Specifications

White Paper
© 2009 Cisco Systems, Inc. All rights reserved. This document is Cisco Public Information. Page 3 of 89
Table of Contents
Terminology .....................................................................................................................................5
Abstract ............................................................................................................................................6
1. What is Layer 2 and Layer 3 QoS ...............................................................................................7
2. Why The Need for QoS in a Switch ............................................................................................7
3. Hardware Support for QOS in the Catalyst 6500.......................................................................8
3.1 Policy Feature Card (PFC) ..........................................................................................................8
3.2 Distributed Forwarding Card (DFC) ...........................................................................................10
3.3 Linecard Port ASIC Queue Structure.........................................................................................11
3.3.1. 10/100 Line Cards (WS-X6148 Series) ..........................................................................12
3.3.2. 10/100 Line Cards (WS-X6148A Series)........................................................................12
3.3.4. 10/100 Line Cards (WS-X6524-100FX-MM)...................................................................14
3.3.5. Gigabit Ethernet Line Cards (WS-X6408A, WS-X6516A) ..............................................15
3.3.6. 10/100/1000 (WS-X6148-GE-TX, WS-X6548-GE-TX) ...................................................15
3.3.7. Gigabit Ethernet Line Cards (WS-X6724, WS-X6748)...................................................16
3.3.8. 10-Gigabit Ethernet Line Cards (WS-X6704-10GE).......................................................17
3.3.9. 10-Gigabit Ethernet Line Cards (WS-X6708-10GE-3C,WS-X6716-10GE-3C) ..............18
3.4 Catalyst 6500 QoS Hardware Summary....................................................................................19
4. Catalyst 6500 Software support for QoS .................................................................................19
4.1 Priority Mechanisms in IP and Ethernet.....................................................................................19
4.1.1. Type of Service (ToS).....................................................................................................20
4.1.2. Class of Service (CoS) ...................................................................................................21
5. QoS Flow in the Catalyst 6500..................................................................................................21
6. Queues, Buffers, Thresholds and Mappings...........................................................................23
6.1 Queues ......................................................................................................................................23
6.2 Buffers .......................................................................................................................................23
6.3 Thresholds.................................................................................................................................23
6.4 Mappings ...................................................................................................................................24
6.5 Weighted Random Early Discard and Round Robin Scheduling...............................................25
6.5.1. WRED ............................................................................................................................25
6.5.2. WRR...............................................................................................................................27
6.5.3. Deficit Weighted Round Robin .......................................................................................28
6.5.4. Shaped Round Robin .....................................................................................................29
6.5.5. Strict Priority Queuing.....................................................................................................30
7. Configuring (Port ASIC based) QoS on the Catalyst 6500 .....................................................30
7.1 Enabling QoS.............................................................................................................................32
7.2 Trusted and Un-trusted Ports ....................................................................................................35
7.2.1. Un-trusted Ports (Default setting for ports).....................................................................35
7.2.2. Trusted Ports..................................................................................................................35
7.3 Preserving the Received ToS Byte (DSCP Transparency)........................................................36
7.4 Port based vs. VLAN Based QoS..............................................................................................36
7.5 Setting the Switch to Queuing-Only Mode.................................................................................36
7.6 Input Classification and Setting Port Based CoS.......................................................................36
7.7 Applying CoS Mutation on 802.1Q Tunnel Ports .......................................................................36
7.8 Configure Receive Drop Thresholds..........................................................................................37
7.9 Configuring Transmit Drop Thresholds......................................................................................41
7.10 Mapping CoS to Thresholds ....................................................................................................42
7.11 Configure Bandwidth on Transmit Queues..............................................................................42