Product Endorsement

Geek alert, in the form of a quiz.

Question: What is unusual about this tcpdump output (and no, it’s not that my workstation is called pimp):

(note: displaying that as html requires this, if you ever need it)

This is so very cool. It works exactly as advertised. The short summary: it encapsulates TCP in ICMP echo request / reply (aka ‘ping’) packets.

If the value of this is not immediately obvious, you’re probably not the sort of person who’d find it so useful (this is probably a good thing ;). The gist of it is that there’s a lot of public wireless networks where you can connect to the network, but when you actually try to hit any sites, all you get is a welcome page asking you to sign up for an account and pay money to access the internet (certainly, there is also LOTS of intentionally free wifi to be had).

For some reason, many of pay-for-use networks allow ping packets (that use the ICMP network protocol) while restricting TCP packets that are used for just about all the meaningful things that people do with computer networks (mail, web, ssh, etc). ICMP is traditionally sort of a maintenance / debugging / testing type of protocol; it’s there more to facilitate the proper functioning of networks than to carry meaningful data itself. ProxyTunnel changes all that, and thus my endorsement as the Coolest App Of 2005 (so far ;)

Now, you might be thinking… why on earth would you tell people how to invalidate the business model of pay-for-use wifi providers? Well, don’t worry… even if this got popular enough to actually make a dent in anybody’s bottom line (which I highly doubt), it’s such a simple fix to completely break it – just block ICMP until somebody pays up.