Figure 47: Fault Tolerant Fabric with Redundant Links
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.
Failover Scenarios for PortChannels and FSPF Links
The SmartBits traffic generator was used to evaluate the scenarios displayed in Figure 48: Failover Scenario
Using Traffic Generators, on page 187. Two links 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 percent utilization at 1 Gbps in two scenarios:
• Disabling the traffic link by physically removing the cable (see Table 17: Physically Removing the Cable
for the SmartBits Scenario , on page 187).
• Shutting down the links in either switch 1 or switch 2 (see Table 18: Shutting Down the links in Switch
for the SmartBits Scenario , on page 187).
Figure 48: Failover Scenario Using Traffic Generators
Table 17: Physically Removing the Cable for the SmartBits Scenario
FSPF Scenario (Equal cost ISL)PortChannel Scenario
Switch 2Switch 1Switch 2Switch 1
130+ msec (~4k frame drops)110 msec (~2K frame drops)
100 msec (hold time when a signal loss is reported as mandated by the standard)
Table 18: Shutting Down the links in Switch for the SmartBits Scenario
FSPF Scenario (Equal cost ISL)PortChannel Scenario
Switch 2Switch 1Switch 2Switch 1
130+ msec (~4K frame drops)110 msec (~2K frame drops)~0 msec (~8 frame
drops)
Signal loss on switch 1
No hold time neededSignal loss on switch 1No hold time needed
Cisco MDS 9000 Series Fabric Configuration Guide, Release 8.x
187
Configuring Fibre Channel Routing Services and Protocols
Failover Scenarios for PortChannels and FSPF Links
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