H3C Technologies H3C S6300 Series Switches - Manual (Page 91)

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Appendix B Introduction to packet precedences
IP precedence and DSCP values
Figure 23 ToS and DS fields
As shown in Figure 23 , the ToS field in the IP header contains eight bits. The first three 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, 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 9 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 10 DSCP values
DSCP value (decimal) DSCP value (binary) Description
46 101110 ef
10 001010 af11
12 001100 af12
14 001110 af13
18 010010 af21
20 010100 af22
22 010110 af23
26 011010 af31
M
B
Z
RFC 1122
IP Type of Service (ToS)
RFC 791
Must
Be
Zero
RFC 1349
IPv4 ToS
byte
0 7 6 1 5 4 3 2 Bits:
Preced
ence
Type of
Service
0 7 6
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 5 4 3 2 Bits:
CU