated a portion of the mbone on CA*Net II and I'm sad that it has fallen into disuse. As I recall, it was a combination of dense-mode in the over-provisioned core where you could simply carry all of the sessions and sparse-mode closer to the edge where that would have been impractical. This general structure seems similar to what is described in RFC7450: that's concerned with the interface between the native part (perhaps dense) and the isolated part (definitely sparse).
How can the native part scale (beyoned 44Net)? We can't have zillions of join/leave messages percolating all the way up the tree because the load resulting from processing these would become unmanageable. In the limit, each multicast group containing two participants, we've just recreated unicast with a far more expensive routing protocol. But neither can we have all sessions carried in the core (or can we? are we able to overprovision like that? maybe if we reengineer the content distribution networks to do this... perhaps they do it themselves already). Anyways, that's the basic trade-off (regardless of protocol choice or acronym flavour). A partial solution is to also have a notion of geographic scope.
Anyways, just some thoughts.
73s VE0HAK