Switching Modes; Configuring The Switch Fabric Module - Cisco 7604 Configuration Manual

Chapter 6 Configuring the Supervisor Engine 2 and the Switch Fabric Module
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Switching Modes

When you install a Switch Fabric Module, the traffic is forwarded to and from modules in one of the
following modes:
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Table 6-1
Table 6-1
Modules
Between fabric-enabled modules (when no nonfabric-enabled modules are
installed)
Between fabric-enabled modules (when nonfabric-enabled modules are also
installed)
Between fabric-enabled and nonfabric-enabled modules
Between non-fabric-enabled modules
1. In show commands, displayed as dcef mode for fabric-enabled modules with DFC installed; displayed as fabric mode for
2. Displayed as fabric mode in show commands.

Configuring the Switch Fabric Module

These section describe configuring the Switch Fabric Module:
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OL-4266-08
A PFC2 makes all forwarding decisions for each packet that enter the router through a module
without a DFC.
A DFC makes all forwarding decisions for each packet that enters the router on a DFC-enabled
module in these situations:
– If the egress port is on the same module as the ingress port, the DFC forwards the packet locally
(the packet never leaves the module).
If the egress port is on a different fabric-enabled module, the DFC sends the packet across the
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SFM to the egress module, which sends it out the egress port.
If the egress port is on a different nonfabric-enabled module, the DFC sends the packet across
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the SFM to the Supervisor Engine 2. The Supervisor Engine 2 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 router 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 router uses this mode for traffic between fabric-enabled modules when there
are both fabric-enabled and nonfabric-enabled modules installed. In this mode, the router 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 router 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.
Switching Modes with Switch Fabric Module Installed
other fabric-enabled modules.
Configuring the Switching Mode, page 6-4
Cisco 7600 Series Router Cisco IOS Software Configuration Guide, Release 12.2SX
Configuring the Switch Fabric Module
Switching Modes
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Compact
2
Truncated
Bus
Bus
6-3