[lwip-users] Ethernet frames with extra padding bytes

[Keith Rubow]

I am trying to use LWIP 2.0.3 using a Wiznet ethernet module in MAC raw 
mode as my ethernet interface. It's a long story. The Wiznet modult 
implements the entire TCP/IP stack, but has a bug with missing ARP 
requests. I can fix it in software using LWIP by putting the Wiznet 
module into MAC raw mode so it acts as just an ethernet interface 
sending and receiving raw ethernet frames, and using LWIP to do 
everything else.

The problem is that the Wiznet module seems to pad out all ethernet 
frames to a minimum length of 64 bytes. For example, a received ARP 
request is only 42 bytes long (confirmed my Wireshark), but the Wiznet 
module gives me a frame of 64 bytes. There are an extra 22 bytes 
appended to the end of the frame, and the extra bytes are not all zero.

LWIP does not seem to be working. Will these extra non-zero padding 
bytes cause problems with LWIP?

Note that a different Wiznet module padds out all frames to 60 bytes 
minimum, but is padding with all zero bytes. This module is working fine 
with LWIP.

Keith Rubow