QOS in a Campus network

[daniele matta]

Dear All,

i m opening a discussion regarding the QOS as i have read different configuration documents and best practice,

but still i have some doubt.

I have 3 layer network where the access layer is composed by

2960x with 20Gb PO

connected to the distribution layer composed by

2 x 4500x in VSS mode

connected to the core layer composed by 6500 with sup2t and WS-X6908-10G.

The 6500 is connect to another one where there is then the same topology

briefly:

phone ==> 2960x PO==> 4500x PO==> 6500 ==> 6500 PO==> 4500x PO==> 2960x ==>

Now i have to deploy the QOS to guarantee the necessary bandwidth to the phones:

I don't know if i got the sense, but i think that something like this should work:

Access switch port connected to the phone:

 mls qos trust cos

 auto qos voip trust

On the access switch PO to the distribution

 mls qos trust cos
 auto qos trust

On the distribution PO to the Access

 auto qos trust

On the distribution PO to the Core

 auto qos trust

and so on till the other side of the network.

I know i made it simple... could anyone give me a suggestion for such scenario?

Thanks

[Reza Sharifi]

Hi,

On the 2960x access switches, you can enable auto QOS for all the access ports with a couple commands and also enable "auto qos trust" on the uplink ports to the 4500x.

see link below:

http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst2960x/software/15-0_2_EX/qos/configuration_guide/b_qos_152ex_2960-x_cg/b_qos_152ex_2960-x_cg_chapter_011.html#d25414e745a1635

You can also enable the same trust command on the 4500 side connecting to your access switches.

As for the 6500 with Sup-2T, the QOS architecture has completely changed. I would start with this document:

http://www.cisco.com/c/en/us/products/collateral/switches/catalyst-6500-series-switches/white_paper_c11-652042.html

HTH

[daniele matta]

Reza thank you for the reply,

I have already read the docs you attached,

what i don't understand yet is:

imagine my voice packet as source 10.0.0.1 destination 192.168.0.1

for every l2 that the packet go trough if i trust the COS the value stays the same and that's clear.

So should i trust the COS in every uplink ports?

Once the packet has arrived to the L3 SVI interface, should i also configure the auto QOS there?

[Reza Sharifi]

Hi Daniele,

In order for QOS to be effective, it has to be applied end-to-end, if not the traffic will have a higher priority in one uplink and not on the next device, which will negates the purpose.  So, I would say you need to apply it on all devices on the path to 192.168.0.1

HTH

[Erico Verissimo]

Hello,
QoS is really a complex matter specially on L2. I had some doubt about that, but I focused on method that I was going to deploy. For example:

2960 do not support CBWFQ and consequently do not do output policy. In this devise is nice to use auto QoS doing a trust dscp or cos on input, the switch will maintain the dscp or cos consulting the dscp or cos MAP crieted after you have used the command auto qos and obvioslly mls qos.
I did this:

2960 - input interface connected with ip-phone:
mls qos trust device cisco-phone
mls qos trust cos
auto qos voip cisco-phone

2960 and 6500- output interface connected with router/uplinks
In this way you need to do queuing and in L2 is a little complex, for example you have to see what the capabilities of interface (1P3Q3T, 1P7Q2T, etc)

4500 - This device have support qos MQC CBWFQ with output queueing. In this devise you do marking (acl, interface, dscp, etc), classification class-maps, policies, congestion avoidance, etc. After you do all these steps you put the service-policy on interface.
QoS is so complex and need a lot of steps to deploy. In my case the marking step was more complex becouse it was hard to undestand each application IP/Port. All of devises on network need threat packets remember the QoS is PHB - Per Hop Behavior.

Following a nice doc to deploy qos.

best regards!