Re: [lwip-users] ppp-new IP forwarding only works one direction (Ethernet to PPP)

[Sylvain Rochet]

Hello Charles,

On Wed, Apr 09, 2014 at 06:47:43PM +0000, address@hidden wrote:
> 
> My test setup is like this:
> 
>                         Ethernet                                              
>   PPP
>              PC   -------------  My gateway device  --------  Linux PPP server
> 192.168.0.211       192.168.0.50        192.168.1.105       192.168.1.106
> 
> I ping from my PC to the PPP server. Here's some logging messages 
> showing the modified ip_forward function works as expected.
> 
> ip_input: iphdr->dest 0x6a01a8c0 netif->ip_addr 0x3200a8c0 (0x1a8c0, 0xa8c0, 
> 0x6a000000)
> ip_input: iphdr->dest 0x6a01a8c0 netif->ip_addr 0x6901a8c0 (0x6a01a8c0, 
> 0x6901a8c0, 0x0)
> ip_input: packet not for us.
> ip_forward: forward packets to interface.pp
> ip_forward: forwarding packet to 192.168.1.106
> ip_input: iphdr->dest 0xd300a8c0 netif->ip_addr 0x6901a8c0 (0xd300a8c0, 
> 0x6901a8c0, 0x0)
> ip_input: iphdr->dest 0xd300a8c0 netif->ip_addr 0x3200a8c0 (0xa8c0, 0xa8c0, 
> 0xd3000000)
> ip_input: packet not for us.
> ip_forward: forward packets to interface.em
> ip_forward: forwarding packet to 192.168.0.211
> 
> I captured PPP traffic on the serial port and also captured Ethernet 
> traffic using Wireshark. I can clearly see PPP traffic on both 
> directions(into and out from the PPP server) and they are correct 
> frames as expected. However, the traffic from PPP server to my PC 
> NEVER showed up in Wireshark. It seems lwIP silently drop those 
> packets. What should I do to find out the cause of the problem?

First, thank you, I trimed most but everything was really helpful, I 
enjoy getting such well-written investigation pattern :)

Well, ip_forward() should call netif->output(), which in our case is 
ppp_netif_output_ip4(), could you first check that ?

You can also enable PPP_DEBUG in your lwipopts.h, this will display 
discarded frames in ppp_netif_output_ip4() if any.

Sylvain

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