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BIOS Configuration Overview
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in your CPC5565 application software, then you may wish to provide redundancy through the
use of Spanning Tree on the fabrics. In this scenario, each CPC5565 has a path at layer-2 to
both fabrics by placing the CPSB ports into a common VLAN. This allows the fabrics to pass
Spanning Tree BPDUs through the embedded switch on each CPC5565 and allows the fabrics
to block the redundant paths.
This technique can be used with or without tagged interfaces. To allow for tagged interfaces,
you must enable Port-Mode VLANs in the BIOS. Untagged interfaces can be used with the
default Dot1Q-Mode (see
“VLAN Configurations,” on page 42 ).
Figure 3-13 illustrates an example where two CPC5565s are used in a network that has three
VLANs. The VLANs all use tagging. In order to support tagging, both CPC5565s are configured
for Port-Mode VLANs. In order to support redundancy, redundant paths are provided via the
two fabric switches and Spanning Tree is utilized to create a loop-free topology.
In this example, two external Layer-2 switches are connected via fabric uplink ports. There is a
cable fault to the VLAN-3 switch so traffic to that device goes through Fabric-B. Otherwise, all
of the traffic flows through Fabric-A. Example traffic for each VLAN is illustrated with the color-
coded dashed lines.
Figure 3-13: Spanning Tree Redundancy
In addition to protecting the system against cable faults to external devices, this mode of
operation also protects the system against internal fabric faults. If Fabric-A fails, Fabric-B
unblocks all of the paths to the CPC5565s and the VLAN-2 switch and all traffic flows through
Fabric-B.
CPC5565-B
(VLANs 1,2)
C PSB-A
C PSB-B
VLAN 2 Switch
Port A
VLAN 3 Switch
Port A
Port B
FABRIC -A
vlan3
vlan 2
vlan 1
FABRIC -B
vlan3
vlan2
vlan1
CPC5565-A
(VLANs 1,3)
C PSB-A
C PSB-B
Port B
X
C able Fault
Blocked B locked B locked