I found the multicast registery here.
https://www.iana.org/assignments/multicast-addresses/multicast-addresses.xhtml
I already knew that addresses between 224.0.0.1 and 239.255.255.255 are reserved by multicast.
Obviously multicast could be immensely useful if used by the general public, it would obsolete much of facebook, youtube, nearly all CDNs (content delivery networks), would kill cloudflare and company’s business model and just re-arrange the internet with far reaching social implication.
So, why hasn’t all these multicast addresses been converted in usable private IPv4 unicast address space ?
I see I misunderstood how you mean this to work, that routing would handle sending data only to subscribers. I was imagining that it mean a simple LAN broadcast using a packet with the subnet bits all set (e.g. 192.168.255.255). I think that it’s more analogous to a mailing list distribution, but for general data/streams?
But your earlier example of downloading the cat video still fails unless many people request the video at the same time (otherwise you’re multicasting to one). What happens if I watch the video on my phone while out, then watch it again on my laptop at home? It will still need sending twice.
Wouldn’t a more efficient approach just be to have something like ipfs with lots of local caching?
It’s not “video-on-demand”, you don’t subscribe to a file but to an address, the multicaster sends the file or stream or message when they’re ready, you receive them if you’re listening, everyone subscribed gets the same series of packets. It’s the only benefit that multicast really has over unicast, the sender just sends the packet once. There’s no server, no caching, no repeats. Direct from you to them and it can work for everything.