The Modular Quality of Service CLI (MQC) Review – Policy Maps


In the first part of the MQC review – we examined class maps. These devices place our traffic into containers that we can assign QoS actions to. In this article, we are going to look at policy maps for assigning those actions.

Here I will create a quick class map, verify the class map, and then enter policy map configuration mode:

R1(config)#class-map match-any CM_ICMP
R1(config-cmap)#match access-group 100
R1#! The access-list 100 is not shown in this configuration
R1#show class-map
 Class Map match-any class-default (id 0)
   Match any 
 Class Map match-any CM_ICMP (id 1)
   Match access-group  100 
R1#conf t
R1(config)#policy-map PM_ICMP
Policy-map configuration commands:
  class        policy criteria
  description  Policy-Map description
  exit         Exit from policy-map configuration mode
  no           Negate or set default values of a command
  rename       Rename this policy-map

As you can see from the above configuration, there is not much going on in policy map configuration mode. We can add a description or rename the policy map but that is about it. The magic happens when we enter policy map class configuration for one of the classes that we configured:

R1(config-pmap)#class CM_ICMP
Policy-map class configuration commands:
  bandwidth        Bandwidth
  compression      Activate Compression
  drop             Drop all packets
  exit             Exit from class action configuration mode
  log              Log IPv4 and ARP packets
  netflow-sampler  NetFlow action
  no               Negate or set default values of a command
  police           Police
  priority         Strict Scheduling Priority for this Class
  queue-limit      Queue Max Threshold for Tail Drop
  random-detect    Enable Random Early Detection as drop policy
  service-policy   Configure Flow Next
  set              Set QoS values
  shape            Traffic Shaping

Notice these are the QoS actions we are so excited about – things like bandwidth and priority for CBWFQ, compression, policing and shaping, and random-detect for WRED. Notice also you can next policy maps inside each other for even more control. The service-policy keyword would allow this. Thanks to this third step of the MQC process, this service-policy assigns a policy map into this policy map.

Notice also the drop keyword you could use. What a powerful security mechanism this is, dropping the packets specified in your class map.

I hope you will join me in the third part of this series where we examine the third step- the service policy and verification of MQC.

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