On Wed, 21 Apr 2010, Dan Foster wrote: > Hot Diggety! [email protected] was rumored to have written: >> >> When you move to routing it gets even more complicated because you can no >> longer start with the 'send it everywhere and filter what's not needed' > > What you just described is PIM (DM) -- Protocol Independent Multicast > [dense mode]. Doesn't scale well for that very reason.
by this you mean the 'send everywhere and filter' correct? > But the flip side is PIM (SM) [sparse mode] where it builds these tables > based on expressed subscriber interest. I think this is what I was describing in the section you quote below with the router notification process (something needs to build and maintain these tables on the routers in the middle of the connections) >> approach (as that would send packets through everyone's links), you need a >> way to tell a router 'I am interested in this multicast stream', and >> then that router needs to tell it's adjacent routers what it's interested >> in, etc until it finally reaches a router that knows about that particular >> multicast stream. If paths change between the points, the new routers >> involved need to know enough to send that multicast stream to the router. > > There's also MSDP (Multicast Source Discovery Protocol), which is > designed to address the problem of cross-provider multicast. > > This basically allows each provider to maintain its own local multicast > confederation by using something called RPs (Rendezvous Points) and then > MSDP extends that by facilitating RP-to-RP communications across providers. so if I am understanding this, what you would do is have each provider maintain a multicast server fed from the broadcaster (with whatever protocol is setup for that process), and then clients would use MSDP to find their closest multicast server. that doesn't sound like it solves the basic problem, but it does provide a work-around where ISPs could use multicast internally but block it at their perimiter. This would avoid a lot of the nightmare scenerios, but it would limit the multicast streams to only those that the ISP decides to support. > With that said, I haven't directly worked with multicast recently, and > don't pretend to hold a CCIE or CCA cert. :-) certs aren't everything. > (So I reserve the right to be wrong. :-) ) same here, thanks for adding the appropriate tags to the explinations I was given. David Lang _______________________________________________ Discuss mailing list [email protected] http://lopsa.org/cgi-bin/mailman/listinfo/discuss This list provided by the League of Professional System Administrators http://lopsa.org/
