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Webcast-Catalyst9k
New Member

QoS: Nested policies and traffic shaping

Hi all

We have an 8mb ethernet bearer (10MB access) so I have attempted to configure a nested policy map to include traffic shaping.

If I apply the 8M_out map to the outgoing interface I do not see packets in the priority queue when I do "show policy-map interface f0". If I change the interface to use the QOS_out policy (which means I don't have shaping) the priorty queue is recording packets.

Have I configured this incorrectly?

Thanks

class-map match-any REAL_TIME

match ip dscp ef

match ip precedence 5

match ip dscp af31

match access-group name EF

match ip dscp cs2

class-map match-any MGT

match ip precedence 6

match ip precedence 7

match access-group name RIP

!

!

policy-map QOS_out

class MGT

bandwidth remaining percent 5

class REAL_TIME

priority 3500

set dscp ef

policy-map 8M_out

class class-default

shape average 8000000

service-policy QOS_out

Queueing

Strict Priority

Output Queue: Conversation 264

Bandwidth 3500 (kbps) Burst 87500 (Bytes)

(pkts matched/bytes matched) 1892/142908 <<<< These are 0 when 8M_out is used

(total drops/bytes drops) 0/0

2 ACCEPTED SOLUTIONS

Accepted Solutions

Re: QoS: Nested policies and traffic shaping

This is expected behavior in this scenario. With the 8m_out policy applied to the interface, the queuing policy (QOS_out) will only become active if shaping is taking place. Shaping will only be active if you're exceeding 8Mb.

Hope this helps. If so, please rate the post.

Brandon

Super Bronze

Re: QoS: Nested policies and traffic shaping

Logically, your configuration looks correct. As Brandon notes, until you load the shaper, queues won't form in the child policy. (A quick test, reduce the shaper's bandwidth to induce congestion earlier if you want to see the policy in action. Use with caution, as doing so would slow traffic in a production environment.)

Some other tips:

Router interfaces sometimes have a hardware FIFO queue that you can adjust, usually with the tx-ring-limit. For highly sensitive traffic like VoIP, you may need to adjust the hardware queue size smaller so the traffic is pushed into the software queues where your LLQ will send such traffic first. Likewise, you may need to decrease the time interval used by the shaper. (My experience has been, at least on some platforms and IOSs, a shaper used with a child policy seems to still maintain its own WFQ queues. Haven't found a method to minimize those so that the child policy queues handle congestion as desired.)

3 REPLIES

Re: QoS: Nested policies and traffic shaping

This is expected behavior in this scenario. With the 8m_out policy applied to the interface, the queuing policy (QOS_out) will only become active if shaping is taking place. Shaping will only be active if you're exceeding 8Mb.

Hope this helps. If so, please rate the post.

Brandon

New Member

Re: QoS: Nested policies and traffic shaping

I read this also.

Will voice still be ok in this scenario?

(Will rate ofc)

Thanks

Super Bronze

Re: QoS: Nested policies and traffic shaping

Logically, your configuration looks correct. As Brandon notes, until you load the shaper, queues won't form in the child policy. (A quick test, reduce the shaper's bandwidth to induce congestion earlier if you want to see the policy in action. Use with caution, as doing so would slow traffic in a production environment.)

Some other tips:

Router interfaces sometimes have a hardware FIFO queue that you can adjust, usually with the tx-ring-limit. For highly sensitive traffic like VoIP, you may need to adjust the hardware queue size smaller so the traffic is pushed into the software queues where your LLQ will send such traffic first. Likewise, you may need to decrease the time interval used by the shaper. (My experience has been, at least on some platforms and IOSs, a shaper used with a child policy seems to still maintain its own WFQ queues. Haven't found a method to minimize those so that the child policy queues handle congestion as desired.)

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