3845 router ATM sub-interface Modular QOS

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Dec 29th, 2008
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Hi All,

We were trying to configure Modular QOS on an ATM sub-interface in output direction on a Cisco 3845 router and we get an error message stating CBWFQ not supported on sub-interfaces.The sample config as below

policy-map x

class w

priority percent 20

class y

bandwidth percent 10

We have class-map configured appropriately.

Any help would be appreciated.



Anantha Subramanian Natarajan

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Overall Rating: 3.5 (2 ratings)
Giuseppe Larosa Tue, 12/30/2008 - 00:25
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Hello Anantha,

have you configured the ATM class of service on the associated PVC ?

if UBR it doesn't allow to use the CBWFQ because it sees the ATM subif without guaranteed BW resources

Hope to help


anasubra_2 Tue, 12/30/2008 - 05:58
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Hi Giuseppe,

Thanks for the response,Let me check whether UBR been used on that ATM subif.

Once again thank you very much


Anantha Subramanian Natarajan

lloydardoin Tue, 12/30/2008 - 08:27
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Hi anasubra,

We have several 3845s in our environment doing MQC. They act as ATM hosts for our client edge sites and we then connect to the AT&T network MPLS network to back haul to their perspective HQs. On the MPLS circuits the policy will need to go under the PVC like this.

interface ATM0/IMA1.1 point-to-point

description xxxxxxxxxxxxxxxxxxxx

bandwidth 1216

ip vrf forwarding xxxxxxx

ip address xx.xx.xx.xx

pvc 1/32

vbr-nrt 1216 1216 1

tx-ring-limit 3

oam-pvc manage 0

encapsulation aal5snap

service-policy output

On the ATM host side it goes directly under the sub-interface like this..

interface ATM0/IMA0.58 point-to-point

ip vrf forwarding xxxxxxx

ip address xx.xx.xx.xxx

service-policy input

pvc 1/40

encapsulation aal5snap



anasubra_2 Tue, 12/30/2008 - 08:45
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Hi Lloyd,

Thank you very much for the response. Actually with respect to your scenario,the ATM host side is our Cisco 3845 router having the point-to-point pvc and when we tried to configure the service-policy under the subif,it didn't take the command and gives the message that CBWFQ not supported on the subif,,,,also we tried configure the service-policy under the pvc and it takes the command without any error message but didn't show in the configuration.

Any help would be appreciated.



Anantha Subramanian Natarajan


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