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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).

2 Answers 2

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

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  • 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.
    – Mathäus
    Nov 24, 2014 at 11:34
  • 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 Feb 27, 2015 at 15:29
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Fedora 37

Following the instructions of https://superuser.com/a/843285/1782169, I installed firewall-config using this instructions and added GRE protocol on FedoraWorkstation -> Protocols -> Add -> Other protocol and typing GRE. Now my vpn is working

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