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Author Topic: IP Multicast Query  (Read 2598 times)

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Offline topendharness

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IP Multicast Query
« on: June 16, 2013, 08:38:27 AM »
Hi guys,
I have a general question regarding multicast operations and hopefully some can answer this one for me.

If a source is sending a number of data streams using the same group address e.g. but there are multiple ports e.g. 36841-36844, does that mean that if you initiate a subscription to join one of these, that the whole group (with all the ports) will be sent across the network via a PIM join message?
I suppose what i'm concerned about is if the multicast group has a lot of traffic in it and i only want one of the feeds from a particular port, do i get the whole lot or just the one that i want on my network segment?

Hopefully thats not a dumb question given there are a million utube videos being transferred across the internet at any one time!


Offline Michael McNamara

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Re: IP Multicast Query
« Reply #1 on: June 18, 2013, 02:43:36 PM »
Hi Wayne,

IGMP only concerns itself with Multicast addresses/groups, it doesn't care about TCP/UDP ports. So any device that issues an IGMP join will get the traffic addressed to that Multicast address. It's up to the host to discard the traffic if it doesn't want/need it.

Good Luck!
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Offline topendharness

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Re: IP Multicast Query
« Reply #2 on: June 18, 2013, 09:19:44 PM »
Thanks Michael, that makes perfect sense and gives me more of an appreciation for the amount of traffic that will traverse the network based on certain subscriptions.  ;D