I really stuck here (help me please ):

I'm trying to set a IPSec based VPN tunnel up.
Everything works till the point where data should be transmitted, so I get "IPsec SA established" on both linux boxes.

If I try to ping the destination host (any of them) I get 100% packet lost.

The ifconfig -i ipsec0 output looks like:
ipsec0 Link encap:IPIP Tunnel HWaddr
inet addr:195.222.10.67 Mask:255.255.255.192
UP RUNNING NOARP MTU:16260 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:4 overruns:0 carrier:0
collisions:0 txqueuelen:10
RX bytes:0 (0.0 b) TX bytes:0 (0.0 b)

The tcpdump on ipsec0 says:
16:56:43.686674 unknown ip 0
16:56:44.700074 unknown ip 0
16:56:45.700077 unknown ip 0
16:56:46.700063 unknown ip 0
16:56:47.710419 unknown ip 0

So all the packets get dropped by the ipsec interface. Any ideas?

Thanx in advance,

Sergej.

local boxes or over the internet?

over the internet RFC 1918 drops the private addresses

on a LAN
you have something else wrong

Well the external interfaces of the boxes use real IP-Addresses.
They are actually even in the same subnet just couple of meters away...

But I actually thought VPN can be used to connect two private networks, why is it dropping the packets than?

Thnx anyway :-)