Ubuntu supports strongSwan in main as of release 14.04. This driver will provide the choice for the customers to run strongSwan on it.
strongSwan driver is very similar with openswan driver in addition to quite difference of their configuration files.
So the currently implemented methods are:
The latest strongSwan 5.x has different attributes than the previous version. For example, 5.x has abandoned some configurations like plutostart, nat_traversal, virtual_private, pfs etc, and some configurations also have the default value like strictpolicy=no, charonstart=yes.
OpenSwan has more similiar attributes with the previous version of strongSwan 5.x, but not with strongSwan 5.x. Initial efforts only support 5.x and implement an equivalent psk net-to-net vpn service based on recommended configuration in the link  just as openSwan did in the past. Future blueprints will extend other features for strongSwan, like API, auth modes, roadwarrior-to-net etc.
So the capabilites provided by this initail implementation of the strongSwan driver are the same with openSwan driver :
But the parmeters are somewhat different, like:
Therefore, the resources API (service, ikepolicy, ipsecpolicy, ipsec-site-connection) will also do the corresponding code adjustment.
User will need to configure the INI file for the strongSwan driver.
No effect to the VPNaaS performance.
Other alternatives will be lack of community support.
Not applicable. use advanced service tests to cover.
New neutron functional tests will be added to cover below scenario.
The default vpn_device_driver is still openSwan, so need to update vpn_device_driver to use strongSwan in the file /etc/neutron/vpn_agent.ini in addition to installing strongSwan package. vpn_device_driver=neutron.services.vpn.device_drivers.ipsec.StrongSwanDriver
API document mentioned above should also be updated, as part of this effort.