[lwip-users] I cannot get PPP-new IP forwarding and pppapi_set_default() work

[LMao]

Hi Sylvain,

Here's my scenario: 
I am developing a gateway between Ethernet and PPP using ppp-new branch. The 
gateway device has one Ethernet port(IP 192.168.0.50, i.e., 0x3200a8c0) and one 
PPP port (IP 192.168.1.105, i.e., 0x6901a8c0). For testing purpose, I connected 
the Ethernet port to a PC (IP 192.168.0.211, i.e., 0xd300a8c0) and connected 
the PPP port to a Linux PPP server's PPP port(IP 192.168.1.106, i.e., 
0x6a01a8c0). PPP connection has been successfully built up. From my PC, I can 
ping my gateway's PPP port (192.168.1.105) but I couldn't ping PPP server 
(192.168.0.106). I am sure I have set PC routing correctly because the ping 
packet can reach my gateway's serial port as the debug message shows below. 
Here are the debug messages, the first part shows the success of ping my 
gateway's PPP port while the second part shows the failure of ping PPP server.

First log - success of ping my gateway's PPP port
----------------------------------------------------------
ip_input: iphdr->dest 0x6901a8c0 netif->ip_addr 0x3200a8c0 (0x1a8c0, 0xa8c0, 
0x69000000)
ip_input: iphdr->dest 0x6901a8c0 netif->ip_addr 0x6901a8c0 (0x6901a8c0, 
0x6901a8c0, 0x0)
ip_input: packet accepted on interface pp
ip_input: 
IP header:
+-------------------------------+
| 4 | 5 |  0x00 |        60     | (v, hl, tos, len)
+-------------------------------+
|      736      |000|       0   | (id, flags, offset)
+-------------------------------+
|  128  |    1  |    0xb454     | (ttl, proto, chksum)
+-------------------------------+
|  192  |  168  |    0  |  211  | (src)
+-------------------------------+
|  192  |  168  |    1  |  105  | (dest)
+-------------------------------+
ip_input: p->len 60 p->tot_len 60
ip_output_if: em0
IP header:
+-------------------------------+
| 4 | 5 |  0x00 |        60     | (v, hl, tos, len)
+-------------------------------+
|      736      |000|       0   | (id, flags, offset)
+-------------------------------+
|  255  |    1  |    0x3554     | (ttl, proto, chksum)
+-------------------------------+
|  192  |  168  |    1  |  105  | (src)
+-------------------------------+
|  192  |  168  |    0  |  211  | (dest)
+-------------------------------+
netif->output()


Second log - Fail to ping PPP server
----------------------------------------------------------
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: not bouncing packets back on incoming interface.

I enabled IP_FORWARDING and also called pppapi_set_default() function. Should I 
expect the above scenario working? Or I have to implement my own static routing?

Another thing I noticed is ip_forward function seems give false debugging 
information " ip_forward: not bouncing packets back on incoming interface". The 
packet was coming from Ethernet interface (from my PC) and its destination 
should be PPP interface, so there's not bouncing back packet.


Thanks,

Charles