Error 721 when VPN

Posted on 2006-06-09
Last Modified: 2010-05-18
I have a laptop that I use at work and I created a VPN connection to access my network drives, but it doesn't work, I get error 721 Remote not responding. Everyone else can connect using VPN and I can connect when I am at home using my desktop computer. Why do I get this error on the laptop? I tried so many things, I recreated the connection, I made sure that I have the PPTP VPN in the Networking Tab, I added UDP port 500 in the firewall exceptions. I have Windows XP Professional SP2. Can you please help? Thanks.
Question by:Bob Macpherson
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Expert Comment

by:Rob Williams
ID: 16874879
You are saying you can connect from home with the desktop computer but not with the laptop from the same physical location ?
Are you using a wired connection or wireless ? If wireless try a wired connection.
The Windows firewall should not block the outgoing traffic, but regardless PPTP uses TCP port 1723 not UDP 500, that is part of an IPSec VPN configuration. PPTP also requires GRE, protocol 47 (not port 47), but again the Windows firewall should not block that. Try disabling the firewall altogether as a test. Also disable any other software firewalls such as ZoneAlarm, or Symantec. If you have Symantec virus protection, disable the "Internet Worm Protection" feature. One final thing is many routers will only support 1 VPN tunnel. Make sure you do not have it enabled on the PC at the same time.

For the record a 721 error usually indicates the GRE traffic is being blocked somewhere.

Author Comment

by:Bob Macpherson
ID: 16878686
Right now I am in Seattle at a Conference. I tested this laptop before I left Chicago and I could VPN with no problem. I asked those people and the Convention Center and they say that their firewall is not interfering. We have cable network here and I can open the Internet browser and I'm on the internet, I can even telnet and ping my office but I cannot VPN from here. It puzzles me, and I don't get it... what is wrong?
LVL 77

Accepted Solution

Rob Williams earned 500 total points
ID: 16879465
Are you getting the same 721 error?

At the conference if they have multiple routers between you and the Internet you may not be able to connect. Also though they may not be blocking anything they may not be enabling PPTP/GRE pass-through. And the other option is many routers only support a single PPTP pass-through tunnel.
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Author Comment

by:Bob Macpherson
ID: 16886427
Is there anything I can tell them to do so I would not get error 721 anymore?
LVL 77

Expert Comment

by:Rob Williams
ID: 16886480
You could ask them if they have a "Enable PPTP-Pass-trough" option, but depending on the make it may be more involved than that, and their actual physical network may not support it.

Author Comment

by:Bob Macpherson
ID: 16886541
Thanks so much!
LVL 77

Expert Comment

by:Rob Williams
ID: 16886600
Very welcome. Thank you. Good luck with it.

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