H3C WX1804H - Appendix C Introduction to Packet Precedences; IP Precedence and DSCP Values

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Port priority
Local precedence
4 4
5 5
6 6
7 7
Appendix C Introduction to packet precedences
IP precedence and DSCP values
Figure 9 ToS and DS fields
As shown in Figure 9, the ToS field in the IP header contains 8 bits. The first 3 bits (0 to 2) represent
IP precedence from 0 to 7. According to RFC 2474, the ToS field is redefined as the differentiated
services (DS) field. A DSCP value is represented by the first 6 bits (0 to 5) of the DS field and is in the
range 0 to 63. The remaining 2 bits (6 and 7) are reserved.
Table 8 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
Table 9 DSCP values
DSCP value (decimal)
DSCP value (binary)
Description
46 101110 ef
10 001010 af11
12 001100 af12
M
B
Z
RFC 1122
IP Type of Service (ToS)
RFC 791
Must
Be
Zero
RFC 1349
IPv4 ToS
byte
0 761 5432Bits:
Preced
ence
Type of
Service
0 76
DSCP
Class Selector
codepoints
Differentiated Services
Codepoint (DSCP)
RFC 2474
Currently
Unused
DS-Field
(for IPv4,ToS
octet,and for
IPv6,Traffic
Class octet )
1 5432Bits:
CU