JUNOS CoS processing building block with related CLI commands

Juniper CLI learning is a little challenge for junior network engineers or Cisco IOS engineers, because the JUNOS modular and hierarchical structure design.
Some features may need several command line which were configured under different hierarchical levels, then combined all of them together in another hierarchical level.
Such kind of CLI design especially not easy to learn when apply CoS on juniper device.(I believe many Cisco IOS engineers don't want to switch to JUNOS because of this...)


As above figure is my understanding about the related JUNOS command which is using in our production network.


Some CoS features was missed on the figure:
  • The most important key points of JUNOS CoS is the traffic classification of Forwarding-class. If you made mistake or missed configuration of BA or MF classifier blocks, then your CoS must be not running correctly.
  • We still not apply the Forwarding-Policy based on BA or DSCP. If you have different quality/latency of circuit or routing path, you can leverage this feature to assign different next-hop to differentiate the traffic priority.
  • H-CoS, if you enabled hierarchical-scheduler to control interface-set(groups of specific use purpose VLANs), then you might need to configure traffic-control-profiles in additional for shaping/shceduling.
  • Schedulers priority definition is very important, especially how to ensure Voice traffic was classified and assigned to strict-high queue(and map to correct Forwarding-class) then apply an reasonable bandwidth policer to prevent it exhausts all interface bandwidth and make other traffic starve to death.

I hope this can help you to learn something from this when you troubleshoot your end-to-end QoS configuration, you can check the configuration followed by referring to this JUNOS CoS processing flow.
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