IP: ESP transformation

modulename: esp4.ko

configname: CONFIG_INET_ESP

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

If unsure, say Y.

source code:
net/ipv4/esp4.c


is selected by
CONFIG_INET_ESPINTCP