QOS output drops

Unanswered Question
Feb 26th, 2008

I use embedded QOS with shaping at a parent level and bandwidth statements at a child level, on both the inbound and outbound interfaces of a router. I am seeing lots of output drops on the inbound interface (inbound to LAN). However I am seeing this counter increase even when the interface is not congested.

Here are the errors:

GigabitEthernet0/0 is up, line protocol is up

Input queue: 0/75/7162/7 (size/max/drops/flushes); Total output drops: 78027

Queueing strategy: fifo

I have attached the embedded QOS configuration. I know it's not a problem with the police command as I am seeing the same errors on other routers that only use bandwidth statements for QOS.

I've not posted the output of a show policy-map int as like I mentioned the errors are increasing even when the interface is not congested. The show policy-map int does show the drops by class.

Has anyone experienced similar problems?

Thanks in advance.

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Kevin Dorrell Tue, 02/26/2008 - 08:03

Do the classes cover all the possible traffic? Do you need to define what happens to class class-default?

Kevin Dorrell

Luxembourg

chris morris Tue, 02/26/2008 - 08:25

Hi Kevin - thanks for your response.

The class-default is not a class as such rather a requirement to create the parent shaping policy. My example is probably a bad example as this is an internet circuit and an inbound filter filters all traffic not destined for one of the classes, however I see the same output drops incrementing on our MPLS connected routers too (that have Parent/child QOS enabled). Therefore I know there is something I am not configuring correctly.

For example this is some output showing the drops within the class. This appears normal behaviour to me as the class is going to queue and ultimately drop packets in times of congestion, however why when the circuit is not congested? Also I need to work out if the output drops on the interface are normal behaviour for this kind of QOS configuration.

Class-map: Best_Effort_IN (match-any)

70970234 packets, 20505459981 bytes

5 minute offered rate 806000 bps, drop rate 0 bps

Match: access-group name BEST_EFFORT_QOS_IN

70970233 packets, 20505459895 bytes

5 minute rate 806000 bps

QoS Set

dscp default

Packets marked 70970235

Queueing

Output Queue: Conversation 141

Bandwidth 1900 (kbps)Max Threshold 64 (packets)

(pkts matched/bytes matched) 6948978/4482399452

(depth/total drops/no-buffer drops) 0/29697/0

Thanks

Joseph W. Doherty Tue, 02/26/2008 - 17:28

The classes without policers can push the shaper to full capacity. From my experience, the parent shaper appears to continue to have its own queues and drops seem to be able to happen there (where they're also, it seems, only registered as interface drops). Since you have a parent shaper, the interface itself shouldn't show congestion.

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