AI, ML, Development + Cisco Learning Blog Learning about Machine Learning, Artificial Intelligence, related devlopment topics and formerly Routing and Switching, Datacenter, Security and other topics, CCIE #23664, Frank Wagner

As my last project would haven’nt been about qos, i would have not been that good and it would have not been that easy. I’m on my way to the CCVP cert. Currently i just hope i can learn things as quickly as possible. This test has not been that difficult. QoS is a topic that has not changed a lot in the last years. Even cisco’s design guide for campus qos is about 2 years old from 2005. So things you will learn are about standards, that have not changed a lot since.

What i haven’t seen is an RSVP or IntServ implementation. I would like to test it a bit with dynamips, but i have to keep an going.

Just know now how to implement LLQ, CBWFQ, PQ, CQ and WRED for example. Knowing about COS and DSCP values. I have not had anything about thresholds in the test. I had 45 questions and the passing score was 790 points. Thanks to the good vue testcenter. I had quite a lot of problems with prometric. Probably this is the reason why cisco changed to use only vue as a testing center for cisco tests. Everythings was working fine. I did the test at OpenLine, Maastricht in the Netherlands.

I have implemented a QoS design for a customer with about 5000 nodes per campus. The design is relatively straigt through. Once you have decided with classes you want to implement, you have to configure the different devices. There has been an access, distribution and core layer. It’s the best to mark as close to the apllications as possible. So at the access layer we had 3750, 4000/4500. The 3750 supports srr and for the 4000 it’s dependend on the module. But for the 4000/45000 you don’t have input queues. As forexample the 6500 it depends all also on the module. You have to find out what kind of hardware queues there are. It’s probable a notation like 1P3Q8T, what means something like, 1 priority queue, 3 normal queues and 8 thresholds per queue. Sometime you can find also the notation 4Q8T/1P3Q8T, that means the one priority queue is able to be a normal or a prio queue.

If you have measurements about the actual network traffic, you can distribute the traffic on the different queues and thresholds. If not, it’s maybe good enough to have a priority queue and to roughly estimate the other queues, but maybe not go to deep into changing the default thresholds. Later it might be necessary. If you don’t have enough queues left and you want to keep up you queuing schema.

There is a good design guide for enterprise campus QoS implementation and i suggest taking this as a good starting point in you QoS campus design. It coves all the different catalyst types and also gives some suggestions about the ECN/DBL (dynamic buffer limiting) marking espacially for the 4000/4500’er catalyst.

This could be a good feature when both stations (server/client) support the ECN flag. I read about the xp/vista does it not have enabled by default. But it’s only available at the 4000/4500’er.

Make sure you use hardware queueing and not queuing in software. This will save you from having problems with cpu overload. As long queueing is done in hardware, you will be on the safe side.

Avaya does not have recomandations about qos implementations on cisco hardware. Phones can be configures like setting voice bearer traffic to COS 5 and Signaling traffic to COS 3. You can overwrite the data port with the PC connected to COS 0. This would be a relativ straight forwarded setup.

QoS is a quite complex task. It’s necessary to develop and administrate the current needs constantly.

Source:

http://www.cisco.com/univercd/cc/td/doc/solution/esm/qossrnd.pdf

http://de.wikipedia.org/wiki/Network_congestion_avoidance

Currently going for the first QoS test for the CCVP. Think this is the most difficult one. I like to take the hard part first. I haven’t seen any RSVP implementations. I wonder if it’s really widely used outside in the network for QoS. I will write some comments to my QoS implementation for a customer with about 5000 access ports per site in the next days.

QoS can be quite a complex task. It seems simple, but implementing it continuously on differnt kinds of hardware queues and different queueing techniques, could be quite callenging.