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how to limit the flodding of UDP traffic

Hello All,

We are troubleshooting a performance issue in our Network. UDP traffic from a particular application is completely congesting the link.

Though we have QoS to throttle the traffic from the application to use only 9% bandwith of the link but that application flodding the traffic around 80% of the link. The traffic from the application is getting categorised as default traffic CS0.


Class class-default
      bandwidth remaining 9 (%)


Is there anything we are missing in the configuration of the class-map that is alowing the flodding of the UDP traffic?









New Member

If you use a router you must

If you use a router you must configure a policy-map as below (example):

class-map match-any TrafficoVoipCTRL
 match protocol skinny
 match access-group name TrafficoVoiceCtrl
 match access-group name TrafficoICM
 match protocol sip

policy-map QosIdcToTrapani
 class TrafficoVoipCTRL
  set ip dscp af31
  priority percent 20
policy-map QosIdcToTrapani
 class TrafficoROUTING
  set ip dscp cs6
  bandwidth percent 3


interface GigabitEthernet0/0
 service-policy output QosIdcToTrapani


Super Bronze

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You might misunderstand the purpose of the CBWFQ bandwidth statement.  It guarantees a minimum, it doesn't limit the class from using all the link bandwidth.

The latter, though, isn't necessarily bad. Other classes should be able to obtain their bandwidth guarantees, and as you've defined FQ in the class, a high rate flow shouldn't monopolize the bandwidth (i.e. other flows will get their share to).

With QoS, the question shouldn't be whether your UDP traffic can acquire 80% of the link, but rather it is adverse to other applications when it does acquire 80%.  If it is adverse, you can often just lower its bandwidth guarantee.

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