multicast ip subnetting

Posted on 2006-06-01
Last Modified: 2007-12-19
    I want to setup multicast on an internal LAN. Do I have to use the ip subnet defined for multicast in order to get anything to talk to each other? Or can I just turn it on and configure IGMP. We have a Cisco enviroment 6509, 4009, 2950G EI switchs..
Question by:Fubyou
    LVL 12

    Expert Comment

    Just need to turn it ON
    LVL 5

    Accepted Solution

    Turn on the IGMP and use the multicast desitnation IP address - its reserved. No need to change source IP address to match this subnet.

    Good Luck
    LVL 9

    Assisted Solution

    Well that will work (maybe) if you have a flat Layer 2 network.  Depending on the type of Multicast you wish to do you may want to investigate what is already running on the network.  And what may be impacted if you don't throttle the Multicast.  With all the expensive hardware you have I imagine your net is pretty sizable.  And probably routed.  Is that the case?

    If so - you will need to "turn on" Multicast at Layer 2 and Layer 3.  In fact, even if your net is all Layer 2 you will still need an IGMP querier. which is generally a Layer 3 device.

    You will likely need IGMP Snooping on your Layer 2 devices (not IGMP) and IGMP (not snooping) or a multicast routing protocol (PIM, MOSPF etc.) on your Layer 3 devices.

    The Multicast addresses operate over the same wire as your LAN.  Doesn't have to be on your subnet and you do not have to change your addressing.  


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