Cisco Systems 4500 Shaping, Sharing (Bandwidth), Priority Queuing, Queue-Limiting and DBL

37-75
Software Configuration Guide—Release 15.0(2)SG
OL-23818-01
Chapter 37 Configuring Quality of Service Configuring QoS on Supervisor Engine 6-E, Supervisor Engine 6L-E, Catalyst 4900M, and Catalyst 4948E
Policy Map police
Class ipp5
police cir percent 20 pir percent 30
conform-action set-cos-transmit 3
conform-action set-dscp-transmit af11
exceed-action set-cos-transmit 4
exceed-action set-dscp-transmit af22
violate-action drop
Marking Statistics
The marking statistics indicate the number of packets that are marked.
For unconditional marking, the classification entry points to an entry in the marking action table that in
turn indicates the fields in the packet that are marked. The classification statistics indicates the
unconditional marking statistics.
For a conditional marking using policer, provided the policer is a packet rate policer, you cannot
determine the number packets marked because the policer only provides byte statistics for different
policing results.
Shaping, Sharing (Bandwidth), Priority Queuing, Queue-Limiting and DBL
Catalyst 4900M, Catalyst 4948E, Supervisor Engine 6-E, and Supervisor Engine 6L-E support the
classification-based (class-based) mode for transmit queue selection. In this mode, the transmit queue
selection is based on the output QoS classification lookup.
Note Only output (egress) queuing is supported.
Catalyst 4900M, Catalyst 4948E, Supervisor Engine 6-E, and Supervisor Engine 6L-E hardware support
eight transmit queues per-port. Once the forwarding decision has been made to forward a packet out a
port, the output QoS classification determines the transmit queue into which the packet needs to be
enqueued.
By default, in Catalyst 4900M, Catalyst 4948E, Supervisor Engine 6-E, and Supervisor Engine 6L-E,
without any service policies associated with a port, there are two queues (a control packet queue and a
default queue) with no guarantee as to the bandwidth or kind of prioritization. The only exception is that
system-generated control packets are enqueued into a control packet queue so that control traffic
receives some minimum link bandwidth.
Queues are assigned when an output policy attached to a port with one or more queuing-related actions
for one or more classes of traffic. Because there are only eight queues per-port, there can be at most eight
classes of traffic (including the reserved class, class-default) with queuing action(s). Classes of traffic
that do not have any queuing action are referred to as non-queuing classes. Nonqueuing class traffic uses
the queue corresponding to class class-default.
When a queuing policy (a policy with queuing action) is attached, the control packet queue is deleted
and the control packets are enqueued into respective queue per their classification. Note that this differs
from the way control-traffic was prioritized in the Catalyst 4924, Catalyst 4948, Catalyst 4948-10GE,
and the Supervisor Engines II+, II+10GE, IV, V, and V-10GE. On these platforms, by default, control
traffic was guaranteed 25 percent of the link bandwidth whether QoS was configured. If this same
behavior is required on Catalyst 4900M, Catalyst 4948E, Supervisor Engine 6-E, and Supervisor Engine
6L-E, an egress QoS class must be configured to match IP Precedence 6 and 7 traffic, and a bandwidth
guarantee must be configured.