QoS marking

The term—QoS marking—is the process of initially changing the packet QoS information for the next hop.

Layer 2 (802.1p) and Layer 3 (Differentiated Services Code Point (DSCP)) information in a packet can be marked. As an example of marking traffic coming from a device that does not support DSCP, you can change the packet IP precedence value into a DSCP value before forwarding the packet.

Class of Service (CoS) is a 3-bit field within an Ethernet frame header known as the Priority Code Point (PCP) when using a 802.1 network. This field specifies a priority value between 0 and 7, inclusive, that can be used by Quality of Service (QoS) to differentiate traffic.

The Differentiated Services Code Point (DSCP) is a 6-bit field in an IP header for the classification of packets. Differentiated Services is a technique used to classify and manage network traffic and it helps to provide QoS for modern Internet networks. It can provide services to all kinds of networks.

You can mark a packet’s Layer 2 CoS value, its Layer 3 DSCP value, or both values. The Layer 2 CoS or DSCP value that the device marks in the packet is the same value that results from mapping the packet QoS value into a Layer 2 CoS or DSCP value.

Marking is optional and is disabled by default.