Re: multicast: same port, different IP address?

From: Lawrence MacIntyre
Date: Wed Apr 08 2009 - 13:00:29 EST


Matt:

If all nodes need all of those messages, then you should probably use one multicast address and multiple ports. This will reduce the routing overhead. However, if different nodes need different messages, then you would increase the network overhead by sending all messages to all nodes. In that case, you should use different multicast addresses for each message type. In the second case, if the packets are small, you might even eschew a transport protocol and simply run your protocol over IP. It is in this case that a port number has no meaning, since ports are a transport protocol mechanism.

On Apr 8, 2009, at 12:42 PM, Matt Garman wrote:

I don't really understand what the concept of a port is in Linux with
regards to multicast.

Basically, I want to use multicast on an internal network with many
nodes. I want to use multicast IP addresses to delineate the message
*type*. E.g., 239.0.0.1 for status monitoring, 239.0.0.2 for control
messages, 239.0.0.3 for heartbeats, 239.0.0.4 for chatting, etc etc.

Since I'm using the address space to delineate messages, can I just
hard-code my port (i.e. make it always the same)?

Put another way: what is the effect of having one host subscribe to
multiple multicast streams, where each stream has the same port, but a
different ip address? Is there a performance impact?

Thanks,
Matt
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Lawrence
~

Lawrence MacIntyre macintyrelp@xxxxxxxx Oak Ridge National Laboratory
865.574.8696 Cyber Space and Information Intelligence Research Group
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