"Error 678 the remote computer did not respond" VPN outside a firewall.

I shall try and be as detailed as possible.

Windows Server 2003 SBS R2 Standard (non-isa)
- Inside a Netgear DG834 Wired router on ADSL.
- 1701, 50,51, 500, 4500 ports forwarded too the server.
Windows XP SP2 Laptop client on a remote network
- Inside a Linksys Router.

2003 server setup for L2TP/IPSEC VPN with computer/user certificate
authentication.

Tested VPN inside the SBS network - works fine.....

Outside the network you get "Error 678 the remote computer did not respond"

Microsoft Network Monitor 3.1 is installed on the server and on the client
to troubleshoot this.

You can see the client sending data on UDP 500 and UDP 4500 towards the
server.
You can see the server receive data on UDP 500 and UDP 4500.
You can see the server send data on UDP 500 and UDP 4500
You can then see the client recieve data on UDP 500 and UDP 4500

No other ports show up, whist some traffic is clearly flowing I still get:
Error 678 the remote computer did not respond.

Any ideas?

I also found this in the SBS event log:

Security 547 11/27/2007 15:52 3 *
IKE security association negotiation failed. Mode: Key Exchange Mode (Main Mode) Filter: Source IP Address 10.20.1.X Source IP Address Mask 255.255.255.255 Destination IP Address 86.16.184.XX Destination IP Address Mask 255.255.255.255 Protocol 0 Source Port 0 Destination Port 0 IKE Local Addr 10.20.1.2 IKE Peer Addr 86.16.184.XX IKE Source Port 4500 IKE Destination Port 0 Peer Private Addr Peer Identity: Certificate based Identity. Peer IP Address: 86.16.184.XX Failure Point: Me Failure Reason: Negotiation timed out Extra Status: Processed second (KE) payload Responder. Delta Time 64 0x0 0x0

Ok solved it myself. But hope this helps someone!

Instructions for Vista
http://support.microsoft.com/kb/926179

Instructions for XP SP2
http://support.microsoft.com/default.aspx?kbid=885407

Hello Rbansk, in case you have configured SBS003 as L2TP VPN server using RRAS then just try going through the following steps and see if it works for you:

• Take a cross over cable, attach the same to laptop directly to the server's external NIC and try to create VPN. Are you able to see the successful connection?
  
  
• After this you need to rerun CEICW wizard which will help you fix the network related issues.
  
  
• If still you getting some problem the visit VPN with both PPTP and L2TP IPsec, can this be successfully?

if you read the posts above yours, you would know I resolved the problem.