Multiple LANs, 1 LAN interface
I need to split my network into a trusted and an untrusted part. The untrusted part is for a wifi hotspot. The trusted is for my servers. I would install a third interface, but I can't put my servers offline. I have a USB-Network adapter, but when I connect through it, it is insanely slow.
Yes, if you have to provide real performance, then don't use a USB Network Adapter.
If you have only 1 physical port available for LAN, then you are going to need VLANs - buy a VLAN switch and connect it to the LAN port… There is going to be downtime in changing over!