IPv6: tunnel transformation

modulename: tunnel6.ko

and/or

xfrm6_tunnel.ko

configname: CONFIG_INET6_TUNNEL

Linux Kernel Configuration
└─>Networking
└─>Networking options
└─>IPv6: tunnel transformation
In linux kernel since version 2.6.12  
Support for generic IPv6-in-IPv6 tunnel transformation, which is
required by the IPv6-in-IPv6 tunneling module as well as tunnel mode
IPComp.

If unsure, say Y.

source code:
net/ipv6/xfrm6_tunnel.c
selects
CONFIG_XFRM