Re: what is VPN?
Warning: technical rant ahead. The state of VPN technology is awful. There are open-source VPN solutions, but none of them use commodity protocols. It is unlikely that you will find one single VPN technology to meet your requirements in any event, especially if you use a smartphone or tablet.
Most people, when they say "VPN", mean either one of two things:
A service that allows you to connect to the Internet by way of the service, so that you can do things--possibly naughty, illegal things--more anonymously.
Programs or protocols that facilitate connection of private networks over a public network, like the Internet, with encryption and authentication to protect the data.
In general, the second meaning is subdivided again into two:
Technologies that are fit for either corporate or business network uses, like IPSec (with or without L2TP) or PPTP, which mostly use I P-layer tunnelling
Personal-use or SOHO VPNs that implement layer 2 (i.e. Ethernet) bridging (Hamachi, OpenVPN, freelan, etc.)
Generally when all you require is IP-layer connectivity--in other words, you don't need to use more than typical Internet applications like web browsers or BitTorrent clients or email clients or chat clients with well-known services on the Internet--then you can use a VPN service with a commodity protocol, in the business category above. Smartphones support these, and you generally get adequate performance with all of them, although security is weaker in PPTP. Quite a few VPN providers now also support OpenVPN just for Internet use, as it gets around more obstacles to connections (NATs in small networks, restrictive firewalls, etc) which would otherwise hamper the others.
If you want to interconnect local networks--to play network games, or to share files using broadcast or multicast instead of using DNS (i.e. the va st majority of home and small business networks)--then you will use one of the protocols in the personal-use category. These aren't universally implemented, except as application software which may or may not run on the target platform (almost no smartphone use), they might or might not be Open Source, and they might or might not require the setting up of servers. Hamachi, notably, is very easy to set up because LogMeIn facilitate connections using their own servers, which arguably makes it less secure.
Technically, there are other types of tunnels, and all of them could be considered VPN if you take the view that they mediate your communication through someone else. For example, an IPv6 tunnel broker gives you IPv6 connectivity, which just so happens to have the side-effect of allowing you to "Come in" from anywhere, and emerge at a fixed point. The trick of being portable even without security is sometimes very useful, a bit like having a portable phone line. Some people like this, for example, because you can use it to get around geographic blocking. Likewise, you can set up proxy servers, or SSH, to run application traffic through an additional point. For large networks with direct connections, MPLS is another layer 2 protocol that just happens to be useful for running VPNs. I would venture that these are not really VPNs in and of themselves, because they don't have the single purpose of carrying sensitive traffic over an insecure network, but they can be used in this way.
And finally: I said above that the state of VPN is terrible. The main reason for this is that there is no single protocol that is both standardised and in wide use on all platforms, while actually doing what we need it for. Specifically, IPSec was really designed for use with IPv6, and is complicated to run on IPv4 (because of NAT/connection sharing). Moreover, right now it's only really good for IP traffic--although L2TPv3 specifies how to carry Ethe rnet frames, it's almost completely unimplemented except on heavy iron routers from Cisco, perhaps as a direct result of the first issue. If you aren't large and powerful, with public IP addresses at either end of the tunnel (happily many businesspeople will visit coffee shops, where that isn't available), getting the full and effective benefits of a VPN requires going to the lesser protocols. Maybe one day IPv6 will fix it, but that's another discussion.
URL: http://forum.audiogames.net/viewtopic.php?pid=166414#p166414
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