[j-nsp] DSCP-marked traffic mysteriously being dropped by MX960

[John Neiberger]

Well, we have applied the scheduler map to the interface but we're
still seeing 100% drops in queue 1, which is where CS2 is hitting. It
is literally dropping every packet in queue 1, but I don't understand
enough about what I'm seeing to understand why.

 Queue counters:       Queued packets  Transmitted packets      Dropped packets
    0 HSD, BASIC-D                4775                 4775                    0
    1 MNGMT, VOIP-                4913                    0                 4913
    2 UET, CDN, VO                   0                    0                    0
    3 VOIP-BEARER,                  81                   81                    0


show configuration class-of-service interfaces ge-2/2/0
apply-groups CRAN-P2P-COS;

show configuration groups CRAN-P2P-COS
class-of-service {
    interfaces {
        <*> {
            scheduler-map QOS-MAP;
            unit 0 {
                classifiers {
                    dscp DSCPV4-CLASSIFIER;
                    dscp-ipv6 DSCPV6-CLASSIFIER;
                    exp EXP-CLASSIFIER;
                }
                rewrite-rules {
                    dscp DSCPV4-REWRITE;
                    dscp-ipv6 DSCPV6-REWRITE;
                    exp EXP-REWRITE;

show class-of-service interface ge-2/2/0
Physical interface: ge-2/2/0, Index: 270
Queues supported: 8, Queues in use: 4
  Scheduler map: QOS-MAP, Index: 26435

  Logical interface: ge-2/2/0.0, Index: 205
    Object                  Name                   Type                    Index
    Rewrite                 DSCPV4-REWRITE         dscp                    39698
    Rewrite                 DSCPV6-REWRITE         dscp-ipv6                6938
    Classifier              DSCPV4-CLASSIFIER      dscp                     7318
    Classifier              DSCPV6-CLASSIFIER      dscp-ipv6               40094

show class-of-service scheduler-map QOS-MAP
Scheduler map: QOS-MAP, Index: 26435

  Scheduler: TRAFFIC-CLASS-1-SCHEDULER, Forwarding class: BASIC-DATA,
Index: 34325
    Transmit rate: 20 percent, Rate Limit: none, Buffer size: 50000
us, Priority: low
    Excess Priority: unspecified
    Drop profiles:
      Loss priority   Protocol    Index    Name
      Low             any         41108    DROP-LOW
      Medium low      any             1    <default-drop-profile>
      Medium high     any             1    <default-drop-profile>
      High            any          2270    DROP-HIGH

  Scheduler: TRAFFIC-CLASS-2-SCHEDULER, Forwarding class:
PRIORITY-DATA, Index: 34329
    Transmit rate: 30 percent, Rate Limit: none, Buffer size: 20000
us, Priority: low
    Excess Priority: unspecified
    Drop profiles:
      Loss priority   Protocol    Index    Name
      Low             any         41108    DROP-LOW
      Medium low      any             1    <default-drop-profile>
      Medium high     any             1    <default-drop-profile>
      High            any          2270    DROP-HIGH

  Scheduler: TRAFFIC-CLASS-3-SCHEDULER, Forwarding class: VOD, Index: 34333
    Transmit rate: 45 percent, Rate Limit: none, Buffer size: 10000
us, Priority: low
    Excess Priority: unspecified
    Drop profiles:
      Loss priority   Protocol    Index    Name
      Low             any             1    <default-drop-profile>
      Medium low      any             1    <default-drop-profile>
      Medium high     any             1    <default-drop-profile>
      High            any          2270    DROP-HIGH

  Scheduler: TRAFFIC-CLASS-4-SCHEDULER, Forwarding class:
PREMIUM-DATA, Index: 34305
    Transmit rate: unspecified, Rate Limit: none, Buffer size: 35000
us, Priority: strict-high
    Excess Priority: unspecified
    Drop profiles:
      Loss priority   Protocol    Index    Name
      Low             any             1    <default-drop-profile>
      Medium low      any             1    <default-drop-profile>
      Medium high     any             1    <default-drop-profile>
      High            any             1    <default-drop-profile>


TRAFFIC-CLASS-1-SCHEDULER {
    transmit-rate percent 20;
    buffer-size temporal 50k;
    priority low;
    drop-profile-map loss-priority low protocol any drop-profile DROP-LOW;
    drop-profile-map loss-priority high protocol any drop-profile DROP-HIGH;
}
TRAFFIC-CLASS-2-SCHEDULER {
    transmit-rate percent 30;
    buffer-size temporal 20k;
    priority low;
    drop-profile-map loss-priority low protocol any drop-profile DROP-LOW;
    drop-profile-map loss-priority high protocol any drop-profile DROP-HIGH;
}
TRAFFIC-CLASS-3-SCHEDULER {
    transmit-rate percent 45;
    buffer-size temporal 10k;
    priority low;
    drop-profile-map loss-priority high protocol any drop-profile DROP-HIGH;
}
TRAFFIC-CLASS-4-SCHEDULER {
    buffer-size temporal 35k;
    priority strict-high;


On Fri, Jul 20, 2012 at 10:39 PM, John Neiberger <jneiberger at gmail.com> wrote:
> On Fri, Jul 20, 2012 at 3:49 PM, Wayne Tucker <wayne at tuckerlabs.com> wrote:
>> Does show interfaces <blah> extensive on the interface between Router A and
>> Device A show any drops?  IIRC, the default scheduler map does not define
>> schedulers for anything other than be and nc - so if you're classifying the
>> packets on input then it could be that they're going to a class that has no
>> resources on the egress interface.
>>
>> :w
>
> This is certainly what is happening. I checked and saw that we're
> seeing output drops in queue 1, but based on the reading I did
> tonight, it sounds like the default is for 95% of the bandwidth to be
> assigned to best effort in queue 0 and 5% is set aside for network
> control in queue 3. The fact that we're seeing all those drops in
> queue 1 pretty much proves the issues. We have some groups configured
> that have the right scheduler map on them. I just need to determine
> exactly which group is the right one and apply it to the right
> interfaces.
>
> I haven't had a chance to apply the fix yet, and all of the people who
> have access to the end devices for testing are gone for the weekend,
> but I wanted to thank everyone for the help on this. I'm pretty new to
> Juniper and I (and everyone else looking at this, including JTAC) were
> stumped.
>
>
> Thanks again,
> John