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A lot of hotels, coffee shops, and airports are sporting pay-per-hour 802.11 service these days. In most cases, you'll be presented with what appears to be an open hotspot and a DHCP server will give you an IP address. When you open your web browser, though, a transparent proxy will deliver you a page that asks for you to enter a credit card number. Until you've paid, outgoing TCP traffic will be blocked.
More often than not, though, the network is configured to allow ICMP packets through unfiltered. If you find one of these lucky hotspots, you can ping google.com or another external server and you'll get a response back. You can use this feature to tunnel TCP traffic through an ICMP echo request to a proxy server that you've set up on an unrestricted network!
Ptunnel is an application that allows you to reliably tunnel TCP connections to a remote host using ICMP echo request and reply packets, commonly known as ping requests and replies.Setting: You're on the go, and stumble across an open wireless network. The network gives you an IP address, but won't let you send TCP or UDP packets out to the rest of the internet, for instance to check your mail. What to do? By chance, you discover that the network will allow you to ping any computer on the rest of the internet. With ptunnel, you can utilize this feature to check your mail, or do other things that require TCP.
To use Ptunnel, you'll need a server to run the proxy on. Your bandwidth will be a bit limited, but the software includes a simple authentication mechanism so that you can ensure you're the only one using your proxy. The way it works, it's more useful for connecting to your server via ssh than it is browsing the web. That said, it's pretty darn cool and awfully handy, especially if you need to check your mail and don't feel comfortable passing a credit card to a random wireless account server.
Download Ptunnel here and give it a shot - Link.
Nulldigital.net has a good writeup on configuration and usage - Link.
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