Date: Fri, 9 Nov 2012 08:51:46 -0800 From: Adrian Chadd <adrian@freebsd.org> To: Andre Oppermann <andre@freebsd.org> Cc: pyunyh@gmail.com, FreeBSD Net <freebsd-net@freebsd.org>, Pyun YongHyeon <yongari@freebsd.org> Subject: Re: svn commit: r242739 - stable/9/sys/dev/ti Message-ID: <CAJ-Vmo=MeSEx3cSERnzaqCOhLdNxqCQV0yhpQMRcWFLP475zHA@mail.gmail.com> In-Reply-To: <509CBA0C.3070008@freebsd.org> References: <201211080206.qA826RiN054539@svn.freebsd.org> <CAJ-VmomEOPGbLwmOmL0EdenZA7QKbV5P-hAYsTRcwLao2LbAqg@mail.gmail.com> <20121108023858.GA3127@michelle.cdnetworks.com> <CAJ-Vmoma1DJRT8_ezdEpVYrZXak%2B2B4mBHAPxhoUKr0nUrO6YQ@mail.gmail.com> <509BC2E2.4030907@freebsd.org> <CAJ-Vmo=QuP1s=ppnp2u%2BVpuJRbncaHLwi_0ku5=dr9%2BReYp79w@mail.gmail.com> <509C4684.2030102@freebsd.org> <CAJ-VmonUhcNgZojevpjNCZP41VKRZwFY7NM773NiZ9oM3PFOkg@mail.gmail.com> <509CBA0C.3070008@freebsd.org>
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On 9 November 2012 00:08, Andre Oppermann <andre@freebsd.org> wrote: > Firewalling doesn't change the packet and no checksum is needed. > NAT does change the packet and the pesky pseudo-header in the TCP/ > UDP checksum. However here only the pseudo-header checksum is > recalculated and reintegrated into the one-complement payload checksum. > The payload itself is not being looked at, except for protocols that > do contain IP addresses in their internal commands or such. There > the payload is modified. The same reintegration trick can be used. > In the majority of cases these packets are very small though and > the entire checksum is simply recalculated. As the packets are very > small no fragmentation is occuring. > The IPv4 header checksum is never ever a problem and always works. > > Can we please put this to rest now. Andre, I'm assuming that Pyun fixed a real bug that he really did see. My day job is dealing with these kinds of corner cases with embedded hardware that does offload-y type stuff. So yes, I'd really like to know what's going on under the hood and fix it. You may be able to make it all go away with a bunch of logical reasoning but if it weren't a problem, Pyun would've never stumbled across it and had to disable checksumming. I'll chase this up privately with him and see what was really going on. Thanks, Adrian
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