Forwarding behavior determines the priority and drop precedence of traffic flows that are about to be forwarded to the network. You can choose two major forwarding behaviors: prioritizing the flows of a class in relationship to other traffic classes or dropping the flows entirely.
The Diffserv model uses the marker to assign the chosen forwarding behavior to traffic flows. IPQoS offers the following marker modules.
Note that the suggestions in this section refer specifically to IP packets. If your IPQoS system includes a VLAN device, you can use the dlcosmk marker to mark forwarding behaviors for datagrams. For more information, refer to Using the dlcosmk Marker With VLAN Devices.
To prioritize IP traffic, you need to assign a DSCP to each packet. The dscpmk marker marks the DS field of the packet with the DSCP. You choose the DSCP for a class from a group of well-known codepoints that are associated with the forwarding behavior type. These well-known codepoints are 46 (101110) for the EF PHB and a range of codepoints for the AF PHB. For overview information on DSCP and forwarding, refer to Traffic Forwarding on an IPQoS-Enabled Network.