Need help when configuring L2TP on ubuntu

I want to set up a L2TP server on my Linode (i've already set up a PPTP using pptpd successfully). I followed a tutorial. Following are the root shell commands.

apt-get install openswan
for each in /proc/sys/net/ipv4/conf/*
do
echo 0 > $each/accept_redirects
echo 0 > $each/send_redirects
done
ipsec verify
sudo /etc/init.d/ipsec restart
apt-get install xl2tpd
/etc/init.d/xl2tpd restart
iptables –table nat –append POSTROUTING –jump MASQUERADE
echo 1 > /proc/sys/net/ipv4/ip_forward

content of ipsec.conf

config setup
    nat_traversal=yes
    virtual_private=%v4:10.0.0.0/8,%v4:192.168.0.0/16,%v4:172.16.0.0/12
    oe=off
    protostack=netkey

conn L2TP-PSK-NAT
    rightsubnet=vhost:%priv
    also=L2TP-PSK-noNAT

conn L2TP-PSK-noNAT
    authby=secret
    pfs=no
    auto=add
    keyingtries=3
    rekey=no
    ikelifetime=8h
    keylife=1h
    type=transport
    left=XXX.XXX.XXX.XXX
    leftprotoport=17/1701
    right=%any
    rightprotoport=17/%any

content of ipsec.secrets

XXX.XXX.XXX.XXX %any: PSK “presharedSecret”

content of xl2tpd.conf

    [global]
    ipsec saref = yes

    [lns default]
    ip range = 10.1.2.2-10.1.2.255
    local ip = 10.1.2.1
    ;require chap = yes
    refuse chap = yes
    refuse pap = yes
    require authentication = yes
    ppp debug = yes
    pppoptfile = /etc/ppp/options.xl2tpd
    length bit = yes

content of options.xl2tpd

    require-mschap-v2
    ms-dns 208.67.222.222
    ms-dns 208.67.220.220
    asyncmap 0
    auth
    crtscts
    lock
    hide-password
    modem
    debug
    name l2tpd
    proxyarp
    lcp-echo-interval 30
    lcp-echo-failure 4

The Openswan(2.6.24), IPSEC, xl2tpd all succeeded in starting. But none of my devices can connect to L2TP while the PPTP service works properly. After I executed 'xl2tpd -D' and had my iOS connect to it, no debug messages appeared.

It would be greatly appericated if anyone could tell me the way to solving the problem and what "/8","16" & "/12" in "virtual_private=%v4:10.0.0.0/8,%v4:192.168.0.0/16,%v4:172.16.0.0/12" means?

Thanks very much.