VLAN and untagged VLAN environments

QoS operates in VLAN-tagged and untagged environments. If your network does not use multiple VLANs, you can still implement the 802.1Q VLAN capability to allow packets to carry an 802.1p priority to the next downstream device. To do so, configure the ports on links to other network devices as VLAN-tagged members.

In a tagged or untagged VLAN, you can also ensure that IPv4/IPv6 packets carry an 802.1p priority to downstream devices by configuring DSCP marking in the ToS/Traffic Class byte.

The following table summarizes the QoS options for traffic-marking in VLAN-tagged and untagged environments.

QoS traffic marking supported in tagged and untagged VLANs

QoS marking supported on outbound packets

Port membership in VLANs



Assign an 802.1p priority that determines the outbound port queue to which a packet is sent



Carry the 802.1p priority to the next downstream device


Not Supported

Carry a DSCP policy (DSCP codepoint1 and associated 802.1p priority2 ) to downstream devices




DSCP marking (DSCP codepoint and associated 802.1p priority) are not supported on non-IP packets and packets selected using the following global QOS classifiers: Layer 3 Protocol and IP-Precedence. Also, in order for DSCP policy marking to be honored on a downstream device, the device must be configured to use the DSCP policy in IP packet headers.


The 802.1p priority associated with a DSCP codepoint is used to determine the packet's outbound port queue. When used in a VLAN-tagged environment, an 802.1p priority is also carried in the 802.1Q field of outbound packet headers.