Simplified QoS on 3850 with MQC

Configuring QoS has been much improved in Cisco’s new 3850 line of switches thanks to its implementation of MQC (Modular QoS Cli) configuration instead of the old “mls qos” commands from the 3750 and 3560 lines of switches.  Here I will show just how easy it is to generate a simple QoS config to handle voice and video traffic.

First we define what traffic we would like to work with.  In this case it is voice traffic marked as dscp ef and video traffic marked as dscp af41.

class-map match-any VIDEO
 match ip dscp af41 
class-map match-any VOICE
 match ip dscp ef

Easy enough. Now lets configure the policy maps to actually do something with this traffic. I will configure two separate policy maps. one for user facing ports and one for the uplinks to my distribution layer.

I would like to prioritize both voice and video traffic over everything else but I want voice to be prioritized over everything. The 3850 actually has 2 priority queues that enable me to do this, a level 1 and level 2 priority queue.

policy-map UPLINK
 class VOICE
    priority level 1 percent 10
    police cir percent 10    conform-action transmit     exceed-action drop 
 class VIDEO
    priority level 2 percent 20
    police cir percent 20    conform-action transmit     exceed-action drop 
 class class-default
    bandwidth remaining percent 100

policy-map USER
 class VOICE
    priority level 1 percent 1
    police cir percent 1    conform-action transmit     exceed-action drop 
 class VIDEO
    priority level 2 percent 5
    police cir percent 5    conform-action transmit     exceed-action drop 
 class class-default
    bandwidth remaining percent 100

Above I have separate policy maps based on if it’s a user or uplink port. For user ports, voice traffic is put in priority queue 1 and guaranteed 1% or 10Mbps of throughput. I also capped it at 10Mbps with the police command to prevent this queue from hogging bandwidth. Same process is followed for voice. It is placed in priority queue 2 and it is guaranteed 50Mbps throughput. On the uplinks, the only change is the percentages of guaranteed bandwidth has been increased.All other traffic gets 100% of the remaining bandwidth.

All that is left is to apply these policy maps to some interfaces.

interface GigabitEthernet1/0/1
 switchport access vlan 302
 switchport mode access
 switchport voice vlan 402
 trust device cisco-phone
 spanning-tree portfast
 service-policy output USER

interface GigabitEthernet1/1/1
 description --- UPLINK ---
 switchport trunk allowed vlan 302,402
 switchport mode trunk
 service-policy output UPLINK
 ip dhcp snooping trust

Done! We can even get some meaningful stats now as well. I haven’t pushed any traffic through this switch yet but you get the idea.

3850#sh policy-map int gig 1/1/1
 GigabitEthernet1/1/1 

  Service-policy output: UPLINK

    queue stats for all priority classes:
      Queueing
      priority level 1
      
      (total drops) 0
      (bytes output) 0

    queue stats for all priority classes:
      Queueing
      priority level 2
      
      (total drops) 0
      (bytes output) 0

    Class-map: VOICE (match-any)
      Match: ip dscp ef (46)
      Priority: 10% (100000 kbps), burst bytes 2500000, 
      
      Priority Level: 1 
      police:
          cir 10 %
          cir 100000000 bps, bc 3125000 bytes
        conformed 0 bytes; actions:
          transmit 
        exceeded 0 bytes; actions:
          drop 
        conformed 0000 bps, exceed 0000 bps

    Class-map: VIDEO (match-any)
      Match: ip dscp af41 (34)
      Priority: 20% (200000 kbps), burst bytes 5000000, 
      
      Priority Level: 2 
      police:
          cir 20 %
          cir 200000000 bps, bc 6250000 bytes
        conformed 0 bytes; actions:
          transmit 
        exceeded 0 bytes; actions:
          drop 
        conformed 0000 bps, exceed 0000 bps

    Class-map: class-default (match-any)
      Match: any 
      Queueing
      
      (total drops) 0
      (bytes output) 0
      bandwidth remaining 100%

As you can see pretty painless QoS implementation. Of course you can get much more complicated if needed with nested policy-maps, table maps etc. Here is the IOS-XE QoS documentation if you want to delve further into QoS IOS XE QoS Config Guide”