Cisco 6500 - Catalyst Series 10 Gigabit EN Interface Module Expansion Configuration Manual - Page 3

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Cisco 6500 - Catalyst Series 10 Gigabit EN Interface Module Expansion Configuration Manual

Chapter 4

Configuring a Supervisor Engine 720

Understanding How the Switch Fabric Functionality Works

These sections describe how the switch fabric functionality works:

•

Switch Fabric Functionality Overview

The switch fabric functionality is built into the Supervisor Engine 720 and creates a dedicated

connection between fabric-enabled modules and provides uninterrupted transmission of frames between

these modules. In addition to the direct connection between fabric-enabled modules provided by the

switch fabric funtionality, fabric-enabled modules also have a direct connection to the 32-Gbps

forwarding bus.

Forwarding Decisions for Layer 3-Switched Traffic

Either a PFC3 or a Distributed Feature Card 3 (DFC3) makes the forwarding decision for Layer

3-switched traffic as follows:

•

Switching Modes

With a Supervisor Engine 720, traffic is forwarded to and from modules in one of the following modes:

•

Table 4-1

OL-3999-08

Switch Fabric Functionality Overview, page 4-3

Forwarding Decisions for Layer 3-Switched Traffic, page 4-3

Switching Modes, page 4-3

A PFC3 makes all forwarding decisions for each packet that enters the switch through a module

without a DFC3.

A DFC3 makes all forwarding decisions for each packet that enters the switch on a DFC3-enabled

module in these situations:

If the egress port is on the same module as the ingress port, the DFC3 forwards the packet

–

locally (the packet never leaves the module).

–

If the egress port is on a different fabric-enabled module, the DFC3 sends the packet to the

egress module, which sends it out the egress port.

–

If the egress port is on a different nonfabric-enabled module, the DFC3 sends the packet to the

Supervisor Engine 720. The Supervisor Engine 720 fabric interface transfers the packet to the

32-Gbps switching bus where it is received by the egress module and is sent out the egress port.

Compact mode—The switch uses this mode for all traffic when only fabric-enabled modules are

installed. In this mode, a compact version of the DBus header is forwarded over the switch fabric

channel, which provides the best possible performance.

Truncated mode—The switch uses this mode for traffic between fabric-enabled modules when there

are both fabric-enabled and nonfabric-enabled modules installed. In this mode, the switch sends a

truncated version of the traffic (the first 64 bytes of the frame) over the switch fabric channel.

Bus mode (also called flow-through mode)—The switch uses this mode for traffic between

nonfabric-enabled modules and for traffic between a nonfabric-enabled module and a fabric-enabled

module. In this mode, all traffic passes between the local bus and the supervisor engine bus.

shows the switching modes used with fabric-enabled and nonfabric-enabled modules installed.

Catalyst 6500 Series Switch Cisco IOS Software Configuration Guide, Release 12.2SXF

Configuring and Monitoring the Switch Fabric Functionality

4-3