3-3
Figure 3-1
Priority mapping procedure for an Ethernet packet
Which priority is
trusted on the
port?
Receive a packet
on a port
Use the port priority
as the 802.1p priority
for priority mapping
N
Look up the dot1p-dp
and dot1p-lp
mapping tables
Mark the packet with
local precedence and
drop precedence
Is the packet
802.1q tagged?
Y
DSCP
in packets
Look up the dscp-dp,
dscp-dot1p, and dscp-
dscp mapping tables
802.1p
in packets
Mark the packet with
802.1p priority, drop
precedence, and new
DSCP precedence
Look up the dot1p-lp
Mapping table
Mark the packet with
local precedence
Look up the dot1p-dp
and dot1p-lp mapping
tables
Mark the packet with
local precedence and
drop precedence
Schedule the packet
according to its local and
drop precedence
Use the port
priority as the
802.1p priority for
priority mapping
Look up the dot1p-
dp, and dot1p-lp
mapping tables
Mark the packet
with local
precedence and
drop precedence
Port priority
The priority mapping procedure presented above applies in the absence of priority marking. If priority
marking is configured, the device performs priority marking before priority mapping, and then uses the
re-marked packet-carried priority for priority mapping or directly uses the re-marked scheduling priority
for traffic scheduling depending on your configuration. In this case, neither priority trust mode
configuration on the port nor port priority configuration takes effect.
Priority Mapping Configuration Tasks
You can modify priority mappings by modifying priority mapping tables, priority trust mode on a port, and
port priority.
You are recommended to plan QoS throughout the network before making QoS configuration.
Complete the following task to configure priority mapping:
