C H A P T E R 37 Configuring The Switch Fabric Module; Switch Fabric Module Slots; Switch Fabric Redundancy; Forwarding Decisions For Layer 3-Switched Traffic - Cisco 7609 Configuration Manual

Understanding How the Switch Fabric Module Works

Switch Fabric Module Slots

With a WS-C6513 chassis, install the Switch Fabric Modules in either slot 7 or 8.
Note In a WS-C6513 chassis, only slots 9 through 13 support dual-switch fabric interface switching modules
(for example, WS-X6816-GBIC).
With all other chassis, install the Switch Fabric Modules in either slot 5 or 6.

Switch Fabric Redundancy

The Switch Fabric Module first installed functions as the primary module. For redundancy, you can
install a redundant Switch Fabric Module. When two Switch Fabric Modules are installed at the same
time, the module in the upper slot functions as the primary module, and the one in the lower slot
functions as the backup. If you reset the module installed in the upper slot, the one in the lower slot
becomes active.
No configuration is required for Switch Fabric Module redundancy. The module in the upper slot
functions as the primary module and a redundant Switch Fabric Module in the lower slot automatically
takes over if the primary module fails.

Forwarding Decisions for Layer 3-Switched Traffic

Either a PFC2 or a Distributed Feature Card (DFC) makes the forwarding decision for Layer 3-switched
traffic as follows:
•
•

Switching Modes

When you install a Switch Fabric Module, the traffic is forwarded to and from modules in one of the
following modes:
•
Cisco 7600 Series Router Cisco IOS Software Configuration Guide—12.1E
37-2
A PFC2 makes all forwarding decisions for each packet that enters the switch through a module
without a DFC.
A DFC makes all forwarding decisions for each packet that enters the switch 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
–
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
–
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.
Chapter 37 Configuring the Switch Fabric Module
78-14064-04