RE: [lwip-users] Max throughput and LWIP

[Kieran Mansley]

On Mon, 2008-02-04 at 11:41 -0500, Bill Auerbach wrote:
> The biggest thing which significantly increased the speed was to turn
> off incoming IP/UDP/TCP checksum checking.  If I leave the checking
> on, I get around 650MbS with jumbo frames.  This ~940MbS was standard
> frames.  Since the Ethernet controller has CRC checks, I don’t think
> the lwIP checking is required.  I was going to pose to the group this
> week what is the downside of this disabling of the checksumming,
> because the speed impact is substantial.

This is a really bad idea if you care about your data (though there are
some example of where you might legitimately not care).  The CRC
protects against bit errors on each link.  It is a point-to-point check,
recomputed at each node in the network.  Therefore if any piece of
equipment or software on the route of your packet has a bug that
corrupts the data it is unlikely that the CRC will protect you.  The
checksums are end-to-end, so are computed and checked only at the source
and destination, so any (well, most) errors generated in between will be
spotted.  The simple answer is you need checksums on unless you have a
good understanding of why you don't!  And even then you probably need
them on.

Kieran