I ran into an interesting issue when I upgraded from Buster to Bullseye. Before upgrading I had been using the firmware-realtek package for my NIC. After upgrading I discovered that whenever I would do a reboot the NIC would would be a in an unusable state. From my research it appears that the specific chipset that I have sets a bit in a register and that bit doesn't get reset during a warm reboot, thus preventing use. Bummer. However, by installing the r8168-dkms package everything works fine. This is my controller:
product: RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller
And from the package description in Synaptic Package Manager:
r8168 is the Linux device driver released by RealTek for their network
controllers with PCI-Express interface:
* 10/100/1000M Gigabit Ethernet: RTL8111B, RTL8111C, RTL8111D, RTL8111E,
RTL8111F, RTL8111G(S), RTL8111H(S), RTL8118(A)(S), RTL8119i, RTL8111L,
RTL8168B, RTL8168E, RTL8168H, RTL8111DP, RTL8111EP, RTL8111FP, RTL8411,
This driver should only be used for devices not yet supported by the
in-kernel driver r8169.
Apparently something changed in Bullseye such that the firmware-realtek package no longer works as it did previously. Maybe somebody is working on the realtek-firmware package to rectify this issue, but it's not a big deal for me as the r8168-dkms package works for me. But this might be heads up for others that might be having a similar problem.
I'm not irrational, I'm just quantum probabilistic.