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"Broadcast suppression" and recommendations

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  • 1.  "Broadcast suppression" and recommendations

    Posted Feb 06, 2014 05:33 AM

    Hello

     

    I ask myself the following question:
    what is the value recommended for the command "broadcast-suppression" (in percentage or pps ? ).
    I have the switches with 1Gbps ports for users, and 10Gbps for uplink to Core.

     

    Is it a command to be applied to general way or occasionally to solve problems?

     

    Thank you for your recommendations.

     

    Laetitia.



  • 2.  RE: "Broadcast suppression" and recommendations

    Posted Feb 06, 2014 05:22 PM

    Depends on if you expect to have plenty of broadcast traffic or not.

     

    For a corporate net with many windows clients there can be plenty of actions taken through broadcast. Also depending on how many machines you will have per vlan.

     

    Out of the blue I think these values should be ok, not to low and yet not to high:

     

    broadcast-suppression pps 100

    multicast-suppression pps 100

    unicast-suppression pps 100

     

    Note however that you of course shouldnt use multicast suppression if you use multicastbased routing protocols or have multicast traffic for other use (iptv or such)- or if you do you would most likely need a higher pps value than 100.

     

    The unicast-suppression, if Im not mistaken, is regarding packets where the device doesnt have a match for in its arp table. This is also called DLF (Destination Lookup Failure) - in these cases the packet will be broadcasted on all interfaces which belongs to the same vlan except the interface the packet arrived at.

     

    The point of unicast-suppression would be if a client gets a DDoS attack and disconnects - if you are unlucky the incoming traffic would then be "mirrored" to all the other clients in the same vlan in the same switch (and a unicast-suppression of pps 100 would limit this "mirrored" DDoS towards the other clients in the same vlan on the same switch).