Enterprise QoS Solution Reference Network Design Guide

Chapter 2 Campus QoS Design
Catalyst MLS QoS Verification Commands
Version 3.3
Catalyst 3550—QoS Considerations and Design
The Catalyst MLS QoS verification commands for Conditionally-Trusted IP Phone + PC + Scavenger
(Advanced) Model include the following:
show mls qos
show mls qos map
show mls qos interface
show mls qos interface policers
show mls qos statistics
show class-map
show policy-map
show policy interface
Catalyst 3550—Queuing and Dropping
Configuration
This section includes the following topics:
Configuration
Advanced Tuning Options
Catalyst MLS QoS Verification Commands
Like the Catalyst 2950, the Catalyst 3550 supports a 1P3Q1T queuing model for all ports.
GigabitEthernet ports have the additional option of being configured as 1P3Q2T, with either tail-drop or
WRED thresholds. However, unlike the Catalyst 2950, the Catalyst 3550 queuing parameters are set on
a per-interface basis and not globally. Nonetheless, uniform queuing policies can be expeditiously
deployed via the interface range configuration command.
The strict-priority queue is enabled on a per-interface basis on the Catalyst 3550 with the priority-queue
out interface command. Bandwidth is allocated among the remaining queues via the wrr-queue
bandwidth command. A twist with the Catalyst 3550 is that Queue 4’s WRR weight is set to 1
(indicating that it does not participate in the WRR scheduler since it is configured as a strict-priority
queue), instead of 0 (as is the case on the Catalyst 2950). Recommended remaining bandwidth
allocations (after the PQ has been fully serviced) are 5% for the Scavenger queue (Q1), 25% for the
Best-Effort queue (Q2), and 70% for the preferential application queue (Q3).
Following this, CoS 1 (Scavenger/Bulk) would be assigned to Q1; CoS 0 (Best Effort) would be assigned
to Q2; CoS values 2 (Transactional Data and Network Management), 3 (call signaling and
Mission-Critical Data), 4 (Interactive and Streaming-Video, 6 (Internetwork Control) and 7 (Network
Control/Spanning-Tree) would be assigned to Q3; CoS 5 (voice) would be assigned to the strict-priority
Q4. These assignments and allocations are illustrated in Figure 2-15 (the thresholds shown in Q1 and Q3
are discussed shortly).
Enterprise QoS Solution Reference Network Design Guide
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