HP 6125G HP 6125G & 6125G/XG Blade Switches ACL and QoS Configuration - Page 77

Appendix B Packet precedences, IP precedence and DSCP values

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Appendix B Packet precedences IP precedence and DSCP values Figure 24 ToS and DS fields As shown in Figure 24, the ToS field in the IPv4 header contains eight bits, where the first three bits (0 to 2) represent IP precedence from 0 to 7; the Traffic Classes field in the IPv6 header contains eight bits, where the first three bits (0 to 2) represent IP precedence from 0 to 7. According to RFC 2474, the ToS field in the IPv4 header or the Traffic Classes field in the IPv6 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 Description on IP precedence IP precedence (decimal) 0 1 2 3 4 5 6 7 IP precedence (binary) 000 001 010 011 100 101 110 111 Description Routine priority immediate flash flash-override critical internet network Table 8 Description on DSCP values DSCP value (decimal) 46 10 12 14 18 DSCP value (binary) 101110 001010 001100 001110 010010 71 Description ef af11 af12 af13 af21

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71
Appendix B Packet precedences
IP precedence and DSCP values
Figure 24
ToS and DS fields
As shown in
Figure 24
, the ToS field in the IPv4 header contains eight bits, where the first three bits (0 to
2) represent IP precedence from 0 to 7; the Traffic Classes field in the IPv6 header contains eight bits,
where the first three bits (0 to 2) represent IP precedence from 0 to 7. According to RFC 2474, the ToS
field in the IPv4 header or the Traffic Classes field in the IPv6 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
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
Table 8
Description on DSCP values
DSCP value (decimal)
DSCP value (binary)
Description
46
101110
ef
10
001010
af11
12
001100
af12
14
001110
af13
18
010010
af21