8-2
Input priority value dscp-lp mapping dscp-dot1p mapping
40 to 47 5 5
48 to 55 6 6
56 to 63 7 7
Appendix B Introduction to Packet Precedences
IP Precedence and DSCP Values
Figure 8-1 ToS and DS fields
As shown in Figure 8-1
, the ToS field in the IP header contains eight bits. The first three 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 six bits (0 to 5) and is
in the range 0 to 63. The remaining two bits (6 and 7) are reserved.
Table 8-3 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 8-4 Description on DSCP values
DSCP value (decimal) DSCP value (binary) Description
46 101110 ef
10 001010 af11
12 001100 af12
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