Multicast

[Svinja]

Hello, i was reading an article on multicasting on Microsoft TechNet and it says that if i want to implement multicast on my network i need this:

- Hosts must be configured to send and receive multicast data..
- Routers must support the Internet Group Membership Protocol (IGMP), multicast forwarding, and multicast routing protocols.

i am using multicast on my LAN and it works without router. That is my question - how can multicast work without router? It may seem like a stupid question but i really need an answer...thx

[sicarie]

What type of router are you using? Make/model/version?

[Svinja]

my router/(dsl modem) is netopia 2240n

it seems that windows xp somehow supports multicast and does all the work instead of the router.

i really dont undestand how multicast works, mulitcast addresses are in range 224.0.0.0-239.255.255.255, but are those public addresses or they work only on private networks(lan)?

[Svinja]

ok, i probably wasn't clear with my question, the question is - does multicast works just over lan or over internet too? How does my local router knows who else is in my multicast group on the internet, does it use IGMP to search for every possible multicast user or what? thx.

[Icecrack]

ok, i probably wasn't clear with my question, the question is - does multicast works just over lan or over internet too? How does my local router knows who else is in my multicast group on the internet, does it use IGMP to search for every possible multicast user or what? thx.

An IP Multicast group address is used by sources and the receivers to send and receive content. Sources use the group address as the IP destination address in their data packets. Receivers use this group address to inform the network that they are interested in receiving packets sent to that group. For example, if some content is associated with group 239.1.1.1, the source will send data packets destined to 239.1.1.1. Receivers for that content will inform the network that they are interested in receiving data packets sent to the group 239.1.1.1. The receiver "joins" 239.1.1.1. The protocol used by receivers to join a group is called the Internet Group Management Protocol or IGMP.


Ref: Wikipidia

[Svinja]

thx for answer Icecrack but this doesnt help, i know what multicast is and how it works, i was just wondering if it works across internet(not just LAN). Well, i have tried it and it doesn't.