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Link scheduler configuration task list 160
IPLink Software Configuration Guide 14 • Link scheduler configuration
The type-of-service (TOS) byte in an IP header specifies precedence (priority) and type of service (RFC791,
RFC1349). The precedence field is defined by the first three bits and supports eight levels of priority. The next
four bits—which are set by the
set ip tos
command—determine the type-of-service (TOS).
Historically those bits had distinct meanings but since they were never consistently applied routers will ignore
them by default. Nevertheless you can configure your routers to handle specific TOS values and IPLink soft-
ware allows you to inspect the TOS value in the ACL rules and to modify the TOS value with the link sched-
uler
set ip tos command.
Mode: Source
Specifying the precedence field
The set ip precedence command specifies the precedence marking applied to packets of the class name. Pre-
cedence and DSCP markings cannot be used at the same time.
The type-of-service (TOS) byte in an IP header specifies precedence (priority) and type of service (RFC791,
RFC1349). The precedence field is defined by the first three bits and supports eight levels of priority. The low-
est priority is assigned to 0 and the highest priority is 7.
The
no
form of this command disables precedence marking.
Mode: Source
Specifying differentiated services codepoint (DSCP) marking
Differentiated services enhancements to the Internet protocol are intended to enable the handling of “traffic-
classes” throughout the Internet. In this context the IP header TOS field is interpreted as something like a
Table 8. TOS values and their meaning
TOS Value
IPLink software
Value
Meaning
1000 8 Minimize delay.
0100 4 Maximize throughput.
0010 2 Maximizes reliability.
0001 1 Minimize monetary costs.
0000 0 All bits are cleared, normal service, “default TOS.”
Command Purpose
node(src)[ name ]#set ip tos value Defines the type-of-service (TOS) value applied to packets of for the
selected class or policy
name . Standard ToT values are 0, 1, 2, 4,
and 8, as given in
table 8
on page 160, but any number from 0 to
15 can be configured.
Command Purpose
node(src)[ name ]#set ip precedence value Defines the precedence marking value applied to pack-
ets of for the selected class or policy
name . The range
for value is from 0 to 7, but only values from 0 to 5
should be used.