You might have to add MPLS VPN which is the most widely used one or could be even a GRE with BGP as the routing protocol.
Cheers, - Balaji On Fri, Apr 27, 2012 at 1:32 PM, Girish Venkatachalam < [email protected]> wrote: > What is a VPN? > > A VPN otherwise known as virtual private network creates a tunnel between > two > endpoints on the Internet. > > A typical case would be between a company's branch office and head office. > > I will explain more about this since there are plenty of things nobody > will tell you. > > No article or literature will specify what all goes into this > seemingly easy technology. > > I used to think it was easy since I am the spam guy. I solved how > e-mail security can be > assured to organizations which is a much bigger problem but then it > turned out that > VPN was also a big problem. > > It took me close to 4 years to get it right. > > Anyway this article will only speak about the higher level > interactions and big picture. > > The reality of today's Internet is that there are not as many public > IPv4 addresses as we prefer. > > Hence all organizations go for a private address space in one of > rfc1918 IP address blocks. > > Say 192.168.0.0/16, 10.0.0.0/8 or 172.16.0.0/12 addresses. > > None of these addresses are routable over the net since millions or > networks will be using > the same IP addresses. > > What a VPN enables is to route them across the Internet by > encapsulating them inside like our > tanjavur bommai. > > So we have an outside IP header which contains the two public IP > endpoints and the inside > IP has the private IP endpoints. > > Thereby we can actually talk to your LAN machines and access all of > the applications, even obtain > a DHCP address from the remote network using a VPN. > > Now VPN is often thought of as having to do with encryption but that > is only an aside. > > You can jolly well have VPNs without any crypto and key setup. > > PPTP and L2TP VPNs are in that category I think. > > Let us leave aside crypto for now. > > The biggest issue is that of being able to talk to a remote LAN > without using a known IP address or a > static IP address. > > You can do that when you are a VPN client but you can also do that > when you are a VPN server by using > dynamic DNS services. > > The applications that are not network aware are NetBIOS file > sharing(Windows shares) and layer II protocols > and various other things like tally applications, db apps and so on. > These work inside a LAN. > > And moreover you don't want to purchase a separate license for each site. > > If you have Internet setup a VPN and connect to the head office. That > is how all major companies function. > > Now you also have another way to use a VPN. Let us say you are at an > airport or you are at home. You are a single > person accessing the office LAN. Either with your laptop or on a > public computer. > > VPN enables that as well. > > We will close this article with discussing the different kinds of VPN > technologies I know of: > > 1) OpenVPN > 2) IPsec VPN > 3) OpenSSH VPN > 4) L2TP > 5) PPTP (Windows free software) > > And VPN can work in tunnel mode or transport mode, normally we are > only bothered about tunnels. > > -Girish > > -- > Gayatri Hitech > http://gayatri-hitech.com > _______________________________________________ > ILUGC Mailing List: > http://www.ae.iitm.ac.in/mailman/listinfo/ilugc > _______________________________________________ ILUGC Mailing List: http://www.ae.iitm.ac.in/mailman/listinfo/ilugc
