Operation Manual – QoSH3C S7500E Series Ethernet Switches Chapter 5 Priority Mapping5-1Chapter 5 Priority MappingWhen configuring priority mapping, go to these sections for information you areinterested in:z Priority Mapping Overviewz Configuring a Priority Mapping Tablez Configuring the Port Priorityz Configuring Port Priority Trust Modez Displaying and Maintaining Priority Mapping5.1 Priority Mapping OverviewWhen a packet reaches a switch, the switch assigns the packet parameters accordingto it configuration, such as 802.1p precedence, DSCP precedence, IP precedence,local precedence, and drop precedence.The local precedence and drop precedence are described as follows.z Local precedence is the precedence that the switch assigns to a packet and it iscorresponding to the number of an outbound queue on the port. Local precedencetakes effect only on the local switch.z Drop precedence is a parameter that is referred to when dropping packets. Thehigher the drop precedence, the more likely a packet is dropped.S7500E series Ethernet switches provide the following two priority trust modes:z Trusting the DSCP precedence of received packets. In this mode, the switchsearches the dscp-dot1p/dp/dscp mapping table based on the DSCPprecedence of the received packet for the 802.1p precedence/dropprecedence/DSCP precedence to be used to mark the packet. Then the switchsearches the dot1p-lp mapping table based on the marked 802.1p precedence forthe corresponding local precedence and marks the received packet with the localprecedence.z Trusting the 802.1p precedence of received packets. In this mode, if a packet isreceived without an 802.1q tag, the switch takes the priority of the receiving port asthe 802.1p precedence of the packet and then based on the priority searches thedot1p-dp/lp mapping table for the local/drop precedence for the packet. If packetis received with an 802.1q tag, the switch searches the dot1p-dp/lp mapping tablebased on the 802.1p precedence in the tag for local/drop precedence for thepacket.The default dot1p-lp/dp mapping and dscp-dot1p/dp/dscp mapping provided byS7500E series Ethernet switches are shown in the following two tables.
