How does FreeBSD handle tcp checksum offloading

[Andrew Falanga]

On 5/24/07, Erik Trulsson <ertr1013 at student.uu.se> wrote:
>
> Checksum offloading is usually enabled by default for hardware that supports
> it (assuming that the driver for that hardware also supports it of course.)
>
> To see if a particular interface uses checksum offloading you can look at
> the output of 'ifconfig -m'.
> The "options" line in the output refers to those features that are enabled,
> while the "capabilities" line refers to those features that are available.
> (Checksum offloading for receive and transmit show up as RXCSUM and TXCSUM
> respectively.)
> Ifconfig can also be used to enable/disable the offloading - see the
> ifconfig(8) manpage for details and syntax.
>
> It can sometimes be desirable to turn of checksum offloading if one suspects
> that the hardware has some bugs in it that can cause the checksum to be
> wrong.  (For those cases were the hardware has known bugs in this area, the
> driver normally disable checksum offloading by default.)
>
>
> Most hardware supported by the fxp(4) driver do not have support for
> checksum offloading, but some do.
> (The fairly commonly used  82559 chip does not support checksum while the
> less common 82550 chip does, for example.)
>
>
>

Thanks for the info.  This is cool.  My Intel NIC is the 82550.  That
explains a few things.  Thanks again for the info on how these are
used FreeBSD.

Andy