I've recently set up a firewall in our house, running Debian. It's using iptables to do packet filtering. When I installed it, my mother started having problems connecting through VPN to her company (MAPICS). The connection starts fine, but after 5-10 minutes, it disconnects. I do not have this problem connecting to other VPN servers (such as to my employer) using her computer, so I know this is specific to their system. Previously, we were using a Linksys router, and it worked fine. Now, my first idea was that the firewall was blocking a certain type of packet, thus causing the connection to be terminated. However, running tcpdump on the internal and external interfaces show that everything is passing through nicely. Of note is that every time, right before the disconnect, their VPN server sends a PPTP Echo-Request to her client. The response from her client is a TCP RST, and the connection is terminated. I have verified this repeatedly, and this is the case every time. However, there are dozens of other times during the connection where a PPTP Echo-Request is sent from their server, and her client responds with the correct PPTP Echo-Reply, and they respond with a TCP ACK on that reply. In other words, the echo handshake goes back and forth several times throughout the connection, correctly, and at one of them her client decides not to reply, and simply RST the connection. I've examined the packets containing the Request from both a completed handshake and from the terminated one, and they both appear to be identical, excluding sequence numbers and acknowledgment numbers. I'm attaching packet captures from ethereal in the libpcap format--one from the perspective of the internal interface, and one from the external. These are pre-filtered, so they contain *all* network traffic at the time, so I'm positive that nothing that could identify the problem is left out. The VPN server is 220.127.116.11, and her client is 192.168.1.102. It's over a PPTP connection, with a Windows-based VPN server--I'm guessing Windows 2000 Server. If anyone could help me discover what the problem is, or point me in the direction of someone who could, I would be *extremely* grateful. -- Stephen Touset <firstname.lastname@example.org> "What do you mean, 'Veritas is acting screwy'? Veritas is the shit!"
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