QSFP Splitting

A nice feature with QSFP (Quad Small Form-factor Pluggable) is that you can turn a single QSFP port into 2 or 4 independent ports using a breakout cable.

In my home lab, I have an Nvidia/Mellanox SN2100 switch running Onyx (MLNX-OS), which I use for my iSCSI network. I also have an HPE MSA 2040 SAN. The HPE MSA 2040 SAN only has 10GB SFP (Small Form-factor Pluggable) ports.

I will use a breakout cable to use the SN2100 with the MSA 2040. The breakout cable will connect to the QSFP port on the SN2100 and give me 4 SFP connections that I will connect to the MSA 2040 SFP ports.

In this post, I will show you step-by-step how to split and unsplit an interface on an Nvidia/Mellanox SN2100 switch running Onyx (MLNX-OS).

Split Port

• SSH into the switch.
• Enter configuration mode with the command configure terminal

• Shutdown the interface you want to split out.

The interface I will be splitting is ethernet 1/1. The command I will run is interface ethernet 1/1 shutdown.

• To split the interface, we will use the command module-type qsfp-split-4 or the command module-type qsfp-split-2

Split 4 will split the QSFP module into four 25 Gbps ports. Split 2 will split the port into two 50 Gbps ports.

I will be splitting the port 1/1 into four 25 Gbps ports. The command I will run is interface ethernet 1/1 module-type qsfp-split-4

• Confirm you want to split the port by typing YES.

If you enter the command show interface status you will see that the port is now split. For me port 1/1 is now 1/1/1, 1/1/2, 1/1/3, and 1/1/4

Each of the 4 new ports can be configured independently of each other. Which just blows my mind.

• Save your changes with the command write memory

Unsplit Port

• SSH into the switch.
• Enter configuration mode with the command configure terminal

• Shutdown each sub-interface of the interface you want to unsplit.

The interface I want to unsplit is 1/1. However, 1/1 is currently 1/1/1, 1/1/2, 1/1/3, and 1/1/4. To combine it, I need to shutdown each of those interfaces, which I will do with the following command interface ethernet 1/1/1-1/1/4 shutdown

• On the first interface of the split, turn off splitting with the command no module-type

For me, the first interface of the split is 1/1/1 the command I will run to recombine the port is interface ethernet 1/1/1 no module-type

• Confirm that you want to unsplit the port by entering YES.

If you run the command show interface status you will see that the sub-interfaces are gone, and you are left with a single port again.

• Save your changes with the command write memory

Summary

That’s all it takes to split and unsplit a port on the Nvidia/Mellanox SN2100 switch running Onyx (MLNX-OS).

If you want to read more about the ethernet interfaces, here is Nvidia’s documentation.