pppt router to router stops working

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px03afk
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Joined: 09 Mar 2012
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PostPosted: Mon Apr 29, 2013 17:59    Post subject: pppt router to router stops working Reply with quote
I have two WNR3500L routers running DD-WRT V24 SP2 with two pppt VPN tunnels between them - one each way. Most of the time they work without any problems but every so often the traffic accross one of the tunnels simply stops happening. I can normally recover the situation by deleting the tunnel on the receiving end router.

Anybody else experienced this kind of problem?
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px03afk
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Joined: 09 Mar 2012
Posts: 95

PostPosted: Tue Apr 30, 2013 11:42    Post subject: Reply with quote
Sorry if I didn't provide sufficient information.

The problem, as I am seeing it, is that nothing is being dropped, as far as the server end of the connection is concerned the tunnel is still active and when I forcibly drop it the client end logs the fact that the server has dropped its end. What I appear to be seeing is that the tunnel is still up but it has stopped passing data across - and that data included regular traffic between machines I have on each end of the tunnels.

As far as how long the tunnels stay up, I've had both of them up for days on end without any apparent problem and then one of them will get stuck, I forcibly restart it and it will stick again within a few hours.

It is very unpredictable and from your reply it suggests that there are no know issues in this area.
px03afk
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Joined: 09 Mar 2012
Posts: 95

PostPosted: Mon May 20, 2013 17:19    Post subject: Reply with quote
I've found an added oddity as well. I have some Linux systems at each end of the VPN tunnel and they communicate with each other without any problems over the VPN (except when it goes down). I recently added some checks to make sure that the VPN was up. Originally the check was to ping the remote machine but then I decided I would change to a ping to the remote router but using it's LAN address, not WAN. Sure enough, the ping works OK in both directions but after some time (so far don;t know if there is a pattern to it), the ping starts failing but the VPN connection is still there and working for other traffic, including ping of the remote machine.

So, what is happening to the ping to the remote router LAN address?
px03afk
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Joined: 09 Mar 2012
Posts: 95

PostPosted: Wed May 22, 2013 21:08    Post subject: Reply with quote
Apart from standard logging, which I have sent to my servers, what other logging can I turn on for PPTP?
px03afk
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Joined: 09 Mar 2012
Posts: 95

PostPosted: Thu May 23, 2013 18:25    Post subject: Reply with quote
Thanks for the feedback. At the moment I've stopped using ping as frequently as I did when I first found this problem and I'm not seeing an issue at present. If it does start up again I'll look in to turning on more logging.

With regard to the possibility of outside influences, I'm not sure what could be changing as I would anticipate that both ends, once they've been established, remain static, at least as far as I know - I'm not making changes and I can't think of any obvious reason why anything else would be causing changes you suggest, but maybe that's because I don't fully understand what might be causing changes to NAT or other parts to be made.
px03afk
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Joined: 09 Mar 2012
Posts: 95

PostPosted: Mon Jul 08, 2013 17:29    Post subject: Reply with quote
Only just caught up with recent posting and thanks for the idea. I'll look carefully the next time the problem occurs and see if I can see if there is a change in the routing table.
px03afk
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Joined: 09 Mar 2012
Posts: 95

PostPosted: Sun Sep 15, 2013 16:54    Post subject: Reply with quote
I've not been able to find anything solid which causes the tunnel to collapse. What I have discovered is that under some circumstances 'vpn go' just drops out of operation and I have to recover it by running 'vpn start' but why it drops out I just can't see, although I have not turned on any additional logging.

Now that I know how to get it back I'm developing a Linux script to look when the link goes down and if necessary run 'vpn start' automatically.
px03afk
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Joined: 09 Mar 2012
Posts: 95

PostPosted: Sun Dec 29, 2013 13:23    Post subject: Reply with quote
I eventually completed a Linux script to check the state of the VPN connection and can now restart or start VPN automatically. What I find is that sometimes the VPN just collapses for no reason, sometimes it is still running but not responding and at other times it is not even running. Sometimes both ends go at the same time and at others only one end goes.

One thing I have found for sure though is that if the router renews its DHCP lease, the tunnel will still be up but it will not be responding.
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