Não use o modo agressivo, a conexão será menos segura. De qualquer forma, tente com essa configuração. Eu uso em um servidor VPN com o strongswan-5.3.5 e o xl2tpd-1.3.6
ipsec.conf
config setup
cachecrls=yes
uniqueids=yes
charondebug=""
conn %default
keyingtries=%forever
dpddelay=30s
dpdtimeout=120s
conn L2TP
dpdaction=clear
#Server IP
left=192.168.1.130
#Server default gateway
leftnexthop=192.168.1.254
leftprotoport=17/1701
rightprotoport=17/%any
right=%any
rightsubnet=0.0.0.0/0
leftauth=psk
rightauth=psk
leftid="<insert-the-public-ip-here>"
ikelifetime=1h
keylife=8h
ike=aes128-sha1-modp1536,aes128-sha1-modp1024,aes128-md5-modp1536,aes128-md5-modp1024,3des-sha1-modp1536,3des-sha1-modp1024,3des-md5-modp1536,3des-md5-modp1024
esp=aes128-sha1-modp1536,aes128-sha1-modp1024,aes128-md5-modp1536,aes128-md5-modp1024,3des-sha1-modp1536,3des-sha1-modp1024,3des-md5-modp1536,3des-md5-modp1024
auto=add
keyexchange=ike
type=transport
conn block
auto=ignore
conn private
auto=ignore
conn private-or-clear
auto=ignore
conn clear-or-private
auto=ignore
conn clear
auto=ignore
conn packetdefault
auto=ignore
ipsec.secrets
<insert-the-left-id-here> %any : PSK "<my-password>"
/etc/xl2tpd/xl2tpd.conf
[global]
ipsec saref = no
debug tunnel = no
debug avp = no
debug network = no
debug state = no
[lns default]
ip range = 10.0.0.20-10.0.0.30
local ip = 10.0.0.1
require authentication = yes
name = l2tp
pass peer = yes
ppp debug = no
pppoptfile = /etc/ppp/options.xl2tpd
length bit = yes
unix authentication = yes
/etc/ppp/options.xl2tpd
ipcp-accept-local
ipcp-accept-remote
ms-dns 10.0.0.1
auth
idle 1800
mtu 1200
mru 1200
nodefaultroute
lock
proxyarp
connect-delay 5000
name l2tpd
ifname l2tp
login
/ etc / ppp / chap-secrets
username * "l2tppassword" *
reiniciar os serviços
sudo service strongswan restart
sudo service xl2tpd restart