flow control on gig networks

Discussion in 'Cisco' started by A. Myer, Feb 3, 2006.

  1. A. Myer

    A. Myer Guest

    I'm setting up full flow control on my hosts (sun boxes) for both sending and receiving. I have 2 Cisco Catalyst 3550 switches that are connected together. Should flow control on the ports that connect the two switches together be configured the same as the ports that are connected to the hosts?

    Thanks,
    Allen

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    A. Myer, Feb 3, 2006
    #1
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  2. A. Myer

    jcottingim Guest

    To answer your question susinctly: No, you should not use flow-control
    between the two switches. It was not intended to be used for end-to-end
    flow-control.

    HOWEVER: You may want to re-think your descision to use flow control at
    all.

    HP Says:
    Flow Control was originally invented to prevent packet drops by
    switches that were running at less than media-speed.

    Cisco Says:
    The problem Ethernet flow control is intended to solve is input buffer
    congestion on oversubscribed full duplex links which cannot handle
    wire-rate input.

    Ethernet flow control is not intended to solve the problem of
    steady-state overloaded networks or links.

    An example of where Ethernet flow control might be used appropriately
    is at the edge of a network where Gigabit Ethernet attached servers are
    operating at less than wirespeed, and the link only needs to be paused
    for a short time, typically measured in microseconds. The use of Pause
    frames to manage this situation may be appropriate under such
    circumstances.

    Unfortunately, Ethernet flow control is commonly misunderstood. It is
    not intended to address lack of network capacity, or end-to-end network
    issues. Properly used, Ethernet flow control can be a useful tool to
    address short term overloads on a single link.

    It will also "break" any QoS you may have set up for the hosts
    involved.


    J.Cottingim
     
    jcottingim, Feb 3, 2006
    #2
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