IP precedence and DSCP values
Figure 25: ToS and DS fields
As shown in Figure 25, 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. A DSCP value is represented by the first 6 bits (0 to 5) of the DS field and is in the range 0 to 63. The remaining 2 bits (6 and 7) are reserved.
Table 7: 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: DSCP values
DSCP value (decimal) | DSCP value (binary) | Description |
|---|---|---|
46 | 101110 | ef |
10 | 001010 | af11 |
12 | 001100 | af12 |
14 | 001110 | af13 |
18 | 010010 | af21 |
20 | 010100 | af22 |
22 | 010110 | af23 |
26 | 011010 | af31 |
28 | 011100 | af32 |
30 | 011110 | af33 |
34 | 100010 | af41 |
36 | 100100 | af42 |
38 | 100110 | af43 |
8 | 001000 | cs1 |
16 | 010000 | cs2 |
24 | 011000 | cs3 |
32 | 100000 | cs4 |
40 | 101000 | cs5 |
48 | 110000 | cs6 |
56 | 111000 | cs7 |
0 | 000000 | be (default) |