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Mapping CoS
Priorities to Internal
DSCP Values
To show the DSCP to internal PHB/drop precedence map:
1.
Click Traffic, Priority, DSCP to DSCP.
2.
Select Show from the Action list.
3.
Select a port.
Figure 133: Showing DSCP to DSCP Internal Mapping
Use the Traffic > Priority > CoS to DSCP page to maps CoS/CFI values in incoming
packets to per-hop behavior and drop precedence values for priority processing.
Command Usage
◆
The default mapping of CoS to PHB values is shown in
◆
Enter up to eight CoS/CFI paired values, per-hop behavior and drop
precedence.
◆
If a packet arrives with a 802.1Q header but it is not an IP packet, then the CoS/
CFI-to-PHB/Drop Precedence mapping table is used to generate priority and
drop precedence values for internal processing. Note that priority tags in the
original packet are not modified by this command.
◆
The internal DSCP consists of three bits for per-hop behavior (PHB) which
determines the queue to which a packet is sent; and two bits for drop
precedence (namely color) which is used by Random Early Detection (RED) to
control traffic congestion.
◆
RED starts dropping yellow and red packets when the buffer fills up to 16
packets on Fast Ethernet ports and 72 packets on Gigabit Ethernet ports, and
– 221 –
Chapter 9
| Class of Service
Layer 3/4 Priority Settings
Table 16 on page
222.
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