IPv6: ESP transformation

modulename: esp6.ko

configname: CONFIG_INET6_ESP

Linux Kernel Configuration
└─>Networking support
└─>Networking options
└─>The IPv6 protocol
└─>IPv6: ESP transformation
In linux kernel since version 2.6.12  
Support for IPsec ESP.

If unsure, say Y.

source code:
net/ipv6/esp6.c