vpn

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From: Tony Lawrence <tony@aplawrence.com>
Subject: Re: Setting up VPN under Open Server 5.0.5
References: <3ada3adb.114443796@news> 
Date: Mon, 16 Apr 2001 05:39:58 -0400

Harry Fine wrote:
> 
> Hello
> 
> I am  interested in setting up a VPN so that I can have people use
> their Windows machines at home over the internet, connect to the
> server over modems, and be able to use file and print sharing.
> Currently, they can log in over a serial connection using TERM for
> Windows, in a terminal emulation window.  I'd like them to be able to
> share files more easily, so that a file they worked on with
> Wordperfect for Unix at the office, can be opened with Wordperfect for
> Windows at home over the VPN on the server.

I'm wondering if you are possibling confusing having a VPN
with having TCP/IP.

A VPN is a Virtual Private Network.  The concept is that you
are using public or other shared lines (generally the
Internet) to connect machines, but that all packets are
encrypted (so your connections are "private").  What happens
is that the person at home first connects to the Internet,
using their modem, DSL, or whatever.  At your connection
point, you have a VPN server sitting at a real ip address on
the Internet.  Often the inside network has private (eg 192.
or 10.) addresses. You have VPN software running on the
client machine, so when they attempt to connect to an
address that the VPN software recognizes as belonging to it
(which is probably one of the internal addresses, such as
192.168.2.3), it routes packets to the real IP address and
in turn to the internal address.  It's all transparent to
the clients: everything looks to them as though they have a
physical connection to your internal network: if they would
"telnet 10.1.36.3" in the building, that's just what they'd
do from home.

Ordinary TCP/IP over dial up PPP just requires an inbound
PPP connection.  The clients use DUN to acccess a modem at
your location, nothing to do with the Internet.  Again,
their perception of addressing doesn't change.  My
experience is that dial-in ppp is usually faster than a VPN
over dial-up internet access; the overhead of the VPN seems
generally to be more than the possible gain of 56K to an isp
vs. 33.6 to another modem.  People sometimes find this
confusing, but think of the Internet as one giant private
network and your local connection as a smaller version. 
Once you are appropriately connected to either one, you have
access to that network.  

If you have a real ip address on the Internet, you can also
do something similar using ssh.  This is not really a VPN,
it's just encryption of packets.  The difference is that
your clients connect to that known, public IP address, not
to the internal addresses you could use with a true VPN. 
However, this requires much less work to set up, and of
course once they connect to that address you can
automagically send them along to where you really want
them.  

Some VPN solutions include proprietary ones like Cisco and
completely free Linux implementations like PopTop (
http://poptop.lineo.com/ ).  The proprietary packages
generally require their own clients to be installed on the
Windows machines, PopTop uses the built in Windows VPN
client that Microsoft expected you to use with their NT VPN
server.  If you don't want Cisco, but aren't up to doing
PopTop by yourself, there is some middle ground: folks like
E-Smith ( http://www.e-smith.com - home office up in your
neck of the woods ) provide a packaged PopTop and NetMax (
http://www.netmax.com/ ) has a Linux based VPN that does
require its own clients.

I've been selling the E-Smith for a few months now; I've
used it for both VPN and ssh style connections and am at
least so far pretty happy with it.  However, I also have
clients with Cisco VPN's and other stuff.  My problem is
that the client side software doesn't play well with other
clients so if I have to access them through the VPN I'd
rather they didn't use proprietary clients.  

Well, that wasn't exactly a FAQ, but maybe it's the
beginning of one..

-- 
Tony Lawrence (tony@aplawrence.com)
SCO/Linux articles, help, book reviews, tests, 
job listings and more : 

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