Configuring LLQ – Low Latency Queuing
Well, since I covered the CBWFQ in my last post I think it’s only natural I jump into the configuration of yet another QoS configuration Low Latency Queuing or LLQ. LLQ simply builds off the CBWFQ, let’s look at the configuration from my last post concerning CBWFQ:
Now let’s configure LLQ:
See the difference? Notice the priority keyword, that is what configures LLQ. Not too complicated right? Now what does this priority command really do for us, well it creates a low latency queue for traffic that needs to be transmitted before other type of data. So if there is data in the low latency queue when does the data in the other queue’s get transmitted, easy when the low latency queue is empty or when the low latency queue exceeds its specified amount of bandwidth. The low latency queue is also policed by the bandwidth we have allocated it. If the low latency queue ever exceeds the amount of bandwidth it has been allocated it will drop the packet and move to another queue.
Below is a flow chart from the QoS Exam Guide explaining how the LLQ works:
CCIE or Null! 
Keep up the good work. I am definitely following
Blake
December 5, 2011 at 10:55 PM
Quite intriguing topic , thanks for posting .
Elektrische Zahnbuerste
December 7, 2011 at 11:36 PM
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pl3453 understand th1s
December 23, 2011 at 2:52 PM
Thanks for sharing the Low Latency Queuing Information. I look forward to where you take us in 2012!
IT Support Guy
January 5, 2012 at 6:40 PM
Just a side note. It is my understanding that the priority queue is only policed in times of congestion. During times of non-congestion traffic that exceeds the priority queue is placed in class class-default and is not priority queued. In times of congestion the priority queue is policed.
Refer to the table here for times of non-congestion using the priority command.
http://www.cisco.com/en/US/tech/tk543/tk757/technologies_tech_note09186a0080103eae.shtml#whichtrafficclassescanuseexcessbandwidth
lakers0044
February 14, 2012 at 3:17 PM
You are correct LLC policies are only applied during times of congestion, and makes sure the appropriate queue gets its configured bandwidth. However during times of underutilization the LLC configuration pretty much sits idle.
Stephen J. Occhiogrosso
February 14, 2012 at 3:25 PM