Re: problem getting client to connect via pptpd

I'll back up James on that.  I probably have dozens of sites by now with various PPTP servers, some Poptop, some Windows behind my Linux firewalls.  By far, the absolute most common problem I see are routers in front of my clients that don't know how to deal with GRE.  In your case, it's a router in front of your PopTop server, but it's the same issue. 
 
Those home Linksys, Netgear, and others might be the worst culprits, although I also see this in many hotels and other corporate networks.  Some of them have a GUI to turn it on that actually works; many have a GUI that claims to turn it on but doesn't.  The pattern you'll see with tcpdump is, the client and server will go through a whole negotiation with TCP 1723, then one side or the other will send over a GRE packet.  (GRE - IP protocol 47).  So one side sends a GRE packet, but nothing comes back.  So it resends a few times and then the connection eventually drops after a timeout.  
 
That's why you want to watch everything coming from the remote site for troubleshooting.  Well, OK, filter out ssh if you're also connected that way, but capture everything else.  
 
- Greg
 

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