NMC DOiT Vol.2 Scenario 7 Day 4-5 – Cat 3560 Mapping DSCP Values to Specific Queue


Okay.  One last thing, and I’m done blogging about scenario 7.  Really, I promise.  The last major task I was working through was a Cat3560 QoS nested policy map that would mark traffic, map it to a specific queue, and police various traffic to various rates.  Not too hard (a little hard) in concept, mostly a syntax exercise to make sure you’re meeting all the scenario requirements.  This was all syntax I had seen before, and yet one thing still threw me.  I was instructed to map AF11, AF12 and AF13 packets to ingress queue 2.  The answer key showed a solution as follows:

mls qos srr-queue input dscp-map queue 2 threshold 1 10
mls qos srr-queue input dscp-map queue 2 threshold 1 12
mls qos srr-queue input dscp-map queue 2 threshold 1 14

I thought I was losing my mind.  They requested AF11, AF12 and AF13, and yet they were mapping 10, 12 and 14 instead of 11 through 13!  Why?  The answer, of course, is that the assured forwarding class number has nothing to do with the corresponding DSCP number.

Read here for some common QoS PHB DSCP values.

By Ethan Banks

Ethan Banks is a podcaster and writer with a BSCS and 20+ years in enterprise IT. He's operated data centers with a special focus on infrastructure — especially networking. He's been a CNE, MCSE, CEH, CCNA, CCNP, CCSP, and CCIE R&S #20655. He's the co-founder of Packet Pushers Interactive, LLC where he creates content for humans in the hot aisle.