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QoS test


I want to perform some tests in order to demonstrate that QoS really works. The main test ideas are listed above. The switches are 3560 series, the bridges are 1310 and the IP camera will be a non Cisco one. I will use iperf to generate traffic in VLAN 1 and I'll measure it using wireshark. In the moment when I will start the video transmission from camera to the laptop in VLAN 2, I expect to obtain a decreased amount of traffic in VLAN 1. Basically I want to prioritize the traffic in VLAN 2.

I don't have to much experience with QoS so I'm asking if someone can tell me how to configure QoS based on the tests that I want to do.


Andrei Muresan


Re: QoS test


This is a pretty big question within a very big topic. Here are things to consider:

  • You have to mark traffic that you want to have higher priority on your network. This means that your camera has to mark it or else you have to mark it at the ingress switchport where the camera is connected.

  • You have to trust marked traffic across your network. Whenever one of your network devices passes traffic onto the next device, make sure that the receiving device trusts the markings on the packets it's receiving. E.g., the switch should trust traffic it gets from the bridge.

  • You have to make sure that your traffic is queued properly for ingress/egress handling. You don't want to have higher priority traffic getting misqueued and dropped in favor of best effort traffic.

  • QoS is only as good as the poorest flow handler in the chain of devices handling the flow. You have to configure QoS at each step along the way or else your overall result is going to be less than optimal.

  • With respect to the setup in your diagram, you have two different things to think about: 1) QoS on your switches and 2) QoS on your bridges. They are different, follow different rules, and require that you understand how their mechanisms work independently. Once you have that figured out, it will become much clearer how to make them work together.

Check out this post here to get an idea of how to configure QoS on the bridges:

If your switches are relatively newer Catalyst switches, look here for Cat QoS pointers (there are loads of resources on this subject, but this one is fairly concise and should touch on the elements you need in your config):

Finally, if QoS is a pretty new concept for you and you need something to break the cruft loose and get your brain's QoS gears turning (or if you just want to round things out), Kevin Wallace has recorded an amazing series of videos on the subject. Check out his QoS Labs 1 through 12: These focus more on router QoS (MQC), but lend enormous understanding to QoS as a concept and the basic building blocks that one needs to consider in any QoS implementation, be it switching, over-the-air, or across a router.

I would like to suggest this to you: Look at some of the resources above and then try to put together a working configuration in your lab. If you get stuck along the way, post back here and we'll help you along. Since you have wireshark, you are pretty well armed with a great diagnostic tool. Just stick it into your network at a couple of different test points and look at your traffic. First make sure you are seeing your markings preserved end-to-end. Then from there you can figure out if your high priority traffic is getting dropped by looking at interface statistics.


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