/etc/network/interfaces

# IP over DNS
iface tun0 inet static
        address 10.0.0.42
        netmask 255.255.255.0
        mtu 500 # optional, may solve ssh problems
        post-up route add -host `grep nameserver /etc/resolv.conf |head -1|awk '{print $2}'` gw `netstat -rn | grep ^0.0.0.0 | awk '{ print $2 }'` ; route del default ; route add -net default gw 10.0.0.1
        post-down dhclient

/etc/default/nstx

NSTX_DOMAIN="tunnel._your_domain"

NSTX_DNS_SERVER=`grep nameserver /etc/resolv.conf |head -1|awk '{print $2}'`

start_nstxcd=yes

ifup_tun=tun0