NAT before IPSEC - reply packets stuck at enc0

[Muenz, Michael]

Am 25.07.2017 um 17:38 schrieb Andrey V. Elsukov:
> On 25.07.2017 17:06, Muenz, Michael wrote:
>>> As I said already, the NAT thinks that both packets are inbound and does
>>> translation for source address each time. You need to do translation for
>>> both directions on enc0 interface like I described, or you need to
>>> somehow hack/modify ipfw_nat.
>>>
>>> You do not need to create SA for 10.26.2.0->10.24.66.0, you only need
>>> create security policy, that will "route" such packets into the IPsec
>>> tunnel. The translation will be done inside IPsec before IP
>>> encapsulation and encryption. Since you are using tunnel mode IPsec,
>>> replies will be returned to your external IP address, and this SA is
>>> exists already. After decryption and IP decapsulation the destination
>>> address of packet will be translated back to 10.26.2.N on if_enc(4).
>> Can I use this spdadd command also when using strongswan? (Please excuse
>> stupid questions)
> I'm not familiar with strongswan configuration, but you can just try and
> check that the proposed configuration will work.

When I type setkey -PD I get:

10.24.66.0/24[any] 10.26.1.0/24[any] any
         in ipsec
         esp/tunnel/81.24.74.3-213.244.192.191/unique:2
         created: Jul 26 11:03:53 2017  lastused: Jul 26 11:40:02 2017
         lifetime: 9223372036854775807(s) validtime: 0(s)
         spid=5 seq=1 pid=4292
         refcnt=1
10.26.1.0/24[any] 10.24.66.0/24[any] any
         out ipsec
         esp/tunnel/213.244.192.191-81.24.74.3/unique:2
         created: Jul 26 11:03:53 2017  lastused: Jul 26 11:40:02 2017
         lifetime: 9223372036854775807(s) validtime: 0(s)
         spid=6 seq=0 pid=4292
         refcnt=1


So it's in use.

But when I type in your command it just "hangs". Not the system, but the 
command doesn't get completed.

root at PB-FW1-FRA:~ # setkey -v -c spdadd -4 10.26.2.0/24 10.24.66.0/24 
any -P out ipsec esp/tunnel/213.244.192.191-81.24.74.3/require ;
<waiting cursor>

dmesg and syslog is clean, no error. Also adding the -v for verbose 
doesn't output anything.

Will have to investigate on this.

>
>>> ipfw nat 1 config ip 10.26.1.1 log
>>> ipfw add 179 nat 1 all from 10.26.2.0/24 to 10.24.66.0/24 out xmit enc0
>>> ipfw add 179 nat 1 all from 10.24.66.0/24 to 10.26.1.1 in recv enc0
>>>
>> Ok so your 3 nat commands will only match when there's a new spd like
>> above right?
>> Since there's nothing on enc0 without it.
> Yes, it is. A security policy will route requests from 10.26.2.0/24 into
> IPsec tunnel, where they should be translated, and then replies will be
> received.
>
Ok, then it's clear why it doesn't work. Thanks for you efforts!
Will debug with the OPNsense dev's to catch this one ..

Michael