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Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
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Chapter 33 Configuring QoS
Configuring QoS
Default QoS Configuration
There are no policy maps, class maps, table maps, or policers configured. At the egress port, all traffic
goes through a single default queue that is given the full operational port bandwidth. The default size of
the default queue is 160 (256-byte) packets.
The packets are not modified (the CoS, DSCP, and IP precedence values in the packet are not changed).
Traffic is switched in pass-through mode without any rewrites and classified as best effort without any
policing.
QoS Configuration Guidelines
•
You can configure QoS only on physical ports.
•
On a port configured for QoS, all traffic received through the port is classified, policed, and marked
according to the input policy map attached to the port. On a trunk port configured for QoS, traffic
in all VLANs received through the port is classified, policed, and marked according to the policy
map attached to the port. If a per-port, per-VLAN policy map is attached, traffic on the trunk port is
classified, policed, and marked for the VLANs specified in the parent-level policy, according to the
child policy map associated with each VLAN.
•
If you have EtherChannel ports configured on your switch, you must configure QoS classification,
policing, mapping, and queuing on the individual physical ports that comprise the EtherChannel.
You must decide whether the QoS configuration should match on all ports in the EtherChannel.
•
Control traffic (such as spanning-tree bridge protocol data units [BPDUs] and routing update
packets) received by the switch are subject to all ingress QoS processing.
•
You are likely to lose data when you change queue settings; therefore, try to make changes when
traffic is at a minimum.
•
When you try to attach a new policy to an interface and this brings the number of policer
instances
to more than 255, you receive an error message, and the configuration fails.
•
When CPU protection is enabled, you can configure only 45 policers per port. Disabling CPU
protection allows you to configure up to 64 policers per port. You can enter the
show policer cpu
uni-eni
{
drop
|
rate
} privileged EXEC command to see if CPU protection is enabled.
Note these
limitations when you disable CPU protection:
–
When CPU protection is disabled, you can configure a maximum of 63 policers per port (62 on
every 4th port) for user-defined classes and one for class-default.
–
On Cisco ME 3400G-12CS switches, due to hardware limitations, you can attach 64 per-port,
per-VLAN policers to a maximum of 6 ports. If you attempt to attach more than 6 per-port per
VLAN 64-policer policy maps, the attachment fails with a
VLAN labels exceeded
error message.
–
If you disable CPU protection and attach a policy map with more than 45 policers, and then
enable CPU protection again, and reload, 19 policers per port are again required for CPU
protection. During reload, the policers 46 and above will reach the
policer resources exceeded
error condition and no policers are attached to those classes.
See the configuration sections for specific QoS features for more configuration guidelines related to each
feature.
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