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Junos CoS Classification

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  • 1.  Junos CoS Classification

    Posted 24 days ago

    I am reviewing the JNCIE-ENT self study bundle and am confused by some CoS configuration. The examples given guide the user through creating both dscp and ieee802.1p classifiers. Then they are instructed to apply the dscp classifiers to all L3 interfaces and apply the ieee802.1p classifiers to all L2 interfaces. The guide then goes on to apply the ieee802.1p classifiers to several access and trunk interfaces (so as instructed, all L2 iterfaces).

     

    But  an access interface will receive only untagged traffic, that traffic will not have any 802.1q header and no PCP bits. So I don't think a classifier based on iee802.1p will actually do anything. I have tested this in a lab and as I predicted the ieee802.1p classifier applied on the access interface does nothing. It is only when you change that interface to a trunk and tagged traffic sent to the interface that the classifier starts classifying traffic to the correct Queues. If I apply a dscp classifier on the access interface, it works as expected, classifying traffic based on the inbound dscp value. 

     

    Interestingly the default classifier applied to an access interface is ieee802.1p-untrust, which basically assigns all incoming frames with a pcp 0-7 to best-effort. But this doesn't make sense to me as the incoming traffic will not contain pcp bits. Could someone please clarify if a ieee802..1p classifier applied to a access interface serves any purpose??? if not then would it make far more sense to apply a dscp classifier, where it can be configured to trust the markings coming from the end device placing traffic in appropriate FCs, or simply bleach the traffic into a single FC and rewrite the dscp or pcp on exit?

     

    Thanks in advance. 

     

     


    #EX
    #class-of-service
    #QOS


  • 2.  Re: Junos CoS Classification
    Best Answer

    Posted 24 days ago

    Hello,

     


    @alkavana wrote:

    The guide then goes on to apply the ieee802.1p classifiers to several access and trunk interfaces (so as instructed, all L2 iterfaces).

     

    But  an access interface will receive only untagged traffic, that traffic will not have any 802.1q header and no PCP bits.


     

    Well, there also are "tagged access" interfaces but in general yes, 802.1ieee classifier does not work on Ethernet frames which do not have a 802.1Q VLAN tag.

     


    @alkavana wrote:

     

    would it make far more sense to apply a dscp classifier, where it can be configured to trust the markings coming from the end device placing traffic in appropriate FCs, or simply bleach the traffic into a single FC and rewrite the dscp or pcp on exit?

     


     

    dscp classifier would only work on IPv4 packets, not on ARP, not on IPv6, not on L2 control frames such as STP.

    So, if You have L2 interface that receives ONLY frames without 802.1Q VLAN tag, and if You want 100% classification (no missing/incorrect FC) then You have following options:

    1/ configure fixed classifier (a classifier assigned to ingress logical interface, all incoming frames will fall into single FC+LP combo)

    2/ use "family bridge|ccc" (on MX) or "family ethernet-switching" (on EX|QFX) MF classifiers to match on i.e. Ethertype and classify accordingly.

    Obviously, method [1] is less cumbersome than [2] but also less flexible. 

    HTH

    Thx

    Alex     

     

      

     



  • 3.  Re: Junos CoS Classification

    Posted 23 days ago

    Hi @aarseniev, many thanks for the detailed reply, it has cleared up a lot for me.

     

    One final question you may be able to help with. Why is the default classifier on an access interface a ieee802.1p classifier (ieee 802.1untrust)? As we discussed this won't achieve anything.

     

    Thanks in advance

     



  • 4.  Re: Junos CoS Classification

    Posted 23 days ago

    Hello,

     


    @alkavana wrote:

    . Why is the default classifier on an access interface a ieee802.1p classifier (ieee 802.1untrust)?


     

    I don't see this happening (meaning default classifier is not present on L2 interfaces) in my lab with VMX and JUNOS 19.1R3. Configuration below:

     

    set routing-instances VS1 instance-type virtual-switch
    set routing-instances VS1 interface ge-0/0/9.0
    set routing-instances VS1 interface ae6.0
    set routing-instances VS1 interface ae7.0
    set routing-instances VS1 bridge-domains BDOM vlan-id-list 100-110
    set interfaces ge-0/0/9 encapsulation ethernet-bridge
    set interfaces ge-0/0/9 unit 0 family bridge interface-mode access
    set interfaces ge-0/0/9 unit 0 family bridge vlan-id 100
    set interfaces ae6 flexible-vlan-tagging
    set interfaces ae6 encapsulation extended-vlan-bridge
    set interfaces ae6 aggregated-ether-options lacp active
    set interfaces ae6 unit 0 family bridge interface-mode trunk
    set interfaces ae6 unit 0 family bridge vlan-id-list 100-110
    set interfaces ae7 encapsulation ethernet-bridge
    set interfaces ae7 aggregated-ether-options lacp active
    set interfaces ae7 unit 0 family bridge interface-mode access
    set interfaces ae7 unit 0 family bridge vlan-id 100
    

     

    Verification:

     

    show class-of-service interface ge-0/0/9 detail 
    
    Physical interface: ge-0/0/9, Enabled, Physical link is Up
      Link-level type: Ethernet-Bridge, MTU: 1514, MRU: 1522, LAN-PHY mode, Speed: 1000mbps, Loopback: Disabled,
      Source filtering: Disabled, Flow control: Enabled, Auto-negotiation: Enabled, Remote fault: Online
      Device flags   : Present Running
      Interface flags: SNMP-Traps Internal: 0x20004000
      Link flags     : None
    
