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.