Redundant Links; Fail-Over Scenarios For Portchannels And Fspf Links - Cisco AP776A - Nexus Converged Network Switch 5020 Configuration Manual

Chapter 26 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.
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 26-2
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 at 1 Gbps in two
scenarios:
•
•
Figure 26-3
Traffic Generator 1
Table 26-1
PortChannel Scenario
Switch 1
110 msec (~2K frame drops)
100 msec (hold time when a signal loss is reported as mandated by the standard)
OL-18084-01, Cisco MDS NX-OS Release 4.x
Fault Tolerant Fabric with Redundant Links
A B
1
2
3
4
D
Disabling the traffic link by physically removing the cable (see
Shutting down either switch 1 or switch 2 (see
Fail-Over Scenario Using Traffic Generators
Switch 1
Physically Removing the Cable for the SmartBits Scenario
Switch 2
Figure 26-1, each connection between any pair of switches can be
C
E
Table 26-2).
Traffic Generator 2
Switch 2
FSPF Scenario (Equal cost ISL)
Switch 1
130+ msec (~4k frame drops)
Cisco MDS 9000 Family CLI Configuration Guide
About FSPF
Figure 26-2 shows this
Figure 26-3. Two links
Table 26-1).
Switch 2
26-3