[j-nsp] RED Drops with Qos

[Derick Winkworth]

By default, in JUNOS, there is no weighted average for RED.  Queue-depth is evaluated in an instantaneous fashion.  This means, of course, that there is no allowing for transient bursts.

Under the chassis/pic hierarchy you must enable weighted-average RED and you should put a weight of 9 as a start.






________________________________
From: Scott Berkman <scott at sberkman.net>
To: juniper-nsp at puck.nether.net
Sent: Mon, December 21, 2009 3:11:40 PM
Subject: [j-nsp] RED Drops with Qos

Hi All,



                I'm fairly new to Juniper, and I am trying to get our QoS
setup right on a M20 running JunOS 8.3 being used for T1 aggregation.



                The PIC is an IQ-enabled ChOC12 card, and the interfaces are
channelized T1's.  We seem to be classifying traffic into the 4 queues
correctly, but no matter what I change in the settings I am still seeing RED
drops on TCP/Low traffic.



Please find below the base configuration sections I am starting with.  I
have tried some different percentages, and tried defining specific
drop-policies based on some suggestions in the achieves from this list, but
no matter what I still see the drops in the same place.



                Are there any good best-practice guides to QoS on JunOS?  I
see lots about how the different settings effect the flow, but nothing in
terms of what works well for others.  Also is there anything obviously wrong
below?



                Thanks in advance for any help,



                -Scott



classifiers {

    dscp DSCP-CLASS {

        forwarding-class ef {

            loss-priority low code-points 101110;

        }

        forwarding-class af {

            loss-priority low code-points [ 011000 011010 ];

        }

        forwarding-class be {

            loss-priority low code-points 000000;

        }

        forwarding-class nc {

            loss-priority low code-points 111000;

        }

    }



forwarding-classes {

    queue 0 be;

    queue 1 ef;

    queue 2 af;

    queue 3 nc;

}



scheduler-maps {

    VOIP-MAP {

        forwarding-class be scheduler be-sched;

        forwarding-class ef scheduler ef-sched;

        forwarding-class af scheduler af-sched;

        forwarding-class nc scheduler nc-sched;

    }

}


schedulers {

    be-sched {

        transmit-rate percent 10;

        buffer-size percent 10;

        priority low;

    }

    ef-sched {

        transmit-rate percent 80;

        buffer-size percent 80;

        priority strict-high;

    }

    af-sched {

        transmit-rate percent 5;

        buffer-size percent 5;

        priority high;

    }

    nc-sched {

        transmit-rate percent 5;

        buffer-size percent 5;

        priority high;

    }

}



Example interface:

    ds-2/2/0:1:1:1 {

        scheduler-map VOIP-MAP;

        unit 0 {

            classifiers {

                dscp DSCP-CLASS;

            }

        }

    }



I also tested with the following scheduler and still saw the drops:

be-sched {

    transmit-rate percent 80;

    buffer-size percent 80;

    priority high;

}

ef-sched {

    transmit-rate percent 10;

    buffer-size percent 10;

    priority high;

}

af-sched {

    transmit-rate percent 5;

    buffer-size percent 5;

    priority high;

}

nc-sched {

    transmit-rate percent 5;

    buffer-size percent 5;

    priority high;

}

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