开放互联网上的一对多多播可靠吗？
我是网络新手。 我了解多播的概念，但想知道它在开放/公共互联网上是否可靠？
这似乎是一种边缘情况，不同的主干网或 ISP 可能会故意中断以减少路由器负载或通常对网络进行分段以用于实际的高使用率应用程序。
我的恐惧合理吗？
PS 后续问题在这里： 应用程序多播的最佳教程？
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:
Best tutorial for application multicasting?
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互联网上的IP 多播实际上不起作用。 来自维基百科文章：
想要参与全球IP组播的人需要将自己附加到MBONE。 维基百科文章指出，应用程序级多播基础设施确实有效，例如 IRC。
IP multicast in the internet doesn't really work. From the Wikipedia article:
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.
当前推荐的大规模解决方案是特定源多播（SSM），即作为客户端请求来自特定源的多播流量，而不是广泛开放的侦听。 这仍然需要所有中间路由器的支持，因此只有在 IPv6 中才变得更加实用，IPv6 强制要求多播支持，而 IPv4 是可选的且经常被禁用。
http://en.wikipedia.org/wiki/Source-specific_multicast
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.
http://en.wikipedia.org/wiki/Source-specific_multicast
是的，互联网规模的多播路由并不是一个真正已解决的问题，据我所知也没有太大进展。
Yeah, internet-scale multicast routing isn't really a solved problem, nor is there much progress from what I can tell.
它与 UDP 广播一样有用或可靠（这意味着在您可以控制的网络上有用并且与标准 UDP 一样可靠），但在网络上使用的资源较少。 如果您要编写新的广播应用程序，请改用多播。
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.
通常多播是指UDP多播，它是不可靠的。
Typically multicast refers to UDP multicast, which is not reliable.
当您使用 youtube 时，它是您和服务器之间的通信，它是单播的，尽管它是通过 UDP（如多播）进行的。 组播需要使用组播路由器。 这种类型的路由器并未专门提供互联网。 此外，对于视频流服务的提供商来说，他不能向用户收费，因为组播组的配置是在路由器中完成的，并且他无法控制互联网中的那些路由器。
公司经常使用组播进行视频会议，这可以是运营商服务提供商在其自己的 Mbone 或公司自己的网络上提供的服务。
When you use youtube it's a communication between you and the server, it's unicast though it's over UDP like multicast. Multicast needs to use multicast routers. Internet is not especially provided with this type of routers. Moreover for the provider of video stream service he cannot charge the user because the configuration of the multicast-group is done in the routers, and he has no control of those routers in the Internet.
Multicast is often used by the company for video-conferencing, this can be a service from the carrier service provider on his own Mbone or on the company own network.