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IP Expert Volume I – QoS

Posted by Jo on September 13, 2008

I booked a nice early 5am start time again to get my brain going, and got onto the rack session. I had a slight problem accessing Cat1-4, so mailed the IP Expert out of hours support, who responded back within minutes and changed my rack to one that worked. On top of this he added an additional 2 hours to the session – nice work!

This morning I worked on QoS – firstly going through the BLS Volume I labs (sections 18 and 19). These cover a fair proportion of QoS topics, so I have been working through these checking off with the documentation as I went along. The topics covered in these Volume I labs seem pretty straight forward, I seem to be OK doing them in isolation, and am feeling more confident now. The problem comes when I am doing a lab I miss something important out and dont get the points. This is what I want to work on over the next week or so – I will be drilling these and some other QoS labs I have.

A selection of topics covered today have been:

Section 18 – QoS

Custom Queuing

I am OK with this topic now (at least with the labs from Section 18 and 19). All of the config is in the docs, which are pretty easy to follow along.

Priority Queuing

Again, now I feel a lot better at this. Though to be fair there is not much to it – and according to whoever wrote the task, it has a low probability of showing up on the real lab.

Traffic Shaping – Queue Size

Quite an easy command to work out from the ? – but it is with all the other Frame-Relay commands in the WAN section of the config guide.

map-class frame-relay FRTS
frame-relay holdq 100

MIME Types

You can match MIME types within the MQC

A list of MIME types can be found here:

I am not sure if this exists on the Cisco Doc pages anywhere, but I guess it would be useful to memorise a few of the more popular types. An example to match and limit any Web Video streams is provided below: (the set fr-de command just tells the SP that this traffic can be dropped if the line is already conforming to its CIR)

class-map match-all WEB-VIDEO
match protocol http mime “video/*”
policy-map LIMITVID
police 64000 conform-action transmit exceed-action drop
set fr-de

3560 QoS Maps

No rocket science here, just mapping cos-dscp values

mls qos
mls qos map cos-dscp 0 8 16 24 32 46 48 56

This command changes the default value for COS 5 to DSCP 46 (it defaults to 40)

Section 19 – QoS/MQC Conversions

This section basically went over a set of tasks that converted things such as the previous Priority queue section into an MQC based config. I surprised myself on this as they were easy enough to configure. A couple of highlights were:

Cat 3550/3560 Priority Queues

On a 3550 the priority queue is queue 4 and is set as follows

int range f0/19 – 24
wrr-queue cos-map 4 5 6 7
priority-queue out

On a 3560 is it done like this it uses queue 1

mls qos srr-queue output cos-map queue 1 5 6 7
int range f0/19 – 24
priority-queue out

and verified with this (the output is skewed to the left)

Cat3560-2#sh mls qos maps cos-output-q
Cos-outputq-threshold map:
cos: 0 1 2 3 4 5 6 7
queue-threshold: 2-1 2-1 3-1 3-1 4-1 1-1 1-1 1-1


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