In the Diffserv model, the marker marks a packet with a value that reflects a forwarding behavior. Marking is the process of placing a value in the packet's header to indicate how to forward the packet to the network. IPQoS contains two marker modules:
dscpmk – Marks the DS field in an IP packet header with a numeric value that is called the Differentiated Services codepoint, or DSCP. A Diffserv-aware router can then use the DS codepoint to apply the appropriate forwarding behavior to the packet.
dlcosmk – Marks the virtual local area network (VLAN) tag of an Ethernet frame header with a numeric value that is called the user priority. The user priority indicates the class of service (CoS), which defines the appropriate forwarding behavior to be applied to the datagram.
dlcosmk is an IPQoS addition that is not part of the Diffserv model, as designed by the IETF.
For information on implementing a marker strategy for the QoS policy, see How to Plan Forwarding Behavior.