QoS provides high-quality and dedicated network performance for preferred traffic that requires high bandwidth. The QoS mechanism does this by prioritizing sufficient bandwidth, controlling latency and jitter, and reducing data loss for preferred packets even when there is a network congestion. This level of network service is provided by using the existing network resources efficiently.
For this release, shaping and traffic marking namely, CoS and DSCP is supported. The Layer 2 Class of Service (CoS) allows you to specify priority for data packets when traffic is buffered in the logical switch due to congestion. The Layer 3 Differentiated Services Code Point (DSCP) detects packets based on their DSCP values. CoS is always applied to the data packet irrespective of the trusted mode.
NSX-T Data Center trusts the DSCP setting applied by a virtual machine or modifying and setting the DSCP value at the logical switch level. In each case, the DSCP value is propagated to the outer IP header of encapsulated frames. This enables the external physical network to prioritize the traffic based on the DSCP setting on the external header. When DSCP is in the trusted mode, the DSCP value is copied from the inner header. When in the untrusted mode, the DSCP value is not preserved for the inner header.
DSCP settings work only on tunneled traffic. These settings do not apply to traffic inside the same hypervisor.
You can use the QoS switching profile to configure the average ingress and egress bandwidth values to set the transmit limit rate. The peak bandwidth rate is used to support burst traffic a logical switch is allowed to prevent congestion on the northbound network links. These settings do not guarantee the bandwidth but help limit the use of network bandwidth. The actual bandwidth you will observe is determined by the link speed of the port or the values in the switching profile, whichever is lower.
The QoS switching profile settings are applied to the logical switch and inherited by the child logical switch port.