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VPN error 800 - way of testing if access blocked by firewall or something

Posted on 2013-11-04
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Last Modified: 2013-11-04
Hi,
We have a Draytek 2830 onsite that is used as the VPN server which remote users have been able to connect into fine for months. This morning suddenly all users gets error 800.

There is another company that manages the internet connection and state that nothing has changed.
As far as we know the router under our control nothing has changed.
We have not actually restarted the router yet, which most likely (hopefully will resolve it) but as this will bring everyone in the office down for a short while want to avoid it.

Is there anyway of doing a test to ensure that a firewall someone is not blocking the VPN ports?
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Question by:afflik1923
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by:Ernie Beek
ID: 39621296
You could try a site like grc (shieldsup!) from behind your router to see if the correct ports are open: https://www.grc.com/x/ne.dll?bh0bkyd2
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by:Ernie Beek
Ernie Beek earned 500 total points
ID: 39621313
Thinking of it, grc only scans ports (TCP/UDP). For VPN to work you will also need protocol 47 to pass through (GRE).

Depending on your skills, you could try and use something like nmap for that (scanning from the outside): http://www.networkuptime.com/nmap/page3-11.shtml
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Author Comment

by:afflik1923
ID: 39621371
Remote reboot of router solved it with only minimal non noticed downtime to network.
VPN worked after that, but I would still be interested to know if there is a way for future reference.
E.g. like when you Telnet port 25 to check if mail server settings OK.
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Accepted Solution

by:
Ernie Beek earned 500 total points
ID: 39621419
Partly you could check with a telnet to port 1723 (PPTP: Point-to-Point Tunneling Protocol ). If that ports down, VPN will not work. But then, the VPN also uses a different protocol: GRE, protocol number 47 (like TCP is protocol number 6 and UDP is number 17). To check that you need something like the above stated nmap. Or use a tool like PRTG (http://www.paessler.com/router_monitoring) to monitor the draytek.

-edit-

Looks like draytek has some monitoring solutions of it's own: http://www.draytek.co.uk/products/SmartMonitor.html
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Author Comment

by:afflik1923
ID: 39622769
Smart monitor looks great. Downloading this now. Could be very useful indeed.
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Author Closing Comment

by:afflik1923
ID: 39622807
Smart Monitor needs a server etc, but definitely something I'm going to explore in the future. Looks very interesting.
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