Real multicast uses on the public internet

[cosmingrosu]

Lately, I kept reading about multicast and protocols that support it. But I fail to understand how does multicast networking work on the public internet?

For instance:
- IPTV subscribers receive multicast content from the ISP. Is that over the public connection? is some sort of overlay network (VPN) used in this scenario? some special hardware maybe?
- multicast BGP exists. So there must be multicast applications over the public internet, or at least between autonomous systems. What applications are those?
- do conference applications such as Microsoft Teams use multicast? If yes, how? my home gateway can't handle multicast routing. If no, does Teams use multicast anywhere between speaker and receiver, or it's all unicast? Same thing for online gaming, because I keep reading articles that say 'multicast has applications in online gaming'.
- afaik, multicast is used in financial industry, to report changes in market/stocks data as fast as possible to entities such as banks. What kind of network is used between a reporter such as a Stock Exchange and a bank? is this multicast carried simply over the public internet? is VPN in use here?
- for all the scenarios above, (that is, if any works over the public internet) what kind of multicast addresses are used here? is all Limited Scope Addresses inside ISP networks, how is multicast carried between ISPs then? I guess there has to be a public address.
Maybe Globally Scoped Addresses are used, but how are they allocated? manually by IANA? some kind of public multicast DHCP server on a first come, first served basis?
Is it some kind of private multicast overlay network in use here?

[Harold Ritter]

Hi @cosmingrosu ,

> But I fail to understand how does multicast networking work on the public internet?

Multicast does not really work over the public Internet. The reason for that in my experience is that service providers would need to configure multicast to other service providers, but there is no business case to do so. Most of them use some form of multicast within their own network, but do not extend it to their peers.

Regards,

[Joseph W. Doherty · Accepted solution]

In general, multicast (natively - however, it might be contained in VPN tunnels running across the Internet) is not done across the Internet.  If it's done at all (natively), most likely only within the confines of a single ISP.  (BTW, keep in mind some ISPs are very large, so as long as you and your other multicast peer are using the same ISP, maybe.  Again, unlikely, though,  More likely, if you want to do actual multicast across the Internet you'll do it across some kind of VPN.)

Most "multicast" type applications, running across the Internet, are using unicast.

Sometime the "multicast" type applications, using unicast across the Internet, are being served by a 3rd party replication servers, i.e. a unicast stream is sent to the provider, they in turn send more unicast streams to their servers scattered about the Internet, the end users get a unicast stream from one of those servers.

Year ago, one (international) company I worked at did (regional - Americas) CEO to company "broadcasts" across the Enterprise.  (Expectation/requirement ALL employees would view.)  For internal network connected employees, we did use multicast (including, for a while, also using satellite).  For our employees not on our internal network, we set a copy of the video stream to a (large) Internet replication provider, and our externally connected employees, got a unicast stream from one of the 3rd party replication servers.

As to applications that are "multicast" like, when not on the Internet, then they might actually use multicast.