Fibre Channel Addressing and Routing Routing and FSPF
FSPF Load Sharing
• FSPF specifications:
– Least-cost path is fewest hops
– Paths change only in response to changes to the topology
– An unused path with 2 hops will be disregarded in favor of an over utilized path with 1 hop
– All frames in an Exchange follow the same path (according to the specifications)
• FSPF implements load sharing, not load balancing:
– But some vendors support load-balancing using proprietary protocols
The FSPF protocol supports load sharing, in which multiple paths through the fabric can be used, but it does not support true load balancing: • Load sharing is significantly different than load balancing. This distinction can have significant effects for fabric design, especially when tuning performance.
• Load sharing simply means that multiple paths can be used. Load balancing means that actual traffic load is balanced across multiple paths. FSPF supports only load sharing.
• FSPF chooses the least-cost path based only on the number of hops between nodes. In other words, an unused path with 2 hops will be disregarded in favour of an over utilized path with 1 hop.
• Paths are recomputed only when the physical ISL configuration changes. FSPF does not recompute paths based on traffic load.