I have been having trouble with VPN on my router, so I thought that since it allowed VPN Pass-through, I would set up a VPN server on an Ubuntu box here, and pass through to that.
I have set up PPTP, and all works as expected, but for better security I wanted to set up L2TP/IPSEC.
In testing it all on the local lan, I can connect to the VPN server with an L2TP/IPSec connection. But when I try to come in at it externally it times out with not a great many clues, some, just not ones line "Fix that bit....fool"
The pieces of Log I can find (/var/log/auth.log) only show that the main diff between successful local connection and unsuccessful remote connection seems to be that it notices there are more NAT hops involved in the external attempt. Which is correct of course, and I have made sure that the vigor has the correct NAT'd ports for the VPN (When I disable them I see no connection to the internal VPN server, so I am somewhat positive it's correct)
Both attempts have it "establishing a transport mode", then the remote one gives up after a timeout, and the next thing it says is that it's deleting the payload, and then something way more cryptic ...
ERROR: netlink XFRM_MSG_DELPOLICY response for flow eroute_connection delete included errno 2: No such file or directory
and then a series of other delete related commands come up, and it's all over.
Here are the logs, of a successful local(same Lan) connection, and a failed remote (completely different lan) attempt.
Successful: https://dl.dropboxusercontent.com/u/7577481/Log1-successful_SameLan.txt
Unsuccessful: https://dl.dropboxusercontent.com/u/7577481/Log3-unsuccessful_FromExternal.txt
