HP 5900 - Appendix B Introduction to Packet Precedences; IP Precedence and DSCP Values

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Appendix B Introduction to packet precedences
IP precedence and DSCP values
Figure 27 ToS and DS fields
As shown in Figure 27, 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, where a DSCP value is represented by the first 6 bits (0 to 5) and is in the range 0 to 63. The
remaining 2 bits (6 and 7) are reserved.
Table 10 IP precedence
IP
p
recedence (decimal) IP
p
recedence (binar
y
) Descri
p
tion
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 11 DSCP values
DSCP value (decimal) DSCP value (binar
y
) Descri
p
tion
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
07615432Bits:
Preced
ence
Type of
Service
076
DSCP
Class Selector
codepoints
Differentiated Services
Codepoint (DSCP)
RFC 2474
Currently
Unused
DS-Field
(for IPv4,ToS
octet,and for
IPv6,Traffic
Class octet )
15432Bits:
CU