I Google-ed a lot configuring IPSec VPN for iOS with OpenSwan, nothing useful but Iphone/Ipad/Mac OSX IPSEC VPN with Strongswan 5 on Centos/RHEL 6 which is on RHEL/CentOS and with strongswan found. I tried to configure openswan like strong swan, failed.
StrongSwan‘s official wiki helps a lot: http://wiki.strongswan.org/projects/strongswan/wiki/IOS_(Apple)/23
iOS 4 and newer supports native IPsec VPN via IKEv1 (otherwise referred to as Cisco IPSec in iOS) and is able to interoperate with strongSwan.
OS X 10.9
openssl from macports(OpenSSL 1.0.1f 6 Jan 2014).