# if you are logged in with your normal user you have to become root now
sudo su -

# install strongswan
yum install strongswan

# add ipsec config
cat << EOF >> /etc/strongswan/ipsec.conf
conn cmts-cm
        left=<cloud-ip>
        leftsubnet=172.20.0.0/22
        leftid=<cloud-ip>
        leftfirewall=yes
        right=<cmts-ip>
        rightsubnet=10.0.0.0/19
        rightid=<cmts-ip>
        auto=add
        ike=aes256-sha-modp1536
        esp=aes256-sha1-modp1536
        keyexchange=ikev1
        authby=secret

conn cmts-cpepriv
        also=cmts-cm
        rightsubnet=100.64.0.0/22

conn cmts-mta
        also=cmts-cm
        rightsubnet=100.96.0.0/22
EOF

# add pre-shared key
echo '<cloud-ip> <cmts-ip> : PSK "<secret>"' >> /etc/strongswan/ipsec.secrets

# enable strongswan
systemctl enable strongswan