[ECOS]TCP/IP problem

[lqx]

 Hi,all  I have got ecos running on our board using the 
CL_PS7500FE ARM processor. I have included  DM9008  ethernet chip and 
use the tcp/ip stack version 1_0b1 that I downloaded from the 
URL--sourceware.cygnus.com  .The chip really works.But when I ping the ecos 
with a packet more than 1500 bytes,the ecos never send the packet back.Why?Is 
there any bug in the tcp/ip stack?for when I debugged  the net device 
driver, I found the driver received the packet correctly .Anyone can help 
me?
 thanks