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default precedence which is 0.
There are 8 Possible Precedence Levels
Eight precedences exist which are numbered from 0 to 7. Precedence 0 is the least important (lowest
priority) precedence and 7 is the most important (highest priority) precedence. A precedence can be
viewed as a separate traffic queue; traffic in precedence 2 will be forwarded before traffic in
precedence 0, precedence 4 forwarded before 2.
Figure 10.4. The Eight Pipe Precedences
Precedence Priority is Relative
The priority of a precedence comes from the fact that it is either higher or lower than another
precedence and not from the number itself. For example, if two precedences are used in a traffic
shaping scenario, choosing precedences 4 and 6 instead of 0 and 3 will makes no difference to the
end result.
Allocating Precedence to Traffic
The way precedence is assigned to traffic is specified in the triggering pipe rule and can be done in
one of three ways:
• Use the precedence of the first pipe
Each pipe has a Default Precedence and packets take the default precedence of the first pipe
they pass through.
• Use a fixed precedence
The triggering pipe rule explicitly allocates a fixed precedence.
• Use the DSCP bits
Take the precedence from the DSCP bits in the packet. DSCP is a subset of the Diffserv
architecture where the Type of Service (ToS) bits are included in the IP packet header.
Specifying Precedences Within Pipes
When a pipe is configured, a Default Precedence, a Minimum Precedence and a Maximum
Precedence can be specified. The default precedences are:
• Minimum Precedence: 0
10.1.6. Precedences Chapter 10. Traffic Management
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