LLQ and general CBWFQ problems

Unanswered Question
Mar 7th, 2007
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Hi All,


Ive been playing around with different QoS techniques as i'm going for my exam fairly soon. I've read the exam cert guide and think i understand most of the concepts and configuration.


My understanding of LLQ is that it polices traffic.


With the config below im having two issues.


1. Traffic is not policed to 56k, it simply uses what it wants for RDP. If I use the police command instead then it works.


2. A lot of QoS policys I have tried do not always show the packets matched / bytes matched in the queuing section. When it clearly shows the class is being matched.


The below configuration shows the two problems i'm having.


I'd appreciate if anyone can shed some light, as it does not make sense to me!



!

class-map match-any PRIORITY

match access-group name RDP

!

!

policy-map PRIORITY

class PRIORITY

set ip precedence 5

priority 56

class class-default

!

interface Dialer1

bandwidth 256

ip nbar protocol-discovery

service-policy output PRIORITY

!

!


dover#show policy-map int d1

Dialer1


Service-policy output: PRIORITY


Class-map: PRIORITY (match-any)

683 packets, 173617 bytes

1 minute offered rate 0 bps, drop rate 0 bps

Match: access-group name RDP

683 packets, 173617 bytes

1 minute rate 0 bps

QoS Set

precedence 5

Packets marked 682

Queueing

Strict Priority

Output Queue: Conversation 72

Bandwidth 56 (kbps) Burst 1400 (Bytes)

(pkts matched/bytes matched) 0/0

(total drops/bytes drops) 0/0


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

4257 packets, 1967166 bytes

1 minute offered rate 35000 bps, drop rate 0 bps

Match: any






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paul_alexander Wed, 03/07/2007 - 14:54
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Just to add.


If I enable WFQ on the class-default and start up web streams, peer to peer, the queuing statistics don't show anything...Its weird, and annoying.


Chris Deren Wed, 03/07/2007 - 17:46
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LLQ does not police traffic it allows you to prioritize traffic based on your matching classes, so in your example you are prioritzing 56 kbps to your RDP class.

You did not show the RDP access-list, but my guess is that you are not matching the traffic properly hence not seeing it in the output of the "sh policy-map".

If you'd like to police traffic then, use the "police" statement in your policy-map.


HTH,


Chris

paul_alexander Wed, 03/07/2007 - 18:03
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Hi Chris,


Thanks for your reply. Although, im still a little confised. Below is my access list and ive also included a snippet from the QOS book by Wendel.


Extended IP access list RDP

10 permit tcp any any eq 3389 (325411 matches)



"LLQ actually polices the PQ based on the configured bandwidth. By doing so, the packets in the queue that are forwarded still have very low latency, but LLQ also prevents the low-latency traffic from consuming more than its configured amount of bandwidth. By discarding excess traffic, LLQ can still provide bandwidth guarantees to the non-priority queues. The policing function works like policing as described in Chapter 6, but it is automatic in the low-latency queueno additional policing configuration is required."


When I police the queue to 56000, i get really bad performance from RDP. I should expect the same from using the priority 56 commands, except the class will always be serviced first?





Regards,


Paul.







Chris Deren Wed, 03/07/2007 - 18:38
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I think the snippet is from the Policing chapter and means when LLQ in conjunction with policing, such as:


Posted by: paul_alexander - Mar 7, 2007, 2:51pm PST



Hi All,


Ive been playing around with different QoS techniques as i'm going for my exam fairly soon. I've read the exam cert guide and think i understand most of the concepts and configuration.


My understanding of LLQ is that it polices traffic.


With the config below im having two issues.


1. Traffic is not policed to 56k, it simply uses what it wants for RDP. If I use the police command instead then it works.


2. A lot of QoS policys I have tried do not always show the packets matched / bytes matched in the queuing section. When it clearly shows the class is being matched.


The below configuration shows the two problems i'm having.


I'd appreciate if anyone can shed some light, as it does not make sense to me!



!

class-map match-any PRIORITY

match access-group name RDP

!

!

policy-map PRIORITY

class PRIORITY

set ip precedence 5

police 56000 conform-action transmit exceed-action drop

class class-default

!

interface Dialer1

bandwidth 256

ip nbar protocol-discovery

service-policy output PRIORITY

!



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