CBWFQ or other policy / Congestion

Discussion in 'Cisco' started by amyl, Feb 12, 2008.

  1. amyl

    amyl Guest

    I have a remote site that has a point to point T1 to our main site.
    The remote site has an application that streams data at a fairly
    constant rate of 800Kb to the main site (udp based). This stream is
    not 24x7 as it kicks off at various intervals depending on when the
    data is needed.

    We also have a second application that has a data stream of 200Kb
    which is also not constant. This stream when it is being sent is more
    important than the 800Kb stream.

    Every once in a while a user will kick off some file transfer and the
    pipe will get congested and cause issues with starving the two data
    streams. My goal is in times of congestion make sure that both the
    800Kb stream and 200Kb stream are not interrupted.

    I was thinking of implementing CBWFQ for this, but I am not sure if
    this is the right policy.

    My questions is relating to what will happen in times of congestion?

    [1] Between the two classes (critical and priority-data) the
    guaranteed bandwidth is 1125Kbit. This leaves roughly around 400Kbit
    for the default class. Now if the 800Kbit stream is NOT in use will
    the default class be able to tap into that bandwidth? Or will it
    always be limited to the remaining bandwidth left from the other

    [2] If the bandwidth for the priority-data class exceeded 225Kb would
    it be tail dropped even in times where congestion was not present
    (bandwidth was available for it to be used)?

    class-map match-all critical
    match dscp af41

    class-map match-all priority-data
    match dscp af31
    policy-map qos-out-policy
    class critical
    bandwidth 225
    class priority-data
    bandwidth 900
    class class-default

    amyl, Feb 12, 2008
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  2. Yes, default class will be able to tap into that bandwidth.
    It depends. If you are using configuration below - no. If you will use
    "priority 225" instead of "bandwidth 225" excess of traffic will be dropped.
    Andrey Tarasov, Feb 12, 2008
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