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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.

http://www.cisco.com/en/US/docs/ios/qos/configuration/guide/config_cq_ps6350_TSD_Products_Configuration_Guide_Chapter.html
http://www.cisco.com/en/US/docs/ios/qos/command/reference/qos_a1.html#wp1015747

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.

http://www.cisco.com/en/US/docs/ios/qos/configuration/guide/config_pq_ps6350_TSD_Products_Configuration_Guide_Chapter.html#wp1001044
http://www.cisco.com/en/US/docs/ios/qos/command/reference/qos_n1.html#wp1014821

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

http://www.cisco.com/en/US/docs/ios/wan/command/reference/wan_f1.html#wp1014703

MIME Types

You can match MIME types within the MQC

http://www.cisco.com/en/US/docs/ios/qos/command/reference/qos_m1.html#wp1024534

A list of MIME types can be found here:

http://www.iana.org/assignments/media-types/index.html

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
class WEB-VIDEO
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)

http://www.cisco.com/en/US/docs/switches/lan/catalyst3560/software/release/12.2_25_see/configuration/guide/swqos.html#wp1027339

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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