Allied Telesis AT-S62 User Manual
Page 267
AT-S62 Menus Interface User’s Guide
Section II: Advanced Operations
267
Policy Component Hierarchy
The purpose of this example is to illustrate the hierarchy that exists
among the components of a QoS policy and how that hierarchy needs to
be taken into account when assigning new priority and DSCP values. A
new priority can be set at the flow group and traffic class levels, while a
new DSCP value can be set at all three levels -- flow group, traffic class
and policy. The basic rules are:
❑ A new setting in a flow group takes precedence over a
corresponding setting in a traffic class or policy.
❑ A new setting in a traffic class takes precedence over a
corresponding setting in a policy.
❑ A new setting in a policy is used only if there is no corresponding
setting in a flow group or traffic class.
This concept is illustrated in Figure 86 on page 268. It shows a policy for
a series of traffic flows consisting of subnets defined by their destination
IP addresses. New DSCP values for the traffic flows are established at
different levels within the policy.
Traffic flows 149.11.11.0 and 149.22.22.0, defined by classifiers 1 and 2,
are attached to a flow group, traffic class, and policy that contain new
DSCP values. Since a setting in a flow group takes precedence over that
of a traffic class or policy, the value in the flow group is used. The result is
that the DSCP value in the two traffic flows is changed to 10.
The flow group for traffic flows 149.33.33.0 and 149.44.44.0, defined in
classifiers 3 and 4, does not contain a new DSCP value. Consequently,
the new value in the traffic class is used, in this case 30. The policy also
has a DSCP setting, but it is not used for these traffic flows because a
new DSCP setting in a traffic class takes precedence over that of a policy.
Finally, the new DSCP value for traffic flows 149.55.55.0 and 149.66.66.0,
defined in classifiers 5 and 6, is set at the policy level to a value of 55
because the flow group and traffic class do not specify a new value.