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Bekzod Fakhriddinov

serivce policy rules

Hi guys , I have this reules applied on WAN router ports :
policy-map QoS
 class RTP
  priority percent 5
  set dscp ef
 class VoiceSignaling
  bandwidth percent 2
  set dscp cs3
 class class-default
  set ip precedence 0
policy-map SHAPE_16M
 class class-default
  shape average 16000000
   service-policy QoS

does it mean first shape bandwidth and then apply policy-map to shaped narrow pipe? If yes does it mean that if I don't have shape rule so policy-map will cut default 1 gig physical interface bandwidth and for my MPLS vpn pipe 10 MB I will have only RTP traffic running and the rest of the data dropped ? 

Thank you

Joseph W. Doherty
Hall of Fame Expert


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It depends which of the two polices are actually applied to your egress port.

If you apply the SHAPE_16M, it will constrain bandwidth to 16 Mbps, and if that creates queuing, the queues will be managed by the child policy, QoS.

On most CBWFQ Cisco platforms, your RTP class will only enforce the 5 percentage limit if there's congestion, i.e. as a child of the SHAPE_16M, only if the shaper queues traffic.

yes u right, I was meaning that Shape_16 mb ,   also I found this good explanation :
"Hierarchical Traffic Policies.  Child policy (bottom-level)—Identifies one or more classes of traffic and defines QoS behavior for the individual traffic streams. If you specify a class bandwidth in a child policy as a percentage, the router uses the top-level parent shape rate as the bandwidth reference (100 percent) rather than the bandwidth of the network interface. For example, in a nested policy shaped at 2 Mbps with a bottom-level child policy configured for 50 percent bandwidth, the router allocates 1 Mbps of bandwidth to the child policy (50 percent of the parent shape rate).

Parent policy (top-level)—Shapes the output of the traffic classes into a single shape rate. The parent policy can contain only the class-default class with only the shape command specified."