mls qos trust cos vs mls qos trust dscp

[bruce.thornton]

Which value should be used on a trunk link between all Cisco Lan switches:

mls qos trust cos

or

mls qos trust dscp.

If the answer is mls qos trust cos does applying this option apply this config to all ports in that asics group.

[Philip D'Ath]

On all Cisco Catalyst switches you should use:

interface Gigabit a/b/c

  macro apply cisco-switch

This will apply the recommend Cisco settings specific to that model of switch for switch to switch links.

[Chris Deren]

p.dath, I would not say you should use this command as that will enable auto-QoS, which is in my opinion poor's man of configuring QoS.  To configure proper QoS one needs to analyze their environment end to end and line up the queues for all switches as every switch model pretty much provides different capabilities and auto QoS is not that intelligent.

To answer the question this depends on how the switches are connected, Layer2 vs Layer3.  DSCP is L3 and COS is L2 QoS markings. So, apply based on your connection.

I also suggest reason Cisco MediaNet SRND to learn more about QoS.

http://www.cisco.com/c/en/us/td/docs/solutions/Enterprise/WAN_and_MAN/QoS_SRND_40/QoSIntro_40.html

http://www.cisco.com/c/en/us/td/docs/solutions/Enterprise/WAN_and_MAN/QoS_SRND_40/QoSCampus_40.html

http://www.cisco.com/c/en/us/solutions/enterprise/design-zone-application-performance/landing_cVideo.html

[Deven Gandhi]

My rule of thumb is to use "mls qos trust cos" on any switchports connecting to endpoints/L2 devices (i.e. Phones, PCs, Printers, ATAs).  Also, I use "mls qos trust cos" on uplink ports between two switches.    Use "mls qos trust dscp" on switchport facing router/L3 devices.

-Deven Gandhi