Phone Qos Cos o DSCP?

[Pedro Javier Herrera Diaz]

Hi

I want to configured QoS on my network but I don´t how to identified if the phones of the network mark the paccket woth CoS of DSCP? Is there any tool taht can help with this or a command of teh Switch.

All the switch in my network are cisco but the phones don´t.

Regards

[Terry Cheema]

Phone would mark the traffic at both layer 2 (COS) and Layer 3 (dscp). If you trust the COS - the marking will be present only in the VLAN tag and is considered more secure due to the fact that the PC attached to this phone can only send markings in layer 3 header. So if you trust cos, their will be a cos-dscp map which will convert cos to dscp values and transmit across the L3 network.

If you decide to trust the layer 3 dscp markings - they will be carried out pretty much end to end (as long as trunks/uplinks are configured to trust dscp). You can secure these by enabling a conditional trust - that is trusting markings only coming from a configured and trusted device (cisco phone, cts or camera)

mls qos trust device Cisco-phone

Ref: http://www.cisco.com/c/en/us/td/docs/solutions/Enterprise/Video/qoscampuscat3xxxaag.html

You can see the marking by using the command:

sh mls qos interface g1/0/1 stat

Please let me know if you have any more questions.

-Terry

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[Mohammed al Baqari]

Hi,

As mentioned below, the phone will mark both CoS and DSCP and it is your choice to trust CoS and/or DSCP on your switch.

I recommend to use conditional DSCP trust so that you carry the marking end-to-end especially when you are carry Voice traffic over WAN.

If you decide to trust CoS and keep CoS-DSCP mapping on, then there is a glitch to be fixed. Cisco switches by default map CoS 5 (which is marked by phones by default) to DSCP 40. This has to be fixed to map CoS 5 to DSCP EF (46).

You can use below as minimum config template

mls qos map cos-dscp 0 8 16 24 32 46 48 56
mls qos

!

interface x/x
 mls qos trust device cisco-phone
 mls qos trust dscp