[lwip-users] lwIP 1.3.1 : src IP chk drops DHCP (discover) packets

[Mandeep Sandhu]

Hi All,

I'm running my ECOS application with lwIP 1.3.1

The app is a small DHCP server (with limited functionality).

Now DHCP discover packets coming from clients have src addr as 0.0.0.0
and dst IP as 255.255.255.255.

On reception of DHCP discover packets I see that the ip_input function
drops it:

lwip_recvfrom(0, 0x02001c64, 548, 0x0, ..)
lwip_recvfrom: top while sock->lastdata=0x00000000
ip_input: iphdr->dest 0xffffffff netif->ip_addr 0x101010b (0xffffff,
0x1010b, 0xff000000)
ip_input: packet accepted on interface et
ip_input: packet source is not valid.

On looking at the code, I see that we are intentionally dropping
packets with src IP
as either broadcast or 0.0.0.0 (referred to as 'old skool' bcast in code).

We are handling the case of DHCP client packets in a special manner
and exempting
them from the src IP check. Can't extend the check for DHCP server port as well?

Or is there any other way to work around this?

This same app works fine with lwIP 1.1.1 which currently ships with ecos 3.0.

Thanks,
-mandeep