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Author Topic: NAT over IPSec VPN  (Read 5141 times)

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Offline kiddx

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NAT over IPSec VPN
« on: May 24, 2012, 02:54:12 pm »
I have done this on some other firewalls (Sonicwall, Netscreen, Cisco) but wanted to know if this could be done with PFSense. Basically , I want to do an edge-edge VPN but NAT not route the traffic. The reason I want to NAT is because some of the sites may have the same IP range and I do not have control of those networks. We are setting up an RDP cluster for a handful of companies that need access to our system via RDP and only ours. So I just need like a hub/spoke type VPN to allow incoming RDP (3389) traffic from the tunnel. However, if the clients networks overlap I will have an issue with routing obviously.

I couldnt find anything pertaining to it specifically, I was thinking I could test it with the Advanced NAT outbound option , and thought I would ask here while I went off and tried to test myself.

Thanks

Offline cmb

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Re: NAT over IPSec VPN
« Reply #1 on: May 28, 2012, 10:27:27 pm »
For now that's only possible if you separate the NAT and IPsec to two separate systems, which a lot of people do. One system can do NAT, another IPsec. The underlying OS can't support anything else.

Offline shon

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Re: NAT over IPSec VPN
« Reply #2 on: June 05, 2012, 08:56:52 am »

Offline dhatz

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Re: NAT over IPSec VPN
« Reply #3 on: June 05, 2012, 10:00:48 am »
Apparently NAT before IPsec works with pf+OpenBSD and (iirc) ipfw+FreeBSD, but not pf+FreeBSD, hence the problem with pfSense ...

Offline miloman

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Re: NAT over IPSec VPN
« Reply #4 on: June 20, 2012, 06:44:36 am »
just came across this entry: http://blog.pfsense.org/?p=592

does this mean we could get nat over ipsec?

Offline cmb

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Re: NAT over IPSec VPN
« Reply #5 on: June 20, 2012, 09:23:30 am »
just came across this entry: http://blog.pfsense.org/?p=592

does this mean we could get nat over ipsec?

no.

Offline dhatz

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Re: NAT over IPSec VPN
« Reply #6 on: June 20, 2012, 09:29:46 am »
just came across this entry: http://blog.pfsense.org/?p=592
does this mean we could get nat over ipsec?

No, unfortunately not. It is a long-standing issue with pf and FreeBSD and it seems that the only way to solve it would be for FreeBSD to "fork" pf and add "inside NAT" to pf.

Here is the gist, from an old (2009) discussion on this subject:

Quote
NAT before IPsec on FreeBSD:

Need of ipsec vpns beetween RFC1918 colliding networks is pretty usual these days, so has anyone considered working
in this area ?

On Mon, Oct 19, 2009 at 9:18 AM, Eric Masson wrote:
> OpenBSD has support for this kind of setup since last January :
> http://undeadly.org/cgi?action=article&sid=20090127205841
> The commit :
> http://marc.info/?l=openbsd-cvs&m=123246256228242&w=2
>
> >From what I've understood, pf, depending on version in FreeBSD, could
> already support natting on enc interfaces.
>
> The missing part seems to be laying at the IKE daemon level.

I think you should send this email to ipsec-tool mailing list!
Basically the daemon should be modified for this and FreeBSD
is not the owner of such code.

AFAIK, there is not limitation to allow this in the IPSec stack.
So it is purely a daemon perspective to instrument the stack for this.

---------------------------------------------
> I'm not sure that pf & ipsec stack already support this feature. Maybe
> bz@ or vanhu@ will shed a light on this point.

This is a way to do that, but it needs some stuff on both kernel and
userland to be implemented that way.

Another way to have this feature is to implement what we call "NAT
before VPN": you can configure your kernel (or do it for specific NAT
rules if you want to do a more flexible implementation) to do NAT
process before doing IPsec stuff.

Then, you just write your NAT rules to move local/remote traffic
endpoints to distinct networks, and IPsec (both in kernel and
userland) will just have to deal with those NATed networks.

OpenBSD's way of doing things seems interesting while reading very
quickly your link, I'll have to take some more time to really see
exactly what they are doing.....

---------------------------------------------
> OpenBSD's way of doing things seems interesting while reading very
> quickly your link, I'll have to take some more time to really see
> exactly what they are doing.....

Basically they make aware the daemon and the firewall of the nat.

Actually it is more 'user-friendly' to configure though clumsy since you have
to do keep the same information in two places, firewall nat rules and the ipsec
daemon.

You just tell instrument the daemon to inject one 'normal'(out) SA's
match traffic coming from your local network and one SA for incoming
traffic from remote network with the natted network address.

