[Openswan Users] overlapping networks with nat-t

Marco Berizzi pupilla at hotmail.com
Thu Jan 19 12:29:40 CET 2006

John A. Sullivan III wrote:

>On Wed, 2006-01-18 at 19:09 +0100, Paul Wouters wrote:
> > On Wed, 18 Jan 2006, Marco Berizzi wrote:
> >
> > > I have successfully deployed NAT-T on my various
> > > linux 2.6 (netkey) gateways with OSW 2.4.4. It's
> > > working good with Windoze XPsp2. Now, mobile
> > > users are able to connect to my private lan (which
> > > is a from others company private
> > > networks. My osw box is also tunnelling ipsec traffic
> > > from/to a (very common) network. This
> > > prevent roadwarriors which are connected to a
> > > network to connect to my network. I
> > > cannot change any network ip address. Is there any
> > > solution to this problem? DHCP over IPsec? Does
> > > windows XPsp2 support it?
> >
> > an ugly hack is to setup a tunnel for another range,
> > eg and then run SNAT / DNAT on the
> > packets. Be careful not to NAT the ipsec packets
> > though. This will be very hard using netkey.
> >
>This can be a real pain in the neck.  For example, we built the ability
>to do this with a mouse click and few keystrokes into the ISCS network
>security management project (http://iscs.sourceforge.net) but it still
>breaks certain protocols, e.g., network neighborhood browsing (as an
>aside, this is one of the very few things that iptables can't do that a
>PIX can, i.e., NAT NetBIOS packets with embedded IP information in the
>NetBIOS header).

There is also another obvious issue. My company network
is + some other branch offices with 192.168.x.0
Hopefully isn't a common used pool. What happens
if a roadwarrior connect to an other company network which is ;-)

>We finally opted for a slightly different solution for most of our
>production installations.  Not to take anything away from openswan -- a
>truly great project -- but we went with openswan for our LAN-to-LAN
>connections and OpenVPN for our RoadWarriors now that it has matured
>from its early days.  We have been very pleased with the results and,
>since it uses virtual IP addresses for the RoadWarriors, it almost
>doesn't matter what real address they have.

>2) There is no need to regulate the home IP address space.  All
>addresses are virtualized.  This gets us around the problem of multiple
>users behind the same NAT gateway when using L2TP or multiple users with
>the same internal address behind different NAT gateways when using

IMHO virtual addresses is the only proper solution.
Again: but ipsec doesn't handle virtual IP?

>Hope this helps - John

Sure. I will take a look at openvpn.
Thanks John.

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