[Solved] PPTP VPN connects but no internet access

hughw94 · 2017-04-13 15:44:40

I am using NetworkManager with the pptp plugin to connect to my university VPN which uses MSCHAPv2 and MPPE. I have configured all of the settings identicaly to another laptop which runs Ubuntu and successfully connects but when I use my Arch install the VPN connects but there is no internet access. Instead a pptpgw process shoots up to >50% CPU usage. I ave attempted a fresh arch installation but it has not helped, neither has using pptpclient rather than NetworkManager.

tcpdump -n -i ppp0

Reveals a huge volume of outgoing compressed ppp data is being sent from my PC:

 16:40:57.223961 IP 192.168.0.11 > xxx.xxx.xxx.xxx: GREv1, call 52096, seq 410983, length 252: compressed PPP data

Any ideas on how I can troubleshoot the issue? I have looked through the wiki but to no avail, from what I have seen it may be a routing problem but I am unclear on how to proceed on this front. I have connected to this VPN previously from previous Arch installs and it has worked.

Last edited by hughw94 (2017-04-14 11:59:30)

R00KIE · 2017-04-13 16:43:46

Check routing table is correct after you successfully connect and also look into connection tracking helpers, if you have configured a firewall in your machine you probably need to either enable automatic helper assignment or assign the pptp helper manually.

hughw94 · 2017-04-13 16:57:12

I don't currently have a firewall configured, does that mean I can exclude connection tracking helpers as the cause? What I don't really understand is why this has become neccessary as the VPN previously worked without changing route settings etc.

I am really struggling to understand where to begin with the routing as it is a new concept too me and the wiki articles are a little over my head.

Last edited by hughw94 (2017-04-13 17:11:46)

R00KIE · 2017-04-13 20:23:02

If you are sure there is no firewall configured I suppose conntrack helpers can be excluded.

I just said to check the routing table, it doesn't mean you have to change it. You can compare between a system that works and one that doesn't. Another thing that might be a problem is the tunnel mtu size, so you might want to also check that.

If you want more specific tips/help you will have to provide more details, such as vpn configuration files (exclude usernames and passwords obviously), routing table, any relevant logs and any other information you may think is relevant.

hughw94 · 2017-04-14 11:58:28

Thank you very much for your help with this issue. After comparing my routing table with a working install added some routes to in a script in /etc/ppp/ip-up.d/01-routes.sh as described in the pptpclient wiki article. This seems to have solved the issue for the moment, not really sure why this has occurred but hey-ho!

/etc/ppp/ip-up.d/01-routes.sh

#!/bin/bash

# This script is called with the following arguments:
# Arg Name
# $1 Interface name
# $2 The tty
# $3 The link speed
# $4 Local IP number
# $5 Peer IP number
# $6 Optional ``ipparam'' value foo

ip route add default dev ppp0  proto static  scope link  metric 50
ip route add 193.xx.xx.xxx via 192.168.0.1 dev wlp13s0  src $4 
ip route add 193.xx.xx.xxx dev ppp0  proto kernel  scope link  src $5  metric 50

My only remaining question is if the IP beginning 193.xx.xx.xxx likely to change in the future and thus make my script defunct? Is there some way that I can call it as an argument?

R00KIE · 2017-04-14 14:06:02

I don't have much experience with pptp vpns but I'd say a sane routing table (or additions/modifications to routing table) should be done automatically. If this works without a problem in another distro you probably want to compare the versions and configurations of your network managers. If the configurations are similar you will want to check the release notes of the one that doesn't work and see if some previous automatic behavior has been changed.

ReiserFS · 2017-04-17 11:22:42

I updated my system today. I think I also have this problem and that's because pptp doesn't add host route. It worked before. pptp has a --nohostroute option but no --hostroute. Is this a bug?

Last edited by ReiserFS (2017-04-17 11:35:39)

Arch Linux

#1 2017-04-13 15:44:40

[Solved] PPTP VPN connects but no internet access

#2 2017-04-13 16:43:46

Re: [Solved] PPTP VPN connects but no internet access

#3 2017-04-13 16:57:12

Re: [Solved] PPTP VPN connects but no internet access

#4 2017-04-13 20:23:02

Re: [Solved] PPTP VPN connects but no internet access

#5 2017-04-14 11:58:28

Re: [Solved] PPTP VPN connects but no internet access

#6 2017-04-14 14:06:02

Re: [Solved] PPTP VPN connects but no internet access

#7 2017-04-17 11:22:42

Re: [Solved] PPTP VPN connects but no internet access

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