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I have an installation with an MCU with proprietary (unfortunately) and immutable firmware, that provides a serial interface to connect a PC or laptop to. Planning to make it accessible via the network, I was looking into creating a WLAN bridge with a ESP8266 module, like the ESP-12. Espressif provides the AT firmware for doing this kind of thing, however, researching the documentation, I gained the impression that with that firmware it is not possible for the device just to sit there and wait for an incoming connection. This is not made explicit in the documentation, unfortunately, hence my question.

Since I cannot make the aforementioned MCU aware of the bridge, the bridge needs to work in pass-through mode. It seems this mode is only available in TCP-client mode, where it would flood the network with connection attempts if the laptop is not present. Listening to incoming connections seems to require creating a server, which only works in multi-connection mode, which precludes pass-through mode, if my understanding is right.

Is it possible, with the AT firmware, to have the ESP8266 listen for an incoming connection, providing pass-through mode once connected?

Edit: My main objection to the TCP-client mode of course is that the peer needs to fixed in the ESP's configuration, i.e. it would need to be always the same machine. The network being flooded with connection attempts is not nice, but secondary.

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  • An ESP8266 isn't going to do a whole lot of network flooding, especially over an 802.11b wifi connection. It's also going to have to timeout before it tries to connect again. This isn't really going to be a problem for any reasonable network.
    – romkey
    Commented Jul 24, 2022 at 4:00
  • I agree it is just a minor annoyance. That's why I edited the question to explain the real reason why I object to this mode of operation. Commented Jul 24, 2022 at 15:52
  • You mention 802.11b, I'm fairly sure the ESP8266 could saturate such a network. But the ESP8266 is capable of 802.11n, so in a modern network (n, or ac) it won't cause a problem. Commented Jul 24, 2022 at 15:59
  • Yeah, I realized after I couldn't edit the comment that I'd written the wrong 802.11 version. Regardless, it's really not an issue.
    – romkey
    Commented Jul 24, 2022 at 18:50

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