[Openswan Users] Windows L2TP/IPsec tunnel mode configuration - howto?

[Andreas Kemper]

Hi,

I'd like to configure my Windows (XP SP2) box to use tunnel- rather than
transport-mode, which hopefully enables me to use Windows-VPN with my
NAT-passthrough router. The latter doesn't allow for proper NAT-T, which
otherwise would be a solution.

Thus I recently thought about changing mode for the Windows client, instead
of further trying to fix the UDP-checksum problem at the gateway. (It's
obviously caused by mismatching IPs during checksum calculation. Sending
L2TP UDP-packets from Windows the internal IP is used/taken for calculation,
while the OpenS/WAN gateway "sees" the external IP after decryption)

So well, any hints highly appreciated.

Andreas