This is how I configure the route on the FireBrick®
Edit route 1.
This routes the IP address you've
selected (10.1.1.1 in this
case) from your LAN, WAN or both (as I've done above)
over the tunnel we created. Whether you need
Proxy-Arp depends on your
network setup.
In order to get packets from any
source to the proscribed target IP address forwarded over our
tunnel (see the tunnel setup) the route
needs to be one of the first in the list of routes. The FireBrick®;
processes its routes in order, rather than the 'most specific'.