7-1
7
Priority Mapping Configuration
This chapter includes these sections:
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Introduction to Packet Precedences
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Priority Mapping Configuration Task List
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Displaying and Maintaining Priority Mapping
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Priority Mapping Configuration Example
Introduction to Packet Precedences
IP Precedence and DSCP Values
Figure 7-1
ToS and DS fields
As shown in
, the ToS field of the IP header contains eight bits, and the first three bits (0 to 2)
represent IP precedence from 0 to 7. According to RFC 2474, the ToS field of the IP header is redefined
as the differentiated services (DS) field, where a DSCP value is represented by the first six bits (0 to 5)
and is in the range 0 to 63. The remaining two bits (6 and 7) are reserved.
Table 7-1
Description on IP precedence
IP precedence (decimal)
IP precedence (binary)
Description
0 000
Routine
1 001
priority
2 010
immediate
3 011
flash
4 100
flash-override
5 101
critical
6 110
internet
7 111
network
