Thanks,
Silly Andy
"Helge Kruse" <Helge.Kruse-nospam@xxxxxxx> wrote in
message news:20110805142651.296750@xxxxxxx...
> You've forgotten to include the UDP payload in your calculation. For the
> calculation the pseudo header must be in front of UDP header and UDP
> payload.
>
> Helge
>
> -------- Original-Nachricht --------
>> Datum: Fri, 5 Aug 2011 15:45:38 +0200
>> Von: "news.gmane.com" <AndreasSander1@xxxxxxx>
>> An: wireshark-dev@xxxxxxxxxxxxx
>> Betreff: [Wireshark-dev] Question about UDP checksum
>
>> Hello,
>>
>> I try to implement a UDP checksum routine. Unfortunately it calculates a
>> completely different value than Wireshark does. I don't known what I am
>> doing wrong. Can you help me?
>>
>> The calculation is done using a UDP pseudo header with the structure
>>
>> struct pseudo
>> {
>> uint32 source;
>> uint32 destination;
>> uint8 zero;
>> uint8 protocol;
>> uint16 udp_length;
>> };
>>
>> When I have a UDP frame with IP source = "192.168.100.132" and IP
>> destination = "192.168.144.255", and UDP Length = 66 (IP Total_Length =
>> 86)
>> I get this data in the pseudo header:
>>
>> c0 a8 64 84
>> c0 a8 90 ff
>> 00 11 00 42
>>
>> The sum is 0x32874 which is must be folded to 0x2874+0x0003 = 0x8277. The
>> complement is 0xd788.
>>
>> But Wireshark detects an error and says the checksum must be 0x5528. Can
>> anybody give me a hint what's wrong?
>>
