The single CI (cluster Interconnect) topology is supported (but not recommended) on a 2 node switchless configuration.
In a 4 node configuration you need (2) CN1610 switches. The cluster network will consume all available 10GB ports on the 2240, and the 1GB data ports will be used for data traffic (iscsi, etc). The 255x controllers have sufficient ports to support the cluster network and 10GB data traffic concurrently, so those controllers can have 10GB iscsi connections in a 4 node switched configuration.
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