What are currently used L2 and L3 protocols? (other than ethernet and ip4/6) I heard about plenty of alternatives to ethernet like for example token ring, ARCNET, SONET, or to IP4/6 for example IPX but once I decided to look for software and hardware support I realized those are rather historic protocols and no modern, high speed hardware is available. I know that PPP over various serial stuff and DSL family protocols are still widely used by ISP. Also some fibre protocols - GPON/GEPON. So my question is - what are _currently used_ protocols and link technologies capable of being used as interconnect between border TCP/IP networks?. Not necessarily mainstream or super popular - but just still usable with modern hardware/software support.

There's a pretty good Wikipedia article that has a list that's not exhaustive but is quite thorough - check it out here).

As far as _currently_ used? It's probably safe to say that _somewhere_ just about all of them are probably either encapsulated (usually in IP or MPLS) or are soldiering on forgotten in a dusty closet. If one has _truly_ died in the real world someone in a museum has resurrected a bit of it for posterity (or as a cautionary tale).