Chapter 20: Quality of Service (QoS) Commands
338
A new DSCP value can be set at all three levels:
flow group, traffic class, and policy. A DSCP value
specified in a flow group overrides a DSCP value
specified at the traffic class or policy level. A
DSCP value specified at the traffic class level is
used only if no value has been specified at the
flow group level. It will override any value set at
the policy level.
maxbandwidth Specifies the maximum bandwidth available
to the traffic class. This parameter determines
the maximum rate at which the ingress port
accepts data belonging to this traffic class
before either dropping or remarking occurs,
as specified with the EXCEEDACTION
parameter. If the sum of the maximum
bandwidth for all traffic classes on a policy
exceeds the (ingress) bandwidth of the port
to which the policy is assigned, the
bandwidth for the port takes precedence and
the port discards packets before they can be
classified. The range is 0 to 1016 Mbps.
The value for this parameter is rounded up to
the nearest Mbps value when this traffic class
is assigned to a policy on a 10/100 port, and
up to the nearest 8 Mbps value when
assigned to a policy on a gigabit port (for
example, on a gigabit port, 1 Mbps is rounded
to 8 Mbps, and 9 is rounded to 16).
burstsize Specifies the size of a token bucket for the
traffic class. The token bucket is used in
situations where you have set a maximum
bandwidth for a class, but where traffic
activity may periodically exceed the
maximum. A token bucket can provide a
buffer for those periods where the maximum
bandwidth is exceeded.
Tokens are added to the bucket at the same
rate as the traffic class’ maximum bandwidth,
set with the MAXBANDWIDTH parameter. For
example, a maximum bandwidth of 50 Mbps
adds tokens to the bucket at that rate.
If the amount of the traffic flow matches the
maximum bandwidth, no traffic is dropped
because the number of tokens added to the
bucket matches the number being used by