Linux (192.168.2.1):
   /sbin/ip tunnel add tunl1 mode ipip remote 192.168.1.1
   /sbin/ifconfig tunl1 192.168.3.2 pointopoint 192.168.3.1 netmask 255.255.255.252 mtu 1500

Cisco (192.168.1.1):
  interface Tunnel0
    ip address 192.168.3.1 255.255.255.252
    ip mtu 1500
    tunnel source 192.168.1.1
    tunnel destination 192.168.2.1
    tunnel mode ipip