I've set up an L2TP server on a Mikrotik/Routerboard RB750 (PPPoE ADSL connection). Everything seems to be OK, I'm using a pre-shared key. I've configured the Firewall/Filter Rules to allow UDP 500,1701,4500 and protocol 50.
I can connect to it with the two Win7 machines in my home office (different ADSL connection)... but not with my WinXP laptop which is on the same network as the Win7 machines.
The WinXP machines stay in the "Connecting to xxxxx..." phase and eventually time out with a error message. "Error 792: The L2TP connection attempt failed because security negotiation timed out."
I can see the connection attempt appearing in WinBox IP/IPSEC/Remote Peers...
I thought it might have been something in the laptop that was causing the trouble... but if I use my Huawei 3G USB "modem" to connect my laptop to the internet, it works fine and I can connect to the L2TP server and access the internal network via the L2TP connection.
Both WinXp machines at my work (NAT'd ADSL) also cannot connect to the Mikrotik L2TP server, but a Win7 computer belonging to a customer works fine using the same network and ADSL/router connection.
Does WinXp need some "changes" to be made that Win7 does not? What is stopping the WinXP machines behind a NAT router from connecting?
**edit** It appears that if my WinXP laptop is on the LAN side of the Mikrotik RB750 and I "aim" the L2TP connection at the internal IP address, it connects to the L2TP server OK.