Linux (CentOS Openswan) Example Using IKE2 and Preshared keys

yum install openswan

(strongswan is much nicer, but not in yum on centos5. On centos6, use strongswan)

In /etc/ipsec.conf uncomment

include /etc/ipsec.d/*.conf

Put following two files in /etc/ipsec.d/ :

myFireBrick.conf:
conn myFireBrick
       authby=secret
       auto=start
       ikev2=insist
       left=CentOS.IP.Address
       leftid=CentOS.IP.Address
       leftsubnet=CentOS.IP.Address/32
       right=FireBrick.IP.Address
       rightid=FireBrick.IP.Address
       rightsubnet=FireBrick.LAN.SUBNET/24

in: myFireBrick.secrets:

CentOS.IP.Address FireBrick.IP.Address : PSK "yourpasswordhere"

chkconfig ipsec on
service ipsec start

Put the following in the FB at the other end:

<connection name="IPSec" peer-ips=CentOS.IP.Address" auth-method="Secret" secret="yoursecrethere" internal-ipv4="FireBrick.LAN.IP.Address" routes="CentOS.IP.Address" log="default"/>