freebsd vpn server behind nat dsl router

[VANHULLEBUS Yvan]

On Wed, Mar 07, 2007 at 09:59:44AM -0600, Robert Johannes wrote:
> Hello Greg,
> I am writing you, because I saw your responses to a couple of messages on 
> the freebsd-security mailing list related to freebsd vpn and nat.

Well, I'm not Greg, but hi, and here are some informations :-)


> My situations is rather unique, and I am needing an expert's eyes to 
> glance at it and confirm whether it is doable or not.  I have a simple 
> diagram that illustrates what I am trying to do, and it is located here 
> (about 40k): http://www.hamline.edu/~rjohanne/lan.jpg

I'm not sure I understood exactly what you want to do, but I think
your setup is really common.


> In the diag, the dsl modems have dynamic public ips on the internet side, 
> and private ips on the lan side.

If both DSL modems have dynamic IPs, you'll have a first problem:
being able to know the correct IP of your peer, then a second problem:
being able to detect when peer's IP change.

I'll consider you are able to do that.


> As you can see in the diag, I am trying to have the vpn traffic from the 
> internet forwarded to the Freebsd vpn (the machines ending in .254 on each 
> site).  I have followed the Freebsd "VPN over Ipsec" in the handbook, and 
> created a tunnel between the two vpn servers; according to the handbook, I 
> should be able to ping the vpn servers using their private network 
> addresses, but I am not able to do that.  I realize that my implementation 
> is not exactly like the handbook's, but what do I need to do to get it to 
> work?  I have googled, and researched all over the net without much 
> progress.
> 
> I have seen a lot of messages related to nat and enabling vpn passthrough 
> on different dsl modems and so forth, which I have tried to do, but still, 
> no progress.

Some informations:

- FreeBSD handbook talks about Gif interfaces for IPSec tunnels. Just
  forget that part and use directly IPSec tunnels without Gif
  interfaces.

- You'll probably need NAT-T support so your VPN tunnel will be more
  likely to work (well, it may work without NAT-T, but it is more
  complex and needs lots of constraints between both FreeBSD gates).
  Make a quick seach on freebsd-net, get the kernel patch from
  http://ipsec-tools.sf.net/freebsd6-natt.diff, recompile your kernel
  with NAT-T support, reinstall your world, then recompile/reinstall
  ipsec-tools port.

- When your tunnel will be up, you'll probably want to lower the
  TCPMSS for traffic which goes through the tunnel, but this is
  another story :-)



Yvan.

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