ZeroTier without VL2: an ESP32 can peer through NAT and inherits five reliability jobs

Strip VL2 away and the remaining service is narrow: a datagram sent to a cryptographic identity, with path selection and NAT traversal happening below it ^[3][10]. No address assignment, no ARP, no routing table, because there is nothing to be a member of ^[12]. On a sensor that needs to push a few hundred bytes to one server and hear an answer, that removes most of what an IP stack was there for. The same split pays differently upstream: ZtSharp exists so a .NET process can speak the protocol without libzt, P/Invoke, or per-platform native binaries to maintain ^[6], and it carries its own ARP, IPv4, IPv6, UDP and TCP above the virtual Ethernet layer to do it ^[8].

The bill lands in firmware. USER_MESSAGE offers no delivery guarantee, and the author's own list of what an application must add runs to five items: delivery confirmation, sequence numbers, retransmission, duplicate detection and ACK semantics ^[13][16]. The ESP32 test implements the cheapest possible version of that, a reply to each `hello from esp32:N` counted as an acknowledgement by the application rather than by the transport ^[14]. For a demo counter that is fine, and the author is explicit that small telemetry and control traffic is often served well enough ^[15]. A fleet where a missed command matters needs a retry policy and sequence state that survives a reboot, and neither arrives with the protocol.

The quieter loss is admission control. Network configuration is a VL2 function, and in ZtSharp the controller sits inside the node itself ^[4][7]. A VL1-only device joins no network, so no controller ever authorizes it and none can revoke it ^[17]. Acceptance moves into application code, which decides what to do with a sender address and a 64-bit typeId ^[10][11]. That is a reasonable trade for telemetry, provided somebody notices that the revocation story has changed hands.

The one interoperability result on offer, according to the post, sits at VL2 ^[9], and in the ESP32 exchange the counterparty is identified only as a remote peer ^[18]. The half of the design that is new is the half with less evidence behind it. Nor does the material carry a flash figure, a RAM figure, or a peer count for the VL1-only ESP32 build; the writeup as supplied stops mid-sentence at the server-side diagram ^[19][20]. The architecture reads as sound and the sizing is simply unknown.