site_archiver@lists.apple.com Delivered-To: darwin-kernel@lists.apple.com Hello Chris, -josh On Jul 22, 2005, at 9:03 AM, Chris Vitale wrote: What is the secret to the "Weird Apple checksum" bit? This email sent to jgraessley@apple.com _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-kernel mailing list (Darwin-kernel@lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-kernel/site_archiver%40lists.a... The special bit tells the ethernet driver to tell the chip to perform a checksum in hardware. The hardware has a very brain dead hardware checksum. It requires that we stash extra information in to the csum_value field. I would guess that if you aren't clearing these flags, when the packet goes out, the checksum is being calculated again in hardware which leads to an invalid checksum or the data stashed in the csum_value field is no longer valid after the changes you make. With the KPIs on 10.4.x there is a function called mbuf_finalize_packet or something like that. It should look at the flags, calculate any checksums, then clear the flags. There was a bug that prevented it from handling the weird apple checksum bit. That has since been fixed. I've got an NKE protocol filter for panther that touches ip packets and thus recalculates the checksums. TCP packets that travel through my wireless card (which has no HW assist) are fine, so I believe my routines are sound. TCP packets over my copper gig nic have bad tcp checksums. They become bad after I set correct the checksum. The are still bad if I don't do anything to the checksum. I'm pretty sure it has something to do with SUM16 (0x1000) bit that is set in the mbuf's csum_flags. This is the only bit set in csum_flags. vitale _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-kernel mailing list (Darwin-kernel@lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-kernel/jgraessley% 40apple.com This email sent to site_archiver@lists.apple.com