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LLQ Priority , behaviour of bulit in policer

Hi,

we are discussing about the behaviour of the built-in policer of LLQ.

If we configure following service-policy on a WAN-interface in the case there is no other traffic, is traffic which matches the criteria of class QOS-Class-Realtime allowed to exceed the 20% of the total available bandwidth, or is exceeding traffic always dropped independent if the line is congested or not.

policy-map QOS-Policy-WAN

class QOS-Class-Network-Control

class QOS-Class-Realtime

    priority percent 20

class QOS-Class-Platinum

    bandwidth remaining percent 45

class QOS-Class-Gold

    bandwidth remaining percent 10

class QOS-Class-Silver

    bandwidth remaining percent 25

class QOS-Class-Bronze

    bandwidth remaining percent 10

class QOS-Class-Best-Effort

Thx

Hubert

8 REPLIES

Re: LLQ Priority , behaviour of bulit in policer

Hi hubert

The LLQ builtin policed will not take effect until the interface get congested

In other words If the interface is NOT congested the Traffic of the LLQ class cam exceed the LLQ allocated bandwidth

Hope this help

Sent from Cisco Technical Support iPhone App

New Member

Re: LLQ Priority , behaviour of bulit in policer

Thx that what I assumed. If I remember correctly there they noticed in some QOS-guide that you should not configure more than 30% of available BW for the LLQ , I cant find this statement, do you know what could be the reason for this ?

New Member

Re: LLQ Priority , behaviour of bulit in policer

Thx that what I assumed. If I remember correctly there they noticed in some QOS-guide that you should not configure more than 30% of available BW for the LLQ , I cant find this statement, do you know what could be the reason for this ?

Re: LLQ Priority , behaviour of bulit in policer

Not sure if there is such limitation for that but MQC will only allow 75% of the interface bandwidth to be allocated by default and to remove this restriction command -Max-reserved-bandwidth 100 should be used under interface.

Thanks

Ajay

New Member

Re: LLQ Priority , behaviour of bulit in policer

This restriction does not longer exist with 15.0 based images

Re: LLQ Priority , behaviour of bulit in policer

Because the llq will always serviced first in the case of interface congestion it's best practice to allocate around 30 or 33% for VoIP if enough to avoid having the llq class take over other types of traffic

However it is not must if it dosent meet your needs

Hope this help

If helpful rate

Super Bronze

Re: LLQ Priority , behaviour of bulit in policer

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NB: That's correct in that Cisco documents this as the reason for their recommendation.  However, keeping your LLQ to under about 1/3 of link capacity also tends to insure adequate bandwidth to avoid queuing delays against itself.

New Member

LLQ Priority , behaviour of bulit in policer

Hubert, checking your config:

policy-map QOS-Policy-WAN

class QOS-Class-Network-Control

class QOS-Class-Realtime

    priority percent 20

class QOS-Class-Platinum

    bandwidth remaining percent 45

class QOS-Class-Gold

    bandwidth remaining percent 10

class QOS-Class-Silver

    bandwidth remaining percent 25

class QOS-Class-Bronze

    bandwidth remaining percent 10

class QOS-Class-Best-Effort

and... not having a restriction (75% of int bandw) your class REALTIME can use as much bandwidth it needs, IF there's no other classes competing for the bandwidth and we have no congestion.

In case of congestion, LLQ classes will have a MAX  while the others will have a MIN bandwidth guaranteed.

LLQ have strict priority, which means that packets will be fwd as soon as it hits the router. In case the queue is FULL (congestion)  the router will try to transmit, BUT it wont have strict priority

I always configure a policing policy map under the real time classes, to make sure when it exceeds the MAX packet will be dropped.

I hope this helps..

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