Ronen, I am with Tom on this. Cisco routers/Mikrotik have their place later down in the network. By far the most logical way to do an IPIP gateway is with a Linux box. Look into the the various single board computers, you don't need a spinning hard drive if you are worried about dish crashes etc.

Brian Kantor runs the whole thing at UCSD on a dual-core 3.2 Ghz Xeon processor with two 1 GbE ports running a BSD variant on a Compact flash storage device, if I remember correctly.