For the purpose of this article, this configuration and discussion pertains to a Cisco Nexus 5020 switch running NX-OS version 4.1(3)N1(1a). Given what seems to be a variety of changes to the CLI configuration process for the Nexus, this may or may not work for you.

I felt it was important to write myself a reminder of how to create a lossless Ethernet network using Cisco Nexus devices as QoS on this platform seems to be similar, yet, take a divergent path from the methodology of configuring QoS on the Catalyst series. In this example we will assume we are working users that are requesting that any traffic marked with CoS 5 be placed in the no-drop queue. The flagship example of this is the Fiber Channel over Ethernet (FCoE) configuration present in the system configuration, although they use CoS 3, by default.

The first step is to create a qos class-map:

class-map type qos MATCH-COS-FIVE
  match cos 5

Next create a qos policy-map to set the qos-group to 2:

policy-map type qos SET-QOS-GROUP-TWO
  class MATCH-COS-FIVE
    set qos-group 2

qos-group 1 is a system default for the FCoE configuration. Setting this to our own group allows us to have different parameters for FCoE should you need to manipulate it differently in the future.

Next create a network-qos class-map to match qos-group 2:

class-map type network-qos MATCH-QOS-GROUP-TWO
  match qos-group 2

Now, create a policy-map you wish to use to manage QoS on a system wide level and ensure traffic matching qos-group 2 is in the no-drop queue.

policy-map type network-qos SYSTEM-QOS-POLICY
  class type network-qos MATCH-QOS-GROUP-TWO
    pause no-drop
  class type network-qos class-default
    mtu 9216

In this case the class-default matches other traffic and permits the MTU to be jumbo framed at 9216 bytes.

Apply the system policy we created to system qos:

system qos
  service-policy type network-qos SYSTEM-QOS-POLICY

We are now at the point where matching CoS values can be done on a system-wide level or per interface. To apply the policy system-wide:

system qos
  service-policy type qos SET-QOS-GROUP-TWO

Be aware that if you are running within a VPC domain that this may very well cause a system compatibility failure and disable links within your VPC domain. Apply this configuration domain-wide if you are interested in have this feature across multiple switches.

Otherwise you can apply the CoS matching on a per interface level:

interface Ethernet1/1
  service-policy type qos input SET-QOS-GROUP-TWO

To verify packets are matching your newly defined qos-group:

switch# show queuing interface Ethernet 1/10

If traffic is being sent that is tagged with CoS 5 you should be seeing traffic on your qos-group:

qos-group  2:
    q-size: 81920, MTU: 9216
    drop-type: no-drop, xon: 128, xoff: 230
    Statistics:
        Pkts received over the port             : 2767031
        Ucast pkts sent to the cross-bar        : 2767030
        Mcast pkts sent to the cross-bar        : 1
        Ucast pkts received from the cross-bar  : 270664
        Pkts sent to the port                   : 270664
        Pkts discarded on ingress               : 0
        Per-priority-pause status               : Rx (Inactive), Tx (Inactive)

All should be well and drop-type should be reading no-drop. If you are interested in applying bandwidth shaping, then this can be accomplished in a similar manner using the queuing type class and policy maps to map and take action with traffic in qos-group 2. That service policy can also be applied system-wide or on an interface level as shown above.

Jonathan Voss Cisco, Networking Cisco, Networking, Nexus, NX-OS