soekris/sis tx checksum problems

David Cornejo dave at
Wed Jun 20 10:36:12 UTC 2007

the remote machine sees bad checksums - netstat indicates that
received packets are being discarded because of bad checksums.

-txcsum has no effect, I don't think (at least mine) sis support
offloading checksums - the only if flags seem to be VLAN_MTU

dave c

On 6/20/07, Bjoern A. Zeeb <bzeeb-lists at> wrote:
> On Tue, 19 Jun 2007, David Cornejo wrote:
> Hi,
> > I am using CURRENT on a Soekris 4801 (sis ethernet).  With a recent kernel
> > all TCP packets sent via sis0 have a bad checksum.  Other systems using
> other
> > interface types (though I don't have a broad selection to test) don't seem
> to
> > suffer from this problem.
> how do you see the bad checksum? Are you running tcpdump on that sis
> interface or did you have "invalid packets" on the remote machine?
> If it's the former that's because of hardware checksumming and you
> should be able to ignore it.
> You can try
>  	ifconfig sis0 -txcsum
> and tcpdump would be fine again but the soekris cpu itself would
> compute the checksum then.
> /bz
> --
> Bjoern A. Zeeb                                 bzeeb at Zabbadoz dot NeT
> Software is harder than hardware  so better get it right the first time.

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