Appendix B Introduction To Packet Precedences; Ip Precedence And Dscp Values - HP 5920 Configuration Manual

Appendix B Introduction to packet precedences

IP precedence and DSCP values

Figure 27 ToS and DS fields
Bits: 0
Preced
IPv4 ToS
ence
byte
RFC 1122
IP Type of Service (ToS)
As shown in
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 precedence (decimal)
0
1
2
3
4
5
6
7
Table 11 DSCP values
DSCP value (decimal)
46
10
12
14
18
20
22
26
1 2 3 4 5 6 7
M
Type of
B
Service
Z
Must
RFC 1349
Be
Zero
RFC 791
Figure 27, the ToS field in the IP header contains 8 bits. The first 3 bits (0 to 2) represent IP
Bits: 0 1 2 3
DSCP
DS-Field
(for IPv4,ToS
octet,and for
IPv6,Traffic
Class octet )
Class Selector
codepoints
Differentiated Services
Codepoint (DSCP)
RFC 2474
IP precedence (binary)
000
001
010
011
100
101
110
111
DSCP value (binary)
101110
001010
001100
001110
010010
010100
010110
011010
85
4 5 6 7
CU
Currently
Unused
Description
Routine
priority
immediate
flash
flash-override
critical
internet
network
Description
ef
af11
af12
af13
af21
af22
af23
af31