HP ProCurve Secure Router 7203 dl Advanced Management And Configuration Manual page 339

Setting Up Quality of Service
Configuring CBWFQ
To specify bandwidth as a percentage of the bandwidth not allocated to low-
latency queues, use the remaining percent keyword. The remaining per-
cent keyword calculates bandwidth from the amount remaining after the
bandwidth guaranteed to low latency queues has been subtracted from the
available bandwidth. Unlike commands using the percent keyword, this
command does not subtract bandwidth from the bandwidth available for the
low-latency queues.
Percentages must be whole values from 1 to 100, inclusive.
N o t e
The bandwidth available for queues on a ProCurve Secure Router is 75 percent
of an interface's access rate or rate-limited rate. The Secure Router OS will
deactivate a QoS map when you assign it to an interface that does not have
enough bandwidth available to grant the guaranteed rate.
Other traffic can use the remaining 25 percent of the bandwidth, although this
traffic may also be starved out by traffic in a class bursting past its guaranteed
level.
The router automatically provides bandwidth for control traffic such as
routing updates; control traffic takes priority over all classes.
Traffic that does not fit into one of the classes you have defined is served with
typical WFQ. It is divided into conversation subqueues according to source
and destination IP addresses and port, and is allocated a portion of the
remaining bandwidth based on its IP precedence value.
Specifying Bandwidth by Remaining Percent Versus Percent. For
example, you limit an Ethernet interface's rate to 10 Mbps. You guarantee at
least 4 Mbps to low-latency queues. You then assign one class 25 percent of
the remaining bandwidth and another class 15 percent of the remaining
bandwidth. Subtracting 4 Mbps from 10 Mbps leaves 6 Mbps. The first class
receives 1.5 Mbps and the second, 900 Kbps. The bandwidth required for the
map is 6.4 Mbps. The bandwidth available for queues is 75 percent of the rate
limited bandwidth, or 7.5 Mbps. The map can become active.
Now, consider how much bandwidth the classes would receive if you config-
ured the QoS map using the percent keyword rather than the remaining
percent keyword. The first class would receive 25 percent of 10 Mbps, or 2.5
Mbps. The second class would receive 15 percent of 10 Mbps, or 1.5 Mbps.
With the low-latency queues, the bandwidth required for the map is 8 Mbps.
Because queues can only consume up to 7.5 Mbps on the Ethernet interface,
the router would force the map to become inactive. You would have to
reconfigure the QoS map.
7-27