netdev - Re: [PATCH v1 1/6] net: Generalize udp based tunnel offload

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Date:	Mon, 7 Dec 2015 08:20:23 -0800
From:	Jesse Gross <jesse@...nel.org>
To:	David Ahern <dsa@...ulusnetworks.com>
Cc:	Alexander Duyck <alexander.duyck@...il.com>,
	Tom Herbert <tom@...bertland.com>,
	David Miller <davem@...emloft.net>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	John Linville <linville@...driver.com>,
	Anjali Singhai Jain <anjali.singhai@...el.com>,
	Netdev <netdev@...r.kernel.org>,
	Kiran Patil <kiran.patil@...el.com>
Subject: Re: [PATCH v1 1/6] net: Generalize udp based tunnel offload

On Sun, Dec 6, 2015 at 7:02 PM, David Ahern <dsa@...ulusnetworks.com> wrote:
> On 12/6/15 6:20 PM, Alexander Duyck wrote:
>>
>> That works for Linux to Linux, but what about the cases where you have
>> a non-Linux endpoint on the other end such as something like a Cisco
>> switch?
>
>
> Why does is matter what kind of switch the NIC is connected to?

I think Cisco was just an example, not anything particular about their
switches. But there are two general problems:

 * Some protocols, like VXLAN, recommend that the UDP checksum be zero
so this is what pretty much everyone implements. As a result,
independent of the merits of using the checksum, most non-Linux
endpoints won't support it.

* The reason why this recommendation exists in the first place is that
most ASIC based switches can't compute/verify UDP checksums. They
slice off the headers and only run that through the chip's core
memory, so the rest of the packet isn't available to compute a
checksum over.
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