Reply To: WINPKFILTER VXD Packet Filter Driver

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Vadim Smirnov

1514 bytes is a network media limit for 802.3 Ethernet (actually it is 1518 bytes but two extra bytes exist only on the physical media and not visible by software). 14 bytes are used for Ethernet header, so maximum IP MTU is 1500 bytes. All IP packets above this size are fragmented by TCP/IP stack. In your case 7900 bytes UDP packet will be fragmented to 6 IP packets and only first fragment will contain UDP header. You can reconstruct the packet from fragments received from WinpkFilter driver if you need to do so.

Some modern network cards (Gigabit Ethernet) may support frames larger than 1514 bytes (9000 bytes “jumbo frames”). WinpkFilter driver can be extended to work with these larger frames (default on site build does not support them and limits MTU to normal 1514 bytes), but I don’t think this is your case, correct me if I’m wrong.