strongswan is an IPsec VPN client. It is available in most linux distributions.

# Install strongswan. If you are using debian, run:

    $ sudo apt-get install strongswan


# Download the certificate for the CA from the server (the ca.crt file)

# Edit `/etc/ipsec.conf`:

#

    ca example.org
      cacert=ca.crt
      auto=add
    conn server1
      keyexchange=ikev2
      right=server1.example.org
      rightid=%25server1.example.org
      rightsubnet=0.0.0.0/0
      rightauth=pubkey
      leftsourceip=%25config
      leftauth=eap
      leftcert=client.example.org.crt
      auto=route
      eap_identity=username
      auto=add