Why do we need QoS on LAN Switches

This topic is to discuss the following lesson:

Hi Rene,
Could you please do a short demo?
I have 1x3560 and 2x3550, i have configured QoS (similar to the first topology) but i think it is not working well.

Hi István,

What would you like to see? We can do classification, marking, queuing, shaping and policing on the switches :slight_smile:


Hi Rene,

Do we have qos of service on LAN switches only?. Why not on a WAN and Router as well?.
If we can have the same on Router, is it the same procedure as well as well.

Hi Peter,

QoS is applied everywhere, switches and routers. The configuration on routers is very different however…


Hi Rene/Andrew

Can you help me in understanding AutoQoS concept please ?


Hi Abhishek,

Let me jump in to give you a brief explanation of Cisco AutoQos.

Configuring QOS can be a challenge for engineers who aren’t familiar with this topic, but leaving the network without a QOS configuration can cause a lot troubles especially with the bandwidth-hungry applications and the real-time traffic such as VOIP and Video which can partially and/or fully not work if QOS isn’t configured, in addition of problems like latency, jitter, and packet drops.

For this reason, Cisco IOS Software offers a portfolio of QoS features which is enable by a or few commands without an extensive knowledge needed from the IT administrator and it provide the essential QOS needed.

If you want to know more of AutoQOS, I can refer you to this article from Cisco Wesbite.

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Thankyou Maher, That helps !

Hi Rene
In a access ,distribution and core architecture where we should do the qos


Hello Sims

This is a very good question that doesn’t have a clear cut answer.

In the hierarchical model, the core is performing high speed routing and switching to get things from place to place, the distribution layer is applying policies and filtering, and the access layer is providing you with port density and user connectivity. Based on this, and based on most textbooks and CCNP study material, QoS is said to be most commonly applied at the distribution layer.

However, Layer 2 switches at the access layer can perform both marking and queuing and in general it is good design to apply QoS as close to the equipment or services for which you need to guarantee network resources as possible. In a live network that may very well be in the access layer on your switches, or even at the phone port.

I hope this has been helpful!


Hello Lagapides,

Thank you for your answer.

What if we have an access switch connected to each dist switch (2 DIST sw) and our access switch is 48 port x 1Go , on each 1G port (PC + Phone or PC + softphone) ?

How could we manage 48Go of traffic on 2x10Go uplinks on the DIST switchs?
could i use CBWQ + LLQ in the output direction on the access switch ?
what about the incoming traffic from the DIST switch
what is the best methode to classify traffic the incoming from PCs , from phones and from softphones ?
how could i match and remark traffic in the access switch ? and on the DIST switch ?
could i use a policy map in input direction on the voice SVI in the core ? and in the data svi ?

Thank you for your answers

Hello Zouhair

In such a scenario, I assume you are focusing on the QoS mechanisms for the voice packets delivered by the IP phones and softphones. Classification and marking of voice packets should be done at the devices themselves. A more detailed explanation can be found in the Classification and Marking section of the following lesson:

Once voice packets are classified and marked, they must be acted upon by QoS mechanisms. Such mechanisms on a switch must be applied in an outward direction, as incoming traffic on an interface cannot be controlled. This means that any queues you set up must be on the two 10GE uplink interfaces of the access switch, and on any uplink interfaces of the distribution, layer switches as well, if you are applying QoS on the core. More on how this can be applied can be found here:

You can find information about this at the following lesson:

I hope this has been helpful!


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Hello Laz,
It was very hrlpful.
Thank you.

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