Unanswered Question
Mar 2nd, 2008


I just wanted to confirm my understanding..

A. class voice

priority 500

B. class voice

priority 500

police 500

In case A , only in case of congestion voice wil be policed to 500 while in case B it will be always policed to 500 even without congestion..?

Plz comment..



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Overall Rating: 4 (1 ratings)
royalblues Sun, 03/02/2008 - 23:39


Only when there is congesation, the QoS will be applicable.

The priority command will automatically introduce a policing action and hence the police command is not needed explicitly needed


gauravprakash Mon, 03/03/2008 - 02:13

Yes, but I have seen this explicit police command in LLQ class in many config ( specially core network).. so wanted to confirm it..



aravindhs Mon, 03/03/2008 - 02:39

Hi Gaurav,

As Narayan has pointed out rightly, the policing action takes effect only when there is congestion. So, there is no need for a police statement. But, as you have said, when the 'police' command is used, it limits the Voice class traffic is restricted to 500 xbs even at normal traffic times.

But is not recommended to police voice traffic. You do CAC to make decisions at the entry point rather than chopping off traffic at the network core.



Joseph W. Doherty Mon, 03/03/2008 - 20:42

What Narayan noted, is correct, priority is a rate limiter. So having a subordinate policer set to the same value is needless.

However, the priority cap drops traffic but since we can remark with a policer, you could have priority value set as an absolute cap but mark down traffic over a soft policer cap.

E.g. (syntax off)

class voice

priority 500

police 400 transmit dscp ef exceed action transmit dscp af41


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