Modify default values of Auto QoS

[Ccoria1989]

Hi everyone

We have configured auto-QoS on all access switches and core switch but now we have new carrier and they say that the voice should be marked with CS3 label, and data with CS2 label.

Is possible modify the auto-QoS configuration? And how we can modify auto-QoS for this new marking?

I hope you can help me.

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[Terry Cheema]

To answer your question, yes you can modify the auto qos as its just a macro or set of commands generated by using a particular auto qos command. But I would suggest not doing it. Instead of modifying at access level you should consider doing this at the edge router.

General flow of QoS is your VoIP devices (Servers + Phones) mark the traffic, you collect this traffic at access level by trusting the markings, prioritise and pass on to edge devices, where again this will be classified into priority class and sent over to WAN for preferential treatment.

So I would suggest, you should keep access level as it is, for example, VoIP media will be ef(46), when edge router receives this, set a policy here to just re-mark this ef traffic to cs3 and prioritise. This can be easily done under policy-map using set command. This way you would have to just change your edge router config.

If you for some reason want to change the marking at access level switches, normally when you use auto qos, you are trusting cos. Then you map these cos values to dscp - cos 5 is VoIP media - which is mapped to ef (46), one way is you can map CoS5 to CS3(dscp 24), using command: mls qos map cos-dscp X X X X X X

You can also change the marking device (end point, phones or Servers) behaviour by changing default values (in CUCM or any other VoIP server). Then simply trust these values at access level and pass on to router and modify the router config to prioritise this traffic. But having said that reason again doing this is:

There are various reasons for just doing this modification at the edge router:
1) No need to modify access level switches
2) Auto templates are designed considering Cisco's recommended markings, which will not be changed and easy to manage
3) Even if you do at access level you will still need to adjust edge router config so that it prioritises cs3 instead of ef - so why not do it only over there.
4) Easy to revert back to std markings if required in future

In the end its your network and you have better visibility and clarity on what you are trying to achieve so use the above advice accordingly.

Please rate helpful posts.

-Terry

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[Ccoria1989]

Hi Terry

If I understand well I need to configure my switch core for re-marking af to CS3 and don't modify my access switches. Is that correct?

Regards


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[Terry Cheema]

Hi Mate,

Leave your core switches - just change on routers connecting to your MPLS. You receive all VoIP media traffic as ef from your internal network. You just change on the WAN routers sending traffic to your provider and re-mark VoIP traffic according to your provider's requirement.

You can also apply an inbound policy on the WAN link changing back the incoming cs3 marking to ef. But more important is outbound to WAN.

-Terry

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[Ccoria1989]

Hi Terry

Oh I understand that option requires that I talk with the carrier because those routers belong to the carrier.

If my carrier doesn't accept, in my core can I do anything?

Regards

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[Terry Cheema · Accepted solution]

Hi Mate,

If the routers are unmanaged, you certainly can change the markings at access level. But the config will still need to be updated on the routers regardless who does. In your case its clearly provider who should do this. As mentioned before there are many ways:

1) Change the default markings in CUCM Service Parameters - Clusterwide QoS. The phones by default mark VoIP audio as ef(46) and signalling as cs3 or af31.
You can change both the values according to your requirements and set the internal switches to trust the dscp.

2) Or you can set trust cos on the phone ports and just change the cos-dscp map as I had mentioned in my previous post. So that CoS 5 is chaged to cs3 (dscp24) and passed onto routers.
mls qos map cos-dscp 0 8 24 32 24 48 56

I do not know what you need to mark signalling traffic, but you can change that as well.
Refer here for more details:
http://www.cisco.com/en/US/docs/solutions/Enterprise/WAN_and_MAN/QoS_SRND_40/QoSCampus_40.html#wp1098557

3) you can apply a marking model:
C3750-E(config-cmap)#class-map match-all VVLAN-VOIP
C3750-E(config-cmap)# match ip dscp ef

C3750-E(config-cmap)#policy-map PER-PORT-MARKING
C3750-E(config-pmap)# class VVLAN-VOIP
C3750-E(config-pmap-c)# set dscp cs3 << remarks ef to cs3


C3750-E(config-if-range)# mls qos trust device cisco-phone
! The interface is set to conditionally-trust Cisco IP Phones
C3750-E(config-if-range)# mls qos trust cos
! CoS-trust will be dynamically extended to Cisco IP Phones
C3750-E(config-if-range)# service-policy input PER-PORT-MARKING
! Attaches the Per-Port Marking policy to the interface(s)

More details are here:
http://www.cisco.com/en/US/docs/solutions/Enterprise/WAN_and_MAN/QoS_SRND_40/QoSCampus_40.html#wp1098677

I suggest you to read this complete guide so you have better understanding of the techiques and apply it according to your situation:
http://www.cisco.com/en/US/docs/solutions/Enterprise/WAN_and_MAN/QoS_SRND_40/QoSCampus_40.html

-Terry