When I am away from home I sometimes want to be able to connect through my firewall to my PCs at home.

However, I don't like leaving ANY services open to the world, so I have been experimenting with "port knocking", whereby I wake-up my firewall to let me in. It needs no special software installed on the Zaurus other than a working "ping" command (cacko users need to install "hping2").

I've written this up at:
http://www.zaurus.org.uk/portknocking.html

I'd be happy to clarify or explain or help others get this working.