    Physical interface: ge-0/0/9, Index: 161
    Maximum usable queues: 8, Queues in use: 4
    Exclude aggregate overhead bytes: disabled
    Logical interface aggregate statistics: disabled
      Scheduler map: <default>, Index: 2
      Congestion-notification: Disabled
    
      Logical interface ge-0/0/9.0 
        Flags: Up SNMP-Traps 0x24024000 Encapsulation: Ethernet-Bridge
        bridge
    Interface       Admin Link Proto Input Filter         Output Filter
    ge-0/0/9.0      up    up   bridge
    Interface       Admin Link Proto Input Policer         Output Policer
    ge-0/0/9.0      up    up        
                               bridge
    
      Logical interface: ge-0/0/9.0, Index: 381
    
    show class-of-service interface ae6 detail
            
    Physical interface: ae6, Enabled, Physical link is Up
      Link-level type: Extended-VLAN-VPLS, MTU: 9192, Speed: 1Gbps, Loopback: Disabled, Source filtering: Disabled,
      Flow control: Disabled
      Device flags   : Present Running
      Interface flags: SNMP-Traps Internal: 0x20004000
    
    Physical interface: ae6, Index: 147
    Maximum usable queues: 8, Queues in use: 4
    Exclude aggregate overhead bytes: disabled
    Logical interface aggregate statistics: disabled
      Scheduler map: <default>, Index: 2
      Congestion-notification: Disabled
    
      Logical interface ae6.0 
        Flags: Up SNMP-Traps 0x20024000 VLAN-Tag [  ]  Encapsulation: Extended-VLAN-Bridge
        bridge
    Interface       Admin Link Proto Input Filter         Output Filter
    ae6.0           up    up   bridge
    Interface       Admin Link Proto Input Policer         Output Policer
    ae6.0           up    up        
                               bridge
    
      Logical interface: ae6.0, Index: 364
    
      Logical interface ae6.32767 
        Flags: Up SNMP-Traps 0x24004000 VLAN-Tag [ 0x0000.0 ]  Encapsulation: Extended-VLAN-Bridge
        multiservice
    Interface       Admin Link Proto Input Filter         Output Filter
    ae6.32767       up    up   multiservice
    Interface       Admin Link Proto Input Policer         Output Policer
    ae6.32767       up    up        
                               multiservice __default_arp_policer__
    
      Logical interface: ae6.32767, Index: 365
    
    
    show class-of-service interface ae7 detail   
    
    Physical interface: ae7, Enabled, Physical link is Up
      Link-level type: Ethernet-VPLS, MTU: 9192, Speed: 1Gbps, Loopback: Disabled, Source filtering: Disabled, Flow control: Disabled
      Device flags   : Present Running
      Interface flags: SNMP-Traps Internal: 0x20004000
    
    Physical interface: ae7, Index: 148
    Maximum usable queues: 8, Queues in use: 4
    Exclude aggregate overhead bytes: disabled
    Logical interface aggregate statistics: disabled
      Scheduler map: <default>, Index: 2
      Congestion-notification: Disabled
    
      Logical interface ae7.0 
        Flags: Up SNMP-Traps 0x24024000 Encapsulation: Ethernet-Bridge
        bridge
    Interface       Admin Link Proto Input Filter         Output Filter
    ae7.0           up    up   bridge
    Interface       Admin Link Proto Input Policer         Output Policer
    ae7.0           up    up        
                               bridge
    
      Logical interface: ae7.0, Index: 380
    
    show bridge domain 
    
    Routing instance        Bridge domain            VLAN ID     Interfaces
    VS1                     BDOM-vlan-0100           100      
                                                                 ae6.0
                                                                 ae7.0
                                                                 ge-0/0/9.0
    VS1                     BDOM-vlan-0101           101      
                                                                 ae6.0
    VS1                     BDOM-vlan-0102           102      
                                                                 ae6.0
    VS1                     BDOM-vlan-0103           103      
                                                                 ae6.0
    VS1                     BDOM-vlan-0104           104      
                                                                 ae6.0
    VS1                     BDOM-vlan-0105           105      
                                                                 ae6.0
    VS1                     BDOM-vlan-0106           106      
                                                                 ae6.0
    VS1                     BDOM-vlan-0107           107      
                                                                 ae6.0
    VS1                     BDOM-vlan-0108           108      
                                                                 ae6.0
    VS1                     BDOM-vlan-0109           109      
                                                                 ae6.0
    VS1                     BDOM-vlan-0110           110      
                                                                 ae6.0
    

     

    Could You please share Your router/switch model, JUNOS version and  exact configuration where You see "ieee8021p-untrust"  classifier applied by default to L2 interfaces?

    HTH

    Thx

    Alex



  • 5.  Re: Junos CoS Classification

    Posted 21 days ago

    Sorry for the delayed response. all requested detail is below. Code is 18.4, but I don't think anything is wrong. According to junos documentation it is expected behaviour. It just doesn't make sense to me why they would do it.

    alkavana_1-1604699174771.png

     

     



  • 6.  Re: Junos CoS Classification

    Posted 21 days ago
      |   view attached

    Hi @

     
     
     
     


  • 7.  Re: Junos CoS Classification

    Posted 20 days ago

    Hello,

     


    @alkavana wrote:

     
     
     
     

     

     

    Please see https://www.juniper.net/documentation/en_US/junos/topics/concept/classifier-ba-overview-cos-config-guide.html

     

    NOTE

    If you apply an IEEE 802.1 classifier to a logical interface, this classifier takes precedence and is not compatible with any other classifier type. 

     

    HTH

    Thx

    Alex