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Chapter 21
Configuring Fibre Channel Routing Services and Protocols
Redundant Links
To further improve on the topology in, each connection between any pair of switches can be replicated;
two or more links can be present between a pair of switches. shows this arrangement. 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 evaluate the scenarios displayed in
summarized in
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 1G in two scenarios:
•
•
Figure 21-3
Traffic Generator 1
Table 21-1
PortChannel Scenario
Switch 1
110ms (~2K frame drops)
100 ms hold time when a signal loss is reported as
mandated by the standard
OL-7753-01
Fault Tolerant Fabric with Redundant Links
A
B
1
2
3
4
D
Table 21-1
and
Disabling the traffic link by either physically removing the cable.
Shutting down either switch 1 or switch 2.
Fail-over Scenario Using Traffic Generators
Switch 1
Physically Removing the Cable for the SmartBits Scenario
C
E
Table
21-2. Two links between switch 1 and switch 2 exist as either
Switch 2
FSPF Scenario (Equal cost ISL)
Switch 2
130ms+ (~4k frame drops)
Cisco MDS 9000 Fabric Manager Switch Configuration Guide
Figure 21-3
Traffic Generator 2
FSPF Examples
and
21-3
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