Posted by: Richard @ | April 1, 2008

Week 12 summary

Better late than never…..

A summary of my CCIE R&S study week 12 can be found below:

Study time:

Study Hours = 11  inc.
Lab Hours = 0

Total study time so far:
Total Study Hours = 144  inc.
Total Lab Hours = 12

What I have studied this week:
QoS – Classification and Marking
QoS – Congestion Management and Avoidance
QoS – Shaping and Policing

Recent test scores:

I took an additional night off on Friday to spend some extra time with Leanne so I didn’t get quite as much as I should have done last week – it had been a “one thing after another” week for Leanne so I thought it was more important to spend an extra evening with her – we watched a film.  I’m going to look at incorporating an extra hour’s study per day in the mornings from now on to up my efforts down the written exam ‘home stretch’.  I’ve noticed my efforts have probably reduced a little bit over the last few weeks so I need to ‘up my game’

I am currently edging my way through making notes for the last QoS chapter of RSCG2, I have read all three QoS chapters and have completed my notes for the first two chapters and therefore I’m pretty much on target to meet my study plan’s two weeks time allocation for QoS.
I’ve got a tad bit frustrated with the level of detail in RSCG2 over the last few days à Chapter 13 (“Congestion Management and Avoidance”) misses some key bits of information; especially when comparing the 3560 queuing/congestion avoidance logic with the 3550 à Surely the author should mention that the CoS to Queue ID mappings are different on the 3560 (e.g. CoS 5 to Queue 1)?  And, it should also be clearly pointed out that the DSCP drop threshold mappings are configured for DSCP to Queue ID + Drop-Threshold in one global configuration command on the 3560, unlike the 3550 where you configure the mapping indirectly by configuring DSCP to Drop-Threshold ID and Queue ID to Drop-Threshold Values mappings using two separate interface level configuration commands.

I came across the first QoS concept that has really got me scratching my head last night; it’s detailed in Internetwork Experts “Bridging the gap between 3550 and 3560 QoS: Part I” (link below) à I read over the explanation of the 3560 buffer pooling models time and time again, but I just couldn’t grasp any of it, it was 10pm however, so I will come back to it tonight….

Listed below are some useful URLs that I have been/will be basing my notes on:
Quality of Service Networking
Cisco IOS Quality of Service
Cisco Modular Quality of Service Command Line Interface
Class-Based Weighted Fair Queueing
Deploying Quality Of Service For Converged Networks
Catalyst 3560 Switch Software Configuration Guide – Configuring QoS
Catalyst 3550 Switch Software Configuration Guide – Configuring QoS
Distributed Traffic Shaping
Differentiated Services Compliant Distributed Weighted Random Early Detection
Understanding and Configuring MDRR/WRED
Bridging the gap between 3550 and 3560 QoS: Part I and Part II

A note to other CCIE wannabes à The software configuration guides seem to contain rarely found clear and informative QoS information in what I am finding to be a technology that has a thick fog covering it – a lack of useful information and contradicting statements aren’t very helpful L

I have put together a little diagram detailing the default egress queue allocation on a Catalyst 3550 which can be found below:

Cisco Catalyst 3550 Egress Queuing

The diagram probably needs a bit more adding to it (e.g. thresholds) but it gave me an opportunity to try and imprint the default values in my mind.

A Catalyst 3560 version should follow shortly.

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