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I've set up a VPN on a Debian (7.8) server. On a Windows 8 machine, I can set up a VPN connection to the server and it works fine for TCP applications. Everything is going through the VPN.

However, UDP applications don't work. They continue to go through the normal route instead of using the VPN. One such application is Mumble (it's a VoIP application using UDP.)

Is there a way to also get UDP applications to use the VPN?

My /etc/pptpd.conf file is:

option /etc/ppp/pptpd-options
logwtmp
localip 192.168.0.1
remoteip 192.168.0.100-200

My /etc/ppp/pptpd-options file is:

name pptpd
ms-dns 8.8.8.8
ms-dns 8.8.4.4
proxyarp
nodefaultroute
lock
nobsdcomp
noipx
mtu 1490
mru 1490

The iptables commands are:

iptables -t nat -A POSTROUTING -s 192.168.0.0/24 -o eth0 -j MASQUERADE
iptables -A FORWARD -p tcp --syn -s 192.168.0.0/24 -j TCPMSS --set-mss 1356
  • Have you ruled out a (static) routing problem? – CIA Jul 6 '15 at 13:03
  • @CIA Not sure what you mean. – Nikos C. Jul 6 '15 at 15:33
  • UDP and TCP is not distinguished to route differently unless you have specific IPTables rules in place. If you are able to get into the console/cmd/terminal on your VOIP server, can you do a traceroute to something on the VPN? Can something on the VPN traceroute to the VOIP server? If yes, then it's not a UDP/TCP issue. If no, then please provide a printout of your routes from a VPN server and VOIP server – CIA Jul 6 '15 at 15:49
  • @CIA I just had a facepalm moment. The VoiP server is running on the same machine as the VPN server... Ha ha. OK, huge brainfart on my part. At least I think that in this case, the VoIP client would not be VPNed and the server would see and report my real IP (from my ISP) rather than the IP assigned by the VPN (192.168.0.100). – Nikos C. Jul 6 '15 at 15:54
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OK, facepalm time. The issue is that the VoIP server (murmurd) is running on the same machine that runs the VPN server (pptpd).

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