Re: [pptp-devel] Problem connecting to PPTP server

[James C. <qu...@la...>]

Hello Kim,

I agree you don't have the firewall software turned on.  I suggest
looking for iptables or other filtering rules.  I'm not familiar with
OpenSUSE, but on other systems I've used the command iptables-save to
dump all currently active rules.

Looking again at your pppd debug dump and tcpdump;

- the PPTP control connection is established from the pptp program and
  there is good communication with the server over TCP,

- the GRE packets in the tcpdump show the server is negotiating toward
  LCP agreement, as expected, but that the client is repeating the
  same sequence number LCP ConfReq; this means pppd has not heard any
  answers,

- the pppd process is not receiving packets from the server, but is
  able to transmit packets and they are seen in both pppd debug dump
  and tcpdump; this implies that the pptp program is continuing to run
  and is relaying data from the pty to the GRE socket,

- once the negotiation times out, the PPTP control connection properly
  collapses with a call clear request, and the call id fields do match
  the GRE packets; this implies the NAT router that must be nearby is
  modifying the PPTP control connection and the GRE packets
  consistently.

You might look at "ip route" _during_ the connection attempt.

You might use "strace" to instrument the pptp program to see if the
packets from the server shown by tcpdump are being received on the GRE
socket without error.

You might check for log files of the pptp program.

You might check for GRE or PPTP related kernel modules with lsmod;
none of them are expected, they are most often used on routers that
run Linux.

I do have vague memory of one scenario where a NAT router modifies the
packets in a way that works with Windows but doesn't work with Linux.

I'm sure you have a NAT router of some sort, because the client IP
address is 192.168.0.102, in an unroutable subnet.

You might check for later firmware for your NAT router.

Also, if you have any other tunnelling protocol you can use instead,
please do so.  PPTP is weak and fragile, and was not designed for the
environment we have now.

-- 
James Cameron
http://quozl.netrek.org/