HP 6125G HP 6125G & 6125G/XG Blade Switches ACL and QoS Configuration - Page 32

Priority trust mode on a port The priority trust mode on a port decides which priority is used for priority mapping table lookup. Port priority was introduced to use for priority mapping in addition to priority fields carried in packets. The HP Blade 6125 Switch Series provides the following priority trust modes: • Using the 802.1p priority carried in packets for priority mapping. • Using the DSCP carried in packets for priority mapping. The priority mapping procedure varies with the priority modes. For more information, see the subsequent section. Priority mapping procedure On receiving an Ethernet packet on a port, the switch marks the scheduling priorities (local precedence and drop precedence) for the Ethernet packet. This procedure is done according to the priority trust mode of the receiving port and the 802.1q tagging status of the packet, as shown in Figure 6. Figure 6 Priority mapping procedure for an Ethernet packet Receive a packet on a port Which priority is trusted on the port? 802.1p in packets Use the port priority as the N 802.1p priority of the packet Look up the dot1p-dp and dot1p-lp tables Is the packet 802.1q tagged? Y Look up the dot1p-dp and dot1p-lp tables Mark the packet with local precedence and drop precedence Mark the packet with local precedence and drop precedence Schedule the packet according to its local precedence and drop precedence DSCP in packets Look up the dscp-dp, dscpdot1p, and dscp- dscp tables Mark the packet with 802.1p priority, drop precedence, and new DSCP precedence Look up the dot1p-lp table Mark the packet with local precedence The priority mapping procedure shown in Figure 6 applies in the absence of priority marking. If priority marking is configured, the switch performs priority marking before priority mapping. The switch then uses the re-marked packet-carried priority for priority mapping or directly uses the re-marked scheduling 26