===== linux side

    * Server1: 10.0.0.1 / 255.255.255.252
    * Server2: 10.0.0.2 / 255.255.255.252

----- create ipip tunnel interface
ip tunnel add tun0 mode ipip remote 200.200.200.200 local 100.100.100.100 dev eth0

----- set interface IP addresses
ifconfig tun0 10.0.0.1 netmask 255.255.255.252 pointopoint 10.0.0.2

----- bring interface up
ifconfig tun0 mtu 1500 up

----- show config
ifconfig tun0

----- create gif tunnel interface
ifconfig gif0 create

----- set interface transport IP addresses
gifconfig gif0 inet 200.200.200.200 100.100.100.100

----- set interface IP addresses
ifconfig gif0 10.0.0.2 netmask 255.255.255.252 10.0.0.3

----- set interface MTU and bring interface up
ifconfig gif0 mtu 1500 up

===== FreeBSD side
ifconfig gif0
gif0: flags=8051 mtu 1500
        tunnel inet 200.200.200.200 --> 100.100.100.100
        inet 10.0.0.2 --> 10.0.0.1 netmask 0xfffffffc

ping -c 4 10.0.0.2

use an MTU of 1,480 instead 1500 (overhead)

===== RC script
# this should be the IP address of the remote server 
REMOTEIP=64.81.178.37
 
# this is the (routable) IP of the local server
LOCALIP=216.254.21.186

# this is the private (10 net) IP of this end of the tunnel
PRIVATELOCAL=10.13.13.13

# this is the private (10 net) IP of that end of the tunnel
PRIVATEREMOTE=10.13.13.14

# add routes to these networks (separate by spaces)
REMOTENET="$PRIVATEREMOTE/32 20.0.0.0/8 192.168.1.0/24"
 
# this can be whatever; 
TUNDEV=gir

# STOP EDITING HERE
 
start() 
{ 
        iptunnel add ${TUNDEV} mode ipip remote ${REMOTEIP} local ${LOCALIP} ttl 255
        ifconfig ${TUNDEV} ${PRIVATELOCAL} pointopoint ${PRIVATEREMOTE}
          # Note: check the above syntax; each linux seems to want a slightly different 'pointopoint' syntax. -EricJohanson
        for net in ${REMOTENET}; do
                route add -net $net dev ${TUNDEV}
        done
} 
 
stop() 
{ 
        ifconfig ${TUNDEV} down
        iptunnel del ${TUNDEV} 
} 
 
case "$1" in 
        start) 
                start ;; 
        stop) 
                stop ;; 
        restart) 
                stop 
                start ;; 
esac

=====