VPN server behind an ADSL modem/router

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From: Zixiong WANG (z.wang_at_sysium.com)
Date: 03/02/04 

Date: Wed, 3 Mar 2004 00:07:09 +0100

Hi,

We use an ADSL modem/router for sharing a single ADSL link for our LAN.

Now we want to configure a VPN server for allowing remote users accessing
our internal LAN from Internet.

I think there are two possible configurations :
1) configure a VPN server on our LAN, but I can't figure out how to do it
(can I assign IP addresses of the same LAN both to VPN server's NIC and to
remote users ?)
2) insert a VPN server (with 2 NICs) between the ADSL router and the LAN.
Configure the VPN server as router for allowing internal PCs accessing
Internet through it.

I'v successfully configured a VPN server (Win2k) with 2 NICs. One NIC is
connected to the ADSL router, another to the private LAN. A remote user can
call in and establish the VPN connection, then access internal LAN. The
remote user is assigned an internal LAN's IP address.

But I can't figure out how to configure the VPN server to route internal
flow to Internet while the VPN connection is on.

It seems that whenever a NIC is configured as VPN interface, it no longer
respond to ping, so for the first configuration (the VPN server is directly
on the internal LAN), the VPN server is not accessible normally but only by
VPN connection. For the second configuration, the NIC connected to ADSL
router is not responding, so the only link to internet is broken.

What's your solution ?

Thanks in advance. 

-- 
Zixiong WANG
z.wang@sysium.com

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