Re: [lwip-users] routing over PPP using lwip

[Sylvain Rochet]

Hi Ajay,

On Mon, Jan 18, 2016 at 03:04:15PM +0530, address@hidden wrote:
> > Hi Ajay,
> >
> > This is a bit hard to answer an open question like yours.
> >
> > Anyway, last time I tried, IP forwarding between a PPP session 
> > (whatever the low level protocol used) and an Ethernet interface 
> > works smoothly. However, you have to use the Git head, at least IP 
> > forwarding between PPPoS and Ethernet is broken in the 1.4.1 release 
> > (I don't know for PPPoE).
> 
> Thanks for the response. I am using GIT head right now not using 1.4.1 
> release. I just wanted to know is there any hook I need to define to 
> make sure packet forwarding works? Which interface I need to set as 
> default (I tried with PPP as default).
> 
> On PC side my adapter settings are:
> IP: 192.168.37.1
> GW: 192.168.37.2
> Mask: 255.255.255.0
> 
> On LwIP Ethernet:
> IP+GW: 192.168.37.2
> Mask: 192.168.37.2
> 
> PPP: I get PPPos connect up and working smoothly, I tested DNS and 
> ping to google.com which works fine
> 
> But when I try to ping from my PC to google.com or even a static IP 
> say 8.8.8.8 It does not work. Please tell me what more information I 
> can provide so that it becomes easy for you to answer. If any logs are 
> needed, I will provide them too just let me know what Debug flags to 
> enable.

What you are looking for is a NAT[1] implementation, not basic IP 
routing[2], lwIP does not provide NAT at all. There used to be a basic 
NAT feature merged in, but it was removed because the one who proposed 
the patch wasn't allowed to do so.

NAT, other than basic NAT support, is a huge task. Especially for tricky 
protocols (FTP, SIP/RTP, …) which require well designed helpers. I'm not 
sure it qualify as being added in a lightweight stack.

Sylvain

[1] https://en.wikipedia.org/wiki/Network_address_translation
[2] https://en.wikipedia.org/wiki/Packet_forwarding

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