PPTP connection: Timeout sending config requests when in eduroam network

Question

trying to connect to a pptp-vpn from within my university network ('eduroam' standard). connection cannot be established (LCP: Timeout sending Config-Requests). The connection works flawlessly from any other network. I cannot check the logs on the server's side.

I can connect to port 1723 via telnet.

I provide logs both for successful connection attempts (at home, DSL) and unsuccessful ones (at university); additionally some information about my connection at university (netctl connect profile, ifconfig output, routes) in a gist: https://gist.github.com/Foucl/6b842f94ef5042ba2062

I followed the pptp client diagnosis suggestions and the fault tree there (I am out of links) and have added the iptables mentioned. I could not get hping2 to work (it's not producing any output).

Solution

Besides TCP port 1723, PPTP also uses GRE to transport data. You need firewall permission for GRE to your PPTP endpoint.

Comments

[Mathäus]

thank you, that seems to be the problem (at a different university that also uses the eduroam specification the connection works). I will report back as soon as I found out why/how my university deviates from the standard here (GRE should be supported). Maybe I will find information that could be useful to other users. If not, I will close the question.

[Konstantinos]

If you are using linux, you may have to load the nf_conntrack_proto_gre and nf_conntrack_pptp kernel modules for certain PPTP/VPN servers. This can be done with: $ sudo modprobe nf_conntrack_proto_gre nf_conntrack_pptp