You are using Broadcom BES-53248 switches for a cluster interconnect in a base configuration.

Cluster interconnect switches must be connected to each other with Inter-Switch Links (ISLs) to maintain resilient cluster networking and to ensure that cluster LIFs on different switches can communicate properly. In the Broadcom BES-53248 cluster switch documentation, the base configuration explicitly reserves switch ports55–56as “100GbE cluster Inter-Switch Link (ISL) ports, base configuration.”

The fact thattwo specific portsare designated as ISL ports in the base configuration strongly indicates that the expected minimum ISL design istwo ISLs—one per port—between the switch pair. This matches standard NetApp validated cluster switch designs, where redundant ISLs provide resilience against a single ISL failure and help maintain cluster connectivity under maintenance or partial link faults. In installation practice, this is part of “robust and operational” cluster design: redundant paths are preferred/required to avoid single points of failure in the cluster network fabric.

Option A (1 ISL) would create a single point of failure: if that ISL fails, inter-switch cluster connectivity can be compromised. Options C and D are not the “minimum” in the base configuration context; while some architectures may support multiple ISLs for additional bandwidth, the base configuration callout clearly highlights two dedicated ISL ports.

Therefore, in a base configuration for BES-53248 cluster interconnect switches, the minimum number of supported ISLs between the two switches is2.