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CoS assistance needed

  • 1.  CoS assistance needed

    Posted 02-09-2021 00:28
    Juniper Tech support told us to configure the following two lines:

    set class-of-service shared-buffer egress percent 100

    set class-of-service forwarding-classes class best-effort no-loss

    Anyone tells me what these two lines exactly do ?  What are pros and cons for these two lines ?


    thanks a lot !!



  • 2.  RE: CoS assistance needed

    Posted 02-09-2021 08:26
    Below are the copy  paste from the Juniper site and snip about  the command..
    Your Juniper support should be able to tell you why to configure the commands , and send you links to that reason.

    set class-of-service shared-buffer egress percent 100
    The percentage you specify is the percentage of available buffer space allocated to the global shared ingress buffer pool or to the global shared egress buffer pool. If you allocate less than 100 percent of the available buffer space to the shared buffer pool, the remaining buffer space is added to the dedicated buffer pool. (You cannot directly configure the dedicated buffer pool for each port; dedicated buffers are allocated evenly across all the ports.)
    https://www.juniper.net/documentation/en_US/junos/topics/reference/configuration-statement/shared-buffer-edit-class-of-service-qfx-series.html


    set class-of-service forwarding-classes class best-effort no-loss
    no-loss-Guaranteed delivery for TCP no-loss traffic
    https://www.juniper.net/documentation/en_US/junos/topics/task/configuration/cos-forwarding-classes-qfx-series-cli.html

    Mind if I ask what issues you were having for them to suggest those added COS configurations ?


  • 3.  RE: CoS assistance needed

    Posted 02-09-2021 10:37
    thanks !   I did read the above.

    What I need to know pros and cons if that line is set.
    When I run "show class-of-service shared-buffer", the outputs with or without the above line configured are the same.  Also Juniper docs says "

    The default configuration allocates 100 percent of the available buffer space to the global shared buffers". if by default, why configured that line.

    I am learning what no-loss really means.




  • 4.  RE: CoS assistance needed

    Posted 02-09-2021 11:18
    I see what your saying. Just me reading but no vetting from cli.
    So you'd only want to use less than 100%  IF you need buffer space for a dedicated buffer pool..  Saying that.
    Then  Why would they need you to specify the default in your config .  That would be something they should definitely be able tell you why they suggested it..
    My past history with support in general,  Its because that is what I was told todo X time ago or what is considered best practice .

    "If you allocate less than 100 percent of the available buffer space to the shared buffer pool, the remaining buffer space is added to the dedicated buffer pool."

    Sorry I was not helpful.



  • 5.  RE: CoS assistance needed

    Posted 02-09-2021 12:04
    thanks so much for your inputs.
    The reason I am asking here is Tech support told my co-worker to add these lines to resolve some packet loss on one port.  Based on my co-worker, the drop was gone after these lines added.  I tried to figure out what theory behind this.

    Juniper tech support asked to add the three lines:

    set class-of-service shared-buffer egress percent 100

    set class-of-service forwarding-classes class best-effort queue-num 0

    set class-of-service forwarding-classes class best-effort no-loss


    The second line is default configuration
    I am trying to figure out what the first line does. Based on the Juniper docs, it is also the default configuration
    I will dig the third line.

    I am suspicious the drop disappeared because of something else.


  • 6.  RE: CoS assistance needed

    Posted 02-09-2021 11:12

    Hi!

    Is this for EX4200 or another product? In EX4200, the "shared-buffer egress percent 100" tells the switch to allocate only the minimum amount of buffer memory to each interface. The rest is allocated to a shared buffer pool. This is normally what you want if you have lots of interfaces that each have lots of end-points connected to them, like in a distribution switch. In such scenarios you will have temporary buffer needs on various interfaces and the interfaces will be able to "borrow" memory from the shared buffer memory pool.

    The second command seems odd, but it's important to have loss-priority low even on the best-effort class, at least on the EX4200.

    If you post the switch type, someone can surely help you. If it's the EX4200, I can share a config that works really well in a distribution scenario.

    /Fredrik




  • 7.  RE: CoS assistance needed

    Posted 02-09-2021 12:07
    The switch is QFX 5200.

    The reason I am asking here is Tech support told my co-worker to add these lines to resolve some packet loss on one port.  Based on my co-worker, the drop was gone after these lines added.  I tried to figure out what theory behind this.

    Juniper tech support asked to add the three lines:

    set class-of-service shared-buffer egress percent 100

    set class-of-service forwarding-classes class best-effort queue-num 0

    set class-of-service forwarding-classes class best-effort no-loss


    The second line is default configuration
    I am trying to figure out what the first line does. Based on the Juniper docs, it is also the default configuration
    I will dig the third line.

    I am suspicious the drop disappeared because of something else.

    thanks so much !!