ipv6: sr: add support for SRH encapsulation and injection with lwtunnels

This patch creates a new type of interfaceless lightweight tunnel (SEG6),
enabling the encapsulation and injection of SRH within locally emitted
packets and forwarded packets.

>From a configuration viewpoint, a seg6 tunnel would be configured as follows:

  ip -6 ro ad fc00::1/128 encap seg6 mode encap segs fc42::1,fc42::2,fc42::3 dev eth0

Any packet whose destination address is fc00::1 would thus be encapsulated
within an outer IPv6 header containing the SRH with three segments, and would
actually be routed to the first segment of the list. If `mode inline' was
specified instead of `mode encap', then the SRH would be directly inserted
after the IPv6 header without outer encapsulation.

The inline mode is only available if CONFIG_IPV6_SEG6_INLINE is enabled. This
feature was made configurable because direct header insertion may break
several mechanisms such as PMTUD or IPSec AH.

Signed-off-by: David Lebrun <david.lebrun@uclouvain.be>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 12 insertions, 0 deletions

diff --git a/net/ipv6/Kconfig b/net/ipv6/Kconfig
index 2343e4f2e0bf..1123a001d729 100644
--- a/net/ipv6/Kconfig
+++ b/net/ipv6/Kconfig
@@ -289,4 +289,16 @@ config IPV6_PIMSM_V2
 	  Support for IPv6 PIM multicast routing protocol PIM-SMv2.
 	  If unsure, say N.
 
+config IPV6_SEG6_INLINE
+	bool "IPv6: direct Segment Routing Header insertion "
+	depends on IPV6
+	---help---
+	  Support for direct insertion of the Segment Routing Header,
+	  also known as inline mode. Be aware that direct insertion of
+	  extension headers (as opposed to encapsulation) may break
+	  multiple mechanisms such as PMTUD or IPSec AH. Use this feature
+	  only if you know exactly what you are doing.
+
+	  If unsure, say N.
+
 endif # IPV6