ipv6: Add support for IPsec virtual tunnel interfaces

This patch adds IPv6  support for IPsec virtual tunnel interfaces
(vti). IPsec virtual tunnel interfaces provide a routable interface
for IPsec tunnel endpoints.
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

net/ipv6/Kconfig

@@ -153,6 +153,17 @@ config INET6_XFRM_MODE_ROUTEOPTIMIZATION
 	---help---
 	  Support for MIPv6 route optimization mode.
 
+config IPV6_VTI
+tristate "Virtual (secure) IPv6: tunneling"
+	select IPV6_TUNNEL
+	depends on INET6_XFRM_MODE_TUNNEL
+	---help---
+	Tunneling means encapsulating data of one protocol type within
+	another protocol and sending it over a channel that understands the
+	encapsulating protocol. This can be used with xfrm mode tunnel to give
+	the notion of a secure tunnel for IPSEC and then use routing protocol
+	on top.
+
 config IPV6_SIT
 	tristate "IPv6: IPv6-in-IPv4 tunnel (SIT driver)"
 	select INET_TUNNEL

net/ipv6/Makefile

@@ -36,6 +36,7 @@ obj-$(CONFIG_INET6_XFRM_MODE_BEET) += xfrm6_mode_beet.o
 obj-$(CONFIG_IPV6_MIP6) += mip6.o
 obj-$(CONFIG_NETFILTER)	+= netfilter/
 
+obj-$(CONFIG_IPV6_VTI) += ip6_vti.o
 obj-$(CONFIG_IPV6_SIT) += sit.o
 obj-$(CONFIG_IPV6_TUNNEL) += ip6_tunnel.o
 obj-$(CONFIG_IPV6_GRE) += ip6_gre.o