QOS on Nexus 7000 switch Modules
In the core datacenter layer switches usually COS and DHCP marking are not required because mostly these marking are done at access layer or Virtual access layer switches. In this case core layer has main responsibility to manage packet loss and core layer should trust the CoS and DHCP marking on ingress and perform the ingress and egress queuing.
In Nexus 7000 Switches, there are F and M module both supports QoS out of which we will see the differences in architecture and capabilities between these two M2/F2 Modules.
Nexus 7000 supports following QoS policies:
- Qos: This policy is used for marking and policing.
- Network-qos (required on F-Series modules only): Defines the characteristics of network-wide QoS properties and should be applied consistently on all switches participating in the network.
- Queuing: This policy is used for queuing and scheduling.
Nexus 7000 trust the QoS marked traffic by default according to following rule:
- For (L2) bridged traffic, CoS is used for ingress queue selection and DSCP values which is received is transmitted unmodified and are ignored from a QoS perspective. The received CoS markings are used for egress queue selection and are also transmitted unmodified on egress bridged ports.
- For (L3) routed traffic, CoS is used for ingress queue selection; DSCP markings are not modified, but are used to generate new CoS markings derived from the 3 Most Significant Bits (MSB) of the DSCP; these newly generated CoS markings are then used for egress queue selection even if the egress interface is not an 802.1Q trunk and so not carrying CoS within the frame.
Let’s now understand the Nexus 7000 M2 Qos Architecture and Concepts:
Nexus 7000 M2 Module: QoS Design & Architecture
Below figure describes the Nexus 7000 M2 Series Module architecture and also labels the QoS policies applied.
In Nexus 7000 M2 Modules following are QoS policies applied in marked places in above diagram:
- Ingress (type queuing) policies are applied at the ingress physical port.
- Classification, marking and policing (type qos) policies are implemented within the forwarding engine.
- Fabric QoS policies are applied in the VOQs beforethe packet traverses the three-stage switching fabric.
- Egress (type queuing) policies are applied in the VOQs afterthe packet traverses the three-stage switching fabric.
- Egress (type queuing) policies are applied again in the egress physical port.
Here ingress and egress QoS policies can be configured manually or used default but fabric Qos for VOQ Queuing is not configurable and is made standard across nexus 7000 Series.
You have learned how VOQ works in Module 1 Hardware chapter, so here we are only giving snapshot of it. As soon as Qos Marked traffic inters in to Module based on its Ingress queuing policies which will be described later in this chapter, packets are queued in VOQ as per following table: