You're right Simon. Enabling the second interface there made things
work (to some extent).
However, I'm facing a new problem now.
Previously I was using only a single interface (the Linux tap0
device). I have implemented a DHCP server which was working fine until
I enabled the SECOND INTERFACE.
Now, my socket writes on the first interface (the tap0 interface) have
started failing! That is, without changing _any_ code! :( The return
value of sendto is coming as '-1' and the error string is set to 'No
error'. Actually this problem starts even if I don't enable support
for eth1 in the lwIP config. Just enabling the second interface under
"Common ethernet support -> Synthetic target ethernet driver" causes
this problem to surface.
Any clues as to what could be going wrong?