This article explains why Differentiated Services Code Point (DSCP) classifiers may not apply to an interface when Mixed Virtual Chassis configuration is enabled on EX4300 Series switches.

When a VC is configured to use Mixed mode, DSCP classifiers are seen to use default classifiers instead of custom classifiers even though they are configured, thus resulting in loss of prioritization:

VC Mixed Mode

{master:0}
root@EX4300VC> show virtual-chassis    

Virtual Chassis ID: d55b.2006.afa0
Virtual Chassis Mode: Mixed
                                                Mstr           Mixed Route Neighbor List
Member ID  Status   Serial No    Model          prio  Role     Mode  Mode ID  Interface
0 (FPC 0)  Prsnt    PD3710000570 ex4300-48p     128   Master*  Y     VC   1  vcp-255/2/1
1 (FPC 1)  Prsnt    PD3710000470 ex4300-48p     128   Backup   Y     VC   0  vcp-255/2/0

{master:0}[edit]
root@EX4300VC# run show class-of-service interface ge-0/0/1

Physical interface: ge-0/0/1, Index: 646
Maximum usable queues: 12, Queues in use: 7
  Scheduler map: custom-voip-sched-maps, Index: 36622
  Congestion-notification: Disabled

  Logical interface: ge-0/0/1.0, Index: 558
Object            Name                   Type            Index
Classifier        ieee8021p-untrust      untrust         16

Normal VC Mode

{master:0}
root@EX4300VC> show virtual-chassis 

Virtual Chassis ID: d55b.2006.afa0
Virtual Chassis Mode: Enabled
                                                Mstr           Mixed Route Neighbor List
Member ID  Status   Serial No    Model          prio  Role      Mode  Mode ID  Interface
0 (FPC 0)  Prsnt    PD3710000570 ex4300-48p     128   Master*      N  VC   1  vcp-255/2/1
1 (FPC 1)  Prsnt    PD3710000470 ex4300-48p     128   Backup       N  VC   0  vcp-255/2/0

{master:0}
root@EX4300VC> show class-of-service interface ge-0/0/1   

Physical interface: ge-0/0/1, Index: 702
Maximum usable queues: 12, Queues in use: 11
  Scheduler map: custom-voip-sched-maps, Index: 36622
  Congestion-notification: Disabled

  Logical interface: ge-0/0/1.0, Index: 648
Object         Name                      Type         Index
Classifier     custom-dscp-classifier    dscp         22586

Configuration

set class-of-service classifiers dscp custom-dscp-classifier import default
set class-of-service classifiers dscp custom-dscp-classifier forwarding-class custom-voice-fc loss-priority low code-points 101110
set class-of-service classifiers dscp custom-dscp-classifier forwarding-class custom-control-fc loss-priority low code-points 110000
set class-of-service classifiers dscp custom-dscp-classifier forwarding-class custom-control-fc loss-priority low code-points 011000
set class-of-service classifiers dscp custom-dscp-classifier forwarding-class custom-control-fc loss-priority low code-points 011010
set class-of-service classifiers dscp custom-dscp-classifier forwarding-class custom-control-fc loss-priority low code-points 111000
set class-of-service classifiers dscp custom-dscp-classifier forwarding-class custom-video-fc loss-priority low code-points 100010
set class-of-service classifiers dscp custom-dscp-classifier forwarding-class custom-video-fc loss-priority low code-points 010010
set class-of-service classifiers dscp custom-dscp-classifier forwarding-class custom-backup-fc loss-priority low code-points 001010
set class-of-service forwarding-classes class custom-best-effort queue-num 0
set class-of-service forwarding-classes class custom-backup-fc queue-num 2
set class-of-service forwarding-classes class custom-video-fc queue-num 4
set class-of-service forwarding-classes class custom-voice-fc queue-num 5
set class-of-service forwarding-classes class custom-control-fc queue-num 7
set class-of-service interfaces ge-* scheduler-map custom-voip-sched-maps
set class-of-service interfaces ge-* unit 0 classifiers dscp custom-dscp-classifier
set class-of-service scheduler-maps custom-voip-sched-maps forwarding-class custom-voice-fc scheduler custom-voice-scheduler
set class-of-service scheduler-maps custom-voip-sched-maps forwarding-class custom-control-fc scheduler custom-control-scheduler
set class-of-service scheduler-maps custom-voip-sched-maps forwarding-class custom-video-fc scheduler custom-video-scheduler
set class-of-service scheduler-maps custom-voip-sched-maps forwarding-class custom-backup-fc scheduler custom-backup-scheduler
set class-of-service scheduler-maps custom-voip-sched-maps forwarding-class custom-best-effort scheduler custom-data-scheduler
set class-of-service schedulers custom-voice-scheduler buffer-size percent 15

When the VC is configured to use Mixed Mode in EX4300 Series switches, the switch works only as a linecard, resulting in the entire setup using the hardware specifications of the lowest switch even though a high-end switch exists in the same setup. On the other hand, QFX51xx-EX4600-EX4300-48mp Series switches work as the primary VC. Due to this, the CoS configuration changes from enterprise to data center configuration and QFX does not use enterprise CoS configuration.

The default CoS configuration in all QFX platforms (QFX51xx-4600-4300-48mp) is different from what is used in enterprise EX platforms (EX4300). Because of the difference in CoS architecture, EX4300 omits the custom configuration and uses the default CoS configuration.

See Example: Configuring CoS Hierarchical Port Scheduling (ETS) for more details about CoS in QFX51xx-EX4600-EX4300-48MP platforms.

For CoS configuration example for EX4300 platforms, see Example: Configuring Class of Service for the Midsize Enterprise Campus .

This is expected behavior because EX4300-48P is not intended to work as a VC Primary, but only as a linecard in a Mixed VC environment. QFX51xx-EX4600-EX4300-48MP, on the other hand, will function only as a primary.

The solution to resolve this issue would be to revert to VC Normal mode, which will restore the setup wherein EX4300 uses legacy CoS configuration and QFX uses the data center (ETS) configuration.

2021-03-24: Updated the article terminology to align with Juniper's Inclusion & Diversity initiatives