So, as I'm not always sitting directly in front of machines that I'm working on I've been using various tools to get temporary network connections between completely seperate network blocks, for example, sitting on wireless outside of my home, connecting back in to the desktop at home, and then connecting to the virtual machines on that desktop - the virtual machines are on their own private network, which is bridged and then routed through the desktop. The desktop machine has an ipv6 tunnel setup using tinc to my main VPS. That in turn has a tunnel setup to he.net's ipv6 network... I then have my laptop configured to also use tinc to connect to my VPS, so lots of ipv6 over ipv4, really.

From that I can then get a 'direct' ssh connection between my laptop and my desktop (OK, so it's actually going over 2 ipv6 over ipv4 tunnels to get there, but it "looks" direct), so, that gets me as far as the external network on that box. From here, we can run a vde_switch which is connected to a tun/tap interface that's part of the internal bridge, once we've got that running, I bring up another vde_switch on my laptop attached to another tun/tap interface purely for that network with a static ip configure on that interface... using the magic of dpipe I then connect the two vde_switches together using vde_plug, and as if by magic, I then have access to the internal networking of my virtual machines, meaning that I can now ssh directly in to the virtual machines without having to do anymore interesting ssh bouncing and port forwarding.

It's a little sick, but it really does make remote working a lot easier to do, it's a vpn of sorts, I suppose, as all traffic is being thrown over ssh pipes or tinc (which in turn is encrypted using x509 certificates)... probably not the quickest of networks, but very very nice all the same.