TIPHdr = packed record
EthernetHeader : TEthernetHdr;
Verlen : UCHAR;
Service : UCHAR;
Length : WORD;
Ident : WORD;
Flagoff : WORD;
TimeLive : UCHAR;
Protocol : UCHAR;
Checksum : WORD;
Source : DWORD;
Destination : DWORD;
end;

TIPPckt = Packed record
IPHeaderr : TIPHdr;
Data : Array[0..0] of uchar;
End;

TTCPPckt = Packed record
TCPHeader : TTCPHdr;
Data : Array[0..0] of uchar;
End;

TUDPHdr = packed record
IPHeader : TIPHdr;
Source,
Destination,
Length,
Checksum : WORD;
end;

PUDPPckt = ^TUDPPckt;
TUDPPckt = Packed record
TUDPHeader : TUDPHdr;
Data : Array[0..0] of uchar;
End;

UDPHdr里有长度，TCPHdr里好象没看到长度？