Virtualized environments carry different types of traffic, including tenant, storage and management traffic, across the switching infrastructure. Each traffic type has different characteristics and makes different demands on the physical switching infrastructure.

  • Management traffic, although typically low in volume, is critical for controlling physical and virtual network state. 

  • IP storage traffic is typically high in volume and generally stays within a data center. 

For virtualized environments, the hypervisor sets the QoS values for the different traffic types. The physical switching infrastructure has to trust the values set by the hypervisor. No reclassification is necessary at the server-facing port of a leaf switch. If there is a congestion point in the physical switching infrastructure, the QoS values determine how the physical network sequences, prioritizes, or potentially drops traffic.

Figure 1. Quality of Service Trust Point

Two types of QoS configuration are supported in the physical switching infrastructure.

  • Layer 2 QoS, also called class of service.

  • Layer 3 QoS, also called DSCP marking.

A vSphere Distributed Switch supports both class of service and DSCP marking. Users can mark the traffic based on the traffic type or packet classification. When the virtual machines are connected to the VXLAN-based logical switches or networks, the QoS values from the internal packet headers are copied to the VXLAN-encapsulated header. This enables the external physical network to prioritize the traffic based on the tags on the external header.