2020-02-21 19:40:43 +04:00
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esptun
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======
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A tool to tunnel IP packets over UDP over WIFI through an UART connected to a ESP8285 with the
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standard AT firmware.
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Usage
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-----
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esptun <ifname> <uart> <ssid> <passwd> <host> <port>
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This will create tun interface `ifname`. Then, with the with the ESP WIFI
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device on `uart` it connects to the AP `ssid` with password `passwd`.
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It creates a UDP over IP tunnel with the other endpoint `host:port`.
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The new tun device will not be configured, use the `ip` utility to assign an
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IP address and switch the interface on.
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For example:
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/root/esptun tun0 /dev/ttyS1 "accesspointname" "secretpassword" 192.168.122.21 23232
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2020-02-22 18:23:31 +04:00
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/sbin/ip link set dev tun0 mtu 1472
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2020-02-21 19:40:43 +04:00
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/sbin/ip addr add 10.0.1.2/24 dev tun0
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/sbin/ip link set tun0 up
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/sbin/ip route add default via 10.0.1.1 dev tun0
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2020-02-22 18:23:31 +04:00
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(setting the MTU to `1500-20-8` the typical network MTU minus IP and UDP header overhead, because
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otherwise the ESP's network stack will drop the oversized packets)
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2020-02-22 19:01:08 +04:00
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### Baudrate note
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If the tunnel hangs intermittently, the problem may be the `BAUDRATE` setting. The ESP8285 can handle
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baudrates up to `115200*40 = 4608000` baud and `esptun` will try switching to a higher baudrate.
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However, these higher baudrates are unstable as it seems that the UART cannot
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keep up reading in some cases and loses data. This may be a misconfiguration or something that could
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be improved in the `8250_dw` Linux driver for this peripheral (DMA support?).
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Which values work may vary, if you want to be completely safe use `115200`. The value can be changed
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at the top of `esptun.c`.
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2020-02-21 19:40:43 +04:00
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Host side
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---------
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On the other endpoint the tunnel is expected to be a host running `socat` or similar to unwrap
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the tunnel. For example:
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sudo socat UDP:192.168.2.127:23232,bind=192.168.122.21:23232 \
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2020-02-22 18:23:31 +04:00
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TUN:10.0.1.1/24,tun-name=tundudp,iff-no-pi,tun-type=tun,su=$USER,iff-up &
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sudo ip link set dev tundudp mtu 1472
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2020-02-21 19:40:43 +04:00
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Optionally, enable forwarding and masquerading:
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sudo iptables -t nat -F
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sudo iptables -t nat -A POSTROUTING -o ens3 -j MASQUERADE
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echo 1 | sudo tee /proc/sys/net/ipv4/ip_forward
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Linux kernel
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------------
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Until there is a proper solution, you can use the following kernel branch
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to get the UART working on Kendryte K210 under Linux:
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https://github.com/laanwj/linux/tree/kendryte-5.6-rc1-wifi
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This is a hack that configures the FPIOA and GPIOHS manually, and configures UART1
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from the device tree.
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To enable TUN/TAP, enable the following kernel settings:
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```
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CONFIG_NET=y
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CONFIG_INET=y
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CONFIG_TUN=y
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```
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While building the root filesystem, make sure you enable at least `ip` and `ping`
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(and possibly other network tools) for busybox.
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Author
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------
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Copyright (c) 2020 W.J. van der Laan
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Distributed under the MIT software license,
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