That was where I started, too. I was fine with VLANs, routing in general and so on from datacenter/DevOps/Sysadmin work, but BGP and how the wider internet fitted together beyond the basics was mostly beyond me.

DN42 is a great playground for this thing - as long as you're prepared to put the effort in, it's a very friendly and helpful community. It's fun to build things for the heck of it and there's a lot of weird and wonderful stuff being worked on there.

dn42 is really cool for learning networking at the ISP level