472 BigIron RX Series Configuration Guide53-1001986-01Marking18• COS to Internal Forwarding Priority Mapping – You can change the mapping between 802.1p(COS) values and the Internal Forwarding priority value from the default values shown inTable 89 through Table 92. This mapping is used for COS marking and determining the internalpriority when the trust level is COS. “Changing the CoS –> internal forwarding prioritymappings” on page 477.MarkingMarking is the process of changing the packet’s QoS information (the 802.1p and DSCPinformation in a packet) for the next hop. You can mark a packet’s Layer 2 CoS value, its Layer 3DSCP value, or both values. The Layer 2 CoS or DSCP value the device marks in the packet is thesame value that results from mapping the packet’s QoS value into a Layer 2 CoS or DSCP value.Marking is optional and is disabled by default. When marking is disabled, the device still performsmappings for scheduling the packet, but leaves the packet’s QoS values unchanged when thedevice forwards the packet.Configuring DSCP classification by interfaceYou can configure DSCP classification on an interface to set the DSCP value of every packet thatarrives on the interface to a value that you configure. After the packet’s DSCP value has been setusing this command, it is subject to classification, marking, and scheduling operations that areconfigured.To configure the 1/1 interface to set all packets that arrive on it to a DSCP value of 23, use thefollowing command.BigIron RX(config)# interface ethernet 1/1BigIron RX(config-if-e1000-1/1)# dscp 23Syntax: [no] dscp <num>The parameter can be any possible DSCP value from 0 to 63.Configuring port, MAC, and VLAN-based classificationAssigning QoS priorities to trafficBy default, traffic is forwarded using the best-effort queue (qosp0). However, traffic can beclassified into different priorities, based on the following:• Incoming port (sometimes called the ingress port)• Port-based VLAN membership• Static MAC entryThe following sections describe how to change the priority for each of the items listed above.Although it is possible for a packet to qualify for an adjusted QoS priority based on more than one ofthe criteria above, the system determines the priority it will use for forwarding as described in“Processing of classified traffic” on page 469.
