Hi all My board is connected to ethernet hub , and other PCs are connected to this hub , too . The lwip will die when other PCs access the network (like ftp , http . Not access this board , just access internet ). But lwip will not die when it connected to layer 2 switch . My board is STR910-EVAL , FreeRTOS 4.2.1 , lwIP 1.2.0 . Does anyone have the same problem ?

What MAC address are you using?  Is the first octet zero?  If not, try setting it to zero.