VPN Error 732

[PaulD]

Hi all,

I've set up a small office with 4 peer to peer networked computers with one having all the shared data on it. XP Pro all round. It has an ADSL2 connection via a Belkin F5D5730au Modem and Linksys WRT310N Router.

I've set up a Windows VPN server on this main computer for the clients to access the shared files from home.

From my workshop using a laptop running XP Pro I can connect to the VPN in less than a second and can browse the folders, use remote desktop etc.

My setup is a cable broadband modem Motorola Surfboard SB5101i and Dlink DIR-615 router.

When I take exactly the same laptop over to the client's house and plug it into their Siemens Speedstream 4200 ADSL Modem (I've taken their router out of the equation) I can connect to the internet, the VPN connection connects to the ip address and hangs on Verifying User Name and Password.and then we get this:
Error 732: Your computer and the remote computer could not agree on PPP control protocols

When I first set up their VPN access it worked for about 3 days but now it gets the above error every time. Nothing I can think of changed.

I've run wireshark on my connection and their failed connection and compared the captures and the only difference is that on the successful connection we get:
Transmission Control Protocol, Src Port: aplx (1134), Dst Port: pptp (1723), Seq: 0, Len: 0
and on the unsuccessful connection we get:
Transmission Control Protocol, Src Port: ff-sm (1091), Dst Port: pptp (1723), Seq: 0, Len: 0

The unsuccessful connection holds up at the next stage which is Configuration request for the PPP LCP Protocol. It always is rejected.

I'm afraid I don't know what a ff-sm Port is. Could anyone suggest whether this is where it is going wrong and what I might be able to do to fix it?

Thanks very much,

PaulD

[crypto7]

Check the PPTP passthough.

You will need TCP port 1723 (as you can see in the wireshark sniff) and also GRE (IP Protocol 47)

TCP Port 1723 is used to establish a link, then GRE is the tunnel that takes over for the actual data exchange.

Based on a quick test, you should see something like this in wireshark
Client : A
Server : B
A->B SYN to TCP 1723
B->A SYN ACK
A->B Start-Connection Request (TCP 1723)
B->A Start-Connection Reply
A->B Outgoing-Call-Request (TCP 1723)
B->A Outgoing-Call-Reply
All the above was on TCP 1723

Next happens on IP Protocol 47 GRE (note this will apear as PPP in wireshare)

A->B A series of PPP LCP Config. request/acks/rejects
B->A replies....
.... Username/password things
Then some CCP and IPCP request acks/naks.

You will also see the TCP 1723 packets from time to time. These will be session keep-alive messages.

So if you dont see the username password, then have a close look at the sniff and see if there is any gre traffic.

[PaulD]

Thanks for the info crypto7,

As it turns out, I returned to the client's house last night and found the VPN now works without me doing anything (else).

I'm putting it down to a faulty modem and will replace it if it happens again.

Thanks again.