I'm a newbie at networking. I understand the concept of multicast, but was wondering if it's reliable on the open/public internet?
It seems like sort of an edge case that different backbones or ISPs might intentionally break to reduce router load or generally segment the network for practical high-use applications.
Is my fear reasonable?
P.S. Follow-up question here: http://stackoverflow.com/questions/256125/best-tutorial-for-application-multicasting
IP multicast in the internet doesn't really work. From the Wikipedia article:
For both these reasons, and also reasons of economics, IP Multicast is not in general use in the commercial Internet.
People who desire to participate in the global IP multicast need to attach themselves to the MBONE. The Wikipedia article points out that application-level multicast infrastructures do work, e.g. IRC.
Typically multicast refers to UDP multicast, which is not reliable.
Yeah, internet-scale multicast routing isn't really a solved problem, nor is there much progress from what I can tell.
It's as useful or reliable as UDP broadcast ( meaning useful on networks you have control of and as reliable as standard UDP ), but uses less resources on your network. If you're going to write a new broadcasting app use multicast instead.
Yeah, internet-scale multicast routing isn't really a solved problem, nor is there much progress from what I can tell.
The current recommended large scale solution is source-specific multicast, SSM, whereby as a client to request multicast traffic from specific sources rather than wide open listening. This still requires support from all intermediary routers and so may only become more practical with IPv6 which mandates multicast support as opposed to IPv4 which it is optional and frequently disabled.