Appendix B Introduction To Packet Precedences; Ip Precedence And Dscp Values - HP A5120 EI Series Configuration Manual

Appendix B Introduction to packet
precedences

IP precedence and DSCP values

Figure 21 ToS and DS fields
Bits: 0
Preced
IPv4 ToS
ence
byte
RFC 1122
IP Type of Service (ToS)
As shown in
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 6 Description on IP precedence
IP precedence (decimal)
0
1
2
3
4
5
6
7
Table 7 Description on DSCP values
DSCP value (decimal)
46
10
12
14
1 2 3 4 5 6 7
M
Type of
DS-Field
B
Service
Z
(for IPv4,ToS
octet,and for
IPv6,Traffic
Class octet )
Must
RFC 1349
Be
Zero
RFC 791
Figure 21, the ToS field in the IP header contains eight bits. The first three bits (0 to 2)
IP precedence (binary)
000
001
010
011
100
101
110
111
DSCP value (binary)
101110
001010
001100
001110
Bits: 0 1 2 3 4 5 6
DSCP
CU
Class Selector Currently
codepoints Unused
Differentiated Services
Codepoint (DSCP)
RFC 2474
65
7
Description
Routine
priority
immediate
flash
flash-override
critical
internet
Network
Description
ef
af11
af12
af13