vtun

On a conference for sociologists in Glasgow, I found my self in a library providing "Open Access" to the internet. However, the access was filtered, only traffic bound for port 80 was let through. Not even ping was accepted (dns-queries was handled alright of course).

I wanted to send mail that I had already written on my laptop, and I wanted to log in to my computer at work to do computing work there. Thirdly, I had gpg-encrypted mail that I could not read using webmail. Lastly, I wanted to hack me out of this web-jail the library tried to restrict me in.

On the computers provided for visistors to the library, I was able to connect to the desktop on a windows-server at work ("remote desktop"), and from there to log in on my main computer at work with putty. Then I installed vtun on that box and configured it to listen on port 80.

On my laptop I installed vtun (easy, since apt-get uses http:// over port 80) and configured it to connect to port 80 on my computer at work.

Before I had unrestricted internet-access from the library, I had to fix three things

1. Set up ip_forwarding on the server
2. Fix the routing-table on the client
3. Fix the path for DNS-queries (since the library happened to give a private network address for DNS)

The concepts used

Set up ip_forwarding on the server

# echo 1 > /proc/sys/net/ipv4/ip_forward

Fix the routing-table on the client

route add server.bar.com gw gateway.given.by.library
route del default
route add default gw 10.1.0.1

Fix the path for DNS-queries

Simply copy the /etc/resolv.conf from the server.

A Win-win-solution

The library is not responsible for all junk that comes out of my laptop. All network-packets it generates will seem to come from my computer at work, which is what everybody wants.

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Last modified: 2007-09-05