Re: Entirely ignoring TCP and UDP checksum in kernel level

Brad Campbell
2004-08-22T06:16:50Z

Josan Kadett wrote:
> That is certainly what I require but I need some guidelines; I investigated
> into the issue and fount out that;
>
> - By only changing the source address coded in the IP header
> - And by just applying checksum to IP header [Not TCP or UDP]
>
> The problem would be gone since when the source IP in the IP address field
> is validated, the checksum in the underlying protocol is automatically
> validated (because the sender system had already computed this CRC using the
> IP address which we want to write onto the packet)
>
> I do not have much time to build a code just for this purpose and thus I am
> looking for a simple app. or some other way...

So if we took any packet that came in from 192.168.1.1 and substituted 192.178.77.1 for the Source
address and then re-calculated the IP checksum you would be up and running?

Regards,
Brad