how to set up an ikev2 vpn server with strongswan on centos7.8

  1. install strongswan

    yum install strongswan -y

  2. prepare certs

    mkdir /certs && cd /certs
strongswan pki --gen --type rsa --size 4096 --outform pem > ca-key.pem
strongswan pki --self --ca --lifetime 3650 --in ca-key.pem --type rsa --dn "CN=VPN root CA" --outform pem > ca-cert.pem
strongswan pki --gen --type rsa --size 4096 --outform pem > server-key.pem
strongswan pki --pub --in server-key.pem --type rsa | strongswan pki --issue --lifetime 1825 --cacert ca-cert.pem --cakey ca-key.pem --dn "CN=chenshi.de" --san "chenshi.de" --flag serverAuth --flag ikeIntermediate --outform pem > server-cert.pem

  3. prepare configuration files

    # ipsec.conf - strongSwan IPsec configuration file

        config setup
                charondebug="all"
                uniqueids=no

        conn ikev2-vpn
                auto=add
                compress=no
                type=tunnel
                keyexchange=ikev2
                fragmentation=yes
                forceencaps=yes
                dpdaction=clear
                dpddelay=300s
                rekey=no
                left=%any
                leftid=@chenshi.de
                leftcert=/certs/server-cert.pem
                leftsendcert=always
                leftsubnet=0.0.0.0/0
                right=%any
                rightid=%any
                rightauth=eap-mschapv2
                rightsourceip=172.18.18.0/24
                rightdns=9.9.9.9
                rightsendcert=never
                eap_identity=%identity

    # /etc/ipsec.secrets - strongSwan IPsec secrets file

    : RSA /certs/server-key.pem

    chenshi : EAP "chenshi.de"

    : PSK "chenshi.de"

    don’t forget to add dns in charon.conf.

  4. change iptables

    echo net.ipv4.ip_forward = 1 >> /etc/sysctl.conf
sysctl -p
yum install iptables-services -y
iptables -F
iptables -t nat -A POSTROUTING -s 172.18.18.0/24 -o ens192 -j MASQUERADE
service iptables save
systemctl restart strongswan

  5. on windows client

    certlm.msc # import cert
Windows Registry Editor Version 5.00 # add regkey
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\RasMan\Parameters]
"NegotiateDH2048_AES256"=dword:00000001

  6. references:

    https://www.digitalocean.com/community/tutorials/how-to-set-up-an-ikev2-vpn-server-with-strongswan-on-ubuntu-18-04-2