12 Oct
2020
12 Oct
'20
3:04 p.m.
Bjorn Pehrson via 44Net <44net(a)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