Quality of Service (QoS): Managing Bandwidth More Effectively
Preparation for Configuring QoS
The following two CLI commands are unique to the 3400cl/6400cl switches
and are useful for planning and monitoring rule usage in a QoS configuration.
Syntax: qos resources help
Provides a quick reference on how QoS and ACLs use rule
resources for each configuration option. Includes most of the
information in table
8-10, plus an ACL usage summary.
Syntax: show qos resources
Shows the number of rules currently available on each port.
This command is useful for verifying rule availability as you
proceed with configuring QoS, ACL, and/or Rate-Limiting
features available on the switch.
Managing QoS Resource Consumption on the 3400cl/6400cl
Switches
As shown in table 8-10, QoS classifiers use 1, 2, or 8 rules depending on the
classifier selected. Extensive QoS and ACL configurations, with or without
applying Rate-Limiting or a multicast protocol, can either fully subscribe the
120 rules available on a given port or leave an insufficient number of rules
available for configuring another QoS policy on the switch. If there are not
enough rules on the port to support another QoS policy, you cannot configure
an additional policy on that port. Because most QoS features are applied to
all ports, having one or more ports with insufficient rules remaining to support
another QoS policy limits further QoS configurations on the switch to:
• Source-port QoS on ports that have sufficient unused rules
• VLAN QoS on VLANs where all of the member ports have sufficient
unused rules
(This can also block any further ACL and—if not already configured—a
Rate-Limiting configuration on the affected port.)
Problems with insufficient rules available on a port can occur in either of the
following QoS scenarios:
■ Attempting to configure a policy when one or more of the affected ports
have insufficient rules available
■ Attempting to add a port to a QoS-configured VLAN where the policy
already on the VLAN requires more rule resources than the port has
available.
8-17
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