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Re: [lwip-users] lwip PPPoS + ESP8266 wifi module

From: Sylvain Rochet
Subject: Re: [lwip-users] lwip PPPoS + ESP8266 wifi module
Date: Fri, 27 Apr 2018 14:22:40 +0200
User-agent: Mutt/1.5.23 (2014-03-12)

Hi Andrea,

On Fri, Apr 27, 2018 at 05:53:27AM +0000, Andrea Marangon wrote:
> Hi everyone,
> I'm using lwip on the ESP8266 wifi module.
> This module is connected to my card and communicates via PPPos (the PPP
> client is the Wifi module).
> Now I need to receive and transmit TCP and UDP packets via Wifi.
> Initially I created two TCP sockets (netconn), one client and the other
> server forwarding the data via buffers, but it is very expensive in time and
> memory.
> I have doubts about this implementation considering that I will have to do
> the same with the UDP transmission.
> Board( --> PPPoS --> netconn TCP client( --> netconn
> TCP server( --> mobile system (
> I thought of using the network interfaces (netif, one the PPPoS and the
> other the WiFi) to do a kind of forwarding...
> could this be the right way? Can the UDP part coexist?
> Do you have any suggestions?

The proper way is to use IP routing(=forwarding) but you will need 
properly set routing table on all hosts, which is generally hard to 
achieve. The other way is to use NAT but lwIP does not support NAT.

In my opinion, the UDP/TCP proxy you did is the easiest way to achieve 
what you need and is, although not the best from the state of the art 
perspective, but a very acceptable solution.

Note you don't need to use the heavy socket/netconn interface since you 
are just forwarding packets inside the lwIP stack at the end, using the 
raw API interface inside the TCP/IP thread would be best suited.


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