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Comment by lvh | Hacker News Reader

The tunnel does not have to encapsulate messages at the same layer as the tunnel itself. Consider this thought experiment: if you send Ethernet frames over WebSockets, what layer is the protocol?

My understanding is the Wireguard messages are IP (L3) but the protocol messages itself are UDP (L4) and it seems reasonable to describe Wireguard as a session layer over UDP given how much state and connection information it maintains.

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I see what you mean. Specifically in the context of VPNs I’ve always interpreted the layer in terms of the payload that’s being encapsulated - which as far as I understand is IP (L3) packets in Wireguard’s case.

Maybe due to my own ignorance I misunderstood the meaning of derefr’s comment. Apologies if I sounded rude!

No worries, you're fine, just trying to clear up the confusion. I've heard both terms used interchangeably depending on context. _Usually_ as an administrator you care about what's in the tunnel, but _usually_ as a designer you're worried about how the tunnel itself is communicated, so, yeah, confusing :)

The internet does not use OSI.

It never ceases to amaze me how stubbornly educators have clung to the OSI model. It describes a non-Internet protocol stack which was designed in the 1970s, and which was never fully implemented. Attempting to use its layers as an ontology for Internet protocols is doomed to failure, as some of its layers (especially Layer 6) describe components which have no direct equivalent on the Internet.

Layer 6 exists, it’s just that most layer 7 protocols “fix” their layer 6 protocol. E.g., JSON/RPC requires JSON; SOAP requires XML; etc.

But Layer 6 is where the difference lies between ASN.1’s representational encodings—DER, BER, XER, etc. You can switch out this “presentation layer” encoding without either your application layer caring (it just sees an ASN.1 codec library) or your transport layer caring (it’s just transporting an opaque octet-stream payload document.)

One might also describe Avro, Parquet, etc. as “presentation formats”—they all have canonical input ADTs, but multiple possible wire encodings depending on the schema supplied at encode time. But all such schemas decode back to the same input ADT.

this is subject to interpretation

L1 to L4 are just a shorthand way network engineers talk about:

  1. The physical connection and voltage/light levels
  2. Switching and MAC addresses
  3. Routing and IP addresses
  4. TCP/UDP and port numbers

Of course we know it's more complicated than that, but it's still a useful simplification.

OK? The Internet does not use OSI, but it sure was helpful just now as an educational tool for describing that "what layer a VPN operates on" can be confusing. Even if you don't literally use OSI layers, knowing that UDP builds on top of TCP and having a common vernacular to express that is pretty useful. Given that the entire thread was already using specific OSI layers (which have clear mappings to things the Internet does do), starting by saying "the OSI model is not what the Internet actually does" does not seem to be the most productive avenue towards fostering understanding :)

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