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PPTP or L2TP VPN-in stopped connecting

Dabbler
Posts: 10
Thanks: 1
Registered: ‎09-04-2019

PPTP or L2TP VPN-in stopped connecting

Hi,
I've used a Hub One to connect to Plusnet fibre for a few years now and could reliably VPN in from my mobile phone to my server2019 machine for ages.
Either PPTP or L2TP worked a treat, and let me do the odd thing from my mobile while out or at work.

I can't remember when exactly but, maybe as far back as January or February, it just stopped connecting.
I've been working from home since December so it wasn't too much of a problem. Going back into the office is being talked about though and I'd really like this to be usable again.

The best I've been able to get since is windows at the server end logging:
A connection between the VPN server and the VPN client *mobile's IP* has been established, but the VPN connection cannot be completed. The most common cause for this is that a firewall or router between the VPN server and the VPN client is not configured to allow Generic Routing Encapsulation (GRE) packets (protocol 47).

I've tried from various devices, using various different internet connections and all seem similar.. something does get to the server but the VPN wont connect.

I've tried disabling the windows firewall on the server, firewall on the router, the PN firewall service and putting the server in the DMZ but nothing improves.
I've reset the router and re-set various combinations of port-forwards.

The server has a static internal IP set in both windows and the router, that's outside the routers DHCP range.
I've restored a disk image of the server machine back to when I first installed the OS and I know it worked, and still get the same.
Port forwards for other services I have running on the same server do work OK.
If I put my mobile on the routers wifi and switch the VPN from my external IP to the servers local IP, it connects just fine.

I cant only think it's something about either the router or PN service, but I don't know what.


Can anyone spot anything I've missed and could try please? Or is there anything about my service I could see if support could try?

I see various posts about certain IP ranges having similar trouble. Is 31.185.* known to be a problem?

Thanks a lot!

9 REPLIES 9
Dabbler
Posts: 10
Thanks: 1
Registered: ‎09-04-2019

Re: PPTP or L2TP VPN-in stopped connecting

Had another look this morning and after just restarting my modem, router & server I saw a PPTP VPN connect for the first time in months.

I hadn't changed the way anything was set since it last failed, just restarted everything.

I couldn't really believe it, and wanted to make sure it wasn't some kind of fluke. I restarted everything again and it broke again. Now it's just teasing me!

I'm back to getting event ID 20209 & 'The most common cause for this is that a firewall or router between the VPN server and the VPN client is not configured to allow Generic Routing Encapsulation (GRE) packets (protocol 47).'

 

I made no change to any setting and powered things on in the same order/way both times (modem>router>server).

Since, I've retried everything as above, disabled firewalls, removed and recreated port-forwards, restored known working install of the server. None get it to connect again.

Newbie
Posts: 2
Registered: ‎22-11-2020

Re: PPTP or L2TP VPN-in stopped connecting

Hi, 

Did you ever figure out a solution to this one, as that's what I'm getting now. 

Thank you

P

 

Dabbler
Posts: 10
Thanks: 1
Registered: ‎09-04-2019

Re: PPTP or L2TP VPN-in stopped connecting

I'm afraid haven't.

I'll post if I do.

 

 

 

Superuser
Superuser
Posts: 9,133
Thanks: 2,218
Fixes: 159
Registered: ‎30-07-2007

Re: PPTP or L2TP VPN-in stopped connecting

Hi @mad_tunes 

I see various posts about certain IP ranges having similar trouble. Is 31.185.* known to be a problem?

There do seem to be problems with some VPN servers and certain IP ranges although this is generally believed to be due to erroneous geolocation on corporate systems. That doesn't appear to be the case in your situation. If I understand it correctly, you are running the VPN server at home and attempting to connect from outside, is that correct ?

Do you happen to know if your public IP had changed when you were able to connect, and if so what range was it ?

 

Newbie
Posts: 2
Registered: ‎22-11-2020

Re: PPTP or L2TP VPN-in stopped connecting

Hi @MisterW 

Thanks for the insight. 

I'm trying to connect to a customer's VPN server, from my machine (via Plusnet).  It has worked in a previous incarnation of Windows, but not this one.  I have had to restart the router a couple of times (seemingly standard procedure with these, as the connection becomes unusable).  I didn't think to look at the public IP address.  

I might be able to find a record of the public IP addresses before and after the router restarts. 

Many thanks

Patrick

 

Aspiring Champion
Posts: 1,545
Thanks: 483
Fixes: 5
Registered: ‎25-07-2007

Re: PPTP or L2TP VPN-in stopped connecting

Superuser
Superuser
Posts: 9,133
Thanks: 2,218
Fixes: 159
Registered: ‎30-07-2007

Re: PPTP or L2TP VPN-in stopped connecting

@bumblebeeworks

I'm trying to connect to a customer's VPN server, from my machine (via Plusnet)

That is different to the problem that @mad_tunes seems to be having. Yours looks more like the normal problem of the remote server not accepting connections due to believing the public IP is not in the UK.

Dabbler
Posts: 10
Thanks: 1
Registered: ‎09-04-2019

Re: PPTP or L2TP VPN-in stopped connecting

Hi @MisterW 

 

"you are running the VPN server at home and attempting to connect from outside, is that correct"
Correct

My IP has changed since I first saw the problem, but VPNing-in still fails in the same way.
I've currently got 31.125.. so I don't think this is due to the issues with 31.185.* that I'd read about, unless those issues are more wide-spread.

 

I have since found it's only an issue when using my mobiles internet connection though, on 3UK. The only device I really want to VPN-in with, typical. If I put the same phone using the same VPN details on a friends wifi, the VPN connects OK.

I've asked 3 to look into it but aren't all that hopeful tbh. My contract with thems up for renewel before very long, if this still isn't going then it may well be a reason to change provider.

 

I'd still really appreciate any input from the plusnet side of things if pos though, as I guess the issue could still be plusnets rather than 3s. Being able to confirm either way would be great if there's any way.

Is there a way to trace traffic that's destined for my IP, inside plusnets network, before it's got to my router? That might show if GREs even getting from my phone to plusnet..?

All Star
Posts: 731
Thanks: 225
Fixes: 24
Registered: ‎19-11-2008

Re: PPTP or L2TP VPN-in stopped connecting

Hi
Mobile networks use Carrier Grade NAT so are not fully routable.
I suspect the problem is that the VPN server traffic cannot route the data back to the mobile.
Three is unusual in that they have two different APNs one uses CGNAT the other provides routable addresses.
I would recommed a better VPN protocol like OpenVPN or wireguard which do not have these problems.
I have both running on Raspberry Pis and have no problem with either over Three or Vodafone.
Regards
Richard