Pruning on 3500 and 3550 series switches

Discussion in 'Cisco' started by Fred Atkinson, Nov 1, 2005.

  1. This morning, I set up a lab experiment to show my students
    how pruning worked. However, after we pruned, the distant switch was
    still getting the frames from the pruned VLAN. We know that is true
    because we could still ping a PC that was connected to that switch
    over the VLAN. By my understanding, we shouldn't have beena able to
    ping it any more after that VLAN was pruned towards it.

    Does anyone have any information to shed some light on this
    mystery? URLs with a solution would be greatly appreciated.


    Fred Atkinson, Nov 1, 2005
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  2. Fred Atkinson

    anybody43 Guest

    after we pruned, the distant switch was
    VLAN pruning is intended to prevent Broadcast and
    Unknown traffic from being needlessly
    flooded along trunks in the case where the
    VLAN has no active ports on the far side of the trunk
    from the source of the traffic.
    In that case pruning would be inappropriate
    since the traffic is required to cross the link.

    For what it's worth I have never liked the idea

    - Few such links are likely in (most) well designed networks.
    - Process sounds complex and potentially
    problem prone.
    - I expect that few people use it so you will
    be a beta tester.

    Good for a class though, you need to know

    addressing (L2)
    forwarding decisions

    If they can get their
    little heads well enough round this to correctly
    predict behaviour then they will be ahead of
    . . .
    some professors.<g>

    I doubt though if the educational potential
    was a consideration for Cisco when they
    spent the money to put it in.

    Maybe the VLAN Policy Server thing
    was put in just for such an eventuality too?
    I suspect that it though has gone.
    anybody43, Nov 1, 2005
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