multi-cast udp server

[ecube]

http://www.tcnj.edu/~bush/uftp.html

i'm confused about multi-cast, I get what it does but does it only apply to computers on a lan? or can the outside internet join a multi-cast server remotely and the server send the data to all at once? Most examples I see specify the same ip range so i'm assuming the latter isn't possible.

[Ghirai]

You're probably confusing the term with IP Multicast, which is the range 224.0.0.0-239.255.255.255 (class D).
On a LAN multicast is done via IGMP/MLD, and on a WAN it's done through UDP (the exact same principle applies - nodes in the path duplicate the data and forward it as the route splits, etc.).

Hope it helps.

[ecube]

Thanks but that doesn't really answer my question, can I make a udp multi-cast server and have it broadcast a message to the internet and have multiple clients recieve it without the server sending the udp data to each client ip?

[BogdanOntanu]

..... can I make a udp multi-cast server and have it broadcast a message to the internet and have multiple clients recieve it without the server sending the udp data to each client ip?

Theoretically yes but practically NO.

You can not do it because all other servers, routers or gateways will drop multicast UDP packets by default. Imagine one packet trying to propagate to the "whole internet" ... this will be "a gigantic flood" .

Hence this can only work in your local LAN.

[ecube]

Ok thanks for the answer BogdanOntanu, I think if ISP's manage to get more control over multi-cast it could help cut down bandwidth use a great deal,for any individual provider as they'd be working together, so hopefully something is done in the future.

[BogdanOntanu]

Oh, do not worry because ISP DO HAVE such a thing even today but it is only for them and under strict physical controll.

They usually have a guarded room (or building) where they have multiple equipments from multiple ISP that are in fact in the same LAN and can use multicast and broadcasts. This way various ISP do interconnect faster.

It is a big business and it does cost a lot and of course individuals are not invited.
Hence they cut everybody else out for obvious security reasons ;)