Distrubution Switch marking capwap packets DSCP 46

[Steve Lattray]

Capwap packets from some access points are getting set to DSCP 46 when traversing the distribution switches.

I was troubleshooting a slow download issue when we noticed this occurring. The odd part is if I replace any of the access points with a spare the problem no longer occurs.

Any idea how the access point can determine if the distribution switch changes the cpawp packet to DSCP 46?

WLC = 5520

Access point=2702i

Closet switch=3750

Distribution switch = 6509 Sup2t

[Rasika Nayanajith]

Did you check what is that capwap traffic ? If it is CAPWAP control traffic (UDP 5246) then it will be marked as CS6

https://www.cisco.com/c/en/us/td/docs/wireless/controller/8-1/Enterprise-Mobility-8-1-Design-Guide/Enterprise_Mobility_8-1_Deployment_Guide/ch5_QoS.html#_Ref167257742

If it is CAPWAP data traffic then check below. 

Is there any classification ACL on that 6500 to macth that AP to WLC traffic and mark it as EF ?

If possible share any policy-map configs associated to the switchport connecting to downstream switch where  directly connected APs.

HTH

Rasika

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[Steve Lattray]

We are testing with iperf all capwap packets are getting marked EF. You can see in the trace were the inner IP header is marked 0 and the outer is marked 46. We also notice that our distribution switch is marking the packet but I don't know why. I replaced one of the access points and the problem stopped for that access point.

[Rasika Nayanajith]

Hi Steve

"You can see in the trace were the inner IP header is marked 0 and the outer is marked 46"

If this is happening with different APs, I would check how you configure QoS on your WLC. Hope you have configured  "Trust  DSCP Upstream" with enabling QoS map ( Wireless > QoS > QoS map > Trust DSCP upstream)

With that setting, for uptream inner DSCP should be copied to outer CAPWAP DSCP. Watch below Ciscolive presentation for more details

QoS Design and Deployment for Wireless LANs - BRKRST-2515

"We also notice that our distribution switch is marking the packet but I don't know why. I replaced one of the access points and the problem stopped for that access point"

If you replace an AP & it fix the issue, that is really odd. Unless that AP is really doing something strange.

HTH

Rasika

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[Steve Lattray]

Thank you for your reply. We found the issue. The Access points use different ephemeral port based on their Mac. We match on a small portion of these port with our voice access list. This was causing our core router to mark up the capwap packets to 46. I am going to move the wireless policy map to the top so the capwap packets will be trusted before being marked up.

[ashmead123]

Hi Rasika

I am observing this same issue with all CAPWAP traffic being marked with DSCP 46.

Do you have a link to explain the motivations behind enabling the QoS mapping and the trusting of upstream DSCP?

My customer currently has the Platinum QoS profile enabled with AVC profiling. QoS mapping is disabled

Many thanks

Ashley

[Rasika Nayanajith]

Hi Ashley,

Pls go through below ciscolive presentation to get good grasp of wireless QoS

BRKRST-2515 QoS Design & Deployment for Wireless LAN

HTH

Rasika

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[ashmead123]

Thanks Rasika

The presentation was very helpful! It looks like our problem was due to the Wireless QoS Peramiter defaults being set to VOICE for unicast and multicast. 

Cheers

Ashley

[Steve Lattray]

policy-map INGRESS-CLASSIFIER

class VOICE

set dscp ef

class VIDEO

set dscp cs4

class RT-DATA

set dscp cs3

class NRT-DATA

set dscp cs1

class WIRELESS

trust dscp