C
HAPTER
35
| Class of Service Commands
Priority Commands (Layer 3 and 4)
– 823 –
DEFAULT SETTING.
COMMAND MODE
Interface Configuration (Port, Static Aggregation)
COMMAND USAGE
◆ The default mapping of CoS to PHB values shown in Table 117 is based
on the recommended settings in IEEE 802.1p for mapping CoS values
to output queues.
◆ Enter a value pair for the internal per-hop behavior and drop
precedence, followed by the keyword “from” and then up to eight CoS/
CFI paired values separated by spaces.
◆ 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 ports 1-24 and 72 packets on ports 25-26, and then
starts dropping any packets regardless of color when the buffer fills up
to 58 packets on ports 1-24 and 80 packets on ports 25-26.
◆ The specified mapping applies to all interfaces.
EXAMPLE
Console(config)#interface ethernet 1/5
Console(config-if)#qos map cos-dscp 0 0 from 0 1
Console(config-if)#
Table 117: Default Mapping of CoS/CFI to Internal PHB/Drop Precedence
CFI
CoS
0 1
0(0,0)(0,0)
1(1,0)(1,0)
2(2,0)(2,0)
3(3,0)(3,0)
4(4,0)(4,0)
5(5,0)(5,0)
6(6,0)(6,0)
7(7,0)(7,0)
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