COMPATIBILITY_ISSUES

* Openswan v2.6.51 and strongSwan default proposals are incompatible.
  To successfully interoperate with strongSwan, it is advised to
  explicitly define the protocols to use; which includes IKE version
  IKE protocols, and ESP/AH protocols.

  A working example:

  OpenSWAN
  ---------
  conn os-ss
    ikev2=insist
    ike=aes128-md5-modp2048
    phase2alg=aes256-sha1
    pfs=no

  strongSwan
  ---------
  conn os-ss
    keyexchange=ikev2
    ike=aes128-md5-modp2048
    esp=aes256-sha1

  Tested protocols:
  * ikev1 and ikev2
  * ipv4, NAT-T, ipv6
  * encryption: aes128, aes256
  * integrity: md5, sha1
  * DH-group: modp2048

* There is an interoperability issue between Openswan and strongSwan
  when pfs=yes

  In the case of pfs=yes configuration, a DH-group must be negotiated
  for the child/ESP SA. Currently, the latest version of pluto will not
  include the DH-group when negotiating ESP.

  Therefore, it is advised to explicitly disable PFS.