This all is because pf(4) cannot do 'incoming nat' by default.
---------------------------------------------
> OpenBSD's way of doing things seems interesting while reading very
> quickly your link, I'll have to take some more time to really see
> exactly what they are doing.....

I agree with Ermal that duplicating nat information in pf and isakmpd is
suboptimal and probably error-prone, but it seems to me that it's less
intrusive than altering the ip stack.
---------------------------------------------
Bjoern A. Zeeb-2
Oct 20, 2009; 9:00pm
Re: IPSec, nat on enc device

On Tue, 20 Oct 2009, Eric Masson wrote:
> vanhu <[hidden email]> writes:
>
> 'Lut Yvan,
>
>> Another way to have this feature is to implement what we call "NAT
>> before VPN": you can configure your kernel (or do it for specific NAT
>> rules if you want to do a more flexible implementation) to do NAT
>> process before doing IPsec stuff.
>
> I've used it last week on a 8.0.2 F200. The major drawback is that an
> existing nat ruleset must be adapted (nomap rules for vpn networks that
> dont need nat) and that it can cause issues when activated
> (a reverse proxy located on a machine behind a bidirectionnal map woes
> when nat before vpn is activated, that's why I have to setup another box
> for natted vpns...)
>
>> OpenBSD's way of doing things seems interesting while reading very
>> quickly your link, I'll have to take some more time to really see
>> exactly what they are doing.....
>
> I agree with Ermal that duplicating nat information in pf and isakmpd is
> suboptimal and probably error-prone, but it seems to me that it's less
> intrusive than altering the ip stack.
... [show rest of quote]

I only had a quick look at the commit message being on the road.

I think OpenBSD seems to move further and further in the direction to be
an operating system around pf, rather than pf being a firewall
implementation for the OS, in some areas.  That kind of worries me -
also for further code sharing wrt to pf(4).

What I said before and will repeat is that if you want to use NAT and
VPN you want to do inside NAT (admittingly handling the local machine
is a different story). I have done that years ago with ipfw. Then your
SA works on the NAT IP. I used it to avoid formerly RFC1918 address
collisions by NATing to an unrouted public IP for just the VPNs.
THe NAT IP will not be bound to any interface at all.

There is a reason major vendors have been doing inside and outside NAT
for ages now.  That pf cannot do that is bad and a design problem there.
The "commit Theo calls me insane for"  moves into the direction of
fixing that but when I talked to OpenBSD people at EuroBSDCon they said
something along the lines of "it's not entirely there yet and still
disabled because there are a few things that would work entirely as
expected".

There is abosultely no need to change the IP stack to accomplish that.


If you want to do it with pf + enc + NAT you can actually do that even
without patches but a bad ugly not to publish hack, that you will most
likely only want to do if you control all endpoints:
you add two policies: one with your internal network and one with your
NAT IP on both sides. racoon , configured correctly, will negotiate the
SA and share it for the tunnel endpoints for both policies.
The remote destination will never see a packet with a src of your
internal IPs but it will have a policy for it - else negotiation would
fail.  You may need to assure that no packets travel your way with the
1st, internal, policy in the firewall.

What I see with the OpenBSD change is that their hack does nothing but
get rid of the 1st policy for the internal network on the peer. Not
sure if they still need it locally or if they hacked the stack for
that; from what I see FreeBSD would have to do that.

/bz

Offline miloman

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Re: NAT over IPSec VPN
« Reply #7 on: June 25, 2012, 03:48:12 am »
For now that's only possible if you separate the NAT and IPsec to two separate systems, which a lot of people do. One system can do NAT, another IPsec. The underlying OS can't support anything else.


Could anyone explain to me how this works?

Offline jmcentire

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Re: NAT over IPSec VPN
« Reply #8 on: July 21, 2012, 06:14:58 pm »
Does anyone know of another open source firewall that can do this?  I know Endian can(that is what I'm currently using to make this work), but honestly I can't stand it so I'm looking for a different one.

Also if anyone is curious, my idea is to use pfsense as my main firewall then setup endian or something else as a virtual server to handle the nat and ipsec.  So in pfsense I will have a static route for the vpn endpoint route to the endian firewall which will then nat the traffic and send over the vpn.  This way I don't have to add any extra hardware or interfaces in my current setup.(if that made sense, it is more difficult to explain than I thought)
« Last Edit: July 21, 2012, 06:17:38 pm by jmcentire »

Offline jmcentire

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Re: NAT over IPSec VPN
« Reply #9 on: July 23, 2012, 04:59:03 pm »
My idea did not work, endian doesn't play nice when it's not the main firewall.