Networking step by step (beginner level).

[EdwinKM]

Get rid of the router provided by the ISP.  Get decent network cards for your computer and forget about USB.  Get a switch that can be managed; unmanaged ones are for special cases only and are of very limited use.

You can skip 2.5Gbit and better either stick with 100MB (which is plenty for learning and inexpensive) or 1GB (which is fine for anything but special cases).  Then if you really do need more bandwidth, go straight for 10Gbit.  (What's the point of 2.5?  If you have that much data to transfer and if your hardware is fast enough for it, then 2.5 is a bottleneck and you want 10Gbit.  2.5 is merely a bad joke.)

What exactly are you trying to accomplish?

Although you have some valid points. I think the topic starter  first needs to address (learn) the problem. Basically you are saying: "throw everything in the bin. What are your needs and requirements?".

Sure crappy (usb) NICs can cause problems but is this the case? (i doubt it). We do not know.

If the topicstarter cant make this double NATted network work, how will a managed switch fix this?

[defaultuserfoo]

I'm not suggesting that a managed switch should be used to fix issues.  I'm suggesting to use hardware (and software) which isn't likely to bring about issues by itself and which is useful for the purpose.  The OP has set out to learn about networking step by step, and to do that successfully, aquiring good hard- and software is one of the first steps.

And yes, I throw hard- and software that gives me issues in the bin.  There is no other way, for lots of reasons, unless your purpose is messing with that kind of hard- and software.

How useful is an unmanaged switch to learn networking step by step?  How useful is it to mess with USB things which may work or not, or maybe sometimes work, and which don't have anything to do with networking when the purpose is learning about networking?

You can do double-NAT just fine (NAT kinda doesn't get worse than it already is just because you do it multiple times), and doing it can be useful for learning.  Yet what do you do when it comes to IPv6?  I can only suggest not to learn networking without IPv6.  What do you do when you start setting up VPN connections between different sites?  Having a router and firewall getting in your way isn't helpful for that.  And what if you want to make your web server accessible from the internet when you have a firewall/router in the way which blocks access?  What if you want to run your own email and/or XMPP server?

But maybe that's not what the OP wants, hence my question what exactly they are trying to accomplish.