PPTP Won't Connect

14 Nov 2006 6:59 PM

Hobby_Farm

I am tryping to set up a PPTP tunnel between 2 XP Pro hosts on the same
subnet (192.168.1.0). I have 3 different computers and the problem is the
same regardless of which ones act a clients and which ones act as servers
(i.e. they are set up to receive incoming connections). The client starts to
connect and then gives error 651 (I have read other posts on this but have
not seen any solutions). I put a protocol analyzer on the link (wireshark)
and I see the client starting the TCP handshake to port 1723 with SYN. The
server host responds with a SYN ACK and then the client sends the PPTP
start-control connection request message. At this point the server seems to
hang. It does not acknowledge receipt of the PPTP message and sends another
SYN ACK as if it only received the opening SYN. The client resends the PPTP
message and the server again sends a SYN ACK. This continues until the
client times out and gives the 651 error message. I have a decode file which
I will be happy to send if it helps but this one has me stumped. As I said I
have tried this with various combinations of clients and servers and the
result is always the same. Any help would be appreciated.

15 Nov 2006 5:12 PM

Robert L [MVP - Networking]

Please use pptpsrv and pptpclnt to test GRE and PPTP. Post back with any errors.

VPN troubleshooting toolsVPN Troubleshooting Tools. 1. PPTPclnt and PPTPsrv to test GRE and PPTP. 2. IPCONFIG to troubleshooting connection and name resolution issues ...
www.chicagotech.net/vpnissues/vpntools.htm

Bob Lin, MS-MVP, MCSE & CNE
Networking, Internet, Routing, VPN Troubleshooting on http://www.ChicagoTech.net
How to Setup Windows, Network, VPN & Remote Access on http://www.HowToNetworking.com

"Hobby_Farm" <Hobby_F***@discussions.microsoft.com> wrote in message news:F7475AB4-3988-44B7-9B35-42BB5DFC4A7A@microsoft.com...

I am tryping to set up a PPTP tunnel between 2 XP Pro hosts on the same
subnet (192.168.1.0). I have 3 different computers and the problem is the
same regardless of which ones act a clients and which ones act as servers
(i.e. they are set up to receive incoming connections). The client starts to
connect and then gives error 651 (I have read other posts on this but have
not seen any solutions). I put a protocol analyzer on the link (wireshark)
and I see the client starting the TCP handshake to port 1723 with SYN. The
server host responds with a SYN ACK and then the client sends the PPTP
start-control connection request message. At this point the server seems to
hang. It does not acknowledge receipt of the PPTP message and sends another
SYN ACK as if it only received the opening SYN. The client resends the PPTP
message and the server again sends a SYN ACK. This continues until the
client times out and gives the 651 error message. I have a decode file which
I will be happy to send if it helps but this one has me stumped. As I said I
have tried this with various combinations of clients and servers and the
result is always the same. Any help would be appreciated.

15 Nov 2006 6:50 PM

Hobby_Farm

Thanks for the help. I was not aware of those tools. I ran pptpsrv and
pptpclnt between 2 XP hosts and the test shows that both connectivity and gre
encapsulation are working. To do this I first had to remove the "Incoming
connections" on the host acting as the server. When I reinstalled the
"Incoming connections" and tried to connect normally I got the same problem
as before. I am running the protocol analyzer on the host acting as the VPN
server and I can see the PPTP Incoming connection request packet arriving. I
checked it against RFC 2637 and it looks properly formed. The server just
does not respond to it. It is as if TCP is not passing the information up to
the application.

Show quoteHide quote

"Robert L [MVP - Networking]" wrote:

> Please use pptpsrv and pptpclnt to test GRE and PPTP. Post back with any errors.
>
> VPN troubleshooting toolsVPN Troubleshooting Tools. 1. PPTPclnt and PPTPsrv to test GRE and PPTP. 2. IPCONFIG to troubleshooting connection and name resolution issues ...
>       www.chicagotech.net/vpnissues/vpntools.htm
>
>
> Bob Lin, MS-MVP, MCSE & CNE
> Networking, Internet, Routing, VPN Troubleshooting on http://www.ChicagoTech.net
> How to Setup Windows, Network, VPN & Remote Access on http://www.HowToNetworking.com
>   "Hobby_Farm" <Hobby_F***@discussions.microsoft.com> wrote in message news:F7475AB4-3988-44B7-9B35-42BB5DFC4A7A@microsoft.com...
>   I am tryping to set up a PPTP tunnel between 2 XP Pro hosts on the same
>   subnet (192.168.1.0). I have 3 different computers and the problem is the
>   same regardless of which ones act a clients and which ones act as servers
>   (i.e. they are set up to receive incoming connections). The client starts to
>   connect and then gives error 651 (I have read other posts on this but have
>   not seen any solutions). I put a protocol analyzer on the link (wireshark)
>   and I see the client starting the TCP handshake to port 1723 with SYN. The
>   server host responds with a SYN ACK and then the client sends the PPTP
>   start-control connection request message. At this point the server seems to
>   hang. It does not acknowledge receipt of the PPTP message and sends another
>   SYN ACK as if it only received the opening SYN. The client resends the PPTP
>   message and the server again sends a SYN ACK. This continues until the
>   client times out and gives the 651 error message. I have a decode file which
>   I will be happy to send if it helps but this one has me stumped. As I said I
>   have tried this with various combinations of clients and servers and the
>   result is always the same. Any help would be appreciated