I am trying to port forward for a VPN over PPTP. I've done this in the past by simply port forwarding TCP 1723; however, in my current situation it doesn't seem to be working.
What I have done:
-Enabled Routing & Remote Access on a Windows 2003 Server
-Tested the VPN connection inside the local network with success
-Port Forwarded TCP 1723 on the router
-Tested other port forwards on the router successfully (port 80, 443, etc)
-Attempted unsuccessfully to access from outside the router. I get to the Verifying Username & Password screen, but never any further. I would assume this shows that I'm having an issue with GRE 47, but I wasn't aware that I had to do anything to enable this protocol; moreover, on the firewall there is no option to enable this.
Any ideas?
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Okay, so the problem is that I'm not receiving the GRE 47 packets. As I suspected. The router is a symantec 360. It actually has a service pre-listed call VPN PPTP. That is what I used to do the port forward, but I guess it is not letting the GRE 47 protocol through.
I can't seem to find any PPTP passthrough options. I have fuond some IPSec passthrough options, but I know that doesn't help.
Any ideas?
Oh, I forgot to say, when I run pptpsrv on the server side I get an error.
Error 10048 binding Socket:
WSAEADDRINUSE: Address is already in use
Created socket for GRE protocol test
Listening on PROTOCOL 47 for incoming GRE packets...
--------------
So it would seem as though it is still listening for GRE packets right?
If it has a service you can forward, that probably looks after GRE. The problem may lie somewhere else.
Any chance there are 2 NAT (Network Address Translation) devices, such as a modem that is a combined modem and router? That can block GRE. If that is the case the modem needs to be put in bridge mode and the ISP connection configured on the router. If the WAN/public side of the router has a private IP the modem is performing NAT.
There are lots of other things that block GRE such as software firewalls, some anti-virus and such but you have tested locally so that would not be the case.
If stuck, double check with your ISP. A few block 1723, PPTP or GRE, in one way or another.
It's also possible the client location is blocking it. Out going is usually allowed/enabled, but not always.
Just to verify, when you say "tested from outside the router", you were off site, not on-site trying to connect to the external interface? Cannot connect to external IP from LAN side.
Not to desert you, but I won't be around for the next 8 hours. I will check back then.
Yes, tested outside the router was offsite. The symantec has a public IP so unless there is some weird config in the modem, it should be working bridged. He does have dual WAN connections to it so I'm going to have him unplug the second and retest just incase it is trying to come back out on a different line than I'm coming in on.
If that doesn't work I will contact the ISP and see was the deal is with the GRE. Thanks for the help!
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by: RobWillPosted on 2007-06-08 at 05:59:59ID: 19241487
On a few routers forwarding port 1723 also enables GRE, but not many. On many routers it is done by choosing "enable PPTP pass-through". On Netgear routers it is done by forwarding a service (PPTP) rather than the ports. The latter does both. On other routers, more commercial units, you have to allow or forward protocol 47 (not port 47), and still others such as Cisco require specific commands. I assume you are getting a 721 error.
Also keep in mind some routers, and a few modems and ISP's do not support PPTP/GRE.
There are a couple of tests you can do to check if port forwarding for PPTP is configured correctly and that GRE is allowed to pass.
To verify PPTP, port 1723, is forwarded; from the VPN server go to the following site and test for port 1723:
http://www.canyouseeme.org
Assuming that is working correctly, Microsoft has a pair of test tools pptpsrv and pptpclnt, to test for GRE pass-through, which are available as part of the Windows resource kit or from:
http://www.microsoft.com/d
Log onto the client or VPN server machine and connect to the other with remote desktop, or a similar remote management tool. At a command line on the client machine, run pptpclnt and on the server run pptpsrv. The client machine will send a set of GRE packets to the server and it should show as received if GRE is able to pass. The server is then supposed to respond and the client indicate received, but I have never had that part work. The one direction client to server is usually enough to test.
Following links outline the use of the test tools:
http://www.howtonetworking
See VPN traffic:
http://www.microsoft.com/t