linux strongswan client l2tp ipsec psk to windows server behind nat

ipsec.conf

config setup

conn %default
    ikelifetime=60m
    keylife=20m
    rekeymargin=3m
    keyingtries=1
    ike=3des-sha1-modp1024!
    esp=3des-sha1!

conn vpn_psk
    keyexchange=ikev1
    left=%defaultroute
    auto=add
    authby=psk
    type=transport
    leftprotoport=17/1701
    rightprotoport=17/1701
    right=xxx.xxx.xxx.xxx  # Public IP or FQDN of the VPN server
    rightid=xxx.xxx.xxx.xxx  # Local IP (if server behind NAT)
    rightsendcert=never

ipsec.secrets

: PSK "your pre-shared key"

options.l2tpd.client

ipcp-accept-local
ipcp-accept-remote
refuse-chap
refuse-eap
refuse-pap
require-mschap-v2
noauth
idle 1800
mtu 1410
mru 1410
nodefaultroute
debug
connect-delay 5000
name "username"
password "password"

up.sh

systemctl start strongswan xl2tpd
ipsec up vpn_psk
echo 'c vpn_psk' > /var/run/xl2tpd/l2tp-control

xl2tpd.conf

[global]
access control = yes
debug tunnel = yes
 
[lac vpn_psk]
lns = xxx.xxx.xxx.xxx  # Public IP or FQDN of the VPN server
ppp debug = yes
pppoptfile = /etc/ppp/options.l2tpd.client
length bit = yes