Running 40Gb QSFP+ on Dell’s S5048-ON Switches

Subtitle: Remember kids, read the documentation

Recently at work, we upgraded the top-of-rack switches in our datacenter from Dell S4810 to Dell S5048F-ON. The process was supposed to be simple. Both switches ran Dell Networking OS 9 (a rebrand of Force10), and we mirrored to port, port-channel, and VLAN configurations exactly.

Things went well for 2 hours of the process. All the 1/10Gb DACs and fiber transceivers moved to the S5048 switches and worked with no problem. The problem we ran into centered around the 40Gb transceivers. We used QSFP+ SR units from Dell and assumed they be plug and play in the S5048’s 100Gb QSFP28 ports. Surprise, they didn’t. Well, they did, but we had to make a config change. After an hour of troubleshooting, we discovered the command we needed, AND it was well documented. If only we had read the manual…

https://www.dell.com/support/manuals/us/en/04/networking-s5048f-on/s5048f-on-9.14.2.6-config-pub/splitting-100g-ports?guid=guid-60943ca1-cbf8-4958-aa54-4e8d00e331b2&lang=en-us

If you are going to use 40Gb QSFP transceivers or DACs on Dell’s S5048 switches be sure to run the following command

stack-unit <stack unit number> port <port number> portmode single speed 40g

Have fun.
-Tony