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Anleitung Zusammenfassung
The markers can be externally visible fields (DSCP value, 802.1p value) and/or internally visible fields (bandwidth class and queue number). These markers are explained in "Packet markers" on page 4. • Policing Packets belonging to any given class map can be assigned a colour (bandwidth class) based on whether they are inside or outside the bandwidth limits set for that class map. The packets are marked with the colour that was applied to them, and at various points in the QoS process, decisions on the packets' fate can be made on the basis of what colour they have been marked with. • Remarking After policing, remarking can update packets’ QoS markers depending on how well the flow conforms to its bandwidth limits. For example, if a flow exceeds its bandwidth requirements, QoS can update the packets’ DSCP values. • Per-port control over egress queue parameters Queue lengths, scheduling process, relative weights, etc can be set on all queues on a per- port basis. • Highly configurable default class map All the parameters that can be set on a normal class map can also be set on the default class map (the catch-all class map that matches all traffic that does not explicitly match any other class map). C613-16120-00 REV A • Ability to see the current state of egress queues There are commands that enable you to see statistics relating to every egress queue on every port. Each of these features is discussed in much more detail later on in this document. Contents Introduction .............................................................................................................................................. 1 Which products and software version does this Note apply to? ................................................. 3 The process flow and methodology of the QoS system ................................................................ 3 Packet markers ................................................................................................................................. 4 Outline of the QoS processing flow ................................................................................................... 5 Initial mapping to an egress queue, based on 802.1p value .................................................... 5 Classification ...................................................................................................................................... 6 Premarking ......................................................................................................................................... 6 Policing ................................................................................................................................................ 7 Limiting or remarking (dropping non-conformant packets) ................................................... 7 Queue shaping .................................................................................................................................. 8 Scheduling .......................................................................................................................................... 9 Details of the component processes, and how to configure them ............................................ 10 QoS elements: policy maps, class maps, policers, matches .................................................. 10 Diagram of the overall QoS process flow ................................................................................ 11 Enabling QoS globally .................................................................................................................... 12 Initial mapping to queue based on tag ....................................................................................... 12 Classification .................................................................................................................................... 13 Premarking ....................................................................................................................................... 13 Policing .............................................................................................................................................. 16 Remarking ........................................................................................................................................ 22 Queue shaping—queue sets, RED, and tail-drop .................................................................... 23 Scheduling ........................................................................................................................................ 27 Egress bandwidth limiting .................................................................................................................... 29 Policing Examples ................................................................................................................................... 30 1: Policing separate traffic types on separate ports ....