mpls: allow TTL propagation to IP packets to be configured

Provide the ability to control on a per-route basis whether the TTL
value from an MPLS packet is propagated to an IPv4/IPv6 packet when
the last label is popped as per the theoretical model in RFC 3443
through a new route attribute, RTA_TTL_PROPAGATE which can be 0 to
mean disable propagation and 1 to mean enable propagation.

In order to provide the ability to change the behaviour for packets
arriving with IPv4/IPv6 Explicit Null labels and to provide an easy
way for a user to change the behaviour for all existing routes without
having to reprogram them, a global knob is provided. This is done
through the addition of a new per-namespace sysctl,
"net.mpls.ip_ttl_propagate", which defaults to enabled. If the
per-route attribute is set (either enabled or disabled) then it
overrides the global configuration.

Signed-off-by: Robert Shearman <rshearma@brocade.com>
Acked-by: David Ahern <dsa@cumulusnetworks.com>
Tested-by: David Ahern <dsa@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 7 insertions, 0 deletions

diff --git a/net/mpls/internal.h b/net/mpls/internal.h
index 76360d8b9579..62928d8fabd1 100644
--- a/net/mpls/internal.h
+++ b/net/mpls/internal.h
@@ -90,6 +90,12 @@ struct mpls_nh { /* next hop label forwarding entry */
 	u8			nh_via_table;
 };
 
+enum mpls_ttl_propagation {
+	MPLS_TTL_PROP_DEFAULT,
+	MPLS_TTL_PROP_ENABLED,
+	MPLS_TTL_PROP_DISABLED,
+};
+
 /* The route, nexthops and vias are stored together in the same memory
  * block:
  *
@@ -116,6 +122,7 @@ struct mpls_route { /* next hop label forwarding entry */
 	u8			rt_protocol;
 	u8			rt_payload_type;
 	u8			rt_max_alen;
+	u8			rt_ttl_propagate;
 	unsigned int		rt_nhn;
 	unsigned int		rt_nhn_alive;
 	struct mpls_nh		rt_nh[0];