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Mapping IP Precedence
The Type of Service (ToS) octet in the IPv4 header includes three
precedence bits defining eight different priority levels ranging from highest
priority for network control packets to lowest priority for routine traffic.
The default IP Precedence values are mapped one-to-one to Class of
Service values (i.e., Precedence value 0 maps to CoS value 0, and so forth).
Bits 6 and 7 are used for network control, and the other bits for various
application types. ToS bits are defined in the following table.
Priority Level
7
6
5
4
Command Attributes
•
IP Precedence Priority Table – Shows the IP Precedence to CoS
map.
•
Class of Service Value – Maps a CoS value to the selected IP
Precedence value. Note that "0" represents low priority and "7"
represent high priority.
Table 3-11. IP Precedence Prioruty
Traffic Type
Network Control
Internetwork Control
Critical
Flash Override
C
S
LASS OF
ERVICE
Priority Level
3
2
1
0
C
ONFIGURATION
Traffic Type
Flash
Immediate
Priority
Routine
3-171
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