question on tunnels (VPN)

[Mikhail P.]

Dear users,

I have been experimenting with simple gif tunnels (no IPSec) in local network 
(192.168.0.0/24). I have used the following scenario between two hosts (both 
running FreeBSD-5.2.1):

HOST_A [192.168.0.1]:
ifconfig gif0 create
ifconfig gif0 tunnel 192.168.0.1 192.168.0.2
ifconfig gif0 10.0.0.1 10.0.0.2 netmask 255.255.255.255

and on -

HOST_B [192.168.0.2]:
ifconfig gif0 create
ifconfig gif0 tunnel 192.168.0.2 192.168.0.1
ifconfig gif0 10.0.0.2 10.0.0.1 netmask 255.255.255.255

The above works well for me, and I can send traffic on 10.0.0.1 and 10.0.0.2.

The next thing I wanted to implement is to create similar tunnel from our 
local router (which is FreeBSD too) to remote server, however there is small 
problem which stops me - router has no public IP, and it sees internet 
through DSL router, so basically that router is NAT'ed behind DSL router.
As far as I understand, it appears to be that I won't be able to create such a 
simple tunnel, unless my router gets public IP address.

What I tried next was MPD pptp link (which is known to work behind NAT, unlike 
above example), but something (ISP? DSL router?) cuts GRE packets on their 
way, so MPD can't establish LCP connection with remote host.

I'm now in loss as to what to try next - could someone please advise what 
other techniques will work in my scenario (where I want to connect machine 
which is behind NAT and no GRE packets will go through)?

regards,
M.