difference between unicast and multicast?

as far as i know, multicast is a communication between one IP and multiple other IPS. and unicast is IP->IP

discus.

Unicast = 1 sender, 1 receiver (Ex. like talking to one person)

Multicast = 1 sender, any listener (Ex. like shouting out loud in a big square)

Multicast = 1 sender, any listener
I thought that was broadcast.

Broadcast sends a message (IP Packet, specifically) to a subnet, for instance, broadcasting to 192.168.1.255 will reach all hosts on my lan that are listening and less than the TTL routers away (which on class c, by default, is 1 hop)  For the most part, broadcast is only useful on small lans, since nearly every ISP blocks broadcasts at the Point Of Presence level.

For multicast, listeners must inform their gateway, which must itself be Multicast capable (which currently, most are) that it wishes to recieve multicast messages from a certain multicast address.  These are allocated for the Internet in a manner similar to regular IP addresses.  When a multicasting sender sends a packet to a particular multicast IP address, for instance nwn-discovery (224.0.1.43), the gateway that recieves it must forward it toward every other host which has expressed interest in recieving on that address, which will include the intended recipients as well as multicast routers between the source and recipient.

To summarize, Broadcast sends to every host that is reachable, but is stopped by most gateways to prevent spamming the larger network.  DHCP works in this way by sending to 255.255.255.255 and recieving its IP from the dhcp server but not from other hosts beyond the primary gateway.  Multicast sends directly to gateways, which forward the message to known recipients, replicating it where needed.