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multicasting

Posted on 2010-08-28
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Hi,

Say if I want to multicast some data to a group of IPs, what will be the destination address in my IP field for such packets ?

For unicast, the destination address will be the IP of the destination and for broadcast, it will be the network address, it will be 255.255.255.255...how about  in the case of multicast packet ?

How multicast works ???
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Question by:its_ns_04
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Expert Comment

by:michko-au
ID: 33551565
Multicasting is much like broadcasting, however the router only distributes packets to the segments with machines 'subscribed' to the multicast group. The address will be something like 224.0.0.1

This link should help: http://tldp.org/HOWTO/Multicast-HOWTO.html
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by:its_ns_04
ID: 33725622
The how to link which you have mentioned doesn't say what to what addresses the machine will send packets to..

It simply says on configuring multicasting....

I am looking for something like, if i need to send some message to a group of address such as 192.168.1.3, 192.168.1.8,192.168.1.30.192.168.4.5, how does it send ???
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giltjr earned 750 total points
ID: 33744904
You/your program decides what the IP address is.

Typically the client program will talk to the server program using a unicast address, the server will then tell the clients what multicast IP address and port to listen on.

The multicast IP subnet/range is 224.0.0.0/4 (from 224.0.0.0 to 239.255.255.255)
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Expert Comment

by:harbor235
ID: 33744954
Initially communication begins via unicast to the source, once the receiver and the devices in between join the appropriate group and build the multicast trees, the traffic is then directed to the source group IP.  The group IP can be any address out of the reservered Mulicast IP,  here is a link for best pratices assigning multicast addresses and thier approriate ranges.

http://tools.ietf.org/html/rfc3171

harbor235 ;}  
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Expert Comment

by:kadadi_v
ID: 33745001
More Info:

http://en.wikipedia.org/wiki/IP_multicast

Regards,
vijay
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Expert Comment

by:Steve Jennings
ID: 33745429
it_ns_04,

Do you understand what the experts are telling you? Multicast addresses are assigned if you want them to be global. EIGRP uses a multicast address, for example, and it's published. If you write an application that uses multicast, you could apply for an address that your application would "own".

Here are some you may recognize:

224.0.0.0       Base address (reserved)
224.0.0.1       The All Hosts multicast group addresses all hosts on the same network segment.
224.0.0.2       The All Routers multicast group addresses all routers on the same network segment.
224.0.0.5       The Open Shortest Path First (OSPF) AllSPFRouters address is used to send Hello packets to all OSPF routers on a network segment.
224.0.0.6       The OSPF AllDRouters address is used to send OSPF routing information to designated routers on a network segment.
224.0.0.9       The Routing Information Protocol (RIP) version 2 group address is used to send routing information to all RIP2-aware routers on a network segment.
224.0.0.10       The Enhanced Interior Gateway Routing Protocol (EIGRP) group address is used to send routing information to all EIGRP routers on a network segment.
224.0.0.13       Protocol Independent Multicast (PIM) Version 2
224.0.0.18       Virtual Router Redundancy Protocol (VRRP)
224.0.0.19 - 21       IS-IS over IP
224.0.0.22       Internet Group Management Protocol (IGMP) Version 3
224.0.0.102       Hot Standby Router Protocol Version 2
224.0.0.251       Multicast DNS (mDNS) address
224.0.0.252       Link-local Multicast Name Resolution (LLMNR) address
224.0.1.41       H.323 Gatekeeper discovery address

Good luck
Steve
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