On Fri, Feb 19, 2016 at 12:27 PM, Tom Herbert <t...@herbertland.com> wrote:
> I would also note RFC7348 specifies:
>
> UDP Checksum: It SHOULD be transmitted as zero. ...
>
> The RFC doesn't provide any rationale as to why this is a SHOULD
> (neither is there any discussion as to whether this pertains to IPv6
> which has stronger requirements for non-zero UDP checksum). I think
> there are two possibilities in the intent: 1) The authors assume that
> computing UDP checksums is a significant performance hit which is
> dis-proven by this patch 2) They are worried about devices that are
> unable to compute receive checksums, however this would be addressed
> by an allowance that devices can ignore non-zero UDP checksums for
> VXLAN ("When a decapsulating end point receives a packet with a
> non-zero checksum, it MAY choose to verify the checksum value.")It's #2. All of the performance concerns around checksums and tunneling stem from devices implemented using switching ASICs. In those devices, computing/verifying checksums is so slow (software path) that they are effectively unable to do it.
