•
Location of congestion points in the network.
QoS ACL Guidelines
Follow these guidelines when configuring QoS with access control lists (ACLs):
•
It is not possible to match IP fragments against configured IP extended ACLs to enforce QoS. IP fragments
are sent as best-effort. IP fragments are denoted by fields in the IP header.
•
Only one ACL per class map and only one match class-map configuration command per class map are
supported. The ACL can have multiple ACEs, which match fields against the contents of the packet.
•
A trust statement in a policy map requires multiple hardware entries per ACL line. If an input service
policy map contains a trust statement in an ACL, the access list might be too large to fit into the available
QoS hardware memory, and an error can occur when you apply the policy map to a port. Whenever
possible, you should minimize the number of lines is a QoS ACL.
Related Topics
Creating an IP Standard ACL for IPv4 Traffic, on page 584
Creating an IP Extended ACL for IPv4 Traffic, on page 586
Creating an IPv6 ACL for IPv6 Traffic, on page 588
Creating a Layer 2 MAC ACL for Non-IP Traffic, on page 590
Policing Guidelines
To use policing, the switch must be running the LAN Base image.Note
•
The port ASIC device, which controls more than one physical port, supports 256 policers (255
user-configurable policers plus 1 policer reserved for system internal use). The maximum number of
user-configurable policers supported per port is 63. Policers are allocated on demand by the software
and are constrained by the hardware and ASIC boundaries.
You cannot reserve policers per port; there is no guarantee that a port will be assigned to any policer.
•
Only one policer is applied to a packet on an ingress port. Only the average rate and committed burst
parameters are configurable.
•
On a port configured for QoS, all traffic received through the port is classified, policed, and marked
according to the 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 you have EtherChannel ports configured on your switch, you must configure QoS classification,
policing, mapping, and queueing on the individual physical ports that comprise the EtherChannel. You
must decide whether the QoS configuration should match on all ports in the EtherChannel.
•
If you need to modify a policy map of an existing QoS policy, first remove the policy map from all
interfaces, and then modify or copy the policy map. After you finish the modification, apply the modified
Consolidated Platform Configuration Guide, Cisco IOS Release 15.2(4)E (Catalyst 2960-X Switches)
540
Prerequisites for QoS
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