IPSec NAT-T in transport mode

David Murray david000 at davidmurray.name
Thu Jan 21 16:50:09 UTC 2010


On 10-01-20 Wed 1:04 pm, VANHULLEBUS Yvan wrote:

> On Wed, Jan 20, 2010 at 03:16:02PM +0600, Rabidinov M.A. wrote:
>> Does FreeBSD 8.0 support IPSec NAT-T in transport mode?
>> I want to create a L2TP/IPSec server. My VPN clients are NATed.
>> L2TP server (MPD5.x) makes tunnel, so I need working IPSec NAT-T in 
>> transport mode.
> It may work..... or not....
> The missing part is support of NAT-OA payloads, which are used to 
> update checksums when receiving packets.
> But afaik, most L2TP implementations computes checksums, so they will 
> be checked, and of course will be wrong....

On 2010-01-20 Wed 1:22 pm, Crest wrote:

> Yes the NAT-T Patch has been integrated into FreeBSD 8.0.
> Just rebuild your kernel with this options:
> device crypto # IPsec depends on this
> options IPSEC
> options IPSEC_DEBUG
> options IPSEC_NAT_T

I'm trying to do the same thing as the OP, so thanks for these replies.

However, they seem to be at odds.  Are we saying that the NAT-T patch is 
there, but is missing checksum re-calculation, so MPD's packets are 
going to be discarded?

(FWIW, this seems to be what happens.  All the negotiation to set up 
IPSEC SAs happens, but MPD's log never shows a single entry.  I hadn't 
got as far as packet dumps when this thread popped up.)

David Murray

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