Transformation user configuration interface

modulename: xfrm_user.ko

configname: CONFIG_XFRM_USER

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

If unsure, say Y.

source code: