Priority Mapping Overview - 3Com Switch 4800G 24-Port Configuration Manual

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Priority Mapping
Overview
P M
RIORITY
When configuring priority mapping, go to these sections for information you are
interested in:
"Priority Mapping Overview" on page 883
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"Configuring a Priority Mapping Table" on page 884
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"Configuring the Port Priority" on page 885
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"Configuring Port Priority Trust Mode" on page 886
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"Displaying and Maintaining Priority Mapping" on page 887
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When a packet reaches a switch, the switch assigns the packet parameters
according to 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.
Local precedence is the precedence that the switch assigns to a packet and it is
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corresponding to the number of an outbound queue on the port. Local
precedence takes effect only on the local switch.
Drop precedence is a parameter that is referred to when dropping packets. The
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higher the drop precedence, the more likely a packet is dropped.
the Switch 4800G provide the following two priority trust modes:
Trusting the DSCP precedence of received packets. In this mode, the switch
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searches the dscp-dot1p/dp/dscp mapping table based on the DSCP
precedence of the received packet for the 802.1p precedence/drop
precedence/DSCP precedence to be used to mark the packet. Then the switch
searches the dot1p-lp mapping table based on the marked 802.1p precedence
for the corresponding local precedence and marks the received packet with the
local precedence.
Trusting the 802.1p precedence of received packets. In this mode, if a packet is
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received without an 802.1q tag, the switch takes the priority of the receiving
port as the 802.1p precedence of the packet and then based on the priority
searches the dot1p-dp/lp mapping table for the local/drop precedence for the
packet. If packet is received with an 802.1q tag, the switch searches the
dot1p-dp/lp mapping table based on the 802.1p precedence in the tag for
local/drop precedence for the packet.
The default dot1p-lp/dp mapping and dscp-dot1p/dp/dscp mapping provided
by the Switch 4800G are shown in the following two tables.
APPING