netdev - Re: [PATCH v2 net-next 1/5] net: local checksum offload for encapsulation

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Date:	Thu, 7 Jan 2016 17:54:09 +0000
From:	Edward Cree <ecree@...arflare.com>
To:	David Laight <David.Laight@...LAB.COM>,
	David Miller <davem@...emloft.net>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-net-drivers@...arflare.com" <linux-net-drivers@...arflare.com>,
	"Tom Herbert" <tom@...bertland.com>
Subject: Re: [PATCH v2 net-next 1/5] net: local checksum offload for
 encapsulation

On 07/01/16 17:22, David Laight wrote:
> Isn't it even simpler than that?
> The checksum of the inner packet (including its header) is ~0 (ie 0).
> So the checksum of the whole packet (for the outer header) is the same
> as that of the packet down to the start of the inner header.
Not quite.  The inner pseudo-header is included in the inner checksum
 calculation, but does not actually appear in the packet.  Thus the checksum
 of the inner packet is ~sum_of_inner_pseudo_header.

-ed