IPsec user configuration interface

modulename: xfrm_user.ko

configname: CONFIG_XFRM_USER

Linux Kernel Configuration
└─>Networking
└─>Networking options
└─>IPsec user configuration interface
In linux kernel since version 2.6.12  
Support for IPsec user configuration interface used
by native Linux tools.

If unsure, say Y.

source code:
net/xfrm/xfrm_user.c