1. Problem Connecting to VPN thru a linux Gateway
I am having a problem trying to connect to a remote VPN from a win2k
machine that is attached to my local network thru linux gateway.
Typically I would connect a laptop to my local LAN and use it to access
the internet and VPN into my company network. However, recently I have
been having problems connecting to the VPN. It would fail during the
verification of the user and password stage (no it is not a password
problem). If I connect the laptop directly to my cable modem, then I can
VPN fine. So I concluded that I must have changed something in my
configuration on the server to cause this to happen. However, I can not
figure out what.
I have a RH9 Linux server connected to my cable modem on eth1. Eth0 is
connected to a switch which enables my local LAN. This server acts as the
gateway to the internet. It employs Iptables as the firewall.
After scouring the configuration and documentation, I have come up empty
as to the problem.
My VPN connection uses PPTP. My iptables configuration uses POSTROUTED
SNAT to allow clients access to the internet. The GRE Protocol as well as
the VPN port (1723) are given inbound access (as well as other services).
Outbound access is also open.
I had even set all my chains to accept everything and I still was unable
to establish a VPN connection.
Finally I used ethereal to look at the packets and I noticed something
I saw that every packet from the client machine (on eth0) was replicated
on eth1 from the server. This I realized must be because of SNAT.
However, I noticed that any packet for the GRE protocol was not being
replicated (hence, not being SNATed or forwarded). Additionally, when the
remote VPN server sent a PPP LCP Configuration Request packet over GRE, my
Linux gateway would reply with an ICMP (Destination Unreachable) instead
of forwarding it to the client laptop.
My guess is that SNAT is unable to determine how to properly route those
packets. But this is a guess and I'm probably off the mark.
Anyway, if you think you can help me with this problem, then send me an
email directly. I have been buried in this for awhile now, so I realize
that my description above may be a bit weak and lacking of details. So if
you require any other information, then please let me know.
2. I am k00l, coz I use Linux (man, get a life) [Was: Boycott Microsoft!!!]
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