[Openswan dev] A question about NAT-OA

[Kevin Wilson]

Hello,
  I saw that when working in transport mode and
using NAT-traversal, you should send in the two first Quick mode IKE message
the OA (original address) of one side. This should be received by the
other side and used for checksum calculation (since the original address
was changed by a NAT).

My question is: where is this checksum calculation done ? is it done
in the kernel ? I tried for hours to find where is the Linux kernel
stack this is done, and I could not find anything.

I would appreciate if somebody can point me.

Rgs,
Kevin