3850 QOS query

[mark.carroll]

Hi

i have some old 3550s that are being swapped out for 3850s, some of the QOS config from 3550 wont tranfer accross, not know much about it i hoped someone could tell me how to achieve same on 3850, here is 3550 config im talking about

class-map match-all cda_urgent
  match access-group 104
class-map match-all cda_high
  match access-group 105
!
!
policy-map cda_policy
  class cda_urgent
    set ip dscp 56
  class cda_high
    set ip dscp 46

interface GigabitEthernet0/1
 switchport access vlan 101
 switchport mode access
 wrr-queue bandwidth 1 2 3 4
 service-policy input cda_policy

[Mark Malone]

Hi
all that qos is doing is classifying voice DSCP 46 and CS7 not sure why your using that usually CS6 for mgmt , then your matching it based on the access-list subnets

Now 3850 is auto qos so depending on the command you enter at access port is based on the class/policy maps that are generated , depending onteh syntax you use alters the ytype of auto class-maps and polices generated

Now if you check this doc and got to Configuration Examples for Auto-QoS you will see which maps wil be created , i think you would get away with using auto qos trust by itself and it wil generate a class/policy map that should easily cover both of those DSCP markings , obviuosly it will create a bit more so i would look at the examples

https://www.cisco.com/en/US/docs/switches/lan/catalyst3850/software/release/3.2_0_se/multibook/configuration_guide/b_consolidated_config_guide_3850_chapter_010001.html#reference_348F7F64846344C5ACC4D2F2F33E0D14

you could tweak the auto polices or try create a smaller custom policy

https://edennington.wordpress.com/2013/08/09/simplified-qos-on-3850-with-mqc/

[mark.carroll]

thanks for that

[Mark Malone]

One other thing if DSCP is being marked at the source say by a phone as most would on your access ports , you actually don't need to apply anything on a 36/3850 switch , ios-xe software trusts DSCP markings by default and does not alter them unlike your older 3550 , the fact your not setting anything in the original qos but to make sure those subnets get those values the 3850 will do the same for those 2 subnets once the end devices mark at the source already

so if its a load of Cisco phones or Lync softphone they mark at the source and DSCP wil be carried by default without any config through the 3850