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QoS on ATM DSL interface

Unanswered Question
May 3rd, 2006
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using the document "QoS Solutions for PPPoE and DSL Environments" as a reference I'm trying to implement Quality of Service for a DSL connection via the ATM interface on a 2821 router.

So I apply the service-policy under ATM VC configuration mode (PVC 8/35) and the command is accepted with no complaints, but when I do a show run, I realize the command is not there:


interface ATM0/0/0.1 point-to-point

pvc 8/35

encapsulation aal5snap

pppoe-client dial-pool-number 1



Any Idea why is this happening ?, we have version 12.3(14)T7. Is this the right way to configure QoS for DSL, or should I configure QoS on the dialer interface instead ? Any suggestions are welcome.

The document I checked can be found here.



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spremkumar Wed, 05/03/2006 - 21:49
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Can you user show policy-map interface command to check whether your service policy has been binded under the ATM interface ? can you also post the output for the command here ?


jaregalado Thu, 05/04/2006 - 07:14
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Hi, of course,

whenever I try to configure a service-policy under pvc mode as recommended on the Cisco docs the command is accepted but it just doesn´t show up in the final config, also using the command you mentioned I can clearly see that the policy is not operational:

rtr#int atm0.1 point

rtr(config-subif)#pvc 8/35

rtr(config-if-atm-vc)#service-policy output QoS-Policy


rtr#show policy-map interface


This happens on a 2821 router with version 12.3(14)T7 but also happens on a 877 router

with version 12.3(8)YI2

Worth to mention is the fact that the command is accepted and seems to work Ok on the

877 router under atm main interface mode:

rtr#sh running-config interface atm 0

Building configuration...

Current configuration : 120 bytes


interface ATM0

no ip address

service-policy output QoS-Policy

no atm ilmi-keepalive

dsl operating-mode auto


I can clearly see that the policy is in effect:

rtr#show policy-map interface


Service-policy output: QoS-Policy

Class-map: VoIP-RTP (match-any)

0 packets, 0 bytes

5 minute offered rate 0 bps, drop rate 0 bps

Match: protocol rtp audio

0 packets, 0 bytes

5 minute rate 0 bps

Match: access-group name VoIP-RTP

0 packets, 0 bytes

5 minute rate 0 bps


Strict Priority

Output Queue: Conversation 40

Bandwidth 80 (%)

Bandwidth 102 (kbps) Burst 2550 (Bytes)

(pkts matched/bytes matched) 0/0

(total drops/bytes drops) 0/0

QoS Set

dscp ef

Packets marked 0

Class-map: VoIP-Control (match-any)

0 packets, 0 bytes

5 minute offered rate 0 bps, drop rate 0 bps

Match: access-group name VoIP-Control

0 packets, 0 bytes

5 minute rate 0 bps


Output Queue: Conversation 41

Bandwidth 5 (%)

Bandwidth 6 (kbps) Max Threshold 64 (packets)

(pkts matched/bytes matched) 0/0

(depth/total drops/no-buffer drops) 0/0/0

QoS Set

dscp af31

Packets marked 0

Class-map: class-default (match-any)

189 packets, 32032 bytes

5 minute offered rate 2000 bps, drop rate 0 bps

Match: any


Flow Based Fair Queueing

Maximum Number of Hashed Queues 32

(total queued/total drops/no-buffer drops) 5/0/0

However the 2821 router oddly doest´n accept policies under atm main interface mode... (???)

rtr2#interface atm 0/0/0

rtr2#service-policy output QoS-Policy

CBWFQ : Not supported on this interface

Any ideas ?

Best regards.

Michael Stuckey Thu, 05/04/2006 - 13:39
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I believe it is very important to apply the service policy under/after the VCI/VPI because you want it applied to the individual VC not the physical interface.

Sometimes when a virtual-template is created you have to configure it there.

Rate if this helps.


wochanda Mon, 05/08/2006 - 14:45
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You cant apply a QoS policy to an ATM PVC without traffic shaping configured. Best (and most often configured) ATM traffic shaping is vbr-nrt. Basically you plug in your upload bandwidth and it'll traffic-shape you to that rate. More importantly, it helps the QoS schedule allocate bandwidth for the various classes.

Do the following:

interface atm0/0/0.1

pvc 8/35

vbr-nrt 768 768

tx-ring-limit 5

service-policy output

Once you exit out of this, the command should have stuck, and you'll be able to issue a 'show policy-map interface atm0/0/0.1'.

If you're upload speed isn't 768k, change the vbr-nrt statement to whatever the speed is, in kbps.

You may also notice I put in a tx-ring-limit command. This is needed to create backpressure from the module to the router, telling it to use the QoS classes you have configured.

Michael Stuckey Tue, 05/09/2006 - 06:06
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Do you have any links that might help explain this.

Is this the case for all ATM interfaces?




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