[Swan] No ipsec0 device with XFRMi

Antony Antony antony at phenome.org
Thu Jul 30 05:57:15 UTC 2020

On Wed, Jul 29, 2020 at 11:32:58AM +0200, Wolfgang Nothdurft wrote:
> Am Dienstag, 28. Juli 2020 20:25 CEST, schrieb Antony Antony <antony at phenome.org>:
> > ipsec-interface=0 would translate to
> >
> > ip link add ipsec0 type xfrm dev enp0s5 if_id 0
> >
> > when I started adding xfrmi I wasn't sure xfrm if_id 0 would work properly.
> > if_id is a lookup key to find policy and state. I wonder if 0 would mean
> > also a policy with no xfrmi if_id.
> >
> > xfrm if_id 0 was confusing to me. I decided ipsec1 to start with. May be
> > time to review it while xfrmi is still expirimental.
> >
> > and also to avoid confusion from klips.
>  I think the problem with if_id 0 could be the fwmark that is used to route the encrypted packets on the base interface.
>  100:    from all to fwmark 0x1 lookup 50
> With fwmark 0x0 all unmarked traffic to the destination would go through the base interface instead of the ipsec interface.
> But ipsec-interface=0 for ipsec0 would be very useful. All our customers use ipsec0 for the first ipsec device, so the change from klips to xfrmi would either confusing for them or a technical problem that we have to solve.
> At the moment I test patching libreswan to map if_id to device name if_id-1, which works properly. 

are you proposing to keep name ipsec0 (the interface name), while internally 
f_id = 0x1 and fwmark would be 0x1 (by default)?  I had one version of the 
code which did this. UINT32_MAX meant no xfrmi inside pluto. It appeared 
complicated and I dicthed it.  At this stage it is probably easy to go back 
to ipsec0.  Currently ipsec-interface=X is the if_id and the mark.

> But the next problem is that we use the lower 24 bit fwmarks for our 
> firewall rule set. The upper 8 bit was reserved for ipsec (saref) long 
> time ago. So the next problem is that actual the fwmark is not 
> configurable and I have also to patch either libreswan or overwork our 
> complete rule set to reserve the lower bits for ipsec devices.
> Maybe a configurable minimal fwmark could be a nice feature.

the output mark on the ESP packet is not configurable yet. One confusion was 
keywords for the new output mark. Note the conflict with mark-out; used by 
VTI?. The VTI mark-out is a different XFRM attribute than the one needed to 
work with xfrmi. May be I can have different meaning for
mark-out when there is xfrm interface.

or add ipsec-interface-output-mark= as the third mark? because
XFRM has now 3 marks. AFIK mark-out was never used in VTI case.
I don't want to break VTI usecases.

Can you can help create a testcase with fwmark and xfrmi?  you are using 
marks with KLIPS? so it is not really configured in ipsec.conf? I wonder how 
that would translate one-to-one.

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