ISL cabling requirements

When using shared ISLs in a MetroCluster IP configuration, you must be aware of the requirements for the end-to-end MetroCluster ISL running from controller ports on site A to controller ports on site B.

Basic MetroCluster ISL requirements

The following requirements must be met:

A native-speed ISL switch port must connect to a native-speed ISL switch port.
For example, a 40 Gbps port connects to a 40 Gbps port.
A 10 Gbps port that is in native mode (i.e., not using a breakout cable) can connect to a 10 Gbps port that is in native mode.
The ISLs between the MetroCluster IP switches and the customer network, as well as the ISLs between the intermediate switches, follow the same rules in terms of speed.
The number of ISLs that are between the MetroCluster switches and the customer network switches, and the number of ISLs that are between the customer network switches, do not need to match.
For example, the MetroCluster switches can connect using two ISLs to the intermediate switches, and the intermediate switches can connect to each other using 10 ISLs.
The speed of ISLs that are between the MetroCluster switches and the customer network switches, and the speed of ISLs that are between the customer network switches, do not need to match.
For example, the MetroCluster switches can connect using a 40-Gbps ISL to the intermediate switches, and the intermediate switches can connect to each other using 100-Gbps ISLs.
The number of and speed of ISLs connecting each MetroCluster switch to the intermediate switch must be the same on both MetroCluster sites.

Number of ISLs and breakout cables in the shared network

The number of ISLs connecting the MetroCluster IP switches to the shared network varies depending on the switch model and port type.

MetroCluster IP switch model	Port type	Number of ISLs
Broadcom-supported BES-53248 switches	Native ports	4 ISLs using 10 or 25-Gbps ports
Cisco 3132Q-V	Native ports	6 ISLs using 40 Gbps ports
Cisco 3132Q-V	Breakout cables	16 x 10 Gbps ISLs
Cisco 3232C	Native ports	6 ISLs using 40 or 100 Gbps ports
Cisco 3232C	Breakout cables	16 x 10 Gbps ISLs

The use of breakout cables (one physical port is used as 4 x 10 Gbps ports) is supported on Cisco switches.
The RCF files for the IP switches have ports in native and breakout mode configured.
A mix of ISL ports in native port speed mode and breakout mode is not supported. All ISLs from the MetroCluster IP switches to the intermediate switches in one network must be of same speed and length.
The use of external encryption devices (for example, external link encryption or encryption provided via WDM devices) are supported as long as the round-trip latency remains within the above requirements.

For optimum performance, you should use at least a 1 x 40 Gbps or multiple 10 Gbps ISLs per network. Using a single 10 Gbps ISL per network for AFF A800 systems is strongly discouraged.

The maximum theoretical throughput of shared ISLs (for example, 240 Gbps with six 40 Gbps ISLs) is a best-case scenario. When using multiple ISLs, statistical load balancing can impact the maximum throughput. Uneven balancing can occur and reduce throughput to that of a single ISL.