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CoS Rewrite and Classifier

  • 1.  CoS Rewrite and Classifier

    Posted 01-05-2021 13:38
    Hi,

    I'm trying to understand a lab environment for CoS, can someone please explain this to me... 

    The topology is very simple.
    1. There are multiple Customer interfaces connected to a PE router (Both VPLS and VRF), and a few Layer 3 interfaces in GRT
    2. The PE router connects to other P/PE routers via multiple core links


    The CoS classifiers and rewrite rules applied on the core links is as below

    set class-of-service interfaces ae1 scheduler-map sch-map-core
    set class-of-service interfaces ae1 unit 1 classifiers exp exp-core
    set class-of-service interfaces ae1 unit 1 classifiers inet-precedence ipprec-core
    set class-of-service interfaces ae1 unit 1 rewrite-rules exp exp-core
    set class-of-service interfaces ae1 unit 1 rewrite-rules inet-precedence ipprec-core
    set class-of-service interfaces ae1 unit 1 classifiers dscp dscp-core
    set class-of-service interfaces ae1 unit 1 rewrite-rules  dscp dscp-core


    I have following questions

    1. Can DSCP and Inet-precedence exist simultaneously on the same interface? Since Inet-precedence uses the first 3 bits and DSCP the whole 6 bits.
    2. Suppose I receive a packet from the customer interface and is classified into the Best-Effort forwarding-class.
             i)     When sending packet out of the core link, the rewrite rules will be applied. During the rewrite, will it change both the DSCP bits in IP Packet, and the EXP bit in MPLS ?


    Am I correct in assuming that rewrite will change the CoS bits in both (MPLS and Layer 3) types? And this rewrite will be the corresponding rewrite rule configured for Best-effort Forwarding-class.



    Thank You


  • 2.  RE: CoS Rewrite and Classifier

     
    Posted 01-22-2021 03:12
    Hi,

    For the first question i believe if there is no classifier configured then Inet-precedence will be used and if DSCP classifier is configured then DSCP will take precedence.

    https://www.juniper.net/documentation/en_US/junos/topics/reference/configuration-statement/inet-precedence-classifier-edit-cos-interfaces-acx-series.html

    Now for the second question for the rewrite rule for MPLS packets the exp bits in MPLS will be rewritten based on the exp rewrite rules applied on the interface.  For the IP packet it will have a separate DSCP rewrite rule.

    More details on the below link

    https://www.juniper.net/documentation/en_US/junos/topics/concept/mpls-cos-qfx-series


    Hope this helps.