Date: Fri, 09 Nov 2012 00:55:48 +0100 From: Andre Oppermann <andre@freebsd.org> To: Adrian Chadd <adrian@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: <509C4684.2030102@freebsd.org> In-Reply-To: <CAJ-Vmo=QuP1s=ppnp2u%2BVpuJRbncaHLwi_0ku5=dr9%2BReYp79w@mail.gmail.com> 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>
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On 09.11.2012 00:32, Adrian Chadd wrote: > On 8 November 2012 06:34, Andre Oppermann <andre@freebsd.org> wrote: > >> TCP/UDP doesn't (want to) generate any fragments at all and tries >> to avoid it at almost all cost. We want to send very large packets >> and have the NIC fragment/segment it (TSO/UDP frag offload). > > What about if it's a router and the frames don't have DF set? At the risk of repeating myself: when a routed packet is fragmented the payload (layer 4, eg. TCP/UDP/SCTP) is NOT recalculated or changed or anything else. It remains as originally calculated by the sender unchanged in the first fragment L4 header. Only the IPv4 header checksum, which DOES NOT include any payload data, has to be calculated for every fragment. The IPv4 header checksum is offloaded with CSUM_IP and continues to work as expected. :) > Not that it should happen often, however.. -- Andre
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