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MX960, cos, output drops

‎02-06-2016 09:53 AM

Hello everybody!

 

I have a CoS question.

 

There is IP/MPLS network with defined CoS policies (classifires, rewrite rules, schedulers etc).


IP/MPLS --- ae2-mx960-pe1-xe-10/0/0 --- CE

 

MX960-PE1 is configured with 5 forwarding classes.

There is about 4Gb/s output traffic at interface xe-10/0/0.
This interface was configured without any scheduler-map
The default buffer size percentages for queues 0 through 7 are 95, 0, 0, 5, 0, 0, 0, and 0 percent of the total available buffer
http://www.juniper.net/documentation/en_US/junos14.2/topics/usage-guidelines/cos-configuring-the-sch...

 

Some time ago I have noticed that the count of the output drops at xe-10/0/0 was growing up.

username@mx960-pe1-RE0> show interfaces xe-10/0/0 extensive
...
Queue counters: Queued packets Transmitted packets Dropped packets
0 BE                     336790035162             336790035162                      0
1 PREMIUM            9365159195                   9363037174           2122021
2 RT                              27540623                      27540573                       50
3 NC                           387426278                    387426278                         0
4 SIG                          584714866                     584627249              87617

 

I have decided to configure this interface with the scheduler-map BBONE. As I did it, output drops stopped to grow up.
This seemes strange to me... because the router had resources (buffer and bandwith) to forward traffic and i don't know why did it begin to drop packets...


Can anyone please explain me, why did it happen?
By default buffer size for queue BE was 95%. I think that xe-10/0/0 was congested and traffic of other queues was dropped, but why is now BE traffic not dropped when I have the same amount of traffic at this 10g interface...

Below u can find cos configuration of the router.

 

username@mx960-pe1-RE0> show configuration class-of-service             
classifiers {
    dscp DSCP-BBONE {
        forwarding-class BE {
            loss-priority low code-points [ 000000 000001 ];
        }
        forwarding-class PREMIUM {
            loss-priority low code-points [ 010000 011000 ];
        }
        forwarding-class RT {
            loss-priority low code-points 101000;
        }
        forwarding-class NC {
            loss-priority low code-points [ 110000 111000 ];
        }
        forwarding-class SIG {
            loss-priority low code-points 100000;
        }
    }
    exp EXP-BBONE {                     
        forwarding-class BE {
            loss-priority high code-points exp0;
            loss-priority low code-points exp1;
        }
        forwarding-class PREMIUM {
            loss-priority low code-points [ exp2 exp3 ];
        }
        forwarding-class RT {
            loss-priority low code-points exp5;
        }
        forwarding-class NC {
            loss-priority low code-points [ exp6 exp7 ];
        }
        forwarding-class SIG {
            loss-priority low code-points exp4;
        }

    }
}                                       
code-point-aliases {
    exp {
        exp0 000;
        exp1 001;
        exp2 010;
        exp3 011;
        exp4 100;
        exp5 101;
        exp6 110;
        exp7 111;
    }
}
forwarding-classes {
    queue 0 BE;
    queue 1 PREMIUM;
    queue 2 RT;
    queue 3 NC;
    queue 4 SIG;                     
}
interfaces {
    ae2 {
        scheduler-map BBONE;
        unit * {
            classifiers {
                exp EXP-BBONE;
            }
            rewrite-rules {
                exp exp-def1;
            }
        }
    }                              
    ae8 {
        scheduler-map BBONE;
        unit 200 {
            forwarding-class PREMIUM;
        }
        unit 261 {
            forwarding-class SIG;    
        }
        unit 268 {
            forwarding-class RT;
        }
        unit 269 {
            forwarding-class RT;
        }
        unit 274 {
            forwarding-class SIG;
        }
    }
}
routing-instances {
    all {
        classifiers {
            exp EXP-BBONE;
        }
    }                                   
}
rewrite-rules {
    exp exp-def1 {
        import default;
        forwarding-class SIG {
            loss-priority low code-point 100;
        }
    }
}
scheduler-maps {
    BBONE {
        forwarding-class BE scheduler BE;
        forwarding-class PREMIUM scheduler PREMIUM;
        forwarding-class RT scheduler RT;
        forwarding-class NC scheduler NC;
        forwarding-class SIG scheduler SIG;
    }
}                                       
schedulers {
    BE {
        transmit-rate {
            remainder;
        }
        buffer-size {
            remainder;
        }
        priority low;
    }
    PREMIUM {
        transmit-rate percent 30;
        buffer-size percent 31;
        priority medium-low;
    }
    RT {
        transmit-rate {
            percent 50;                 
            rate-limit;
        }
        buffer-size temporal 100;
        priority strict-high;
    }
    NC {
        transmit-rate percent 5;
        buffer-size percent 20;
        priority high;
    }
    SIG {
        transmit-rate percent 5;
        buffer-size percent 10;
        priority medium-high;
    }
}

{master}

 

1 REPLY 1
Junos

Re: MX960, cos, output drops

‎02-10-2016 01:08 PM

Does anybody have any ideas? Smiley Sad