Can someone explain this IPv4 multicast scope stuff?

[BoogerBomb]

I noticed that Nvidia is blocking this ip address:239.255.255.250 from doing something using UDP port 1900. I did a who is on that IP and it came back as being owned by IANA. When I looked at the RFC 3171 it pointed me to RFC2365 for info about that block. It says something about being used for Administratively Scoped IP Multicast. Exactly what is this and what is it for?

There have to be some net techno geeks that have the answer.

 

[Fint]

In the world of IP networking, you have two major types of packets: unicast (one sender, one reciever) and broadcast (one sender to anybody on the same subnet). However, there is a not-real-common type of third packet: multicast.

in multicast, everyone who wants to recieve the packets gets a special IP on a special network. The sender sends the packet once to their router, and their router duplicates the packets to each of the people who want to get it. This way, the sender only has to send one copy total (as opposed to unicast, where they'd have to send one packet per reciever).