Default auto-qos configuration

[Vincenzo Santoro]

Hi All,

After having upgraded one Cisco 3560V2 from 12.2(26) to the version 12.2(55), I realized that the standard auto-qos generated config after applying either the "auto qos trust" or "auto qos voip cisco-phone" on a specific interface is not the one I obtained before the upgrade.

There were several changes (input bandwidth,output buffers, dscp-map threshold, class-map, policy-map... ). Attached you'll find the 2 different generated config respectively with the old and new firmware.

I'm wondering when and why Cisco decided to apply those changes?

Moreover, could you please confirm that if I apply the "auto qos voip cisco-phone" command on a interface where I'm connecting a non-Cisco VOIP phone which doesn't support cdp, even if I'm trusting dscp, the QoS traffic coming from the VOIP phone will not be trusted?

Thanks and regards,

Vin

[Ton V Engelen]

Hi,

i did a very quick scan of the auto configs.

1. From what i can see the new auto qos config defines priority queue, and the old one doesn t. This is what explains the differences i guess. (But then again, i did a very quick scan).

2. I think the auto qos voip cisco-phone config for a non cisco phone is useless as it isn t recognized. On the other hand, if the non cisco phone marks traffic with a correct dscp, why not trust it. (mls qos trust dscp)

[Vincenzo Santoro]

Hi,

Thanks for the answer.

Is there any method in order to classify STP BPDU traffic? Basically I'd like to classify all the stp traffic through an ACL and attribute it to one specific egress queue.

Thanks and regards,

Vin

[Ton V Engelen]

Hi

stp bpdu's should have cos 7 / dscp value 56 and would  be placed into queue 2, when looking at both auto qos examples you ve posted.

Good luck

Ton

[Vincenzo Santoro]

Hi,

Yes you're right, it was exactly this point that arised my question.

Basically I want to understand if cos 7 / dscp  56 are the default values of STP traffic in CISCO switches or it's the auto qos that changes the value of the STP data traffic to cos 7/dscp 56? If the second option is true, could you please explain in which way the auto qos selects the STP traffic and changes the cos and dscp values just for the STP traffic to respectively 7 and 56?

I need this info as I want to adapt the auto-qos configuration to my specific needs.

Thanks,

Vincenzo

[Vincenzo Santoro]

Hi Ton,

Attached you'll find my QoS configuration (at the moment STP traffic is not classified). If I'm able to select the STP traffic, I'll classify this traffic to a specific ingress/egress queue as well.

Could you please provide me your feedback?

Assumptions:

1) all switches must trust DSCP

2) DSCP settings for the VOIP phones are 46 (VOIP data) and 31 (VOIP signaling)

3) at least four traffics need to be classified:

a) VOIP

b) IPTV

c) Management

d) Data traffic

Below there is an high level description of the configuration:

*****

ingress queue 1: priority queue, 30 percent weight, 30 percent remaining weight

ingress queue 2: 70 percent remaining weight

egress queue 1: 10 percent weight (bandwidth garanteed), 15% buffer size

egress queue 2: 10 percent weight, 25% buffer size

egress queue 3: 60 percent weight, 40% buffer size

egress queue 4: 20 percent weight, 20% buffer size

******

DSCP mapping to ingree queues

******

ingress queue 1: VOIP data (threshold 3), VOIP signal (threshold 3)

ingress queue 2: management (threshold 2), IPTV (threshold 2), all other traffic (threshold 2)

*****

DSCP mapping to egress queues

******

egress queue 1: VOIP data (threshold 3)

egress queue 2: VOIP signal (threshold 3) , management (threshold 2)

egress queue 3: IPTV (threshold 3)

egress queue 4: all other traffic (threshold 1)

Thanks a lot,

VIn

[Ton V Engelen · Accepted solution]

Hi,

the switch will mark this management traffic, you wont have to do that.

management traffic should then be mapped to the appropriate queue (s).

Most management traffic will be cs7 or cs6.

This book explains more into detail.

http://www.cisco.com/en/US/docs/solutions/Enterprise/WAN_and_MAN/QoS_SRND_40/QoSCampus_40.pdf

Assumptions:

1) all switches must trust DSCP

(or cos) and this is to trust the cos or dscp value set by the device connected to the accessport and trust this traffic on the trunkport uplinks

2) DSCP settings for the VOIP phones are 46 (VOIP data) and 31 (VOIP signaling)

Yes

3) at least four traffics need to be classified:

Not neccesarily. Different traffic could end up in the same queue but with different tresholds. In your example VOIP signal (threshold 3) , management (threshold 2) both end up in queue 2. But basicly thats the idea.

a) VOIP

b) IPTV

c) Management

d) Data traffic

Weight and buffer sizes depends on the kind and amount of traffic on the network. I think you have a good start here. You might have to tweak some after a while based on what happens in the queue's, like drops.

Regards,

Ton