[ale] SSL-based VPNs (OpenVPN) vs IPSec

[Christopher Fowler]

Meet in the middle type negotiated is a problem.  Same reason I can't
simply use a tun device either.  For double NAT you need a client and
server model.  That is why I have to use SSL based Vtun

On Thu, 2005-02-24 at 21:31, Michael H. Warfield wrote:
> On Thu, 2005-02-24 at 20:48 -0500, Christopher Fowler wrote:
> > My #1 problem with IPSec is how it has to be used.  I have two devices
> > that needs a tunnel between them.  Both devices are behind a NAT
> > Firewall.  They do not have a public interface.  This is where IPSec is
> > useless.  IPSec requires that these devices have public interfaces.  In
> > my case I can only use a SSL based VPN like Vtun.  There are not any
> > other options.
> 
> > Maybe I'm wrong about IPSec but based on what I've read it can't be
> > natted.  It has to be on a public interface.
> 
> 	IPSec can be NAT'ed under a variety of circumstances.  Some devices
> actually attempt to NAT protocols 50 and 51 but this is highly
> unreliable.  A better option is IPSec NAT-T, which is IPSec over UDP,
> which is now supported by a released RFC.  What happens there is that
> BOTH IKE and IPSec AH/ESP get encapsulated in UDP on port 4500.  That
> fixes the single NAT case.  FreeSwan / Openswan / Stronswan all support
> IPSec NAT-T, as does L2TP on Windows XP.  If you have a double NAT case,
> I'm not sure how you would manage the "meet in the middle" negotiation
> issue.  How does OpenVPN handle it?  In the IPv6 world, we have critters
> such as Teredo which operate between two NAT'ed clients but it requires
> the mediation of a Teredo server on a public address.  I can see
> establishing a VPN tunnel (IPSec or SSL or IPv6) across clients that are
> each NAT'ed as long as you have a public "touch stone" where they can
> negotiate across a server.  But, one way or the other, the two NAT'ed
> clients have to establish their endpoints from behind those NAT devices.
> 
> > On Thu, 2005-02-24 at 18:54, Michael H. Warfield wrote:
> > > On Tue, 2005-02-22 at 15:06 -0500, M Raju wrote:
> > > > I have been thinking of playing with OpenVPN and convert my existing
> > > > setup at home which comprises of mainly an IPSec VPN for WiFi/External
> > > > access - OpenBSD Firewall/Access Point running (ISAkmpd), Racoon on OS
> > > > X and OpenSWAN for Linux.
> > > 
> > > > Anyone prefer SSL over IPSec? Found an interesting paper on OpenVPN Security -> 
> > > 
> > > > http://www.sans.org/rr/papers/20/1459.pdf
> > > 
> > > 	Personally, I would avoid an ssl based VPN like the plague.  There is
> > > no "perfect forward secrecy" or rekeying and the session keys can be
> > > determined from the PKI authentication keys (in other words, if you
> > > compromise the key from either end, you can decrypt the traffic, which
> > > is not the case with IPSec w/ PFS and Diffie-Hellman).
> 
> 
> > > > _Raju
> 
> 	Mike