Showing results for 
Search instead for 
Did you mean: 

LLQ+CBWFQ to prioritize VoIP on Customer router connected to Service provider router



  have to configure LLQ+CBWFQ to prioritize VoIP traffic and Guarantee BW to Signalling traffic and Best effort for all other traffic.

I have a CISCO 2901 ver 15.1.4 and the output interface is a subinterface of the GigabitEthernet0/1 interface (GigabitEthernet0/1.3113) due to fact that Service provider interface need a tagged VLAN 3113 for input traffic.

Service provider router limit the input traffic to 10Mbps on is Ethernet 100Mbps interface therefore as input traffic reach the 10Mbps the traffic is dropped or shaped (I don’t know).


First as from my understanding I have to configure shape in the output subinterface:

and then apply a service policy child to the parent policy map.






class-map match-all VOICE

match ip dscp ef ! IP Phones mark Voice to EF


class-map match-any CALL-SIGNALING

match ip dscp cs3 ! Future Call-Signaling marking

match ip dscp af31 ! Current Call-Signaling marking



policy-map SES-policy

 class VOICE

  priority 2000 !Max BW 2Mbps 


  bandwith 1000

  ! Garated BW 1Mbps

 class class-default

  fair-queue ! All other data gets fair-queuing



policy-map WAN-shape-policy-out

 class class-default

  shape average 10m

  service-policy SES-policy





service-policy WAN-shape-policy-out



Please may you help me to understand if the way it work is like this:

In front of my 2901 router there is a provider router that allow only 10Mbps (even if the interface is a 1000Mbps/full duplex) therefore if from my LAN there is a internet traffic that need more than 10Mbps the "shape average 10m command" on parent policy start to drop packet this will drive to congestion that call the child policy where VOICE traffic goes on LLQ and signalling on CBWFQ and all other traffic to fair-queue mechanism.

Is that correct ? My doubt is that provider limit traffic to 10Mbps even if the provider interface is 100Mbps therefore I have to start to do QoS already at 10Mbs, is that correct ?

1 Reply 1

Joseph W. Doherty
Hall of Fame Master Hall of Fame Master
Hall of Fame Master


The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages wha2tsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.


Yes, you understand correctly.

However, I believe on many Cisco devices, the shaper doesn't count L2 overhead but providers often police CIR as a L2 values.  So, what you may need to do is shape about 10 to 20% slower then the CIR rate to allow for L2 overhead.

Also with your policy, I would suggest your class-default also use the bandwidth statement.

Optionally, you might also use FQ in your CALL-SIGNALING or you might eliminate this as a class as FQ in class-default may be "good enough".

Getting Started

Find answers to your questions by entering keywords or phrases in the Search bar above. New here? Use these resources to familiarize yourself with the community:

Recognize Your Peers