C
HAPTER
37
| Class of Service Commands
Priority Commands (Layer 3 and 4)
– 1175 –
DEFAULT SETTING
COMMAND MODE
Interface Configuration (Port)
COMMAND USAGE
◆ The default mapping of CoS to PHB values shown in Table 148 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.
◆ Random Early Detection starts dropping yellow and red packets when
the buffer fills up to 0x60 packets, and then starts dropping any
packets regardless of color when the buffer fills up to 0x80 packets.
◆ 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 148: 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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