If IPsec tunnel tear down happens and when a new tunnel is created with same peer, usually new IP gets allocated each time. With this in some case, there in-occurs a need to reconfigure peer's environment. In order to avoid such scenario, preservation of allocated internal IP is suggested for some configured timer.
IP preservation is with respect to WSG RAS mode only. IP Address Stickiness is not required for S2s mode.
IPv6 allocated IP will not be preserved and is out of scope of this feature.