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Catalyst 6500 Series Switch Software Configuration Guide—Release 8.7
OL-8978-04
Chapter 52 Configuring QoS
Understanding How QoS Works
Note
The drop indication flag applies to the excess rate policer and cannot be set for the normal rate
policer. To achieve the effect of a drop indication flag for the normal rate aggregate policer, set
the excess rate equal to the normal rate and set the drop indication flag. Alternatively, you can
set the normal rate without specifying an excess rate, which automatically sets the excess rate to
the normal rate when the drop indicator flag is on.
You can include both a microflow policer and an aggregate policer in each ACE to police a flow that is
based on both its own bandwidth utilization and on its bandwidth utilization combined with that of the
other flows.
For example, you could create a microflow policer named “group_individual” with the bandwidth limits
that are suitable for the flows of the individuals in a group, and you could create an aggregate policer
named “group_all” with the bandwidth limits that are suitable for the group as a whole. You could
include both policers in the ACEs that match the group’s traffic. The combination would affect the
individuals separately and the group cumulatively.
For the ACEs that include both a microflow policer and an aggregate policer, QoS responds to an
out-of-profile status from either policer, and as specified by the policer, applies a new DSCP value or
drops the packet. If both policers return an out-of-profile status, then if either policer specifies that the
packet is to be dropped, it is dropped; otherwise, QoS applies a new DSCP value.
Follow these guidelines when creating policers:
•
You can include a microflow policer in the IP ACEs. You cannot include a microflow policer in the
IPX or MAC ACEs. The IPX and MAC ACEs support only the aggregate policers.
•
By default, the microflow policers do not affect the bridged traffic. To enable microflow policing of
the bridged traffic, enter the
set qos bridged-microflow-policing
command (for more information,
see the
“Enabling or Disabling Microflow Policing of Bridged Traffic” section on page 52-62
).
•
With a Layer 3 Switching Engine II, to do any microflow policing, you must enable microflow
policing of the bridged traffic.
•
With an MSFC, QoS does not apply the microflow policers to the Multilayer Switching (MLS)
candidate frames (MSFC2 does not use candidate and enabler frames).
•
To avoid inconsistent results, all ACEs that include the same aggregate policer must use the same
ACE keyword:
trust-dscp
,
trust-ipprec
,
trust-cos
, or
dscp
. If the ACE uses the
dscp
keyword, all
traffic that matches the ACE must come through the ports that are configured with the same port
keyword:
trust-dscp
,
trust-ipprec
,
trust-cos
, or
untrusted
. If the ACL is attached to a VLAN, you
must configure all ports in the VLAN with the same port keyword.
PFC2 Policing Decisions
With PFC2, the policing decision consists of two levels:
•
Normal Police Level—Set if either the microflow policer or the aggregate normal rate policer
returns an out-of-profile decision.
•
Excess Police Level—Set if the aggregate excess rate policer returns an out-of-profile decision.
The packets are dropped if the excess rate aggregate policer returns an out-of-profile decision and the
drop indication flag is set or if the microflow policer returns an out-of-profile decision and the drop
indication flag is set.
