Re: [lwip-users] PPP shared Internet

[Sylvain Rochet]

Hi Richard,

On Mon, Jan 17, 2022 at 11:53:32AM +0000, Richard Bailey wrote:
> Hi,
> 
> I am working on an IoT solution. I've bumped into an issue around 
> using LWIP. If I describe the scenario and what I'm trying to achieve, 
> perhaps you can tell me if what I'm trying to do is in theory is 
> possible or if I need to approach it another way.
> 
> It has a main NXP PCB, with a Microsoft Azure Sphere, secure Wi-Fi 
> module attached. The Azure Sphere is a bit of a black box, but it 
> handles communication to Microsoft's Azure Servers over Wi-Fi. It can 
> also work over Ethernet, but it will not have a physical Ethernet Port 
> on the device. There will be scenarios where Wi-Fi is not an option, 
> so we need a backup solution.
> 
> The main NXP PCB has a BG95 modem.
> It has an internal circuit-based Ethernet connection between the NXP 
> and the Azure Sphere module. The plan is for the Azure Sphere module 
> to communicate out over the BG95 modem via the internal Ethernet.
> 
> The main NXP PCB is running FreeRtos, with LWIP 2.1.3.
> I was hoping to simply set up two NetIf adaptors:
>  * PPPOS for the modem, with the Internet connection
>  * Ethernet.
>  Then enable IP_FORWARD.

IP forwarding between PPP and Ethernet works and a custom IPv4 routing 
table can be added by using LWIP_HOOK_IP4_ROUTE.


> Would that approach work allowing the Azure Sphere to communicate with 
> the outside world, over the internal Ethernet and forwarding to the 
> PPP modem (in both directions)?

It depends if IP forwarding is enough for you. Beware that IP forwarding 
is IP routing, not NAT.


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What should I do with that ?


Sylvain

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