Messages in this thread | | | Date | Mon, 23 Aug 2004 00:58:33 +0200 | From | Olivier Galibert <> | Subject | Re: Cursed Checksums |
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On Sun, Aug 22, 2004 at 11:03:54PM +0200, Josan Kadett wrote: > Perhaps there is a way to recompute IP header checksums before they get into > the interface? As I outlined, I have found a way to manipulate IP source > address before the packet is flushed to system, but a means of recalculating > the IP header checksum after that manipulation should be found. Because even > if I ignore IP header CRC in one system, all other boxes connected to this > machine has to be patched the same. That is impossible anyway. > > Only if I could find a way to recalculate the checksum in IP headers by > doing a simple hack to the kernel, everything would be alright.
Why don't you patch the checksum when you change the IP? It's just a not of the sum the 16-bit words so take the old one, not it, add the two 16-bits differences, re-not it and write it back.
OG.
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