I found the FTOS concept of a “default VLAN” confusing and inconsistent. Begin with the first sentence under the “Default VLAN” heading on page 918 in the user manual: When you configure interfaces for Layer 2 mode, they are automatically placed in the Default VLAN as untagged interfaces. This sounds promising. It looks like all interfaces will belong to this VLAN by default, but could be removed if needed. This is incorrect....
The support site for the Dell S4820T claims the switch supports QSFP to 4x SFP+ breakout cables (the supported ones at least), but I had trouble tracking down how to enable this for a given port (by default, only one physical interface appears in the OS for the 40G ports). The answer is on page 464 of the FTOS Configuration Guide for the S4820T (FTOS 8.3.19.0) System. 40G QSFP+ to (4) SFP+ breakout cable Dell sells supported cables, but it appears cheaper “non-qualfied” cables work as well (YMMV)....
I picked up a used Dell S4820T 10GBase-T switch for a work project recently. Here are the steps I took to wipe, upgrade, and perform the initial configuration. Serial Console Before doing anything with the switch, it’s worth investing in an RJ45 to USB (or USB-C) serial cable. They can be found for $10-15 in the usual places. In my case, I could not login to the switch over the network when I received it, so this was the only way to perform the initial configuration....