Redundant Link Example; Fspf Global Configuration - Cisco Nexus 5000 Series Configuration Manual

Configuring Fibre Channel Routing Services and Protocols

FSPF Global Configuration

For example, if all links are of equal speed, the FSPF calculates two equal paths from A to C: A-D-C (green)
and A-E-C (blue).

Redundant Link Example

To improve on the topology, each connection between any pair of switches can be replicated; two or more
links can be present between a pair of switches. The following figure shows this arrangement. Because Cisco
SAN switches support SAN port channels, 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 SAN port channel. This configuration also improves the resiliency of the network. The
failure of a link in a SAN port channel does not trigger a route change, which reduces the risks of routing
loops, traffic loss, or fabric downtime for route reconfiguration.
Figure 37: Fault Tolerant Fabric with Redundant Links
For example, if all links are of equal speed and no SAN port channels 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 SAN port channels exist, these paths are reduced
to two.
FSPF Global Configuration
By default, FSPF is enabled on Cisco SAN switches.
Some FSPF features can be globally configured in each VSAN. By configuring a feature for the entire VSAN,
you do not have to specify the VSAN number for every command. This global configuration feature also
reduces the chance of typing errors or other minor configuration errors.
Note FSPF is enabled by default. Generally, you do not need to configure these advanced features.
The default for the backbone region is 0 (zero). You do not need to change this setting unless your region
Caution
is different from the default. If you are operating with other vendors using the backbone region, you can
change this default to be compatible with those settings.
Cisco Nexus 5000 Series NX-OS SAN Switching Configuration Guide, Release 5.2(1)N1(1)
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