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Chapter 21
Configuring Fibre Channel Routing Services and Protocols
S e n d d o c u m e n t a t i o n c o m m e n t s t o m d s f e e d b a c k - d o c @ c i s c o . c o m .
Redundant Links
To further improve on the topology in
replicated; two or more links can be present between a pair of switches.
Because switches in the Cisco MDS 9000 Family support PortChanneling, each pair of physical links can
appear to the FSPF protocol as one single logical link.
By bundling pairs of physical links, FSPF efficiency is considerably improved by the reduced database size
and the frequency of link updates. Once physical links are aggregated, failures are not attached to a single link
but to the entire PortChannel. This configuration also improves the resiliency of the network. The failure of
a link in a PortChannel does not trigger a route change, thereby reducing the risks of routing loops, traffic
loss, or fabric downtime for route reconfiguration.
Figure 21-2
For example, if all links are of equal speed and no PortChannels exist, the FSPF calculates four equal
paths from A to C: A1-E-C, A2-E-C, A3-D-C, and A4-D-C. If PortChannels exist, these paths are
reduced to two.
Fail-Over Scenarios for PortChannels and FSPF Links
The SmartBits traffic generator was used to evaluate the scenarios displayed in
between switch 1 and switch 2 exist as either equal-cost ISLs or PortChannels. There is one flow from
traffic generator 1 to traffic generator 2. The traffic was tested at 100% utilization of 1 Gbps in two
scenarios:
•
•
Figure 21-3
Traffic Generator 1
OL-6973-03, Cisco MDS SAN-OS Release 2.x
Fault Tolerant Fabric with Redundant Links
A
B
1
2
3
4
D
Disabling the traffic link by either physically removing the cable (see
Shutting down either switch 1 or switch 2 (see
Fail-Over Scenario Using Traffic Generators
Switch 1
Figure
21-1, each connection between any pair of switches can be
C
E
Table
21-2).
Traffic Generator 2
Switch 2
Cisco MDS 9000 Family Configuration Guide
FSPF Examples
Figure 21-2
shows this arrangement.
Figure
21-3. Two links
Table
21-1).
21-3
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