PPTP VPN server

Lhadatt · 12-02-2004, 02:20 PM

I'm putting together a PPTP VPN server using Slackware Linux 9 and PoPToP. The goal is to allow Windows users to login to the LAN via the Internet. The PPTP server is hosted on a firewall using Shorewall 2 (front-end for iptables).

Problem: I can get it to connect and communicate with the subnet the PPTP hands out IPs for, but it won't communicate with any other subnet.

The server:

- Internet: 192.168.1.1 (for testing) on eth0
- LAN: 10.1.10.0 via eth1 - actual IP is 10.1.10.93
- DMZ: 10.2.10.0 via eth2 - actual IP is 10.2.10.93
- PPTP hands out 10.3.10.2 - 10.3.10.254 to clients
- VPN "local" IP on server: 10.3.10.1

The client:

- Windows 2000 Pro
- Local IP is 192.168.1.2
- Gateway is set to 192.168.1.1 (the server)
- Receives 10.3.10.x from server
- Subnet mask for 10.3.10.x is 255.255.255.255 -- standard for PPTP, I don't think this can change, but I'm still researching that

I think the firewall is basically OK, but might need some tweaking on the masquerading entries or something. The important thing to note with the firewall is it does allow connections, and this issue persists even if the firewall is turned off.

The clients CAN ping 10.1.10.93 and 10.2.10.93, since they are on that server. I believe the issue is route-related -- I don't know what routes to put in though, and whether they should be on the server or client. The server has no problem communicating with anything on any subnet, it's just the client.

My masq entries in Shorewall:

Code:

#INTERFACE              SUBNET          ADDRESS
eth0                    eth1
eth0                    eth2
#ppp0            eth1
#ppp0            eth2
#ppp0:10.1.10.0/24   10.3.10.0/24    10.1.10.93
eth0            ppp0

The interfaces file in Shorewall:

Code:

#ZONE   INTERFACE       BROADCAST       OPTIONS
net     eth0          detect   routefilter,blacklist
loc     eth1    detect  dhcp,blacklist,routeback
dmz     eth2    detect  dhcp
vpn     ppp0    -

/etc/pptpd.conf:

Code:

option /etc/ppp/options-pptpd
localip 10.3.10.1
remoteip 10.3.10.2-254

/etc/ppp/options-pptpd:

Code:

name   *
lock
mtu     1450
mru     1450
proxyarp
defaultroute
auth
ipcp-accept-local
ipcp-accept-remote
lcp-echo-failure    3
lcp-echo-interval   5
deflate 0

# dns and samba
ms-dns  10.2.10.7

# handshake auth method
+chap
+mschap-v2

# data encryption method
mppe required

Please let me know if you would like to see anything else. Does anyone have any ideas?

Thanks!

sigsegv · 12-02-2004, 02:50 PM

If I understand your post correctly, the problem is this -- The client's default gateway is 192.168.1.1. It's VPN IP is 10.3.10.x. The problem is when you're trying to communicate with another subnet (i.e. *not 10.3.10.x), you're going out over 192.168.1.1. Since 10.0.0.0/8 is non-routable to the public 'net, your packets go off into the void

The client's default route needs to change to 10.3.10.1 (if that machine is set to forward) for the duration of the pptp session.

Lhadatt · 12-02-2004, 04:52 PM

Thanks for the reply.

I tried that, it didn't work.

I don't quite know what's going on, but I'll try to brainstorm on it tomorrow.

sigsegv · 12-02-2004, 05:11 PM

What do the routing tables look like? Run netstat -rn on the linux machine and route print on the windows box (scrubbing public IPs as necessary) and post them back here.

scowles · 12-02-2004, 05:42 PM

Looks like you're trying to masquerade vpn traffic when you want the firewall to simply route vpn traffic after it encodes/decodes the packet. In my setup (shorewall/poptop running on the firewall):

I add the pptpserver entry to the shorewall tunnels file. i.e.

Code:

pptpserver            net     0.0.0.0/0

...and

Code:

loc     ppp+            -

to the shorewall interfaces file.

I do not reference the vpn traffic/intefaces in the shorewall masq file.