https://bugs.wireshark.org/bugzilla/show_bug.cgi?id=6556
--- Comment #2 from Chris Maynard <christopher.maynard@xxxxxxxxx> 2011-11-14 14:42:28 PST ---
(In reply to comment #0)
> We have a device that performs IPv4 Fragmentation on Ethernet packets. When
> capturing the output of the device (fragmented packets), wireshark reports TCP
> checksum errors. Manually inspecting the fragmented packets shows this to not
> be true. The TCP checksum in the TCP header in the first of the two packet
> fragments is unchanged, and none of the TCP payload data bytes have been
> altered.
To me, it looks like your device is not RFC 791 compliant when it comes to
fragmentation. According to http://tools.ietf.org/html/rfc791#section-3.2,
"Fragments are counted in units of 8 octets." and "If an internet datagram is
fragmented, its data portion must be broken on 8 octet boundaries." The first
fragment has a 980 byte payload, which is not divisible by 8.
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