Fabric Extenders are used to connect blade server chassis to Fabric Interconnects. The I/O modules act as line cards to the Fabric Interconnects. It is therefore necessary to maintain proper connectivity between IOMs and Fabric Interconnects. Since an IOM becomes part of the Fabric Interconnect, multiple links from a single IOM can only be connected to a single Fabric Interconnect and cannot be connected across to the other Fabric Interconnect. Depending on the IOM model, there can be 1, 2, 4, or 8 links from the IOM to a single Fabric Interconnect. These links can be configured in the port channel for bandwidth aggregation. The chassis discovery process starts as soon as the IOM is connected to the Fabric Interconnect.

In the following diagram on the left-hand side, all links from IOM 0 are connected to a single Fabric Interconnect and can be combined into a single port channel. The diagram on the right shows a configuration in which links from a single IOM module are connected to different Fabric Interconnects. This is an invalid topology, and hence, chassis discovery will fail.

Fabric Interconnect and I/O module topologies: