QoS question

[network770]

We have a nicely sized network and we are running ip phones.  As we are not big experts with Qos so we enabled auto qos on all the user switches - we have 3750's, 3560's and C6K on the core switch, but qos is only on the user switches.  Then we saw that in addtion to the globally qos we have enabled, there is also an option trust cos or dscp on a specific interface....should we do that?

on the user switches we have ports that the users connect to and uplinks to the core

on the core switch we have ports with servers, storage, wan connection, user switches

at some sites we also have routers facing the cloud

when should we trust cos vs dscp, or should we at all? what does that do?

is this all enough to say that we have qos running?

[angel.gino]

Hi Ronni

I don't use autoqos in my LAN, instead of I use this configuration:

Access Switch

mls qos (Global Configuration)

***User Ports***(Interface Configuration)

mls qos trust cos

mls qos trust device cisco-phone

priority-queue out

****Trunk****(Interface Configuration)

mld qos trust cos

priority-queue out

Distribution Switch( you are supossed to have only connections with access and core switches)

mls qos

****Trunk****

mld qos trust cos

priority-queue out

Core switch

mls qos

****Trunk with distribution****

mld qos trust cos

priority-queue out

I use DSCP or PRECEDENCE at the Enterprise Edge(ISPs)

Regards

Gino

[jimmysands73_2]

Gino,

I am a CCNP student studying QOS right now....why not use the auto qos?  Was there a factor in your network that determined auto qos wouldnt work or wouldnt work optimally?

Thank you

[network770]

I am using QoS and I think it's working fine, that's because we have no congestion on the network so I can't really tell if the config is ok... by the way, are there any useful show commands that we can use to see if qos is ok? what should we be looking for?

I was reviewing other configs and I was seeing :

mld qos trust cos

mld qos trust dscp

and i was wondering what the diff between the two and when one should use one over the other. or is auto qos enough, ie. to put 'mls qos trust voice' on all interfaces and that should do it?

[sean_evershed]

It depends on how far your trust boundary extends.

If you trust the DSCP markings coming from the router connected to the switch then configure mls qos trust dscp on the switch interface.

If you have a trunk port between two switches and the first switch trusts the cos markings from the second switch then configure mls qos trust cos on this interface.

If you have a Cisco phone connected to a switchport then use the mls qos trust device cisco-phone

For further reading see http://www.ciscopress.com/bookstore/product.asp?isbn=1587201240

When configuring QoS it is important to check that the QoS markings are preserved end to end.

I had a problem where packets were being marked correctly in a branch but they were being remarked by the carrier as best effort.

Therefore some packets were being dropped when the link became congested.

A good way to check this is to configure Netflow on the branch and head office routers. Netflow can examine the ToS markings on all packets being sent and received.

You can then compare these ToS markings against your QoS policy.

Please remember to rate all posts that are helpful.

[network770]

Thanks but I'm still trying to get the hang of it... unfortunately I am not a qos expert so i am still learning a lot of the terms.

should I be using this:

set ip precedence critical

set ip precedence priority