esp-twin

What it is

A Wi-Fi repeater for a home network, running on an ESP32-S3-DevKitC-1. The chip joins the home router as a station (STA) and runs its own access point (AP) at the same time. Clients on the AP get addresses from the ESP and reach the internet through it.

It’s no_std Rust on esp-hal, with the Embassy async executor, embassy-net and smoltcp for networking, and edge-dhcp for the DHCP server.

Why NAT

The router only accepts frames from the ESP’s own STA MAC address, so a plain bridge won’t work. The repeater has to do what a home router does: rewrite the source MAC, IP address and port of each outgoing packet, keep a table of translations, map replies back to the right client, and recompute the IPv4 and TCP/UDP checksums. No no_std NAT crate exists, so this part is written from scratch on top of smoltcp::wire and heapless.

Frames from AP clients are classified in a wrapper around the AP network driver: traffic for the ESP itself goes to its own stack, and everything else is passed to the NAT task through a zero-copy channel.

What works so far

AP and STA running at the same time
DHCP server for AP clients (192.168.2.0/24)
Classifying client traffic into “for the ESP” and “to forward”
UDP NAT in both directions, tested with DNS queries from a phone

What’s next

TCP, then ICMP
Expiring NAT table entries and removing them when a client disconnects
Handing out the router’s DNS server to AP clients