Error trying to VPN using WAN Miniport L2TP

drest
drest used Ask the Experts™
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Unable to connect using Windows 7 VPN to Windows Server 2003.  I get several messages.  First message is "Verifying Password...", second message "connecting to ip using WAN Miniport (SSTP)', third message connecting to ip using WAN Miniport PPTP,  then last message "Connecting to  IP using "WAN Miniport (L2TP)...Error 800...".  This used to work up until that last few days.  No changes have been made to the network or configuration settings on either side (Client or Server including the PIX Firewall).  any ideas?
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Qlemo"Batchelor", Developer and EE Topic Advisor
Top Expert 2015

Commented:
diprajbasu,
Please don't post just links, and in particular if they only lead to a list of threads not directly related.

drest,
Do you know which one of those protocols have been used actually to connect when it succeeded? It's important since the diagnostics differ for PPTP and L2TP (we can forget about SSTP - not supported with W2003).

Author

Commented:
Genius, i do not know which used to work.  It has been working for over months.  

The only change that was made recently on the network was a local switch went bad (1 of the 2) and had to connect about half the  local workstations to an old backup switch.  The switches are unmanaged.  The Pix and the server are unaffected as the are/were connected to the 1 working existing switch.  No other changes have been made to the network.
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Qlemo"Batchelor", Developer and EE Topic Advisor
Top Expert 2015

Commented:
I agree the switches are not part of the issue. However, there has to be a change somewhere. Look into your server's event log - maybe it's the server's fault. But it could also be a lost or changed setting on the Cisco (about forwarding the necessary ports).

Author

Commented:
Spent the last few hours toubleshooting this.  Got it to work, but don't know exactly why.  Inserted a couple of switches to help me troubleshoot. Bypassing the modem, the pix firewall, and tried several scenerios.  One time i was connected to the VPN and simply reconnected the Modem (DSL) and it immediately brought down the VPN connection.  Logged onto the Modem and saw nothing that would interfere with the VPN (no firewall, everything port forwarded).  Then reconnected bypassing everything but the modem, the pix, and the server...and whalla, i was able to connect.  reconnected everything the way it was originally and the VPN now works.  I do not have any clue as to why it is working!   Maybe the sequence of when the devices are brought up/attached?  Unexplainable!  
Qlemo"Batchelor", Developer and EE Topic Advisor
Top Expert 2015

Commented:
There seem to be too much factors in the equation to really determine what is happening.
Now that the VPN is working, you should take note of whether it is PPTP or L2TP. If you cannot determine it otherwise, just issue a    netstat -an | findstr "1701 1723 500 4500"    to list the ports used.

Author

Commented:
It is PPTP.
Qlemo"Batchelor", Developer and EE Topic Advisor
Top Expert 2015

Commented:
Oy - many, many things can go wrong then. GRE, which is used for encapsulation, is a flaky protocol when crossing NAT devices.
I would wait for at least one day to see whether the effect is retained. If the connection breaks again, I'm afraid nothing else then logging the traffic on at least three locations (client, your router, and server) helps. That is the only way you can make sure you know enough about what is happening (or not).

Author

Commented:
it broke again!
"Batchelor", Developer and EE Topic Advisor
Top Expert 2015
Commented:
We had that with our smart firewall device (Juniper SSG) applying a PPTP application layer gateway, which allows for using more than one PPTP connection in- or outbound with the same public IPs in a double-NAT scenario (ouch). Depending on the GRE session number, or anything exchanged different each time on connection initiation, the connection works or does not. It is random. Yours might be a similar issue.
The official answer for using PPTP behind NAT devices is to use an own public IP per remote target. In your case, if you have an IP address block assigned by your ISP, you can use a different IP for PPTP, and forward that to the W2003 server. That might help, but we cannot know, since we both have no hint yet what really breaks the connection.

Author

Commented:
Thank you for your comments.  it turned out to be the switch.  Since it was the only change, i relaced with a new switch and things began to work again.
Qlemo"Batchelor", Developer and EE Topic Advisor
Top Expert 2015

Commented:
If the switch is a routing one (L3 Switch), that can explain the failure. If not, I was totally off, and should not get points.

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