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6.2 Quality of Service (Implement, optimize and troubleshoot QoS using MQC…

- - - - Differentiated Services Code Point
        
        6 Bits field
        
        Per-Hop Behaviors
        
        Class Selector
        
        The CS PHB simply states that packets with
        larger CS DSCPs should be given better queuing preference than packets with lower CS DSCPs.
        
        Expedited Forwarding
        
        packets marked as EF should be given queuing preference
        so that they experience minimal latency, but the packets should be policed to prevent them from taking
        over a link and preventing any other types of traffic from exiting an interface during periods when this
        high-priority traffic reaches or exceeds the interface bandwidth.
        
        Assured Forwarding
        
        defines four classes for queuing purposes, along
        with three levels of drop probability inside each queue
        
        To convert from the AF name to the decimal equivalent, you can use a simple formula. If
        you think of the AF values as AFxy, the formula is
        8x + 2y = decimal value
        For example, AF41 gives you a formula of (8 4) + (2 1) = 34.
        x=one of the 4 queues
        y=drop probability
      - Class of Service
        
        Ethernet supports a 3-bit QoS marking field, but the field only exists when the Ethernet header
        includes either an 802.1Q or ISL trunking header. IEEE 802.1Q defines its QoS field as the 3 most-
        significant bits of the 2-byte Tag Control field, calling the field the user-priority bits.
- - - - The PHB actions (marking, queuing, and so on) are configured under a policy-map command.
        
        policy-map mypolicy
        class myclass1
        actions
      - The class-map command defines the matching parameters for classifying packets into service
        classes.
        
        class-map myclass1
        matching parameters
      - The policy map is enabled on an interface by using a service-policy command.
        
        interface s0/0
        service policy output mypolicy
  - - - Marking Using Policers
      - Policy Routing
      - Class Based Marking
  - - - Software queue
      - hardware queue
        
        tx-ring
        tx-queue
      - Class Based Weighted Fair Queueing
        
        The CBWFQ scheduler guarantees a minimum percentage of a link’s bandwidth to each class/queue.
        If all queues have a large number of packets, each queue gets the percentage bandwidth implied by the
        configuration.
        
        Classification: MQC
        Drop Policy: Tail Drop or WRED
        No. of Queues: 64
        Max Queue Length: Varies
        Scheduling: FIFO on 63 q, WFQ on class-default
        Scheduling among all queues: Result of scheduler provides a % guaranteed BW to each q #
        
        bandwidth 64 | %
        sets literal or percentage BW for the class
        
        bandwidth remaining percent %
        sets percentage of remaining BW for the class
      - Low Latency Queueing
        
        LLQ looks and acts just like CBWFQ in most regards, except it
        adds the capability for some queues to be configured as low-latency queues. LLQ schedules these
        specific queues as strict-priority queues. In other words, LLQ always services packets in these
        priority queues first.
        
        priority #
  - - - Weighted Random Early Detection