R3303-HP HSR6800 Routers ACL and QoS Configuration Guide

117
In
p
ut
p
riorit
y
value dsc
p
-d
p
ma
pp
in
g
dsc
p
-dot1
p
ma
pp
in
g
24 to 31 0 3
32 to 39 0 4
40 to 47 0 5
48 to 55 0 6
56 to 63 0 7
Appendix C Introduction to packet precedences
IP precedence and DSCP values
Figure 38 ToS and DS fields
As shown in Figure 38, the ToS field in the IPv4 header contains 8 bits, where the first 3 bits (0 to 2)
represent IP precedence from 0 to 7. The Traffic Classes field in the IPv6 header contains 8 bits, where
the first 3 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 DS field, where a DSCP
value is represented by the first 6 bits (0 to 5) and is in the range of 0 to 63. The remaining 2 bits (6 and
7) are reserved.
Table 8 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